EN ISO 4120:2021

Sensory analysis - Methodology - Triangle test (ISO 4120:2021)

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 more efficient than the duo-trio test (described in ISO 10399), but has limited use with products that exhibit strong carryover and/or lingering flavours.
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 homogeneous.
The method is effective for:
a)   determining that:
     either a perceptible difference results (triangle testing for difference);
     a perceptible difference does not result (triangle testing for similarity),
when, for example, a change is made in ingredients, processing, packaging, handling or storage;
b)   selecting, training and monitoring assessors.

Sensorische Analyse - Prüfverfahren - Dreiecksprüfung (ISO 4120:2021)

Dieses Dokument legt ein Verfahren zur Feststellung, ob zwischen den Proben von zwei Prüfmaterialien ein wahrnehmbarer sensorischer Unterschied oder eine Ähnlichkeit vorhanden ist, fest. Bei dem Verfahren wird nach dem „Forced Choice“ Prinzip vorgegangen. Das Verfahren ist anwendbar, wenn ein Unterschied bei einem einzelnen sensorischen Merkmal oder bei mehreren Merkmalen vorliegt.
Das Verfahren ist statistisch aussagekräftiger als die Duo Trio Prüfung (beschrieben in ISO 10399), hat aber eine begrenzte Anwendung bei Prüfmaterialien, die starke überdeckende und/oder nachwirkende olfaktorische/gustatorische Eindrücke hinterlassen.
Das Verfahren ist auch dann anwendbar, wenn die Art des Unterschiedes unbekannt ist (d. h. es bestimmt weder Größe noch Richtung eines Unterschiedes zwischen den Proben noch liefert es Hinweise auf Merkmale, die für den Unterschied verantwortlich sind). Das Verfahren ist nur anwendbar, wenn die Prüfmaterialien homogen sind.
Das Verfahren eignet sich für
a) die Untersuchung daraufhin,
1) ob ein wahrnehmbarer Unterschied resultiert (Dreiecksprüfung auf Unterschied);
2) ob kein wahrnehmbarer Unterschied resultiert (Dreiecksprüfung auf Ähnlichkeit),
wenn zum Beispiel eine Änderung von Zutaten, Verarbeitung, Verpackung, Behandlung oder Lagerung vorgenommen wurde.
b) für die Auswahl, Schulung und Leistungsüberprüfung von Prüfpersonen.

Analyse sensorielle - Méthodologie - Essai triangulaire (ISO 4120:2021)

Le présent document 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 plus efficace que l'essai duo-trio (décrit dans l'ISO 10399), mais est d'une utilisation limitée pour les produits présentant une forte rémanence et/ou des arômes persistants.
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 la ou les propriétés à l'origine de cette différence]. La présente méthode n'est applicable que si les produits sont homogènes.
La méthode est efficace dans les cas suivants:
a)    pour déterminer:
     qu'il existe une différence perceptible (essai triangulaire de différence);
     qu'il n'existe pas de différence perceptible (essai triangulaire de similitude),
quand, par exemple, des modifications sont apportées aux ingrédients, à la transformation, à l'emballage, aux opérations de manutention ou de stockage;
b)    pour sélectionner, entraîner et contrôler les sujets.

Senzorična analiza - Metodologija - Trikotni "triangel" preskus (ISO 4120:2021)

General Information

• Status: Published
• Publication Date: 16-Mar-2021
• Withdrawal Date: 29-Sep-2021
• ICS: 67.240 - Sensory analysis
• Technical Committee: CEN/SS C01 - Food products
• Drafting Committee: CEN/SS C01 - Food products
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 17-Mar-2021
• Completion Date: 17-Mar-2021
• Ref Project: SIST EN ISO 4120:2021 - Sensory analysis - Methodology - Triangle test (ISO 4120:2021)

Relations

• Replaces: EN ISO 4120:2007 - Sensory analysis - Methodology - Triangle test (ISO 4120:2004)
• Effective Date: 08-Jun-2022

Overview - EN ISO 4120:2021 (Triangle test)

EN ISO 4120:2021 (ISO 4120:2021) specifies the accepted procedure for the triangle test, a forced‑choice sensory analysis method used to determine whether a perceptible sensory difference or similarity exists between two product variants. Assessors receive a triad of coded samples - two identical and one different - and must identify the odd sample. The method is applicable when differences may be in one attribute or many, and is statistically more efficient than the duo‑trio test, but it requires homogeneous products and is limited for items with strong carryover or lingering flavours.

