prEN ISO 10399
(Main)Sensory analysis - Methodology - Duo-trio test (ISO/DIS 10399:2025)
Sensory analysis - Methodology - Duo-trio test (ISO/DIS 10399:2025)
ISO 10399 specifies a procedure for determining whether a perceptible sensory difference or similarity exists between samples of two products. The method is a forced-choice procedure. The method is applicable whether a difference exists in a single sensory attribute or in several attributes.
The method is statistically less efficient than the triangle test (described in ISO 4120) but is easier to perform by the assessors.
The method is applicable even when the nature of the difference is unknown (i.e. it determines neither the size nor the direction of difference between samples, nor is there any indication of the attribute(s) responsible for the difference). The method is applicable only if the products are fairly homogeneous.
The method is effective for
a) determining that
either a perceptible difference results (duo-trio testing for difference), or
a perceptible difference does not result (duo-trio testing for similarity) when, for example, a change is made in ingredients, processing, packaging, handling or storage, and
b) for selecting, training and monitoring assessors.
Two forms of the method are described:
- the constant-reference technique, used when one product is familiar to the assessors (e.g. a sample from regular production);
- the balanced-reference technique, used when one product is not more familiar than the other.
Sensorische Analyse - Prüfverfahren - Duo-Trio-Prüfung (ISO/DIS 10399:2025)
Analyse sensorielle - Méthodologie - Essai duo-trio (ISO/DIS 10399:2025)
ISO 10399 spécifie un mode opératoire permettant de déterminer s'il existe une différence sensorielle perceptible ou une similitude entre les échantillons de deux produits. La méthode est une procédure à choix forcé. Elle s'applique s'il existe une différence pour une seule propriété sensorielle ou pour plusieurs.
La méthode est statistiquement moins efficace que l'essai triangulaire (décrit dans l'ISO 4120), mais elle est plus facile à réaliser par les sujets.
La méthode est applicable même lorsque la nature de la différence est inconnue (ce qui signifie qu'elle ne détermine ni la taille ni le sens de la différence entre des échantillons et qu'elle ne donne pas non plus d'indications sur l'attribut/les attributs à l'origine de cette différence). La présente méthode n'est applicable que si les produits sont relativement homogènes.
La méthode est efficace dans les cas suivants:
a) déterminer
qu'il existe une différence perceptible (essai duo-trio de différence), ou
qu'il n'existe pas de différence perceptible (essai duo-trio de similitude), quand, par exemple, des modifications sont apportées aux ingrédients, à la transformation, à l'emballage, aux opérations de manutention ou de stockage, et
b) pour sélectionner, entraîner et contrôler les sujets.
Deux formes de cette méthode sont décrites:
- la technique de la référence constante, utilisée lorsque les sujets connaissent bien un produit (un échantillon de fabrication courante par exemple), et
- la technique de la référence équilibrée, utilisée quand aucun des produits n'est plus connu que l'autre.
Senzorična analiza - Metodologija - Preskus "duo-trio" (ISO/DIS 10399:2025)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2025
Senzorična analiza - Metodologija - Preskus "duo-trio" (ISO/DIS 10399:2025)
Sensory analysis - Methodology - Duo-trio test (ISO/DIS 10399:2025)
Sensorische Analyse - Prüfverfahren - Duo-Trio-Prüfung (ISO/DIS 10399:2025)
Analyse sensorielle - Méthodologie - Essai duo-trio (ISO/DIS 10399:2025)
Ta slovenski standard je istoveten z: prEN ISO 10399
ICS:
67.240 Senzorična analiza Sensory analysis
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
DRAFT
International
Standard
ISO/DIS 10399
ISO/TC 34/SC 12
Sensory analysis — Methodology —
Secretariat: AFNOR
Duo-trio test
Voting begins on:
Analyse sensorielle — Méthodologie — Essai duo-trio
2025-07-01
Voting terminates on:
ICS: 67.240
2025-09-23
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Reference number
ISO/DIS 10399:2025(en)
DRAFT
ISO/DIS 10399:2025(en)
International
Standard
ISO/DIS 10399
ISO/TC 34/SC 12
Sensory analysis — Methodology —
Secretariat: AFNOR
Duo-trio test
Voting begins on:
Analyse sensorielle — Méthodologie — Essai duo-trio
ICS: 67.240 Voting terminates on:
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
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This document is circulated as received from the committee secretariat.
