ISO 6658:2005
(Main)Sensory analysis — Methodology — General guidance
Sensory analysis — Methodology — General guidance
ISO 6658:2005 gives general guidance on the use of sensory analysis. It describes tests for the examination of foods by sensory analysis, and includes some information on the techniques to be used if statistical analysis of the results is required. Generally these tests are intended only for objective sensory analysis. However, if a test can be used for determining preference, this is indicated.
Analyse sensorielle — Méthodologie — Lignes directrices générales
L'ISO 6658:2005 fournit des lignes directrices générales sur la méthodologie de l'analyse sensorielle. Elle décrit des essais destinés à l'examen des produits alimentaires par analyse sensorielle et donne des informations relatives aux techniques à utiliser si une analyse statistique des résultats est requise. Généralement, ces essais sont uniquement destinés à une analyse sensorielle objective. Toutefois, s'il est possible d'utiliser un essai pour déterminer la préférence, cela est précisé.
Senzorična analiza - Metodologija - Splošne smernice
Ta mednarodni standard podaja splošne smernice glede senzorične analize. Opisuje preskuse za pregled hrane s senzorično analizo in vključuje nekatere informacije o tehnikah, ki se morajo uporabiti, kadar je potrebna statistična analiza rezultatov.
V splošnem so ti preskusi namenjeni le objektivni senzorični analizi. Če pa se preskus lahko uporabi za določevanje preferenc, je to navedeno.
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INTERNATIONAL ISO
STANDARD 6658
Second edition
2005-10-01
Sensory analysis — Methodology —
General guidance
Analyse sensorielle — Méthodologie — Lignes directrices générales
Reference number
ISO 6658:2005(E)
©
ISO 2005
---------------------- Page: 1 ----------------------
ISO 6658:2005(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2005
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2005 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 6658:2005(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 General requirements. 1
4.1 Basic information. 1
4.2 Statement of objectives. 2
4.3 Choice of test . 2
4.4 Choosing and training assessors . 2
4.5 Material to be tested . 3
4.6 Test room. 4
4.7 Planning and conduct of the test . 4
5 Methods of test . 5
5.1 General. 5
5.2 Discrimination tests. 5
5.3 Use of scales and categories . 9
5.4 Descriptive tests . 12
6 Analysis of results. 14
6.1 General. 14
6.2 Discrimination tests. 14
6.3 Tests using scales and categories . 16
6.4 Analytical or descriptive tests. 17
Annex A (informative) Statistical terms . 18
Bibliography . 20
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ISO 6658:2005(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 6658 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 12, Sensory
analysis.
This second edition cancels and replaces the first edition (ISO 6658:1985), which has been technically revised.
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ISO 6658:2005(E)
Introduction
This International Standard constitutes a general introduction to the methodology of sensory analysis and
should be read before undertaking the more detailed test procedures described in other International
Standards. It covers the general area of methodology and is intended to fulfil the following functions:
a) to provide a brief background of the essential features of methods of sensory analysis for the user of
specific tests;
b) to provide details of general requirements, procedures and interpretation of results common to all or most
tests;
c) to provide sufficient guidance on requirements, procedures and interpretation of results for the different
specific tests to allow choice of the most appropriate procedure(s) for solution of a particular problem.
It comprises three main aspects, covered in Clauses 4, 5 and 6.
It is essential that Clause 4 “General requirements” be read first. Clause 5 “Methods of test” describes, in a
general manner, all the main tests, under five headings:
⎯ Definition;
⎯ Application;
⎯ Assessors;
⎯ Procedure;
⎯ Analysis of results.
Clause 6 is concerned with some general principles of data collection and analysis of sensory data and also
briefly covers general principles of statistical treatment of the results.
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INTERNATIONAL STANDARD ISO 6658:2005(E)
Sensory analysis — Methodology — General guidance
1 Scope
This International Standard gives general guidance on the use of sensory analysis. It describes tests for the
examination of foods by sensory analysis, and includes some information on the techniques to be used if
statistical analysis of the results is required.
Generally these tests are intended only for objective sensory analysis. However, if a test can be used for
determining preference, this is indicated.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 5492, Sensory analysis — Vocabulary
3 Terms and definitions
For the purposes of this International Standard, the terms and definitions given in ISO 5492 and the following
apply.
3.1
sensory analysis
examination of organoleptic attributes of a product by the sense organs
4 General requirements
4.1 Basic information
This clause covers the general requirements common to all situations encountered in sensory analysis. The
information basic to these requirements is as follows.
a) The human response to one stimulus cannot be isolated from previous experience or from other sensory
stimuli received from the environment.
NOTE Nevertheless, influences arising from these two sources can be controlled and the effect standardized.
a) Variability in sensory response is inherent in any group of people used for testing and is unavoidable; this
can arise from inconsistencies within an individual, and through physiological and psychological
differences between individuals.
NOTE However, with training, such a group can show highly consistent individual responses. Recognition of
these factors is important in the analysis of results.
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ISO 6658:2005(E)
b) Systematic biases in sensory experiments involving human response can result in misleading data and
incorrect interpretation that can be difficult to identify. The factors that can result in bias should be
identified and controlled as far as possible by appropriate experimental design and conduct of the tests.
c) The validity of the conclusions drawn from the results is dependent upon the test used and the way it is
conducted, including the questions that have been asked.
4.2 Statement of objectives
There are three main types of objective, as follows:
a) those in which the primary aim of the test is to categorize, rank or describe the product(s);
b) those in which the aim is to distinguish between two or more products; here it is important to distinguish
between the need to know
⎯ if there is a difference at all,
⎯ how great is the magnitude of the difference,
⎯ the direction (or quality) of that difference,
⎯ the influence of that difference, e.g. with regard to preference, or
⎯ if all or only part of a population is detecting a difference;
c) those in which reassurance is sought that products do not differ.
In sensory analysis, a given problem frequently requires appreciable discussion or thought before an
appropriate test is selected. This is because the initial concept of the problem may require clarification.
4.3 Choice of test
The choice of appropriate test depends largely on the nature of the test objective, but also needs to take
account of factors associated with the product, the assessors, the test environment, and the desired level of
analytical precision and statistical confidence in the conclusions. The action that would occur based on the
outcome of the test should be determined in advance.
For each test, an attempt is made in Clause 5 to give guidance as to its relevance. Preliminary tests may be
necessary to confirm the applicability of a given test.
Because of sensory fatigue and the effects of adaptation, only a limited number of samples can be assessed
during a session, depending on the nature of the test and the type of product. Some of these effects can be
moderated by appropriate rinse procedures and recovery between samples.
Whilst the use of control samples is essential in most cases, their use naturally limits the number of samples
that can be assessed during any given session.
The statistical plan should always be determined before commencing the tests. This is especially
recommended if the number of samples to be evaluated requires more than one session. Details of statistical
plans should be selected from specialized texts. Whatever test method is used, the sequential testing
approach described in ISO 16820 should be considered whenever it is desirable to keep the number of
samples or the number of assessors to a minimum.
4.4 Choosing and training assessors
A sensory analysis panel constitutes a true “measuring instrument”, and consequently the results of the
analyses conducted depend on its members. The recruitment of persons willing to participate in a panel,
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ISO 6658:2005(E)
therefore, needs to be carried out with care and should be considered as a real investment, both in time and
financially. Management support in the organization is necessary if it is to be effective.
Sensory assessment may be made by three types of assessor: “assessors”, “selected assessors” or “expert
assessors”. Assessors can be “naive assessors” who do not have to meet a precise criterion of selection or
training, or people who have already taken part in some sensory tests (initiated assessor). Selected assessors
are assessors who have been selected and trained for the particular sensory test. Expert assessors are
assessors who have been selected and trained for a variety of sensory analysis methods and who
demonstrate particular acuity in panel work.
NOTE Assessors employed by companies to undertake sensory analysis as their primary job function are examples
of expert assessors.
The selection and training methods to be employed depend on the tasks and methods that it is intended to
give to the selected assessors. Procedures for training assessors for descriptive tests are different from those
for training assessors in discrimination tests.
Detailed procedures and methods for selection and training of assessors are given in ISO 8586-1. It should be
noted that these methods sometimes only constitute a way of choosing the better candidates amongst those
who are available, rather than to satisfy predetermined criteria. Also, the selection of assessors for their ability
to discriminate and describe foods is quite different from that used for preference tests. The former tasks
require selection and training, whereas the latter require only that the panel be representative of a specified
sector of the population, for example, a group of consumers.
If a selection procedure is to be carried out, some important criteria for choosing assessors are as follows:
a) general ability to perform the specific sensory task, which may include a particular sensitivity to the stimuli
under investigation;
b) availability with respect to normal employment;
c) motivation (willingness and interest);
d) good health (including the absence of specific allergies or treatment with medications) and good dental
and general hygienic condition.
The performance of selected and expert assessors should be monitored regularly to ensure that the criteria by
which they were initially selected continue to be met.
4.5 Material to be tested
The nature of the product to be tested determines the experimental protocol of the test, and may also have an
influence on the type of test that is required to satisfy the test objectives. For example, a protocol in which
foods are to be consumed hot will need to take into account the cooling rate of the product and the likely effect
on sensory attributes, and the changes in sensory attributes that may occur in keeping the product hot prior to
testing.
Methods of preparation and presentation of samples should be appropriate for the product and to the problem
concerned.
EXAMPLE 1 A product that is normally consumed hot should be prepared in the usual manner and tested hot;
however, elevated temperatures may be used in some circumstances to increase the ease with which some flavours can
be evaluated.
EXAMPLE 2 A product that is normally consumed in discrete pieces should not be homogenized in order to retain
textural characteristics. Care is needed, however, to ensure maximum uniformity between sub-samples for each assessor;
this includes similar portion size and uniformity of composition.
