Maize -- Determination of moisture content (on milled grains and on whole grains)

This document specifies two methods: - a reference method for the determination of the moisture content of maize grains and ground whole maize, groats, grits and maize flour, see Clause 4; - a routine method for the evaluation of the moisture content of maize in whole grains, see Clause 5. The latter is not suitable for use for experts' reports, or for calibration or checking of humidity meters, because of its significant bias to the reference method (see Table B.3).

Maïs -- Détermination de la teneur en eau (sur grains broyés et sur grains entiers)

Le présent document spécifie deux méthodes: - une méthode de référence pour la détermination de la teneur en eau des grains de maďs et de la mouture de maďs entier, des gruaux et de la farine de maďs; voir l'Article 4; - une méthode pratique pour l'évaluation de la teneur en eau des grains de maďs, en opérant sur les grains entiers; voir l'Article 5. Cette derničre ne convient ni pour des expertises ni pour l'étalonnage ou le contrôle des humidimčtres en raison de son biais important par rapport ŕ la méthode de référence (voir le Tableau B.3).

General Information

Status
Published
Publication Date
18-Feb-2021
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
13-Jan-2021
Completion Date
12-Jan-2021
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INTERNATIONAL ISO
STANDARD 6540
Second edition
2021-02
Maize — Determination of moisture
content (on milled grains and on
whole grains)
Maïs — Détermination de la teneur en eau (sur grains broyés et sur
grains entiers)
Reference number
ISO 6540:2021(E)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 6540:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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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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Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 6540:2021(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Reference method ............................................................................................................................................................................................... 1

4.1 Principle ........................................................................................................................................................................................................ 1

4.2 Apparatus .................................................................................................................................................................................................... 1

4.3 Sampling ....................................................................................................................................................................................................... 2

4.4 Preparation of the test sample .................................................................................................................................................. 2

4.4.1 Products not requiring to be ground .............................................................................................................. 2

4.4.2 Products requiring to be ground ........................................................................................................................ 3

4.5 Procedure .................................................................................................................................................................................................... 3

4.5.1 Number of determinations...................................................................................................................................... 3

4.5.2 Test portion .......................................................................................................................................................................... 3

4.5.3 Drying ........................................................................................................................................................................................ 4

4.5.4 Weighing ................................................................................................................................................................................. 4

4.6 Expression of results .......................................................................................................................................................................... 4

4.7 Precision ....................................................................................................................................................................................................... 5

4.7.1 Interlaboratory test ....................................................................................................................................................... 5

4.7.2 Repeatability ....................................................................................................................................................................... 5

4.7.3 Reproducibility .................................................................................................................................................................. 5

4.7.4 Comparison of two groups of measurements in a laboratory .................................................. 5

4.7.5 Comparison of two groups of measurements in two laboratories ....................................... 5

4.7.6 Uncertainty ........................................................................................................................................................................... 6

4.7.7 Comparison with the absolute method ........................................................................................................ 6

4.8 Notes on procedure ............................................................................................................................................................................. 6

4.9 Test report ................................................................................................................................................................................................... 6

5 Routine method on whole grains ........................................................................................................................................................ 7

5.1 Principle ........................................................................................................................................................................................................ 7

5.2 Apparatus .................................................................................................................................................................................................... 8

5.3 Sampling ....................................................................................................................................................................................................... 8

5.4 Procedure .................................................................................................................................................................................................... 8

5.4.1 Test portion .......................................................................................................................................................................... 8

5.4.2 Drying ........................................................................................................................................................................................ 8

5.4.3 Number of determinations...................................................................................................................................... 8

5.5 Expression of results .......................................................................................................................................................................... 9

5.5.1 Method of calculation and formulae ............................................................................................................... 9

5.5.2 Repeatability ....................................................................................................................................................................... 9

5.5.3 Reproducibility .................................................................................................................................................................. 9

5.5.4 Comparison of two groups of measurements in a laboratory .................................................. 9

5.5.5 Comparison of two groups of measurements in two laboratories ....................................10

5.5.6 Application of fidelity limits................................................................................................................................10

5.6 Remark ........................................................................................................................................................................................................10

5.7 Test report ................................................................................................................................................................................................10

Annex A (informative) Absolute method .......................................................................................................................................................11

Annex B (informative) Interlaboratory test results ...........................................................................................................................18

Annex C (informative) Application of fidelity data for the whole grains method ...............................................24

Bibliography .............................................................................................................................................................................................................................25

© ISO 2021 – All rights reserved iii
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ISO 6540:2021(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 Technical Committee ISO/TC 34, Food products, Subcommittee SC 4,

Cereals and pulses, in collaboration with the European Committee for Standardization (CEN) Technical

Committee CEN/TC 338, Cereal and cereal products, in accordance with the Agreement on technical

cooperation between ISO and CEN (Vienna Agreement).