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BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
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Published in Switzerland Reference number
ISO/DIS 10399:2025(en)
ii
ISO/DIS 10399:2025(en)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 General test conditions and requirements . 3
6 Assessors . 4
6.1 Qualification .4
6.2 Number of assessors . .4
7 Procedure . 4
8 Analysis and interpretation of results . 6
8.1 When testing for a difference .6
8.2 When testing for similarity .6
9 Test report . 6
10 Precision and bias . 6
Annex A (normative) Tables . 8
Annex B (informative) Examples .15
Bibliography .22
iii
ISO/DIS 10399:2025(en)
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
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with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of any patent
rights identified during the development of the document will be in the Introduction and/or on the ISO list of
patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL:
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 12,
Sensory analysis.
This fourth edition cancels and replaces the third edition (ISO 10399:2011), of which it constitutes a minor
revision. The document has been generalized beyond food and beverage applications. The description of
how to test for similarity were updated to best practices and some definitions and descriptions amended
to also encompass this scenario. Basic information on how to use the Thurstonian model in addition to the
previously emphasized guessing model has been added. The principle has been expanded slightly to enhance
clarity. Furthermore, R code is provided in the tables of Annex A as one alternative option to derive exact
results, which is exemplified in the examples in Annex B. Example B.2 has been modified to reflect state-of-
the-art testing for similarity, whereas example B.3 has been dropped as the confidence interval approach is
now embedded into the earlier examples. The references have been updated.
iv
DRAFT International Standard ISO/DIS 10399:2025(en)
Sensory analysis — Methodology — Duo-trio test
1 Scope
This document specifies a procedure for determining whether a perceptible sensory difference or similarity
exists between samples of two products. The method is a forced-choice procedure. The method is applicable
whether a difference exists in a single sensory attribute or in several attributes.
The method is statistically less efficient than the triangle test (described in ISO 4120) but is easier to perform
by the assessors.
The method is applicable even when the nature of the difference is unknown (i.e. it determines neither
the size nor the direction of difference between samples, nor is there any indication of the attribute(s)
responsible for the difference). The method is applicable only if the products are fairly homogeneous.
The method is effective for
a) determining that
1) either a perceptible difference results (duo-trio testing for difference), or
2) a meaningful perceptible difference does not result (duo-trio testing for similarity) when, for
example, a change is made in ingredients, processing, packaging, handling or storage, and
b) for selecting, training and monitoring assessors.
Two forms of the method are described:
— the constant-reference technique, used when one product is familiar to the assessors (e.g. a sample from
regular production);
— the balanced-reference technique, used when one product is not more familiar than the other.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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
ISO 8589, Sensory analysis — General guidance for the design of test rooms
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5492 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp
ISO/DIS 10399:2025(en)
3.1
alpha-risk
α-risk
probability of rejecting the null hypothesis by a statistical test when, in fact, the null hypothesis is true
Note 1 to entry: This is also known as Type I error rate, significance level or false positive rate.
Note 2 to entry: When testing for product differences, the alpha risk is the probability of erroneously concluding that
a perceptible difference exists when, in fact, it does not. When testing for similarity, the alpha risk is the probability of
erroneously concluding that the products are perceptibly similar when, in fact, they are not.
3.2
beta-risk
β-risk
probability of failing to reject the null hypothesis by a statistical test when, in fact, the null hypothesis is not true
Note 1 to entry: This is also known as Type II error rate or false negative rate. Furthermore, 1 – β is also known as the
power of the test.
Note 2 to entry: When testing for product differences, the beta risk is the probability of failing to conclude that a
perceptible difference exists when, in fact, the products are perceptually different. When testing for similarity, the
beta risk is the probability of failing to conclude that the products are perceptibly similar when, in fact, they are.
3.3
difference
situation in which samples (3.5) can be distinguished based on their sensory properties
3.4
p
d
The proportion of assessments in which a perceptible difference is detected between the two products is
given the symbol p
d
3.5
product
material to be evaluated
3.6
sample
unit of product (3.4) prepared, presented and evaluated in the test
3.7
sensitivity
< statistic> statistical parameters that measure the performance characteristics of the test
Note 1 to entry: In statistical terms, the sensitivity of the test is defined by the values of α, β and p (or δ).
d
3.8
similarity
situation in which any perceptible differences (3.3) between the samples (3.5) are so small that the products
(3.4) can be used interchangeably
3.9
Thurstonian δ
measure of the magnitude of the sensory difference between two products
Note 1 to entry: The true perceptual difference between two products is denoted δ. The estimate of δ from the data is
denoted d’ (“d-prime”).
Note 2 to entry: For a given protocol, any value of δ is equivalent to a value p so they can be used interchangeably, but
d
[5],[7]
the relationship changes with the test protocol.
ISO/DIS 10399:2025(en)
3.10
triad
three samples (3.5) given to an assessor in the duo-trio test
Note 1 to entry: In the duo-trio test, one sample is labelled as the reference, the other two are marked with different
codes. One of the coded samples is the same product as the reference; the other coded sample is the other product in
the test.
