prEN ISO 21415-2

SLOVENSKI STANDARD
01-september-2025
Pšenica in pšenična moka - Vsebnost glutena - 2. del: Določevanje mokrega
glutena in indeksa glutena na mehanski način (ISO/DIS 21415-2:2025)
Wheat and wheat flour - Gluten content - Part 2: Determination of wet gluten and gluten
index by mechanical means (ISO/DIS 21415-2:2025)
Weizen und Weizenmehl - Glutengehalt - Teil 2: Bestimmung von Feuchtgluten und
Glutenindex durch mechanische Verfahren (ISO/DIS 21415-2:2025)
Blé et farines de blé - Teneur en gluten - Partie 2: Détermination du gluten humide et du
gluten index par des moyens mécaniques (ISO/DIS 21415-2:2025)
Ta slovenski standard je istoveten z: prEN ISO 21415-2
ICS:
67.060 Žita, stročnice in proizvodi iz Cereals, pulses and derived
njih products
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 21415-2
ISO/TC 34/SC 4
Wheat and wheat flour — Gluten
Secretariat: SAC
content —
Voting begins on:
Part 2: 2025-07-24
Determination of wet gluten and
Voting terminates on:
2025-10-16
gluten index by mechanical means
Blé et farines de blé — Teneur en gluten —
Partie 2: Détermination du gluten humide et du gluten index par
des moyens mécaniques
ICS: 67.060
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
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Reference number
ISO/DIS 21415-2:2025(en)
DRAFT
ISO/DIS 21415-2:2025(en)
International
Standard
ISO/DIS 21415-2
ISO/TC 34/SC 4
Wheat and wheat flour — Gluten
Secretariat: SAC
content —
Voting begins on:
Part 2:
Determination of wet gluten and
Voting terminates on:
gluten index by mechanical means
Blé et farines de blé — Teneur en gluten —
Partie 2: Détermination du gluten humide et du gluten index par
des moyens mécaniques
ICS: 67.060
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
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
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Published in Switzerland Reference number
ISO/DIS 21415-2:2025(en)
ii
ISO/DIS 21415-2:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
3 Principle . 1
4 Reagents . 1
5 Apparatus . 2
6 Sampling . 3
7 Preparation of test sample . 3
8 Procedure . 3
8.1 General .3
8.2 Testing .3
8.3 Paste preparation.3
8.4 Paste washing .4
8.4.1 Detection of starch .4
8.4.2 Flour .4
8.4.3 Ground wheat .4
8.4.4 Special case .4
8.5 Spinning and weighing the wet gluten .4
8.6 Determining the gluten index .5
8.7 Number of measurements .5
9 Calculations and record of results . 5
10 Precision . 5
10.1 Interlaboratory tests .5
10.2 Repeatability .6
10.3 Reproducibility . .6
10.4 Critical difference .7
10.4.1 Comparison of two sets of measurements in the same laboratory .7
10.4.2 Comparison of two sets of measurements in two laboratories .8
11 Test report . 8
Annex A (informative) Washing chamber and mill of the Glutomatic unit and centrifuge. 9
Annex B (normative) Preparation of ground wheat .12
Annex C (informative) Results of interlaboratory tests .13
Annex D (informative) Interlaboratory and proficiency test data for commercial flours and
wheats . 17
Bibliography .25

iii
ISO/DIS 21415-2:2025(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
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 on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO's adherence to the WTO principles in the Technical Barriers to Trade (TBT)
see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 34, Food products, Subcommittee SC 4, Cereals and pulses.
This third edition of ISO 21415-2 cancels and replaces the second edition (ISO 21415-2:2015). It has
been technically revised by adding reproducibility requirements (see 10.3) in accordance with practical
observations in proficiency tests (see Annex D).
ISO 21415 consists of the following parts, under the general title Wheat and wheat flour — Gluten content:
— Part 1: Determination of wet gluten by a manual method
— Part 2: Determination of wet gluten and gluten index by mechanical means
— Part 3: Determination of dry gluten from wet gluten by using an oven-drying method
— Part 4: Determination of dry gluten from wet gluten by a rapid drying method