This second edition cancels and replaces the first edition (ISO 6540:1980), which has been technically

revised. The main changes compared with the previous edition are as follows:

— Clauses 7 to 10 and 17 to 20 (now 4.5 to 4.9 and 5.4 to 5.7) and the annexes have been revised.

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
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ISO 6540:2021(E)
Introduction

The basic reference method and the routine reference method relating to cereals (see ISO 712) are

only applicable to other cereals than maize and cereal products. Therefore, this document has been

[4]

developed to specify the two methods for maize on the basis of research works published in 1979 .

The basic reference method for maize, which is called the “absolute method”, requires special equipment

and experienced personnel, and can only be applied in specialized laboratories.

Due to the very high moisture content that can be present in samples of maize (sometimes greater than

a mass fraction of 40 %) and because of the size and texture of the grains, the determination of the

moisture in maize raises problems with regard to its grinding and pre-drying.

Consequently, to allow the pre-drying and grinding to be avoided, this document also describes a

routine method for whole grains. which is easier to use and allows working in series. Its response time

is longer but the workload is lower, because of the absence of grinding. However, this practical whole

grain method has a positive bias of about a mass fraction of 0, 30 % compared to the reference method.

© ISO 2021 – All rights reserved v
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INTERNATIONAL STANDARD ISO 6540:2021(E)
Maize — Determination of moisture content (on milled
grains and on whole grains)
1 Scope
This document specifies two methods:

— a reference method for the determination of the moisture content of maize grains and ground whole

maize, groats, grits and maize flour, see Clause 4;

— a routine method for the evaluation of the moisture content of maize in whole grains, see Clause 5.

The latter is not suitable for use for experts’ reports, or for calibration or checking of humidity meters,

because of its significant bias to the reference method (see Table B.3).
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
moisture content of maize
loss in mass undergone by a product under specified conditions
Note 1 to entry: It is expressed as a percentage.
4 Reference method
4.1 Principle

If necessary, grinding of a sample, after pre-conditioning, if required. Drying of a test portion at a

temperature between 130 °C and 133 °C, under conditions that enable a result to be obtained in

agreement with that obtained by the absolute method (see Annex A).
4.2 Apparatus

4.2.1 Analytical balance, able to weight with an accuracy of ±0,001 g and therefore having a display

accuracy of 0,000 1 g.

4.2.2 Analytical balance, able to weight with an accuracy of ±0,1 g and therefore having a display

accuracy of 0,01 g.
© ISO 2021 – All rights reserved 1
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ISO 6540:2021(E)
4.2.3 Grinding mill, having the following characteristics:
a) made of material that does not absorb moisture;
b) easy to clean and having as little dead space as possible;

c) enabling grinding of 30 g of maize grains to be carried out rapidly and uniformly, without

appreciable development of heat and, as far as possible, without contact with the outside air;

d) adjustable so as to obtain particles of the dimensions indicated in 4.4.1.

4.2.4 Metal boat, without lid, with an effective surface area enabling 100 g of maize grains to be

distributed in a single layer.

4.2.5 Metal capsule, of suitable dimensions, non-corrodible under the test conditions, or, failing this,

a glass dish, with a sufficiently tight-fitting lid, and having an effective surface area such as to allow

distribution of the test portion with no more than 0,3 g per square centimetre.

4.2.6 Constant-temperature oven, electrically heated, adjustable between 60 °C and 80 °C, and with

adequate ventilation.

4.2.7 Constant-temperature oven, electrically heated, capable of being controlled in such a way that

the temperature of the air and of the shelves carrying the test portions is within the range of 130 °C to

133 °C in the neighbourhood of the test portions, in normal working condition.

The oven shall have a heat capacity such that, when initially adjusted to a temperature of 131 °C, it can

again reach this temperature in less than 45 min (preferably in less than 30 min) after insertion of the

maximum number of test portions that can be dried simultaneously.