4 Principle
The number of assessors is chosen based on the sensitivity desired for the test (see 6.2 and the discussion in A.3).
Assessors receive a set of three samples (i.e. a triad), one sample of which is labelled as a reference and the
other two samples have different codes. The two coded samples are comprised of one sample that is the
same product as the labelled reference sample (i.e., the hidden reference) and one sample that is a different
product than the labelled reference sample (i.e., the test sample). The presentation order of the coded
samples is assigned to assessors based on balanced random schemes (see 7.1). The assessors are informed
that one of the coded samples is the same as the reference and that one is different. Based on their training
and the instructions given prior to the test, the assessors report either which of the coded samples they
believe to be same as the reference, or which of the coded samples they believe to be different from the
reference.
The number of correct responses is counted, and the significance is determined by reference to a statistical
table or an applicable computer program or app.
5 General test conditions and requirements
5.1 Clearly define the test objective in writing.
5.2 Carry out the test under conditions that prevent communication among assessors until all the
evaluations have been completed using facilities and booths that conform with ISO 8589.
5.3 Prepare the samples out of sight of the assessors and in an identical manner (i.e. same apparatus, same
vessels, same quantity of product).
5.4 Assessors shall not be able to identify the samples from the way in which they are presented. For
example, in a taste test, avoid any differences in appearance. Mask any irrelevant colour differences using
light filters and/or subdued illumination.
5.5 Code the test samples in a uniform manner, preferably using three-digit numbers, chosen at random
for each test. Each triad is composed of three samples, one labelled as the reference and two labelled with
different codes. Preferably, different codes should be used for each assessor during a session. However,
the same two codes may be used for all assessors within a test, provided that each code is used only once
per assessor during a test session (e.g. if several duo-trio tests on the same or different products are being
conducted in the same session).
5.6 It is preferable to present the samples under the conditions at which the product is generally used
(e.g., when tasting, present the samples at the temperature at which the product is generally consumed). The
serving conditions of the three samples in each triad shall be identical, just as that of all the other samples in
a series of tests on a given type of product.
5.7 The size, quantity or volume presented shall be identical for the three samples in each triad, just as
that of all the other samples in a series of tests on a given type of product. The size, quantity or volume to be
evaluated may be imposed. If it is not, the assessors should be told to take sizes, quantities or volumes that
are always similar whatever the sample.
ISO/DIS 10399:2025(en)
5.8 Depending on the products and test objectives, re-tasting (of the reference or all samples) may be
accepted. The assessors shall be instructed accordingly.
5.9 When tasting, the assessors shall be told whether or not they are to swallow the samples or whether
they are free to do as they please. In this latter case, they shall be requested to proceed in the same manner
for all samples. Depending on project objectives and test products, suitable neutralizing agents may be used
between or even within individual trials. Assessors shall be instructed accordingly.
5.10 During the test sessions, avoid giving information about product identity, expected treatment effects,
or individual performance until all testing is completed.
6 Assessors
6.1 Qualification
All assessors should possess the same level of qualification and training, this level being chosen on the basis
of the test objective (see ISO 8586 for guidance). Experience and familiarity with the product may improve
the performance of an assessor and, therefore, may increase the likelihood of a correct result, which will
then increase the probability of finding a significant difference but would decrease the likelihood to find
significant similarity. Monitoring the performance of assessors over time may be useful for increased
sensitivity.
All assessors shall be familiar with the mechanics of the duo-trio test (i.e. the format, task and evaluation
procedure).
6.2 Number of assessors
Choose the number of assessors so as to obtain the sensitivity required for the test (see discussion in
A.3). Using large numbers of assessors increases the likelihood of detecting small differences between
the products. However, in practice, the number of assessors often is determined by material conditions
(e.g. duration of the experiment, number of available assessors, quantity of product). When testing for a
difference, the typical number of assessors is between 32 and 36. When testing for no meaningful difference
(i.e. similarity), twice as many assessors (i.e. approximately 72) are typically needed for equivalent
sensitivity.
Avoid replicate evaluations by the same assessor whenever possible. However, if replicate evaluations
are needed to produce a sufficient number of total evaluations, every effort should be made to have each
assessor perform the same number of replicate evaluations. For example, if only 12 assessors are available,
have each assessor evaluate 3 triads to obtain a total of 36 evaluations.
NOTE Treating 3 evaluations performed by 12 assessors as 36 independent evaluations is not valid when testing
for similarity using Table A.2. However, the test for difference using Table A.1 is valid even when replicate evaluations
[8],[9]
are performed . Recent publications on replicated discrimination tests suggest alternative, model-based
[6]
approaches for analysing replicated evaluations in discrimination tests , or for analysing replicated evaluations in
[11]
discrimination tests with the purpose of showing similarity .