General principles for product sampling (in accordance with International Standards relating to the product
under test) should be applied for test samples. In all cases, documentation of sample identification codes or
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ISO 6658:2005(E)
lot numbers is necessary. Valid conclusions can be drawn for a product as a whole only if the samples tested
are representative.
Carriers may sometimes be used for tests relating to the evaluation of products for which direct tasting is not
feasible (see ISO 5497), for example food ingredients.
Lighting conditions should be specified when appearance is being assessed. When the test concerns only
differences in flavour, the effect of colour differences may be partially masked by the use of lighting conditions
that minimize the colour difference.
Containers should be chosen so as not to affect the test or the product. These may include washable ceramic
or glass containers, or disposable plastic or paper containers, but must not transfer chemical materials that
could result in taint. In particular, washable containers should be washed only in odour- and taint-free
detergents and rinsed in water, and polymeric and paper containers, including insulated containers used for
hot or cold samples, should be odour- and taint-free.
Palate cleansers may be used by the assessors between samples and between sessions, but care should be
taken to ensure that they do not influence the flavour of products to be assessed. Still and carbonated water
and bland foods (for example, unsalted crackers) may be used between samples and between sessions.
Checks on the water supply are desirable to ensure that it is bland. For particular purposes, deionized water,
glass-distilled water, low mineral content spring water, carbon-filtered water or boiled tap water may be used,
but it should be noted that they are likely to have different flavours.
4.6 Test room
Sensory analysis should be conducted in a dedicated test room (see ISO 8589 for details). The aim should be
to create for each assessor a separate environment with minimum distraction, so that each assessor can
quickly adjust to the nature of the new task(s). Extraneous activities, including preparation of the samples,
should not be allowed during the tests, as these can lead to biased results. The room should be at a
comfortable temperature and should be ventilated with odour-free air; limited airflow is desirable to avoid
excessive temperature fluctuations. Persistent odours, such as tobacco or cosmetics, should not be allowed to
contaminate the environment of the test room.
Sound should be restricted. A low background noise is usually more tolerable than a fluctuating level of noise.
Conversation is more distracting than background noise. Interruptions cause the greatest distraction.
It is usually helpful to have control over both the colour and the intensity of the lighting, although coloured
lights rarely succeed in completely masking differences in appearance.
Surfaces should be non-absorbent and designed to facilitate a high standard of hygiene. The dimensions of
the tasting booths are important; very low ceilings and very narrow booths can be oppressive or can give rise
to a feeling of claustrophobia. Comfortable seating is necessary.
If provision is made for computerized data acquisition, then this should be implemented safely, hygienically,
and in a way that does not compromise sensory judgement.
4.7 Planning and conduct of the test
The planning and operation of the test are determined by the objectives of the programme, the test chosen,
and practical constraints associated with the use of human subjects. In particular, it is important to recognize
the biases that might be inherent in the chosen test, and to operate the test in such a way as to minimize the
effects of any bias. The potential biases can originate from both psychological and physiological sources.
The most serious psychological bias results from assessors interacting to influence each other’s judgements,
and should be minimized by the use of individual booths or adequate separation of the assessors. Moreover,
strict management of the activities of the assessors is necessary.
The manner and order of presentation of the samples are important aspects of the test, and can introduce
psychological biases. For example, the samples should be coded by random three-digit numbers, and the
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ISO 6658:2005(E)
codes should be varied for each test. The order of assessment can also be a source of bias and, in general,
the order should be specified. With a small number of samples and assessors, the order can be balanced so
that every possible order occurs an equal number of times. In larger experiments, the order can be balanced
or randomized.
Physiological biases are frequently associated with the nature of the test samples. In particular, adaptation to
a specific flavour stimulus can occur on repeated exposure to that stimulus, and fatigue can occur when
chewing solid foods. Both factors can impose an upper limit on the number of samples to be assessed in a
session. Expectoration of samples may be recommended with trained panels, but loss of information on
specific sensory attributes may result.
Hunger and satiety can influence an assessor's performance, and, if panels are held too frequently,
performance may deteriorate. If it is possible, assessors should be asked to refrain from smoking and from
consuming snacks such as coffee for 1 h before a test. Assessors should not carry any foreign odours into the
session, for example tobacco or cosmetic odours, as these could influence the responses of other assessors.
The time of day at which the test is conducted is important. The schedule should take into account local
customary mealtimes since performance is generally considered optimum at mid-morning and mid-afternoon.
Assessors suffering from emotional upsets, colds and other illnesses should be excluded from tests until they
recover.
The collation of the results comprises three aspects:
⎯ checking that all data have been recorded accurately, either on computer or manually;
⎯ verification that any additional relevant information which may aid or cast doubt on the interpretation of
the results has been noted;
⎯ checking that the assessors are motivated to continue participating if further testing is planned.
5 Methods of test
5.1 General
The most commonly used tests are divided into three groups:
a) discrimination tests used to determine the probability of difference or similarity between products (see
5.2);
b) tests using scales and categories to estimate the order or size of differences or the categories or classes
to which samples should be allocated (see 5.3);
c) descriptive tests used to identify the specific sensory attributes present in a sample (see 5.4).
For the number of assessors, refer to the corresponding standards, taking into consideration α or β risk
depending on the purpose of the test. Alternatively, sequential analysis (see ISO 16820) may allow a decision
to be made after fewer trials of the test than would be required by conventional approaches that use a
predetermined number of assessments.
The tests may also be quantitative.
5.2 Discrimination tests
5.2.1 General
The following tests are commonly used to determine the probability of difference or similarity between
samples:
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ISO 6658:2005(E)
a) paired comparison test (see 5.2.2);
b) triangle test (see 5.2.3);
c) duo-trio test (see 5.2.4);
d) two-out-of-five test (see 5.2.5);
e) “A — not A” test (see 6.2.6).
For all these tests, there are different manners of analysing the results.
5.2.2 Paired comparison test
5.2.2.1 Definition
This is a test in which samples are presented in pairs for comparison and detection of differences on the basis
of some defined criteria.
See ISO 5495 for details.
5.2.2.2 Application
The paired comparison test is recommended
a) to determine if a perceptible difference exists in a particular attribute (e.g. sweetness), or to determine if
no perceptible difference exists in that attribute,
b) to select, train and monitor the performance of the assessors,
c) to compare two products in terms of preference in the context of consumer tests.
Advantages of the test over other discrimination tests are simplicity and less sensory fatigue.
The disadvantage of the method of paired comparisons is that as the number of samples to be compared
increases the number of inter-comparisons required rapidly becomes impracticable.
5.2.2.3 Procedure
The assessors receive a set of two samples (the pair). They designate the sample that they consider to be the
most intense in the attribute under consideration, even if this choice is only a guess. One of the samples may
be a control. The number of times each sample is selected is counted.
It is necessary to determine, prior to carrying out the test, whether the statistical test that follows is to be
one-sided (i.e. the test supervisor expects a particular direction of difference and the alternative hypothesis
corresponds to the existence of a difference in that direction) or two-sided (i.e. the test supervisor has no
expected direction of difference and the alternative hypothesis corresponds to a difference in either direction).
Questions of difference and preference should not be combined: the recruitment criteria for panels are
different for these questions.
5.2.2.4 Analysis of results
See 6.2.2.
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ISO 6658:2005(E)
5.2.3 Triangle test
5.2.3.1 Definition
This is a discrimination test involving three coded samples, two of which are identical, presented
simultaneously. The assessors are asked to select the odd sample.
See ISO 4120 for details.
5.2.3.2 Application
The triangle test is recommended
a) when the nature of the difference is unknown, and
b) for the selection and training of assessors.
The test should not be used for the determination of preference. Some disadvantages of the test are that
⎯ it is uneconomical for the assessment of a large number of samples,
⎯ it may be more affected by sensory fatigue than the paired comparison test with intensely flavoured
samples,
⎯ if the nature of the difference is known, it is statistically less efficient than some other tests, and
⎯ the method is applicable only if the products are as homogeneous as possible.
5.2.3.3 Procedure
The assessors are each presented with one set of three coded samples, two of which are identical, and are
asked to select the odd sample.
Samples should be presented an equal number of times in each of the two sets of three distinct permutations
of order, which are
BAA ABA AAB
ABB BAB BBA
5.2.3.4 Analysis of results
See 6.2.3.
5.2.4 Duo-trio test
5.2.4.1 Definition
This is a discrimination test in which the reference sample is presented first. It is followed by two samples, one
of which is identical to the reference sample and which the assessors are asked to identify.
See ISO 10399 for details.
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ISO 6658:2005(E)
5.2.4.2 Application
This duo-trio test is used to determine if there is a sensory difference or similarity between a given sample and
a reference. It is especially suitable when the reference sample is well known to the assessors, for example a
sample of regular production.
If there are after-tastes, this test is less suitable than the paired comparison test (5.2.2) or the “A — not A” test
(5.2.6).
5.2.4.3 Procedure
The assessors are first presented with the identified reference sample. This is followed by two coded samples,
one of which is identical to the reference sample. The assessors are asked to identify this sample.
5.2.4.4 Analysis of results
See 6.2.4.
5.2.5 Two-out-of-five test
5.2.5.1 Definition
This is a discrimination test involving five coded samples
...
SLOVENSKI STANDARD
SIST ISO 6658:2011
01-junij-2011
1DGRPHãþD
SIST ISO 6658:1997
6HQ]RULþQDDQDOL]D0HWRGRORJLMD6SORãQHVPHUQLFH
Sensory analysis -- Methodology -- General guidance
Analyse sensorielle -- Méthodologie -- Lignes directrices générales
Ta slovenski standard je istoveten z: ISO 6658:2005
ICS:
67.240 6HQ]RULþQDDQDOL]D Sensory analysis
SIST ISO 6658:2011 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 6658:2011
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SIST ISO 6658:2011
INTERNATIONAL ISO
STANDARD 6658
Second edition
2005-10-01
Sensory analysis — Methodology —
General guidance
Analyse sensorielle — Méthodologie — Lignes directrices générales
Reference number
ISO 6658:2005(E)
©
ISO 2005
---------------------- Page: 3 ----------------------
SIST ISO 6658:2011
ISO 6658:2005(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.