iv
ISO/DIS 21415-2:2025(en)
Introduction
The alternative techniques specified in this part of ISO 21415 and in ISO 21415-1 for isolation of wet gluten
(i.e. manual extraction and mechanical extraction) do not generally yield equivalent results. The reason
for this is that for full development of the gluten structure the dough needs to be allowed to rest. Hence,
the result obtained by manual extraction is usually greater than that obtained by mechanical extraction,
especially in the case of wheat with high gluten content. Therefore, the test report should always state the
technique used.
v
DRAFT International Standard ISO/DIS 21415-2:2025(en)
Wheat and wheat flour — Gluten content —
Part 2:
Determination of wet gluten and gluten index by
mechanical means
1 Scope
This part of ISO 21415 specifies a method for determining the content of wet gluten and the gluten index for
wheat flours (Triticum aestivum L. and Triticum durum Desf.) by mechanical means. This method is directly
applicable to flours. It also applies to common and durum wheat after grinding, if their particular size
distribution meets the specification given in Table B.1.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
wet gluten
viscoelastic substance consisting mainly of two protein fractions (gliadin and glutenin) in hydrated form,
obtained in the way indicated in this part of ISO 21415 or in ISO 21415-1
2.2
gluten index
mass proportion of wet gluten remaining on the sieve after centrifugation
Note 1 to entry: The higher the index, the stronger the gluten is.
2.3
ground wheat
result of experimental grinding of whole wheat with the granulometry cited in Table B.1
2.4
flour
finely ground wheat endosperm with a granulometry of less than 250 µm
3 Principle
Preparation of a paste from a sample of flour or of ground wheat and a sodium chloride solution in the
equipment’s chamber; separation of the wet gluten by washing this paste with a sodium chloride solution,
followed by removal of excess washing solution by centrifugation and weighing the residue. The gluten index
is obtained after centrifuging to force the wet gluten through a special sieve. The percentage of wet gluten
remaining on the sieve after centrifuging is defined as the gluten index.
4 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified and distilled or demineralized
water, or water of equivalent purity.

ISO/DIS 21415-2:2025(en)
4.1 Sodium chloride solution, 20 g/l.
Dissolve 200 g of sodium chloride (NaCl) in water, then dilute to 10 l. When using this, it is recommended
that the temperature of the solution be 22 °C ± 2 °C.
4.2 Solution of iodine/potassium iodide (Lugol’s solution).
Dissolve 2,54 g of potassium iodide (KI) in water. Add 1,27 g of iodine (I ) to this solution and, when the
reagents have completely dissolved, dilute to 100 ml with water.
5 Apparatus
Usual laboratory apparatus and, in particular, the following items.
1)
5.1 Automatic gluten separation unit , (single or double) consisting of a washing/mixing chamber,
mill(s) (see Figures A.1 and A.2) and an electronically controlled distribution device for extracting the gluten.
5.1.1 Mixing/washing chamber(s), fitted with replaceable chrome-plated sieve support(s) with polyester
sieves with an 88 µm mesh gap and polyamide sieves with an 840 µm mesh gap.
The distance between the mixing hook and the chrome-plated sieve support shall be 0,7 mm ± 0,05 mm. This
value should be checked with the calibrated thickness shims supplied.
5.1.2 10 l plastic drum, to contain the sodium chloride solution (4.1) connected to the equipment by a
plastic tube.
5.1.3 Distribution system, consisting of a peristaltic pump allowing the sodium chloride solution (4.1)
used for washing the gluten to be delivered at a constant rate of between 50 ml/min and 56 ml/min.
For a detailed description of the unit and for detailed operating instructions, users of this part of ISO 21415
should consult the leaflet of the maker of the equipment used.
5.2 Dispenser, for the sodium chloride solution, permitting delivery of 3 ml to 10 ml with an accuracy
of ±0,1 ml.
5.3 Centrifuge, capable of maintaining a rotational frequency of 6 000 ± 5 per minute and producing
a radial acceleration of 2 000 g, fitted with 2 perforated plates with holes of diameter 600 µm or 2 sieve
cassettes with a 22 mm in diameter grid containing 600 µm holes, to determine the gluten index (cf.
Figures A.3 and A.4).
5.4 Balance, with a display precision of 0,001 g and capable of weighing to the nearest 0,01 g.
5.5 Stainless steel spatula.
5.6 Beakers with 500 ml capacity (to catch the rinsing water).
5.7 Stainless steel or plastic grippers.
5.8 Lab grinder , capable of producing a ground product with a granulometry meeting the requirements
of Table B.1.
1) The Glutomatic unit (types 2100 and 2200) made by Perten Instruments AB (Sweden) is the mechanical device most
widely used at present for this purpose. This information is given for the benefit of users of this part of ISO 21415 and
in no way implies that ISO approves or recommends exclusive use of this device. Other equipment may also be used if it
yields similar results to those of the Glutomatic unit or those of the method described in ISO 21415-1.