7 Procedure
7.1 If the product is familiar to the assessors (e.g. a control sample from the production line), use the
constant reference technique. If neither product is more familiar than the other, use the balanced-reference
technique:
a) Constant-reference technique: Prepare worksheets and scoresheets (see B.2) in advance of the test
so as to utilize an equal number of the two possible sequences of two products, A and B:
A-REF A B A-REF B A
ISO/DIS 10399:2025(en)
Distribute these at random in groups of two among the assessors (i.e. use each sequence once among the
first two assessors; use each sequence once again among the next two assessors, etc.) This will minimize
the imbalance that results if the total number of assessors is not an even number.
b) Balanced-reference technique: Prepare worksheets and scoresheets (see B.1) in advance of the test
so as to utilize an equal number of the four possible sequences of two products, A and B:
A-REF A B A-REF B A
B-REF A B B-REF B A
where the first two triads contain product A as the reference (i.e. A-REF) and the last two triads contain
product B as the reference (i.e. B-REF). Distribute these at random in groups of four among the assessors
(i.e. use each sequence once among the first group of four assessors; use each sequence once again among
the next group of four assessors, etc.). This will minimize the imbalance that results if the total number of
assessors is not a multiple of four.
7.2 Present the three samples of each triad simultaneously if possible, following the same spatial
arrangement for each assessor (e.g. on a line to be sampled always from left to right, in a triangular array).
Within the triad, assessors are generally allowed to make repeated evaluations of each sample as desired (if,
of course, the nature of the product allows for repeated evaluations).
7.3 Instruct the assessors to evaluate the reference sample first, then evaluate the two coded samples in
the order in which they were presented. Inform the assessors that one of the coded samples is the same as
the reference and that one is different from the reference. Instruct the assessors to indicate either which of
the two coded samples is the same as the reference, or which of the two coded samples is different from the
reference.
NOTE When deciding whether to instruct the assessors to select the sample that is the same as the reference or
to select the sample that is different from the reference, consideration is given to whether or not the panel routinely
uses other discrimination test methods. Many discrimination test methods like the triangle test, for example, focus
on identifying the “odd” or “different” sample in the test. Instructing the assessors to identify the “different” sample
in one method and to identify the “same” sample in another method can cause confusion and lead to higher levels of
incorrect responses.
7.4 Each scoresheet should provide for a single triad of samples. If an assessor is to carry out more than
one test in a session, collect the completed scoresheet and unused samples prior to serving the subsequent
triad. The assessor shall not go back to any samples from previous triads or change the verdict on any
previous test.
7.5 Do not ask questions about preference, acceptance or degree of difference after the assessor has
made a selection. The selection the assessor has just made may bias the reply to any additional questions.
Responses to such questions may be obtained through separate tests for preference, acceptance, degree of
difference, etc., see ISO 6658. A comment section asking why the choice was made may be included for the
assessor’s remarks.
7.6 The duo-trio test is a forced-choice procedure; assessors are not allowed the option of reporting “no
difference”. An assessor who detects no difference between the samples should be instructed to randomly
select one of the samples and to indicate that the selection was only a guess in the comments section of the
scoresheet.
ISO/DIS 10399:2025(en)
8 Analysis and interpretation of results
8.1 When testing for a difference
Use Table A.1 to analyse the data obtained from a duo-trio test. If the number of correct responses is greater
than or equal to the number given in Table A.1 (corresponding to the number of assessors and the α-risk
level chosen for the test), conclude that a perceptible difference exists between the samples (see B.1).
If desired, calculate a confidence interval on the proportion of the population that can distinguish the
samples. The method is described in B.1.5.
8.2 When testing for similarity
NOTE In this document, “similar” does not mean “identical”. Rather, “similar” means that the two products are
sufficiently alike to be used interchangeably. It is not possible to prove that two products are identical. However, it
can be demonstrated that any difference that does exist between two products is so small as to have no practical
significance. The maximum difference that is still considered as small enough (e.g., not deemed consumer-meaningful
by the project team) is indicated by p or δ.
d
Use Table A.2 to analyse the data obtained from a duo-trio test. If the number of correct responses is less
than or equal to the number given in Table A.2 (corresponding to the number of assessors, the α-risk level
and the value of p or δ chosen for the test), conclude that no meaningful difference (i.e. no difference of
d
more than p or δ) exists between the samples (see B.2). If results will be compared from one test to another,
d
then the same value of p or δ should be chosen for all tests.
d
If desired, calculate a confidence interval on the proportion of the population that can distinguish the
samples. The method is described in B.2.5.
9 Test report
Report the test objective, the results and the conclusions. The following additional information is
recommended:
— the purpose of the test and the nature of the treatment studied;
— full identification of the samples (i.e. origin, method of preparation, quantity, shape, stora
...
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