© ISO 2005
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2005 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 6658:2011
ISO 6658:2005(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 General requirements. 1
4.1 Basic information. 1
4.2 Statement of objectives. 2
4.3 Choice of test . 2
4.4 Choosing and training assessors . 2
4.5 Material to be tested . 3
4.6 Test room. 4
4.7 Planning and conduct of the test . 4
5 Methods of test . 5
5.1 General. 5
5.2 Discrimination tests. 5
5.3 Use of scales and categories . 9
5.4 Descriptive tests . 12
6 Analysis of results. 14
6.1 General. 14
6.2 Discrimination tests. 14
6.3 Tests using scales and categories . 16
6.4 Analytical or descriptive tests. 17
Annex A (informative) Statistical terms . 18
Bibliography . 20
© ISO 2005 – All rights reserved iii
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SIST ISO 6658:2011
ISO 6658:2005(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 6658 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 12, Sensory
analysis.
This second edition cancels and replaces the first edition (ISO 6658:1985), which has been technically revised.
iv © ISO 2005 – All rights reserved
---------------------- Page: 6 ----------------------
SIST ISO 6658:2011
ISO 6658:2005(E)
Introduction
This International Standard constitutes a general introduction to the methodology of sensory analysis and
should be read before undertaking the more detailed test procedures described in other International
Standards. It covers the general area of methodology and is intended to fulfil the following functions:
a) to provide a brief background of the essential features of methods of sensory analysis for the user of
specific tests;
b) to provide details of general requirements, procedures and interpretation of results common to all or most
tests;
c) to provide sufficient guidance on requirements, procedures and interpretation of results for the different
specific tests to allow choice of the most appropriate procedure(s) for solution of a particular problem.
It comprises three main aspects, covered in Clauses 4, 5 and 6.
It is essential that Clause 4 “General requirements” be read first. Clause 5 “Methods of test” describes, in a
general manner, all the main tests, under five headings:
⎯ Definition;
⎯ Application;
⎯ Assessors;
⎯ Procedure;
⎯ Analysis of results.
Clause 6 is concerned with some general principles of data collection and analysis of sensory data and also
briefly covers general principles of statistical treatment of the results.
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INTERNATIONAL STANDARD ISO 6658:2005(E)
Sensory analysis — Methodology — General guidance
1 Scope
This International Standard gives general guidance on the use of sensory analysis. It describes tests for the
examination of foods by sensory analysis, and includes some information on the techniques to be used if
statistical analysis of the results is required.
Generally these tests are intended only for objective sensory analysis. However, if a test can be used for
determining preference, this is indicated.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 5492, Sensory analysis — Vocabulary
3 Terms and definitions
For the purposes of this International Standard, the terms and definitions given in ISO 5492 and the following
apply.
3.1
sensory analysis
examination of organoleptic attributes of a product by the sense organs
4 General requirements
4.1 Basic information
This clause covers the general requirements common to all situations encountered in sensory analysis. The
information basic to these requirements is as follows.
a) The human response to one stimulus cannot be isolated from previous experience or from other sensory
stimuli received from the environment.
NOTE Nevertheless, influences arising from these two sources can be controlled and the effect standardized.
a) Variability in sensory response is inherent in any group of people used for testing and is unavoidable; this
can arise from inconsistencies within an individual, and through physiological and psychological
differences between individuals.
NOTE However, with training, such a group can show highly consistent individual responses. Recognition of
these factors is important in the analysis of results.
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b) Systematic biases in sensory experiments involving human response can result in misleading data and
incorrect interpretation that can be difficult to identify. The factors that can result in bias should be
identified and controlled as far as possible by appropriate experimental design and conduct of the tests.
c) The validity of the conclusions drawn from the results is dependent upon the test used and the way it is
conducted, including the questions that have been asked.
4.2 Statement of objectives
There are three main types of objective, as follows:
a) those in which the primary aim of the test is to categorize, rank or describe the product(s);
b) those in which the aim is to distinguish between two or more products; here it is important to distinguish
between the need to know
⎯ if there is a difference at all,
⎯ how great is the magnitude of the difference,
⎯ the direction (or quality) of that difference,
⎯ the influence of that difference, e.g. with regard to preference, or
⎯ if all or only part of a population is detecting a difference;
c) those in which reassurance is sought that products do not differ.
In sensory analysis, a given problem frequently requires appreciable discussion or thought before an
appropriate test is selected. This is because the initial concept of the problem may require clarification.
4.3 Choice of test
The choice of appropriate test depends largely on the nature of the test objective, but also needs to take
account of factors associated with the product, the assessors, the test environment, and the desired level of
analytical precision and statistical confidence in the conclusions. The action that would occur based on the
outcome of the test should be determined in advance.
For each test, an attempt is made in Clause 5 to give guidance as to its relevance. Preliminary tests may be
necessary to confirm the applicability of a given test.
Because of sensory fatigue and the effects of adaptation, only a limited number of samples can be assessed
during a session, depending on the nature of the test and the type of product. Some of these effects can be
moderated by appropriate rinse procedures and recovery between samples.
Whilst the use of control samples is essential in most cases, their use naturally limits the number of samples
that can be assessed during any given session.
The statistical plan should always be determined before commencing the tests. This is especially
recommended if the number of samples to be evaluated requires more than one session. Details of statistical
plans should be selected from specialized texts. Whatever test method is used, the sequential testing
approach described in ISO 16820 should be considered whenever it is desirable to keep the number of
samples or the number of assessors to a minimum.
4.4 Choosing and training assessors
A sensory analysis panel constitutes a true “measuring instrument”, and consequently the results of the
analyses conducted depend on its members. The recruitment of persons willing to participate in a panel,
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therefore, needs to be carried out with care and should be considered as a real investment, both in time and
financially. Management support in the organization is necessary if it is to be effective.
Sensory assessment may be made by three types of assessor: “assessors”, “selected assessors” or “expert
assessors”. Assessors can be “naive assessors” who do not have to meet a precise criterion of selection or
training, or people who have already taken part in some sensory tests (initiated assessor). Selected assessors
are assessors who have been selected and trained for the particular sensory test. Expert assessors are
assessors who have been selected and trained for a variety of sensory analysis methods and who
demonstrate particular acuity in panel work.
NOTE Assessors employed by companies to undertake sensory analysis as their primary job function are examples
of expert assessors.
The selection and training methods to be employed depend on the tasks and methods that it is intended to
give to the selected assessors. Procedures for training assessors for descriptive tests are different from those
for training assessors in discrimination tests.
Detailed procedures and methods for selection and training of assessors are given in ISO 8586-1. It should be
noted that these methods sometimes only constitute a way of choosing the better candidates amongst those
who are available, rather than to satisfy predetermined criteria. Also, the selection of assessors for their ability
to discriminate and describe foods is quite different from that used for preference tests. The former tasks
require selection and training, whereas the latter require only that the panel be representative of a specified
sector of the population, for example, a group of consumers.
If a selection procedure is to be carried out, some important criteria for choosing assessors are as follows:
a) general ability to perform the specific sensory task, which may include a particular sensitivity to the stimuli
under investigation;
b) availability with respect to normal employment;
c) motivation (willingness and interest);
d) good health (including the absence of specific allergies or treatment with medications) and good dental
and general hygienic condition.
The performance of selected and expert assessors should be monitored regularly to ensure that the criteria by
which they were initially selected continue to be met.
4.5 Material to be tested
The nature of the product to be tested determines the experimental protocol of the test, and may also have an
influence on the type of test that is required to satisfy the test objectives. For example, a protocol in which
foods are to be consumed hot will need to take into account the cooling rate of the product and the likely effect
on sensory attributes, and the changes in sensory attributes that may occur in keeping the product hot prior to
testing.
Methods of preparation and presentation of samples should be appropriate for the product and to the problem
concerned.
EXAMPLE 1 A product that is normally consumed hot should be prepared in the usual manner and tested hot;
however, elevated temperatures may be used in some circumstances to increase the ease with which some flavours can
be evaluated.
EXAMPLE 2 A product that is normally consumed in discrete pieces should not be homogenized in order to retain
textural characteristics. Care is needed, however, to ensure maximum uniformity between sub-samples for each assessor;
this includes similar portion size and uniformity of composition.
General principles for product sampling (in accordance with International Standards relating to the product
under test) should be applied for test samples. In all cases, documentation of sample identification codes or
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lot numbers is necessary. Valid conclusions can be drawn for a product as a whole only if the samples tested
are representative.
Carriers may sometimes be used for tests relating to the evaluation of products for which direct tasting is not
feasible (see ISO 5497), for example food ingredients.
Lighting conditions should be specified when appearance is being assessed. When the test concerns only
differences in flavour, the effect of colour differences may be partially masked by the use of lighting conditions
that minimize the colour difference.
Containers should be chosen so as not to affect the test or the product. These may include washable ceramic
or glass containers, or disposable plastic or paper containers, but must not transfer chemical materials that
could result in taint. In particular, washable containers should be washed only in odour- and taint-free
detergents and rinsed in water, and polymeric and paper containers, including insulated containers used for
hot or cold samples, should be odour- and taint-free.
Palate cleansers may be used by the assessors between samples and between sessions, but care should be
taken to ensure that they do not influence the flavour of products to be assessed. Still and carbonated water
and bland foods (for example, unsalted crackers) may be used between samples and between sessions.