ISO/DIS 21415-2:2025(en)
5.9 Watch glass.
6 Sampling
It is important for the laboratory to receive a truly representative sample which has not been damaged or
altered during transport or storage.
The method specified in this part of ISO 21415 does not cover sampling. A recommended sampling method
is given in ISO 24333.
7 Preparation of test sample
Homogenize the samples. Before measuring the gluten content, grind the wheat grains with a lab grinder
(5.8), as indicated in Annex B. Special precautions should be taken during grinding and storing to prevent
any alteration to the moisture content of samples.
8 Procedure
8.1 General
The operations of preparation and washing of the dough are carried out continuously with automatic
equipment (5.1). Follow the instructions supplied by the manufacturer of the equipment used.
Sample and sodium chloride solution shall be equilibrated at temperature of 22 °C ± 2 °C
8.2 Testing
Weigh 10 g of the sample to within 0,01 g for testing and transfer to the unit’s washing/mixing chamber
(5.1.1). Ensure that the washing chamber is fitted with a suitable sieve, which has been previously cleaned
and moistened.
When testing flour samples, one or more fine polyester sieve(s) (88 µm aperture) is/are used. When testing
ground wheat, chrome-plated sieve supports fitted with a slotted ring are also required with polyamide
sieves with a mesh gap of 840 µm. In that case, the test starts with the fine sieve and in addition a coarse
sieve is used for the second step in the method.
The gluten index is generally measured using only 88 µm polyester sieves and 840 µm polyamide sieves for
the preparation of the wet gluten. If metal sieves are used, this shall be clearly noted in the test report.
8.3 Paste preparation
As a starting suggestion, add 4,8 ml of sodium chloride solution (4.1) to the test sample with the dispenser
(5.2). Aim the flow of saline solution at the chamber wall so that it does not go through the sieve. Gently
shake the washing chamber to ensure that the saline solution is uniformly distributed over the flour.
It may be necessary to adjust the amount of saline solution used for samples with very high or very low gluten
content. If forming a consistent paste turns out to be difficult (the chamber is flooded during washing), the
amount of saline solution added should be reduced (minimum of 4,2 ml). If very hard firm gluten forms
during mixing, the amount of solution should be increased to 5,2 ml.
The mixing time is set by the manufacturer at 20 s, but this may be adjusted by the user, if necessary. If so,
the modified mixing time shall be reported when presenting the results in the test report (11). Contact the
manufacturer to obtain information on adjusting the regulator.

ISO/DIS 21415-2:2025(en)
8.4 Paste washing
8.4.1 Detection of starch
The washing time is set by the manufacturer to 5 minutes.
For the detection of starch, press out some drops of the washing solution from the gluten ball into a watch-
glass (5.9) and add a few drops of a solution of iodine (4.2) to it. If the colour of the solution does not change,
the washing out procedure is completed. If the colour of the solution turns into blue, it indicates that starch
is still present and the washing out procedure should be continued until the starch cannot be detected.
If the washing time is modified from the original 5 minutes, the modified mixing time shall be reported
when presenting the results in the test report (11).
8.4.2 Flour
The washing time is set by the manufacturer at 5 min. A volume of 250 ml to 280 ml of sodium chloride
solution is usually required for washing. The solution is delivered automatically by the equipment at a
constant pre-set rate of between 50 ml/min and 56 ml/min (depending on the equipment).
8.4.3 Ground wheat
After 2 min of washing, stop the equipment, remove the washing chamber with the partially washed gluten
and transfer all the content, including bran particles, to another washing chamber containing a large-grade
sieve (840 µm). This can be done by placing the washing chamber beneath a gentle stream of cold water
(turning one sieve round to face the other and positioning the finer sieve on top).
Place the washing chamber with the coarser sieve containing the transferred lump of gluten in the working
position and continue washing until the washing sequence ends.
8.4.4 Special case
If the automatic washing process does not wash the paste sufficiently, and if the equipment allows it, preset
dough mixing time (8.3) at a higher value or adjust distribution system flow rate (5.1.3).
8.5 Spinning and weighing the wet gluten
If the gluten index has to be determined, this operation is not needed, so go directly to 8.6.
When washing is complete, remove the wet gluten from the washing chamber using the grippers (5.7). Check
that no gluten remains inside the washing chamber.
Divide the gluten into two equal lumps and place them on the perforated plates of the centrifuge (5.3),
pressing down on them lightly.
Operate the centrifuge to remove the excess solution from the gluten (the pre-set time is 60 s). Remove the
gluten piece with the metal grippers (5.7) and weigh it all (m ) immediately to within 0,01 g (5.4).
There is no need to divide the gluten if a stabilizer is used inside the centrifuge.
If a double unit is used, two lumps of gluten will be produced. These should be treated separately placed on
one of the perforated plates respectively.
If excess moisture is always present, remove the wet gluten after centrifugation, gently rub t
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