EN ISO 10399:2026

SLOVENSKI STANDARD
01-julij-2026
Senzorična analiza - Metodologija - Preskus "duo-trio" (ISO 10399:2026)
Sensory analysis - Methodology - Duo-trio test (ISO 10399:2026)
Sensorische Analyse - Prüfverfahren - Duo-Trio-Prüfung (ISO 10399:2026)
Analyse sensorielle - Méthodologie - Essai duo-trio (ISO 10399:2026)
Ta slovenski standard je istoveten z: EN ISO 10399:2026
ICS:
67.240 Senzorična analiza Sensory analysis
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 10399
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2026
EUROPÄISCHE NORM
ICS 67.240 Supersedes EN ISO 10399:2018
English Version
Sensory analysis - Methodology - Duo-trio test (ISO
10399:2026)
Analyse sensorielle - Méthodologie - Essai duo-trio Sensorische Analyse - Prüfverfahren - Duo-Trio-
(ISO 10399:2026) Prüfung (ISO 10399:2026)
This European Standard was approved by CEN on 24 May 2026.

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.

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Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
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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
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 10399:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 10399:2026) 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 November 2026, and conflicting national standards
shall be withdrawn at the latest by November 2026.
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 10399:2018.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
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, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 10399:2026 has been approved by CEN as EN ISO 10399:2026 without any modification.

International
Standard
ISO 10399
Fourth edition
Sensory analysis — Methodology —
2026-05
Duo-trio test
Analyse sensorielle — Méthodologie — Essai duo-trio
Reference number
ISO 10399:2026(en) © ISO 2026
ISO 10399:2026(en)
© ISO 2026
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.
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CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 10399:2026(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 . 5
8 Analysis and interpretation of results . 6
8.1 When testing for a difference .6
8.2 When testing for similarity .6
9 Precision and bias . 6
10 Test report . 6
Annex A (normative) Tables . 8
Annex B (informative) Examples . 16
Bibliography .22

iii
ISO 10399:2026(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
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 Technical Committee ISO/TC 34, Food products, Subcommittee SC 12,
Sensory analysis, in collaboration with the European Committee for Standardization (CEN), in accordance
with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This fourth edition cancels and replaces the third edition (ISO 10399:2017), which has been technically
revised.
The main changes are as follows:
— the document has been generalized beyond food and beverage applications;
— the description of how to test for similarity has been updated to best practices and some definitions and
descriptions have been 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;
— R code has been provided in the tables of Annex A as one alternative option to derive exact results, which
is exemplified in the examples in Annex B;
— the example in Clause B.2 has been modified to reflect state-of-the-art testing for similarity, whereas the
example in Clause B.3 has been dropped as the confidence interval approach is now embedded into the
earlier examples;
— the references have been updated.
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
International Standard ISO 10399:2026(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 either:
1) 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;
b) 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 terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/

ISO 10399:2026(en)
3.1
alpha-risk
α-risk
Type I error rate
significance level
false positive rate
α
probability of rejecting the null hypothesis by a statistical test when, in fact, the null hypothesis is true
Note 1 to entry: When testing for product (3.5) differences (3.3), the α-risk is the probability of erroneously concluding
that a perceptible difference exists when, in fact, it does not. When testing for similarity (3.8), the α-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
Type II error rate
false negative rate
β
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: 1 – β is also known as the power of the test.
Note 2 to entry: When testing for product (3.5) differences (3.3), the β-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 (3.8),
the β-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 (3.6) can be distinguished based on their sensory properties
3.4
p
d
proportion of assessments in which a perceptible difference (3.3) is detected between the two products (3.5)
3.5
product
material to be evaluated
3.6
sample
unit of product (3.5) 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 (3.4) (or δ (3.9)).
d
3.8
similarity
situation in which any perceptible differences (3.3) between the samples (3.6) are so small that the products
(3.5) can be used interchangeably
3.9
Thurstonian δ
δ
measure of the magnitude of the sensory difference (3.3) between two products (3.5)
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”).
ISO 10399:2026(en)
Note 2 to entry: For a given protocol, any value of δ is equivalent to a value p (3.4) so they can be used interchangeably,
d
[4][6]
but the relationship changes with the test protocol.
3.10
triad
three samples (3.6) 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 (3.5) 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
Clause 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 comprise 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 state 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 The samples should be presented 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

ISO 10399:2026(en)
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 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 should be chosen based
on the test objective (see ISO 8586 for guidance). Experience and familiarity with the product can improve
the performance of an assessor and, therefore, can 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 the discussion
in Clause A.3). Using large numbers of assessors increases the probability 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).
As examples, first consider testing for product differences, in which the null hypothesis assumes p = 0 %
d
and the desired power is 80 %. If the alternative hypothesis assumes the true p = 30 %, then a test at the
d
10 %-significance level requires 53 assessors. A test at the 5 %-significance level for the smaller effect size
of p = 25 % requires 102 assessors.
d
Next, consider testing for product similarity, in which the alternative hypothesis assumes p = 0 % and the
d
desired power is 80 %. If similarity is evaluated using the equivalence margin of p = 30 %, i.e. the null
d
hypothesis assumes p = 30 %, then a test at the 10 %-significance level requires 49 assessors. A test at the
d
5 %-significance level using the more conservative equivalence margin p = 25 % requires 102 assessors.
d
As these examples show, a test for product differences at a specific α-risk, β-risk, and values for p under
d
the null and alternative hypotheses requires a particular sample size that is nearly the same as, and often
identical to, the sample size needed to test for equivalence given these same parameter values, but where
the p values under the null and alternative hypotheses have been reversed.
d
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

ISO 10399:2026(en)
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 statistically valid
when testing for similarity using Table A.2. However, the test for difference using Table A.1 is statistically valid
[7][8]
even when replicate evaluations are performed. Recent publications on replicated discrimination tests suggest
[5]
alternative, model-based approaches for analysing replicated evaluations in discrimination tests, or for analysing
[10]
replicated evaluations in 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 (see 7.2). If neither product is more familiar than the other, use the balanced-
reference technique (see 7.3).
7.2 Constant-reference technique: Prepare worksheets and scoresheets (see Clause 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
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.
7.3 Balanced-reference technique: Prepare worksheets and scoresheets (see Clause 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.
7.4 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).
7.5 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 sa
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