Checks on the water supply are desirable to ensure that it is bland. For particular purposes, deionized water,
glass-distilled water, low mineral content spring water, carbon-filtered water or boiled tap water may be used,
but it should be noted that they are likely to have different flavours.
4.6 Test room
Sensory analysis should be conducted in a dedicated test room (see ISO 8589 for details). The aim should be
to create for each assessor a separate environment with minimum distraction, so that each assessor can
quickly adjust to the nature of the new task(s). Extraneous activities, including preparation of the samples,
should not be allowed during the tests, as these can lead to biased results. The room should be at a
comfortable temperature and should be ventilated with odour-free air; limited airflow is desirable to avoid
excessive temperature fluctuations. Persistent odours, such as tobacco or cosmetics, should not be allowed to
contaminate the environment of the test room.
Sound should be restricted. A low background noise is usually more tolerable than a fluctuating level of noise.
Conversation is more distracting than background noise. Interruptions cause the greatest distraction.
It is usually helpful to have control over both the colour and the intensity of the lighting, although coloured
lights rarely succeed in completely masking differences in appearance.
Surfaces should be non-absorbent and designed to facilitate a high standard of hygiene. The dimensions of
the tasting booths are important; very low ceilings and very narrow booths can be oppressive or can give rise
to a feeling of claustrophobia. Comfortable seating is necessary.
If provision is made for computerized data acquisition, then this should be implemented safely, hygienically,
and in a way that does not compromise sensory judgement.
4.7 Planning and conduct of the test
The planning and operation of the test are determined by the objectives of the programme, the test chosen,
and practical constraints associated with the use of human subjects. In particular, it is important to recognize
the biases that might be inherent in the chosen test, and to operate the test in such a way as to minimize the
effects of any bias. The potential biases can originate from both psychological and physiological sources.
The most serious psychological bias results from assessors interacting to influence each other’s judgements,
and should be minimized by the use of individual booths or adequate separation of the assessors. Moreover,
strict management of the activities of the assessors is necessary.
The manner and order of presentation of the samples are important aspects of the test, and can introduce
psychological biases. For example, the samples should be coded by random three-digit numbers, and the
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codes should be varied for each test. The order of assessment can also be a source of bias and, in general,
the order should be specified. With a small number of samples and assessors, the order can be balanced so
that every possible order occurs an equal number of times. In larger experiments, the order can be balanced
or randomized.
Physiological biases are frequently associated with the nature of the test samples. In particular, adaptation to
a specific flavour stimulus can occur on repeated exposure to that stimulus, and fatigue can occur when
chewing solid foods. Both factors can impose an upper limit on the number of samples to be assessed in a
session. Expectoration of samples may be recommended with trained panels, but loss of information on
specific sensory attributes may result.
Hunger and satiety can influence an assessor's performance, and, if panels are held too frequently,
performance may deteriorate. If it is possible, assessors should be asked to refrain from smoking and from
consuming snacks such as coffee for 1 h before a test. Assessors should not carry any foreign odours into the
session, for example tobacco or cosmetic odours, as these could influence the responses of other assessors.
The time of day at which the test is conducted is important. The schedule should take into account local
customary mealtimes since performance is generally considered optimum at mid-morning and mid-afternoon.
Assessors suffering from emotional upsets, colds and other illnesses should be excluded from tests until they
recover.
The collation of the results comprises three aspects:
⎯ checking that all data have been recorded accurately, either on computer or manually;
⎯ verification that any additional relevant information which may aid or cast doubt on the interpretation of
the results has been noted;
⎯ checking that the assessors are motivated to continue participating if further testing is planned.
5 Methods of test
5.1 General
The most commonly used tests are divided into three groups:
a) discrimination tests used to determine the probability of difference or similarity between products (see
5.2);
b) tests using scales and categories to estimate the order or size of differences or the categories or classes
to which samples should be allocated (see 5.3);
c) descriptive tests used to identify the specific sensory attributes present in a sample (see 5.4).
For the number of assessors, refer to the corresponding standards, taking into consideration α or β risk
depending on the purpose of the test. Alternatively, sequential analysis (see ISO 16820) may allow a decision
to be made after fewer trials of the test than would be required by conventional approaches that use a
predetermined number of assessments.
The tests may also be quantitative.
5.2 Discrimination tests
5.2.1 General
The following tests are commonly used to determine the probability of difference or similarity between
samples:
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a) paired comparison test (see 5.2.2);
b) triangle test (see 5.2.3);
c) duo-trio test (see 5.2.4);
d) two-out-of-five test (see 5.2.5);
e) “A — not A” test (see 6.2.6).
For all these tests, there are different manners of analysing the results.
5.2.2 Paired comparison test
5.2.2.1 Definition
This is a test in which samples are presented in pairs for comparison and detection of differences on the basis
of some defined criteria.
See ISO 5495 for details.
5.2.2.2 Application
The paired comparison test is recommended
a) to determine if a perceptible difference exists in a particular attribute (e.g. sweetness), or to determine if
no perceptible difference exists in that attribute,
b) to select, train and monitor the performance of the assessors,
c) to compare two products in terms of preference in the context of consumer tests.
Advantages of the test over other discrimination tests are simplicity and less sensory fatigue.
The disadvantage of the method of paired comparisons is that as the number of samples to be compared
increases the number of inter-comparisons required rapidly becomes impracticable.
5.2.2.3 Procedure
The assessors receive a set of two samples (the pair). They designate the sample that they consider to be the
most intense in the attribute under consideration, even if this choice is only a guess. One of the samples may
be a control. The number of times each sample is selected is counted.
It is necessary to determine, prior to carrying out the test, whether the statistical test that follows is to be
one-sided (i.e. the test supervisor expects a particular direction of difference and the alternative hypothesis
corresponds to the existence of a difference in that direction) or two-sided (i.e. the test supervisor has no
expected direction of difference and the alternative hypothesis corresponds to a difference in either direction).
Questions of difference and preference should not be combined: the recruitment criteria for panels are
different for these questions.
5.2.2.4 Analysis of results
See 6.2.2.
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5.2.3 Triangle test
5.2.3.1 Definition
This is a discrimination test involving three coded samples, two of which are identical, presented
simultaneously. The assessors are asked to select the odd sample.
See ISO 4120 for details.
5.2.3.2 Application
The triangle test is recommended
a) when the nature of the difference is unknown, and
b) for the selection and training of assessors.
The test should not be used for the determination of preference. Some disadvantages of the test are that
⎯ it is uneconomical for the assessment of a large number of samples,
⎯ it may be more affected by sensory fatigue than the paired comparison test with intensely flavoured
samples,
⎯ if the nature of the difference is known, it is statistically less efficient than some other tests, and
⎯ the method is applicable only if the products are as homogeneous as possible.
5.2.3.3 Procedure
The assessors are each presented with one set of three coded samples, two of which are identical, and are
asked to select the odd sample.
Samples should be presented an equal number of times in each of the two sets of three distinct permutations
of order, which are
BAA ABA AAB
ABB BAB BBA
5.2.3.4 Analysis of results
See 6.2.3.
5.2.4 Duo-trio test
5.2.4.1 Definition
This is a discrimination test in which the reference sample is presented first. It is followed by two samples, one
of which is identical to the reference sample and which th
...
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Analyse sensorielle -- Méthodologie -- Lignes directrices généralesSensory analysis -- Methodology -- General guidance67.240Sensory analysisICS:Ta slovenski standard je istoveten z:ISO 6658:2005oSIST ISO 6658:2011en,fr01-april-2011oSIST ISO 6658:2011SLOVENSKI
STANDARD
oSIST ISO 6658:2011
Reference numberISO 6658:2005(E)© ISO 2005
INTERNATIONAL STANDARD ISO6658Second edition2005-10-01Sensory analysis — Methodology — General guidance Analyse sensorielle — Méthodologie — Lignes directrices générales
oSIST ISO 6658:2011
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ii © ISO 2005 – All rights reserved
oSIST ISO 6658:2011
ISO 6658:2005(E) © ISO 2005 – All rights reserved iiiContents Page Foreword.iv Introduction.v 1 Scope.1 2 Normative references.1 3 Terms and definitions.1 4 General requirements.1 4.1 Basic information.1 4.2 Statement of objectives.2 4.3 Choice of test.2 4.4 Choosing and training assessors.2 4.5 Material to be tested.3 4.6 Test room.4 4.7 Planning and conduct of the test.4 5 Methods of test.5 5.1 General.5 5.2 Discrimination tests.5 5.3 Use of scales and categories.9 5.4 Descriptive tests.12 6 Analysis of results.14 6.1 General.14 6.2 Discrimination tests.14 6.3 Tests using scales and categories.16 6.4 Analytical or descriptive tests.17 Annex A (informative)
Statistical terms.18 Bibliography.20
oSIST ISO 6658:2011
ISO 6658:2005(E) iv © ISO 2005 – All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 6658 was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 12, Sensory analysis. This second edition cancels and replaces the first edition (ISO 6658:1985), which has been technically revised. oSIST ISO 6658:2011
ISO 6658:2005(E) © ISO 2005 – All rights reserved vIntroduction This International Standard constitutes a general introduction to the methodology of sensory analysis and should be read before undertaking the more detailed test procedures described in other International Standards. It covers the general area of methodology and is intended to fulfil the following functions: a) to provide a brief background of the essential features of methods of sensory analysis for the user of specific tests; b) to provide details of general requirements, procedures and interpretation of results common to all or most tests; c) to provide sufficient guidance on requirements, procedures and interpretation of results for the different specific tests to allow choice of the most appropriate procedure(s) for solution of a particular problem. It comprises three main aspects, covered in Clauses 4, 5 and 6. It is essential that Clause 4 “General requirements” be read first. Clause 5 “Methods of test” describes, in a general manner, all the main tests, under five headings: ⎯ Definition; ⎯ Application; ⎯ Assessors; ⎯ Procedure; ⎯ Analysis of results. Clause 6 is concerned with some general principles of data collection and analysis of sensory data and also briefly covers general principles of statistical treatment of the results.