The effectiveness of the ventilation shall be determined using durum wheat semolina, with a maximum

particle size of 1 mm, as the test material. The ventilation shall be such that, after inserting all the test

portions that the oven can hold and drying at a temperature of 130 °C to 133 °C, the results after a heating

period of 2 h and then a further 1 h will not differ by more than 0,15 g of moisture per 100 g of sample.

4.2.8 Desiccator, containing an efficient desiccant.
4.3 Sampling

Sampling is not part of the method specified in this document. A recommended sampling method is

given in ISO 24333.

The laboratory should be provided with a truly representative sample, in a sealed package, that is

undamaged and unmodified during transport and storage.
4.4 Preparation of the test sample
4.4.1 Products not requiring to be ground

Products that have particles of sizes less than or equal to 1,7 mm, less than a mass fraction of 10 %

being over 1 mm and more than a mass fraction of 50 % being less than 0,5 mm, do not need to be

ground before the determination.
Mix the laboratory sample thoroughly before taking the test portion (see 4.5.3).
2 © ISO 2021 – All rights reserved
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ISO 6540:2021(E)
4.4.2 Products requiring to be ground
4.4.2.1 General

If the laboratory sample does not have the particle size characteristics mentioned in 4.4.1, it shall be

ground either without pre-conditioning (4.4.2.2) or with pre-conditioning (4.4.2.3) as required.

4.4.2.2 Grinding without pre-conditioning

For products that are not likely to undergo variations in moisture content in the course of grinding (in

general, products with a moisture content between a mass fraction of 9,00 % and 15,00 %, see 4.8),

carry out grinding without pre-conditioning.

Adjust the grinding mill (4.2.3) to obtain particles of the dimensions indicated in 4.4.1.

Then quickly grind about 30 g of the laboratory sample, mix with a spatula and proceed immediately as

specified in 4.5.1.
4.4.2.3 Grinding with pre-conditioning

Products that are likely to undergo changes in moisture content in the course of grinding (in general,

products with a moisture content more than a mass fraction of 15,00 % or less than a mass fraction of

9,00 %) shall be pre-conditioned to bring their moisture content to between a mass fraction of 9,00 %

and 15,00 %, see 4.8) before grinding.

If the moisture content is greater than a mass fraction of 15,00 % (which is the more frequent case),

weigh, to the nearest 0,1g, about 100 g of the laboratory sample in the metal boat (4.2.4), place this

in the oven (4.2.7) controlled at between 60 °C and 80 °C, and leave it for the time necessary to bring

the moisture content to between a mass fraction of 9,00 % and 15,00 %. Take the boat out of the oven

and allow it to stand in the laboratory atmosphere for the time necessary (at least 2 h) for the pre-

conditioned sample to return to the laboratory temperature and for the moisture distribution to be

relatively uniform. During this rest, it shall be ensured that no addition or withdrawal of material is

made to the contents of the boat. If necessary, cover it with a sheet of paper but not with a lid, since this

could limit the exchange of moisture between the air and the grain.

After conditioning, weigh the sample to the nearest 0,1 g, then, proceeding rapidly, grind about 30 g of

this product. Mix using a spatula.

If the moisture content is less than a mass fraction of 9,00 %, place about 100 g of the laboratory sample,

weighed to the nearest 0,1 g, in a suitable atmosphere (usually that of the laboratory) and leave it until

a moisture content within the limits specified above is obtained.
4.5 Procedure
4.5.1 Number of determinations
For each laboratory sample, carry out the determination in duplicate.

Carry out one determination on each of the two ground test portions taken from the laboratory sample,

in accordance with 4.5.2 to 4.5.4. If the absolute difference between the two results is greater than the

repeatability limit given in 4.7.2, repeat the determination until the requirements are met.

4.5.2 Test portion

For each sample, tare to the nearest 0,001 g two metal capsules (4.2.5) beforehand. For each capsule,

note the tare t.

Weigh rapidly, to the nearest 0,001 g, approximately (8 ± 1) g of the test sample (see 4.4.1, 4.4.2.2 or

4.4.2.3, as appropriate) into the capsule. Note the mass m′ .
© ISO 2021 – All rights reserved 3
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ISO 6540:2021(E)
4.5.3 Drying

Place the open capsule containing the test portion, and the lid, in the oven (4.2.7) controlled between

130 °C and 133 °C and leave it for 4 h ± 5 min.