Key topics and technical requirements

• Test principle: Forced‑choice triangle format (triad of samples: two alike, one different); count of correct responses used for inference.
• Statistical evaluation: Results are interpreted against statistical tables or software to quantify significance (alpha/beta risk concepts guide sensitivity).
• Assessor requirements: Assessors must be trained and familiar with the triangle test mechanics; choose assessor numbers to meet the desired sensitivity.
• Test conditions: Samples prepared out of sight, identically presented (code masking, controlled lighting, same temperature/volume), and testing conducted in booths conforming to ISO 8589.
• Sample coding & presentation: Randomized codes (preferably three‑digit), identical serving conditions per triad, and instructions about swallowing or expectoration must be given consistently.
• Limitations: The method detects whether a perceptible difference exists but does not indicate the size, direction, or which attribute(s) differ.
• Models referenced: Guidance includes both the traditional guessing model and the Thurstonian model for analysis.

Applications and who uses it

• Product development teams assessing reformulation, ingredient or process changes.
• Quality assurance and control labs verifying interchangeability after packaging, handling, or storage changes.
• Sensory laboratories for assessor selection, training and monitoring.
• R&D groups comparing prototypes or supplier batches where a simple detect/undetect outcome is required. Keywords: triangle test, sensory analysis, EN ISO 4120:2021, triangle testing, sensory difference, forced‑choice.

Practical value

• Rapid, statistically sound way to confirm perceptible difference or similarity.
• Efficient for detecting small differences when products are homogeneous and carryover effects are minimal.
• Useful for go/no‑go decisions (e.g., accept reformulation or proceed with rollout).

Related standards

• ISO 10399 (duo‑trio test) - alternate discrimination method
• ISO 8589 - test room design (referenced)
• ISO 5492 - sensory vocabulary (referenced)
• ISO 8586 - assessor qualification guidance

For implementation, use EN ISO 4120:2021 to design controlled triangle tests, select/monitor assessors, and interpret discrimination results using the prescribed statistical approach.

Standards Content (Sample)

SLOVENSKI STANDARD
01-julij-2021
Nadomešča:
SIST EN ISO 4120:2007
Senzorična analiza - Metodologija - Trikotni "triangel" preskus (ISO 4120:2021)
Sensory analysis - Methodology - Triangle test (ISO 4120:2021)
Sensorische Analyse - Prüfverfahren - Dreiecksprüfung (ISO 4120:2021)
Analyse sensorielle - Méthodologie - Essai triangulaire (ISO 4120:2021)
Ta slovenski standard je istoveten z: EN ISO 4120:2021
ICS:
67.240 Senzorična analiza Sensory analysis
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 4120
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2021
EUROPÄISCHE NORM
ICS 67.240 Supersedes EN ISO 4120:2007
English Version
Sensory analysis - Methodology - Triangle test (ISO
4120:2021)
Analyse sensorielle - Méthodologie - Essai triangulaire Sensorische Analyse - Prüfverfahren - Dreiecksprüfung
(ISO 4120:2021) (ISO 4120:2021)
This European Standard was approved by CEN on 23 February 2021.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4120:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 4120:2021) has been prepared by Technical Committee ISO/TC 34 "Food
products" in collaboration with CCMC.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by September 2021, and conflicting national standards
shall be withdrawn at the latest by September 2021.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 4120:2007.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 4120:2021 has been approved by CEN as EN ISO 4120:2021 without any modification.

INTERNATIONAL ISO
STANDARD 4120
Third edition
2021-03
Sensory analysis — Methodology —
Triangle test
Analyse sensorielle — Méthodologie — Essai triangulaire
Reference number
ISO 4120:2021(E)
©
ISO 2021
ISO 4120:2021(E)
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

ISO 4120:2021(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 General test conditions and requirements . 2
6 Assessors . 3
6.1 Qualification . 3
6.2 Number of assessors . 3
7 Procedure. 4
8 Analysis and interpretation of results . 4
8.1 When testing for a difference . 4
8.2 When testing for similarity. 5
9 Test report . 5
10 Precision and bias . 5
Annex A (normative) Tables . 7
Annex B (informative) Examples .12
Bibliography .17
ISO 4120:2021(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.
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 of 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 www .iso .org/
iso/ foreword .html.
This document was prepared by ISO/TC 34, Food products, Subcommittee SC 12, Sensory analysis, in
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/
SS C01, Food Products, in accordance with the Agreement on technical cooperation between ISO and
CEN (Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 4120:2004), which has been technically
revised. The main changes compared with the previous edition are as follows:
— the document has been generalized beyond food and beverage applications;
— guidance on how to use the Thurstonian model in addition to the previously emphasized guessing
model has been added.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved

INTERNATIONAL STANDARD ISO 4120:2021(E)
Sensory analysis — Methodology — Triangle 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 more efficient than the duo-trio test (described in ISO 10399), but has
limited use with products that exhibit strong carryover and/or lingering flavours.
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 homogeneous.
The method is effective for:
a) determining that:
1) either a perceptible difference results (triangle testing for difference);
2) a perceptible difference does not result (triangle testing for similarity),
when, for example, a change is made in ingredients, processing, packaging, handling or storage;
b) selecting, training and monitoring assessors.
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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
alpha-risk
α-risk
probability of concluding that a perceptible difference exists when one does not
Note 1 to entry: This is also known as Type I error, significance level or false positive rate.
ISO 4120:2021(E)
3.2
beta-risk
β-risk
probability of concluding that no meaningful difference exists when one does
Note 1 to entry: This is also known as Type II error or false negative rate.
3.3
difference
situation in which samples can be distinguished based on their sensory properties
Note 1 to entry: The proportion of assessments in which a perceptible difference is detected between the two
products is given the symbol p .
d
3.4
product
material to be evaluated
3.5
sample
unit of product prepared, presented and evaluated in the test
3.6
sensitivity
statistical parameters that measure the performance characteristics of the test
Note 1 to entry: The sensitivity of the test is defined by the values of α, β and p .
d
3.7
similarity
situation in which any perceptible differences between the samples are so small that the products can
be used interchangeably
3.8
triad
those three samples given to an assessor in the triangle test
Note 1 to entry: In the triangle test, each sample is marked with a different code. Two of the samples are alike (i.e.
from one product) and one is different (i.e. from the other product).
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) and are informed that two of the samples are the
same and that one is different. The assessors report which sample they believe to be different, even if
the selection is based only on a guess.
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 to ISO 8589.
2 © ISO 2021 – All rights reserved

ISO 4120:2021(E)
5.3 Prepare the samples out of sight of the assessors and in an identical manner (e.g. same apparatus,
same vessels, same quantities 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, each with a different code. Preferably,
different codes should be used for each assessor during a session. However, the same three 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 triangle tests on 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. in a taste test, 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 (e.g. in a taste test, the three
samples shall be served at the same temperature), 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.
5.8 In a taste test, 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 the samples.
5.9 During the test sessions, avoid giving information about product identity, expected treatment
effects, or individual performance until all testing is completed. The only necessary information for the
assessor is the nature of the product to be tested and the task to be performed.
6 Assessors
6.1 Qualification
All assessors should possess the same level of qualification, 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 finding a significant
difference. Monitoring the performance of assessors over time may be useful for increased sensitivity.
All assessors shall be familiar with the mechanics of the triangle test (i.e. 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 the 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 is often determined by material conditions
(e.g. duration of the experiment, number of available assessors, quantity of product). When testing
for a difference, typical numbers of assessors are between 24 and 30. When testing for no meaningful
difference (i.e. similarity), twice as many assessors (i.e. approximately 60) are 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
ISO 4120:2021(E)
each assessor perform the same number of replicate evaluations. For example, if only 10 assessors are
available, have each assessor evaluate 3 triads to obtain a total of 30 evaluations.
NOTE Treating three evaluations performed by 10 assessors as 30 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 are performed (see References [8] and [9]). References [4], [5] and [6] on replicated discrimination
tests suggest alternative approaches for analysing replicated evaluations in discrimination tests.
7 Procedure
7.1 Prepare worksheets and scoresheets (see B.1 and B.2) in advance of the test so as to utilize an
equal number of the six possible sequences of two products, A and B:
ABB AAB ABA
BAA BBA BAB
Distribute these at random in groups of six among the assessors (i.e. use each sequence once among the
first group of six assessors; use each sequence once again among the next group of six assessors, etc.).
This will minimize the imbalance that results if the total number of assessors is not a multiple of six.
NOTE The worksheets also can be prepared digitally and made available for the evaluations.
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 samples in the order in which they were presented. Inform
the assessors that two of the samples are the same and that one is different. Each assessor shall then
indicate which one of the three samples is different from the other two.
7.4 The triangle 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. The assessor has one chance out of three of giving the correct answer randomly.
7.5 The assessor shall not go back to any samples from previous triads or change the verdict on
any previous test. If an assessor is to carry out more than one test in a session, it is imperative that
the assessor shall not be able to change their response once given. For example, collect the completed
scoresheet and unused samples prior to serving the subsequent triad or do not allow the assessor to
return to an earlier answer screen once a response is confirmed.
7.6 Do not ask questions about preference, acceptance or degree of difference after the initial selection
of the odd sample. 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 for guidance.) A comment section asking why the choice was made may
be included for the assessor’s remarks.
8 Analysis and interpretation of results
8.1 When testing for a difference
Use Table A.1 to analyse the data obtained from a triangle 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
4 © ISO 2021 – All rights reserved

ISO 4120:2021(E)
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.3.
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.
Use Table A.2 to analyse the data obtained from a triangle 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 β-risk
level and the value of p chosen for the test), conclude that no meaningful difference exists between
d
the samples (see B.2). If results are to be compared from one test to another, then the same value of p
d
should be chosen for all tests.
If desired, calculate a confidence interval on the proportion of the population that can distinguish the
samples. The method is described in B.3.
9 Test report
Report the test objective, the samples that were tested, the results and the conclusions. Include
that the test was conducted in accordance with this document, i.e. ISO 4120:2021,
...