oSIST ISO 6658:2011
oSIST ISO 6658:2011
INTERNATIONAL STANDARD ISO 6658:2005(E) © ISO 2005 – All rights reserved 1Sensory analysis — Methodology — General guidance 1 Scope This International Standard gives general guidance on the use of sensory analysis. It describes tests for the examination of foods by sensory analysis, and includes some information on the techniques to be used if statistical analysis of the results is required. Generally these tests are intended only for objective sensory analysis. However, if a test can be used for determining preference, this is indicated. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 5492, Sensory analysis — Vocabulary 3 Terms and definitions For the purposes of this International Standard, the terms and definitions given in ISO 5492 and the following apply. 3.1 sensory analysis examination of organoleptic attributes of a product by the sense organs 4 General requirements 4.1 Basic information This clause covers the general requirements common to all situations encountered in sensory analysis. The information basic to these requirements is as follows. a) The human response to one stimulus cannot be isolated from previous experience or from other sensory stimuli received from the environment. NOTE Nevertheless, influences arising from these two sources can be controlled and the effect standardized. a) Variability in sensory response is inherent in any group of people used for testing and is unavoidable; this can arise from inconsistencies within an individual, and through physiological and psychological differences between individuals. NOTE However, with training, such a group can show highly consistent individual responses. Recognition of these factors is important in the analysis of results. oSIST ISO 6658:2011
ISO 6658:2005(E) 2 © ISO 2005 – All rights reserved b) Systematic biases in sensory experiments involving human response can result in misleading data and incorrect interpretation that can be difficult to identify. The factors that can result in bias should be identified and controlled as far as possible by appropriate experimental design and conduct of the tests. c) The validity of the conclusions drawn from the results is dependent upon the test used and the way it is conducted, including the questions that have been asked. 4.2 Statement of objectives There are three main types of objective, as follows: a) those in which the primary aim of the test is to categorize, rank or describe the product(s); b) those in which the aim is to distinguish between two or more products; here it is important to distinguish between the need to know ⎯ if there is a difference at all, ⎯ how great is the magnitude of the difference, ⎯ the direction (or quality) of that difference, ⎯ the influence of that difference, e.g. with regard to preference, or ⎯ if all or only part of a population is detecting a difference; c) those in which reassurance is sought that products do not differ. In sensory analysis, a given problem frequently requires appreciable discussion or thought before an appropriate test is selected. This is because the initial concept of the problem may require clarification. 4.3 Choice of test The choice of appropriate test depends largely on the nature of the test objective, but also needs to take account of factors associated with the product, the assessors, the test environment, and the desired level of analytical precision and statistical confidence in the conclusions. The action that would occur based on the outcome of the test should be determined in advance. For each test, an attempt is made in Clause 5 to give guidance as to its relevance. Preliminary tests may be necessary to confirm the applicability of a given test. Because of sensory fatigue and the effects of adaptation, only a limited number of samples can be assessed during a session, depending on the nature of the test and the type of product. Some of these effects can be moderated by appropriate rinse procedures and recovery between samples. Whilst the use of control samples is essential in most cases, their use naturally limits the number of samples that can be assessed during any given session. The statistical plan should always be determined before commencing the tests. This is especially recommended if the number of samples to be evaluated requires more than one session. Details of statistical plans should be selected from specialized texts. Whatever test method is used, the sequential testing approach described in ISO 16820 should be considered whenever it is desirable to keep the number of samples or the number of assessors to a minimum. 4.4 Choosing and training assessors A sensory analysis panel constitutes a true “measuring instrument”, and consequently the results of the analyses conducted depend on its members. The recruitment of persons willing to participate in a panel, oSIST ISO 6658:2011
ISO 6658:2005(E) © ISO 2005 – All rights reserved 3therefore, needs to be carried out with care and should be considered as a real investment, both in time and financially. Management support in the organization is necessary if it is to be effective. Sensory assessment may be made by three types of assessor: “assessors”, “selected assessors” or “expert assessors”. Assessors can be “naive assessors” who do not have to meet a precise criterion of selection or training, or people who have already taken part in some sensory tests (initiated assessor). Selected assessors are assessors who have been selected and trained for the particular sensory test. Expert assessors are assessors who have been selected and trained for a variety of sensory analysis methods and who demonstrate particular acuity in panel work. NOTE Assessors employed by companies to undertake sensory analysis as their primary job function are examples of expert assessors. The selection and training methods to be employed depend on the tasks and methods that it is intended to give to the selected assessors. Procedures for training assessors for descriptive tests are different from those for training assessors in discrimination tests. Detailed procedures and methods for selection and training of assessors are given in ISO 8586-1. It should be noted that these methods sometimes only constitute a way of choosing the better candidates amongst those who are available, rather than to satisfy predetermined criteria. Also, the selection of assessors for their ability to discriminate and describe foods is quite different from that used for preference tests. The former tasks require selection and training, whereas the latter require only that the panel be representative of a specified sector of the population, for example, a group of consumers. If a selection procedure is to be carried out, some important criteria for choosing assessors are as follows: a) general ability to perform the specific sensory task, which may include a particular sensitivity to the stimuli under investigation; b) availability with respect to normal employment; c) motivation (willingness and interest); d) good health (including the absence of specific allergies or treatment with medications) and good dental and general hygienic condition. The performance of selected and expert assessors should be monitored regularly to ensure that the criteria by which they were initially selected continue to be met. 4.5 Material to be tested The nature of the product to be tested determines the experimental protocol of the test, and may also have an influence on the type of test that is required to satisfy the test objectives. For example, a protocol in which foods are to be consumed hot will need to take into account the cooling rate of the product and the likely effect on sensory attributes, and the changes in sensory attributes that may occur in keeping the product hot prior to testing. Methods of preparation and presentation of samples should be appropriate for the product and to the problem concerned. EXAMPLE 1 A product that is normally consumed hot should be prepared in the usual manner and tested hot; however, elevated temperatures may be used in some circumstances to increase the ease with which some flavours can be evaluated. EXAMPLE 2 A product that is normally consumed in discrete pieces should not be homogenized in order to retain textural characteristics. Care is needed, however, to ensure maximum uniformity between sub-samples for each assessor; this includes similar portion size and uniformity of composition. General principles for product sampling (in accordance with International Standards relating to the product under test) should be applied for test samples. In all cases, documentation of sample identification codes or oSIST ISO 6658:2011
ISO 6658:2005(E) 4 © ISO 2005 – All rights reserved lot numbers is necessary. Valid conclusions can be drawn for a product as a whole only if the samples tested are representative. Carriers may sometimes be used for tests relating to the evaluation of products for which direct tasting is not feasible (see ISO 5497), for example food ingredients. Lighting conditions should be specified when appearance is being assessed. When the test concerns only differences in flavour, the effect of colour differences may be partially masked by the use of lighting conditions that minimize the colour difference. Containers should be chosen so as not to affect the test or the product. These may include washable ceramic or glass containers, or disposable plastic or paper containers, but must not transfer chemical materials that could result in taint. In particular, washable containers should be washed only in odour- and taint-free detergents and rinsed in water, and polymeric and paper containers, including insulated containers used for hot or cold samples, should be odour- and taint-free. Palate cleansers may be used by the assessors between samples and between sessions, but care should be taken to ensure that they do not influence the flavour of products to be assessed. Still and carbonated water and bland foods (for example, unsalted crackers) may be used between samples and between sessions. Checks on the water supply are desirable to ensure that it is bland. For particular purposes, deionized water, glass-distilled water, low mineral content spring water, carbon-filtered water or boiled tap water may be used, but it should be noted that they are likely to have different flavours. 4.6 Test room Sensory analysis should be conducted in a dedicated test room (see ISO 8589 for details). The aim should be to create for each assessor a separate environment with minimum distraction, so that each assessor can quickly adjust to the nature of the new task(s). Extraneous activities, including preparation of the samples, should not be allowed during the tests, as these can lead to biased results. The room should be at a comfortable temperature and should be ventilated with odour-free air; limited airflow is desirable to avoid excessive temperature fluctuations. Persistent odours, such as tobacco or cosmetics, should not be allowed to contaminate the environment of the test room. Sound should be restricted. A low background noise is usually more tolerable than a fluctuating level of noise. Conversation is more distracting than background noise. Interruptions cause the greatest distraction. It is usually helpful to have control over both the colour and the intensity of the lighting, although coloured lights rarely succeed in completely masking differences in appearance. Surfaces should be non-absorbent and designed to facilitate a high standard of hygiene. The dimensions of the tasting booths are important; very low ceilings and very narrow booths can be oppressive or can give rise to a feeling of claustrophobia. Comfortable seating is necessary. If provision is made for computerized data acquisition, then this should be implemented safely, hygienically, and in a way that does not compromise sensory judgement. 4.7 Planning and conduct of the test The planning and operation of the test are determined by the objectives of the programme, the test chosen, and practical constraints associated with the use of human subjects. In particular, it is important to recognize the biases that might be inherent in the chosen test, and to operate the test in such a way as to minimize the effects of any bias. The potential biases can originate from both psychological and physiological sources. The most serious psychological bias results from assessors interacting to influence each other’s judgements, and should be minimized by the use of individual booths or adequate separation of the assessors. Moreover, strict management of the activities of the assessors is necessary. The manner and order of presentation of the samples are important aspects of the test, and can introduce psychological biases. For example, the samples should be coded by random three-digit numbers, and the oSIST ISO 6658:2011