Never place moist products in an oven containing test portions at the end of dehydration, nor open the

oven door during drying, nor introduce new wet test samples before removing the dry test portions as

this would rehydrate them.

At the end of the drying time and, proceeding rapidly, take the dish out of the oven, cover it and place it

in the desiccator (4.2.8). When several tests are being carried out simultaneously, never place dishes on

top of one another in the desiccator.
4.5.4 Weighing

When the dish has cooled to laboratory temperature (generally between 30 min and 45 min after it has

been placed in the desiccator), weigh it to the nearest 0,001 g. Note the mass m′ .

4.6 Expression of results

The moisture content, w , expressed as a percentage by mass of the product as received, is given by

H2O
Formulae (1) and (2):
a) without pre-conditioning:
100
w = mm− (1)
H200 1
where
m = m′ – t is the mass, in grams, of the test portion (see 4.5.3);
0 0
m = m′ – t is the mass, in grams, of the test portion after drying (see 4.5.4);
1 1
t is the tare of the capsule, in grams (see 4.5.2).
b) with pre-conditioning:
 
100
wm= −m +−mm (2)
 
H20 01 23
m m
 0  2
 mm 
w =100 1−
 
H20
 
where
m and m have the same signification as in a) above;
0 1
m is the mass, in grams, of the sample before conditioning (see 4.4.2.3);
m is the mass, in grams, of the sample after conditioning (see 4.4.2.3).

Take as the result the average of the two values obtained, provided that the requirement for repeatability

(see 4.7.2) is satisfied. If it is not, repeat the determinations.
Express the result to the second decimal place.
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ISO 6540:2021(E)
4.7 Precision
4.7.1 Interlaboratory test

The details of an interlaboratory test relating to the precision of the method are summarized in

Annex B. Values from this test can only be applied to water content ranges from 11,90 % to 39,20 % and

the studied matrix (maize).
4.7.2 Repeatability

The absolute difference between two independent individual test results, obtained using the same

method on identical material tested in the same laboratory by the same operator using the same

apparatus and within a short time interval, shall be exceed in no more than 5 % of cases the repeatability

limit r.
For maize with water content between 11,90 % and 39,20 %:
— r = 2,8 S
— r = 2,8 × 0,07 = 0,19
4.7.3 Reproducibility

Reproducibility is the absolute difference between two individual test results, obtained with the same

method on identical material tested in different laboratories by different operators using different

equipment.

In practice, it is not appropriate to compare the results of two laboratories if the related test imposes

repeatability conditions.

The appropriate comparison tool is the critical difference as described in 4.7.5.

4.7.4 Comparison of two groups of measurements in a laboratory

The critical difference (D ) is the difference between two averaged values obtained from two test results

under repeatability conditions. Since each result is the average of two values (see 4.6), the comparison

of the two water content results shall be done using the critical difference.

The D between two averaged values each obtained from two test results under repeatability conditions

is shown by Formula (3):
1 1 1
DS=+28,,==28SS19,,80= 14 (3)
rr rr
2nn2 2
where
S is the standard deviation of repeatability;
n and n are the number of test results corresponding to each averaged values.
1 2
4.7.5 Comparison of two groups of measurements in two laboratories

The critical difference (D ) between two averaged values each obtained in two different laboratories

from two test results under repeatability conditions is shown by Formula (4):
1 1
22 22
DS=−28,(S 1−− ),=−28 SS05,,=068 (4)
RR rR r
2nn2
where
© ISO 2021 – All rights reserved 5
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ISO 6540:2021(E)
S is the standard deviation of repeatability;
S is the standard deviation of reproducibility;
n and n are the number of test results corresponding to each averaged values.
1 2
4.7.6 Uncertainty

It is possible to evaluate measurement uncertainties using data obtained from studies carried out in

accordance with ISO 5725-2. The reproducibility standard deviation obtained during an interlaboratory

test is a valid basis to assess measurement uncertainty because, by definition, uncertainty characterizes

the dispersion of values that can be reasonably attributed to the parameter.