ISO 6658:2005(E) © ISO 2005 – All rights reserved 5codes should be varied for each test. The order of assessment can also be a source of bias and, in general, the order should be specified. With a small number of samples and assessors, the order can be balanced so that every possible order occurs an equal number of times. In larger experiments, the order can be balanced or randomized. Physiological biases are frequently associated with the nature of the test samples. In particular, adaptation to a specific flavour stimulus can occur on repeated exposure to that stimulus, and fatigue can occur when chewing solid foods. Both factors can impose an upper limit on the number of samples to be assessed in a session. Expectoration of samples may be recommended with trained panels, but loss of information on specific sensory attributes may result. Hunger and satiety can influence an assessor's performance, and, if panels are held too frequently, performance may deteriorate. If it is possible, assessors should be asked to refrain from smoking and from consuming snacks such as coffee for 1 h before a test. Assessors should not carry any foreign odours into the session, for example tobacco or cosmetic odours, as these could influence the responses of other assessors. The time of day at which the test is conducted is important. The schedule should take into account local customary mealtimes since performance is generally considered optimum at mid-morning and mid-afternoon. Assessors suffering from emotional upsets, colds and other illnesses should be excluded from tests until they recover. The collation of the results comprises three aspects: ⎯ checking that all data have been recorded accurately, either on computer or manually; ⎯ verification that any additional relevant information which may aid or cast doubt on the interpretation of the results has been noted; ⎯ checking that the assessors are motivated to continue participating if further testing is planned. 5 Methods of test 5.1 General The most commonly used tests are divided into three groups: a) discrimination tests used to determine the probability of difference or similarity between products (see 5.2); b) tests using scales and categories to estimate the order or size of differences or the categories or classes to which samples should be allocated (see 5.3); c) descriptive tests used to identify the specific sensory attributes present in a sample (see 5.4). For the number of assessors, refer to the corresponding standards, taking into consideration α or β risk depending on the purpose of the test. Alternatively, sequential analysis (see ISO 16820) may allow a decision to be made after fewer trials of the test than would be required by conventional approaches that use a predetermined number of assessments. The tests may also be quantitative. 5.2 Discrimination tests 5.2.1 General The following tests are commonly used to determine the probability of difference or similarity between samples: oSIST ISO 6658:2011
ISO 6658:2005(E) 6 © ISO 2005 – All rights reserved a) paired comparison test (see 5.2.2); b) triangle test (see 5.2.3); c) duo-trio test (see 5.2.4); d) two-out-of-five test (see 5.2.5); e) “A — not A” test (see 6.2.6). For all these tests, there are different manners of analysing the results. 5.2.2 Paired comparison test 5.2.2.1 Definition This is a test in which samples are presented in pairs for comparison and detection of differences on the basis of some defined criteria. See ISO 5495 for details. 5.2.2.2 Application The paired comparison test is recommended a) to determine if a perceptible difference exists in a particular attribute (e.g. sweetness), or to determine if no perceptible difference exists in that attribute, b) to select, train and monitor the performance of the assessors, c) to compare two products in terms of preference in the context of consumer tests. Advantages of the test over other discrimination tests are simplicity and less sensory fatigue. The disadvantage of the method of paired comparisons is that as the number of samples to be compared increases the number of inter-comparisons required rapidly becomes impracticable. 5.2.2.3 Procedure The assessors receive a set of two samples (the pair). They designate the sample that they consider to be the most intense in the attribute under consideration, even if this choice is only a guess. One of the samples may be a control. The number of times each sample is selected is counted. It is necessary to determine, prior to carrying out the test, whether the statistical test that follows is to be one-sided (i.e. the test supervisor expects a particular direction of difference and the alternative hypothesis corresponds to the existence of a difference in that direction) or two-sided (i.e. the test supervisor has no expected direction of difference and the alternative hypothesis corresponds to a difference in either direction). Questions of difference and preference should not be combined: the recruitment criteria for panels are different for these questions. 5.2.2.4 Analysis of results See 6.2.2. oSIST ISO 6658:2011
ISO 6658:2005(E) © ISO 2005 – All rights reserved 75.2.3 Triangle test 5.2.3.1 Definition This is a discrimination test involving three coded samples, two of which are identical, presented simultaneously. The assessors are asked to select the odd sample. See ISO 4120 for details. 5.2.3.2 Application The triangle test is recommended a) when the nature of the difference is unknown, and b) for the selection and training of assessors. The test should not be used for the determination of preference. Some disadvantages of the test are that ⎯ it is uneconomical for the assessment of a large number of samples, ⎯ it may be more affected by sensory fatigue than the paired comparison test with intensely flavoured samples, ⎯ if the nature of the difference is known, it is statistically less efficient than some other tests, and ⎯ the method is applicable only if the products are as homogeneous as possible. 5.2.3.3 Procedure The assessors are each presented with one set of three coded samples, two of which are identical, and are asked to select the odd sample. Samples should be presented an equal number of times in each of the two sets of three distinct permutations of order, which are BAA ABA AAB ABB BAB BBA 5.2.3.4 Analysis of results See 6.2.3. 5.2.4 Duo-trio test 5.2.4.1 Definition This is a discrimination test in which the reference sample is presented first. It is followed by two samples, one of which is identical to the reference sample and which the assessors are asked to identify. See ISO 10399 for details. oSIST ISO 6658:2011
ISO 6658:2005(E) 8 © ISO 2005 – All rights reserved 5.2.4.2 Application This duo-trio test is used to determine if there is a sensory difference or similarity between a given sample and a reference. It is especially suitable when the reference sample is well known to the assessors, for example a sample of regular production. If there are after-tastes, this test is less suitable than the paired comparison test (5.2.2) or the “A — not A” test (5.2.6). 5.2.4.3 Procedure The assessors are first presented with the identified reference sample. This is followed by two coded samples, one of which is identical to the reference sample. The assessors are asked to identify this sample. 5.2.4.4 Analysis of results See 6.2.4. 5.2.5 Two-out-of-five test 5.2.5.1 Definition This is a discrimination test involving five coded samples, two of which are of one type and three of another. The assessors are asked to group the two sets of samples. 5.2.5.2 Application The two-out-of-five test is recommended to establish a difference more economically than other tests (the method is statistically more efficient). The disadvantages of this test are similar to those of the triangle test (5.2.3). It is more strongly affected by sensory fatigue an
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NORME ISO
INTERNATIONALE 6658
Deuxième édition
2005-10-01
Analyse sensorielle — Méthodologie —
Lignes directrices générales —
Sensory analysis — Methodology — General guidance —
Numéro de référence
ISO 6658:2005(F)
©
ISO 2005
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ISO 6658:2005(F)
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ISO 6658:2005(F)
Sommaire Page
Avant-propos. iv
Introduction . v
1 Domaine d'application. 1
2 Références normatives . 1
3 Termes et définitions. 1
4 Exigences générales . 1
4.1 Informations de base. 1
4.2 Exposé des objectifs . 2
4.3 Choix de l'essai. 2
4.4 Choix et entraînement des sujets . 3
4.5 Produit à soumettre à l'essai. 3
4.6 Local d'essai. 4
4.7 Planification et conduite de l'essai . 5
5 Méthodes d'essai . 6
5.1 Généralités . 6
5.2 Essais de discrimination. 6
5.3 Essais utilisant des échelles et des catégories.9
5.4 Essais descriptifs . 12
6 Analyse des résultats. 15
6.1 Généralités . 15
6.2 Essais de discrimination. 15
6.3 Essais utilisant des échelles et des catégories. 17
6.4 Essais analytiques ou descriptifs . 18
Annexe A (informative) Termes statistiques . 19
Bibliographie . 21
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ISO 6658:2005(F)
Avant-propos
L'ISO (Organisation internationale de normalisation) est une fédération mondiale d'organismes nationaux de
normalisation (comités membres de l'ISO). L'élaboration des Normes internationales est en général confiée
aux comités techniques de l'ISO. Chaque comité membre intéressé par une étude a le droit de faire partie du
comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l'ISO participent également aux travaux. L'ISO collabore étroitement avec
la Commission électrotechnique internationale (CEI) en ce qui concerne la normalisation électrotechnique.
Les Normes internationales sont rédigées conformément aux règles données dans les Directives ISO/CEI,
Partie 2.
La tâche principale des comités techniques est d'élaborer les Normes internationales. Les projets de Normes
internationales adoptés par les comités techniques sont soumis aux comités membres pour vote. Leur
publication comme Normes internationales requiert l'approbation de 75 % au moins des comités membres
votants.
L'attention est appelée sur le fait que certains des éléments du présent document peuvent faire l'objet de
droits de propriété intellectuelle ou de droits analogues. L'ISO ne saurait être tenue pour responsable de ne
pas avoir identifié de tels droits de propriété et averti de leur existence.
L'ISO 6658 a été élaborée par le comité technique ISO/TC 34, Produits alimentaires, sous-comité SC 12,
Analyse sensorielle.
Cette deuxième édition annule et remplace la première édition (ISO 6658:1985), qui a fait l'objet d'une
révision technique.
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ISO 6658:2005(F)
Introduction
La présente Norme internationale constitue une introduction générale à la méthodologie de l'analyse
sensorielle et il convient de la lire avant d'entreprendre d'appliquer les méthodes d'essai plus détaillées
décrites dans d'autres Normes internationales. Elle traite du domaine général de la méthodologie et elle est
destinée à remplir les fonctions suivantes:
a) fournir à l'utilisateur d'essais spécifiques un bref exposé général sur les caractéristiques essentielles des
méthodes d'analyse sensorielle;
b) fournir des détails sur les exigences générales, les modes opératoires et l'interprétation des résultats
communs à tous les essais ou à la plupart d'entre eux;
c) constituer un guide suffisant relatif aux exigences, aux modes opératoires et à l'interprétation des
résultats des différents essais spécifiques, afin de permettre de choisir le ou les modes opératoires les
plus appropriés à la résolution d'un problème particulier.
Elle comprend trois parties principales, faisant l'objet des Articles 4, 5 et 6.
Il est indispensable de lire en premier l'Article 4 «Exigences générales». L'Article 5 «Méthodes d'essai» décrit
les principaux essais, d'une manière générale, sous les cinq rubriques suivantes:
⎯ Définition;
⎯ Application;
⎯ Sujets;
⎯ Mode opératoire;
⎯ Analyse des résultats.
L'Article 6 traite de certains principes généraux relatifs à la collecte et à l'analyse de données sensorielles et
aborde aussi brièvement les principes généraux du traitement statistique des résultats.
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NORME INTERNATIONALE ISO 6658:2005(F)
Analyse sensorielle — Méthodologie — Lignes directrices
générales —
1 Domaine d'application
La présente Norme internationale fournit des lignes directrices générales sur la méthodologie de l'analyse
sensorielle. Elle décrit des essais destinés à l'examen des produits alimentaires par analyse sensorielle et
donne des informations relatives aux techniques à utiliser si une analyse statistique des résultats est requise.
Généralement, ces essais sont uniquement destinés à une analyse sensorielle objective. Toutefois, s'il est
possible d'utiliser un essai pour déterminer la préférence, cela est précisé.
2 Références normatives
Les documents de référence suivants sont indispensables pour l'application du présent document. Pour les
références datées, seule l'édition citée s'applique. Pour les références non datées, la dernière édition du
document de référence s'applique (y compris les éventuels amendements).
ISO 5492, Analyse sensorielle — Vocabulaire
3 Termes et définitions
Pour les besoins de la présente Norme internationale, les termes et définitions donnés dans l'ISO 5492 ainsi
que la définition suivante s'appliquent.
3.1
analyse sensorielle
examen des propriétés organoleptiques d'un produit par les organes des sens
4 Exigences générales
4.1 Informations de base
Le présent article traite des exigences générales communes à toutes les situations que l'on rencontre lors
d'analyses sensorielles et dont les principes de base sont les suivants.
a) La réponse humaine à un stimulus ne peut être isolée d'une expérience précédente ou des autres stimuli
sensoriels provenant de l'environnement.
NOTE Néanmoins, l'influence de ces deux facteurs peut être contrôlée et ses effets normalisés.
b) La variabilité de la réponse sensorielle est inhérente à tout groupe de sujets utilisé pour les essais et elle
est inévitable; elle peut provenir d'incohérences propres à un individu et de différences physiologiques et
psychologiques entre les individus.
NOTE Toutefois, avec de l'entraînement, un tel groupe de sujets peut donner des réponses individuelles très
homogènes. L'identification de ces facteurs est importante lors de l'analyse des résultats.
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ISO 6658:2005(F)
c) Des biais systématiques lors d'expériences sensorielles impliquant une réponse humaine peuvent aboutir
à des données fausses et à une interprétation incorrecte qu'il peut être difficile d'identifier. Il convient
d'identifier les facteurs susceptibles d'aboutir à des biais et de les contrôler, dans toute la mesure du
possible, en concevant et en conduisant les essais de manière appropriée.
d) La validité des conclusions tirées des résultats dépend de l'essai utilisé et de la façon dont il a été conduit
incluant le choix des questions posées.
4.2 Exposé des objectifs
Les trois principaux types d'objectifs sont les suivants:
a) ceux pour lesquels le but principal de l'essai est de catégoriser, de classer par rang ou de décrire le ou
les produits;
b) ceux dont le but est de différencier deux produits ou plus; il est important ici de faire la distinction entre la
nécessité de savoir
⎯ s'il existe bien une différence,
⎯ quelle est l'ampleur de la différence,
⎯ quel est le sens (ou la nature) de la différence,
⎯ quelle est l'influence de cette différence (par exemple sur la préférence), ou
⎯ si la totalité ou seulement une partie de la population détecte une différence;
c) ceux pour lesquels on cherche à obtenir l'assurance que les produits ne sont pas différents.
En analyse sensorielle, le problème donné nécessite fréquemment une discussion ou une réflexion sérieuse
avant de choisir un essai approprié. Cela est dû au fait que le concept initial du problème peut nécessiter une
explication.
4.3 Choix de l'essai
Le choix d'un essai approprié dépend beaucoup de l'objectif de l'essai mais nécessite également la prise en
compte de facteurs liés au produit, aux sujets, à l'environnement d'essai ainsi qu'au niveau recherché de
précision analytique et de confiance statistique des conclusions. Il convient que l'action pouvant découler des
résultats des tests soit déterminée à l'avance.
Pour chaque essai, on a tenté de donner dans l'Article 5 un guide relatif à son domaine d'application. Des
essais préliminaires peuvent s'avérer nécessaires pour confirmer la faisabilité d'un test donné.
En raison de la fatigue sensorielle et de phénomènes d'adaptation, il n'est possible d'évaluer qu'un nombre
limité d'échantillons au cours d'une session, nombre variable selon la nature de l'essai et le type de produit.
Certains de ces effets peuvent être atténués par des procédures appropriées de rinçage et de repos entre
échantillons.
Si des échantillons témoins sont nécessaires dans la plupart des cas, leur utilisation limite naturellement le
nombre d'échantillons qu'il est possible d'évaluer au cours d'une session donnée.
Il convient de toujours déterminer le plan d'expérience avant de commencer les essais, ce qui s'avère
particulièrement recommandé si le nombre d'échantillons à évaluer nécessite plus d'une session. Il convient
de sélectionner les détails des plans statistiques dans des ouvrages spécialisés. Quelle que soit la méthode
utilisée, chaque fois qu'il est souhaitable de minimiser le nombre d'échantillons ou de sujets, il convient
d'envisager l'approche séquentielle décrite dans l'ISO 16820.
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4.4 Choix et entraînement des sujets
Un jury d'analyse sensorielle constitue un vrai «instrument de mesure»; par conséquent, les résultats des
analyses effectuées dépendent de ses membres. Le recrutement de personnes désireuses de faire partie
d'un jury nécessite donc d'être effectué avec soin et d'être considéré comme un véritable investissement, à la
fois en temps et financièrement. L'appui de l'encadrement dans l'entreprise est nécessaire pour qu'il soit
efficace.
L'évaluation sensorielle peut être effectuée par trois types de sujets, à savoir des «sujets», des «sujets
qualifiés» ou des «sujets experts». Les sujets peuvent être des «sujets naïfs», n'ayant pas à remplir de critère
de sélection ou d'entraînement précis, ou encore des personnes ayant déjà pris part à quelques essais
sensoriels (sujet initié). Les sujets qualifiés sont des sujets qui ont été sélectionnés et entraînés pour un essai
sensoriel particulier. Les sujets experts sont des sujets qui ont été sélectionnés et entraînés pour différentes
méthodes d'analyse sensorielle et font preuve d'une acuité particulière pour le travail au sein d'un jury.
NOTE Les sujets employés par les entreprises pour réaliser des analyses sensorielles comme fonction première de
leur travail sont des exemples de sujets experts.
Les méthodes de sélection et d'entraînement à employer dépendent des tâches et des méthodes destinées
aux sujets qualifiés. Les modes opératoires utilisés pour entraîner les sujets aux essais descriptifs sont
différents de ceux utilisés pour entraîner les sujets aux essais de discrimination.
Des détails sur les modes opératoires et les méthodes de sélection et d'entraînement des sujets sont donnés
dans l'ISO 8586-1. Il convient de noter que, parfois, ces méthodes ne font que constituer un moyen de choisir
les meilleurs candidats parmi ceux disponibles, plutôt que satisfaire à des critères préétablis. Il convient
également de noter que la sélection de sujets pour leur aptitude à discriminer et à décrire les produits
alimentaires est tout à fait différente de celle utilisée pour des essais de préférence. Dans le premier cas, il est
nécessaire d'effectuer une sélection et un entraînement alors que, dans le second cas, il est uniquement
demandé au jury d'être représentatif d'une certaine partie de la population, par exemple un groupe de
consommateurs.
Si une procédure de sélection doit être mise en œuvre, quelques critères importants de choix des sujets sont
les suivants:
a) capacité générale à réaliser certaines tâches sensorielles spécifiques, incluant éventuellement une
sensibilité particulière au stimuli à tester;
b) disponibilité par rapport au travail habituel;
c) motivation (volonté et intérêt);
d) bonne santé (y compris l'absence d'allergies particulières ou de traitement médicamenteux) et bonnes
conditions dentaires et d'hygiène générale.
Pour s'assurer que les sujets qualifiés et experts continuent de remplir les critères sur lesquels ils ont été
sélectionnés, il convient de contrôler régulièrement leurs performances.
4.5 Produit à soumettre à l'essai
La nature du produit à soumettre à essai détermine le protocole expérimental de l'essai et peut également
avoir une incidence sur le type d'essai requis pour répondre aux objectifs de l'essai. Par exemple, un
protocole dans lequel les produits alimentaires doivent être consommés chauds nécessite de prendre en
compte la vitesse de refroidissement du produit et son effet probable sur les propriétés sensorielles, ainsi que
les changements des propriétés sensorielles qui peuvent se produire lorsque le produit est maintenu chaud
avant l'essai.
Il convient que les méthodes de préparation et de présentation des échantillons soient adaptées au produit et
au problème posé.
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EXEMPLE 1 Il convient qu'un produit normalement dégusté chaud soit préparé selon la technique habituelle et
dégusté chaud; toutefois, dans certaines circonstances, il est possible d'utiliser des températures élevées afin
d'augmenter la facilité avec laquelle certaines flaveurs peuvent être évaluées.
EXEMPLE 2 Il convient de ne pas homogénéiser un produit normalement dégusté en morceaux distincts afin de
conserver les caractéristiques de sa texture. Il faut cependant prendre soin de s'assurer qu'il y a une uniformité maximale
entre les sous-échantillons destinés à chacun des sujets, ce qui inclut des tailles de portions similaires et une composition
uniforme.
Il convient d'appliquer aux échantillons pour essai les principes généraux d'échantillonnage de produit
(conformément aux Normes internationales portant sur le produit soumis à l'essai). Dans tous les cas, il est
nécessaire d'indiquer les codes d'identification des échantillons ou les numéros de lots. Il n'est possible de
tirer des conclusions valables pour un produit dans son ensemble que si les échantillons soumis à essai sont
représentatifs.
Des supports peuvent parfois être utilisés dans les essais portant sur des produits pour lesquels l'analyse
directe n'est pas possible (voir l'ISO 5497), par exemple des ingrédients alimentaires.
Dans le cas de l'évaluation de l'aspect du produit, il convient de spécifier les conditions d'éclairage. Lorsque
l'essai porte uniquement sur les différences de flaveurs, l'effet des différences de couleur peut être
partiellement masqué en utilisant des conditions d'éclairage qui réduisent au minimum la différence de
couleur.
Il convient de choisir les récipients de manière à ce qu'ils n'affectent pas l'essai ou les produits. Il peut s'agir
de récipients en verre ou en céramique lavables ou de récipients en papier ou en plastique jetables, mais il ne
doit pas se produire de transfert de produits chimiques qui pourraient provoquer des flaveurs ou des odeurs
parasites. Il convient notamment de laver les récipients lavables uniquement à l'aide de détergents inodores
et ne laissant pas de goût anormal et de les rincer à l'eau; il convient que les récipients à base de polymères
et en papier, y compris les récipients isothermes utilisés pour les échantillons chauds ou froids, soient
également inodores et ne laissent pas de goût anormal.
Les sujets peuvent utiliser des rince-bouche entre les échantillons et entre les sessions, mais il convient de
prendre soin de s'assurer qu'ils n'ont pas d'incidence sur la flaveur des produits à évaluer. Il est possible
d'utiliser de l'eau plate et de l'eau gazeuse ainsi que des produits neutres (par exemple des biscuits sans sel)
entre les échantillons et entre les sessions. Il est souhaitable de vérifier l'alimentation en eau, afin de
s'assurer qu'elle est insipide. Dans des cas particuliers, il est possible d'utiliser de l'eau déionisée, de l'eau
distillée dans un appareil en verre, de l'eau de source faiblement minéralisée, de l'eau filtrée sur charbons ou
de l'eau du robinet bouillie, mais il convient de noter qu'elles sont susceptibles d'avoir des flaveurs différentes.
4.6 Local d'essai
Il convient de mener les analyses sensorielles dans un local d'essai prévu à cet effet (voir les détails dans
l'ISO 8589). Il convient que le but recherché soit de créer, pour chaque sujet, un environnement séparé offrant
le moins possible de distractions, de façon à ce que chaque sujet puisse s'adapter rapidement à la nature de
sa (ses) nouvelle(s) tâche(s). Pendant les essais, il convient de ne pas permettre d'activités annexes, y
compris la préparation des échantillons, car elles peuvent biaiser les résultats. Il convient que la pièce soit à
une température confortable et bien ventilée avec de l'air inodore; un débit d'air limité est souhaitable afin
d'éviter des variations de températures trop importantes. Il convient de ne pas laisser les odeurs persistantes,
comme les odeurs de tabac ou de cosmétiques, contaminer l'environnement du local d'essai.
Il convient de limiter le bruit. Un bruit de fond assez bas est généralement plus tolérable qu'un bruit dont le
niveau change. Une conversation est plus gênante qu'un bruit de fond. Ce sont les interruptions qui causent
le plus de perturbations.
Il est généralement utile d'avoir un contrôle simultané de la couleur et de l'intensité de l'éclairage, bien que les
lumières colorées ne réussissent que rarement à masquer complètement les différences d'aspect.
Il convient que les surfaces soient non absorbantes et conçues de manière à garantir un niveau d'hygiène
élevé. Les dimensions des cabines de dégustation sont importantes; des plafonds très bas et des cabines très
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étroites peuvent créer une impression d'oppression ou un phénomène de claustrophobie. Des sièges
confortables sont nécessaires.
Si des dispositions sont prises pour une saisie informatisée des données, il convient de le faire en toute
sécurité, dans des conditions d'hygiène et de manière à ne pas compromettre le jugement sensoriel.
4.7 Planification et conduite de l'essai
Les objectifs du programme, en fonction de l'essai choisi et des contraintes pratiques associées à
l'intervention de sujets humains, déterminent la planification et la conduite de l'essai. Il est notamment
important de reconnaître les biais qui peuvent être inhérents à l'essai choisi et de mener l'essai de manière à
réduire au minimum les effets de n'importe quel biais. Les biais potentiels peuvent avoir des causes à la fois
psychologiques et physiologiques.
Les biais psychologiques les plus sérieux proviennent de sujets s'influençant mutuellement et il convient de
les réduire au minimum en utilisant des cabines de dégustation individuelles ou des séparations adéquates
entre les sujets. De plus il est nécessaire d'organiser de manière stricte les activités des sujets.
Le mode et l'ordre de présentation des échantillons sont des aspects importants de l'essai et peuvent
introduire des biais psychologiques. Il convient, par exemple, de coder les échantillons à l'aide de nombres à
trois chiffres pris au hasard et de varier ces codes à chaque essai. L'ordre d'évaluation peut également créer
des biais et il convient généralement de préciser cet ordre. Avec un petit nombre d'échantillons et de sujets,
l'ordre peut être équilibré de manière à ce que tous les ordres possibles se présentent un même nombre de
fois. Lors d'essais plus importants, l'ordre peut être équilibré ou laissé au hasard.
Les biais physiologiques sont fréquemment associés à la nature des échantillons pour essai. En particulier,
l'exposition répétée à un stimulus de flaveur spécifique peut créer une adaptation à ce stimulus et mâcher des
aliments solides peut provoquer de la fatigue. Ces deux facteurs peuvent imposer une limite supérieure quant
au nombre d'échantillons à évaluer par session. Avec des jurys entraînés, il peut être préconisé de recracher
les échantillons, mais il peut en résulter une perte d'informations portant sur des propriétés sensorielles
spécifiques.
L'état de faim ou de satiété peut influencer les performances du sujet et, si les jurys sont sollicités trop
fréquemment, leurs performances peuvent se détériorer. Dans la mesure du possible, il convient de
demander aux sujets de s'abstenir de fumer et de consommer des en-cas, comme le café, au moins 1 h avant
l'essai. Il convient que les sujets n'introduisent pas d'odeurs étrangères lors de la session, des odeurs de
tabac ou de cosmétiques par exemple, car cela pourrait influencer les réponses des autres sujets.
L'heure du jour à laquelle se déroulent les essais est importante. Les horaires de test doivent prendre en
compte les habitudes locales, étant donné que l'acuité maximale est obtenue au milieu de la matinée et de
l'après-midi. Il convient que les sujets enrhumés, les sujets se trouvant sous le coup d'une émotion ou
souffrant d'autres maladies soient exclus des essais jusqu'à leur rétablissement.
La collecte des résultats comprend trois aspects:
⎯ s'assurer que toutes les données ont été enregistrées avec exactitude soit sur ordinateur, soit
manuellement;
⎯ vérifier que toutes les informations pertinentes complémentaires pouvant aider ou, au contraire, créer un
doute sur l'interprétation des résultats ont été notées;
⎯ s'assurer que les sujets sont toujours motivés pour continuer à participer aux essais, si nécessaire.
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5 Méthodes d'essai
5.1 Généralités
Les essais les plus courants sont divisés en trois groupes:
a) les essais de discrimination utilisés pour déterminer la probabilité de différence ou de similarité entre les
produits (voir 5.2);
b) les essais utilisant des échelles et des catégories, pour estimer l'ordre ou l'ampleur des différences ou les
catégories ou les classes dans lesquelles il convient de répartir les échantillons (voir 5.3);
c) les essais descriptifs, utilisés pour identifier les propriétés sensorielles particulières présentes dans un
échantillon (voir 5.4).
Le nombre de sujets peut être déterminé en se référant aux normes correspondantes, en prenant en
considération les risques α ou β qui sont fonction de l'objectif du test. L'analyse séquentielle (voir l'ISO 16820)
constitue une alternative qui peut permettre de prendre une décision avec moins de sujets qu'avec une
approche conventionnelle qui utilise un nombre prédéterminé d'évaluation.
Les essais peuvent aussi être quantitatifs.
5.2 Essais de discrimination
5.2.1 Généralités
Les essais suivants sont couramment utilisés pour déterminer la probabilité de différence ou de similarité
entre les échantillons:
a) essai de comparaison par paires (voir 5.2.2);
b) essai triangulaire (voir 5.2.3);
c) essai duo-trio (voir 5.2.4);
d) essai deux sur cinq (voir 5.2.5);
e) essai «A — non A» (voir 5.2.6).
Pour tous ces essais, il y a différentes manières d'analyser les résultats.
5.2.2 Essai de comparaison par paires
5.2.2.1 Définition
C'est un essai au cours duquel des échantillons sont présentés par paires en vue de les comparer et de
détecter des différences en se basant sur des critères définis.
Pour les détails, voir l'SO 5495.
5.2.2.2 Application
L'essai de comparaison par paires est recommandé pour
a) déterminer s'il existe ou non une différence perceptible, pour une caractéristique particulière (par
exemple sucré);
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b) sélectionner, entraîner et surveiller les performances des sujets;
c) comparer deux produits en terme de préférence, dans le cadre des essais de consommateurs.
Les avantages de cet essai par rapport à d'autres essais de discrimination sont sa simplicité et une moindre
...
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