The calculated expanded standard uncertainty should be ≤ ±2 reproducibility standard deviations (see

Annex B).
4.7.7 Comparison with the absolute method

Compared to the absolute method (see Annex A), the results generally differ from less than 0,15 g of

water per 100 g of samples.
4.8 Notes on procedure

4.8.1 The range of moisture contents for which the conditioning of the products before grinding is to

be carried out corresponds, in the laboratory, to a temperature of (20 ± 2) °C and a relative humidity of

45 % to 75 %. It should be modified for different atmospheric conditions.

4.8.2 The conditioning and grinding carried out on 100 g and 30 g, respectively, for a test portion of 8 g

are intended to provide a more representative sample. A direct sampling for grinding of only 8 g would

correspond to an insufficient quantity of initial product to be representative and would lead to too great

a dispersion of the results.
4.9 Test report
The test report shall contain at least the following information:

a) all the information necessary for the identification of the sample (type of sample, origin and

designation of the sample);
b) a reference to this document, i.e. ISO 6540;
c) the date and type of sampling procedure (if known);
d) the date of receipt;
e) the date of the test;
f) the test results and the units in which they have been expressed;

g) any operation not specified in the method or regarded as optional which might have affected

the result.
6 © ISO 2021 – All rights reserved
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ISO 6540:2021(E)
a) Without conditioning b) With conditioning
NOTE The weighing operations are boxed.

Figure 1 — Diagram of the two possible procedures for products requiring to be ground

5 Routine method on whole grains
5.1 Principle
Drying of whole grains for 38 h at a temperature between 130 °C and 133 °C.
© ISO 2021 – All rights reserved 7
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ISO 6540:2021(E)
5.2 Apparatus

5.2.1 Metal dish, non-corrodible under the test conditions, with a sufficiently tight-fitting lid, a

diameter of 50 mm to 60 mm and a minimum height of 25 mm.

5.2.2 Constant-temperature oven, electrically heated, capable of being controlled in such a way that

the temperature of the air and of the shelves carrying the test portions is within the range 130 °C to

133 °C, in the neighbourhood of the test portions, in normal working condition.
5.2.3 Desiccator, containing an efficient desiccant.
5.2.4 Analytical balance, capable of weighing with an accuracy of ±0,001 g
...

NORME ISO
INTERNATIONALE 6540
Deuxième édition
2021-02
Maïs — Détermination de la teneur en
eau (sur grains broyés et sur grains
entiers)
Maize — Determination of moisture content (on milled grains and on
whole grains)
Numéro de référence
ISO 6540:2021(F)
ISO 2021
---------------------- Page: 1 ----------------------
ISO 6540:2021(F)
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ii © ISO 2021 – Tous droits réservés
---------------------- Page: 2 ----------------------
ISO 6540:2021(F)
Sommaire Page

Avant-propos ..............................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Domaine d’application ................................................................................................................................................................................... 1

2 Références normatives ................................................................................................................................................................................... 1

3 Termes et définitions ....................................................................................................................................................................................... 1

4 Méthode de référence ..................................................................................................................................................................................... 1

4.1 Principe ......................................................................................................................................................................................................... 1

4.2 Appareillage............................................................................................................................................................................................... 1

4.3 Échantillonnage ...................................................................................................................................................................................... 2

4.4 Préparation de l’échantillon pour essai ............................................................................................................................. 2

4.4.1 Produits ne nécessitant pas de broyage ...................................................................................................... 2

4.4.2 Produits nécessitant un broyage ........................................................................................................................ 3

4.5 Mode opératoire .................................................................................................................................................................................... 3

4.5.1 Nombre de déterminations..................................................................................................................................... 3

4.5.2 Prise d’essai .......................................................................................................................................................................... 3

4.5.3 Séchage ..................................................................................................................................................................................... 4

4.5.4 Pesée ........................................................................................................................................................................................... 4

4.6 Expression des résultats ................................................................................................................................................................. 4

4.7 Fidélité ........................................................................................................................................................................................................... 5

4.7.1 Essai interlaboratoires ........................................................................................................................................... ..... 5

4.7.2 Répétabilité .......................................................................................................................................................................... 5

4.7.3 Reproductibilité ................................................................................................................................................................ 5

4.7.4 Comparaison de deux groupes de mesures dans un laboratoire ........................................... 5

4.7.5 Comparaison de deux groupes de mesures dans deux laboratoires ................................... 6

4.7.6 Incertitude ............................................................................................................................................................................. 6

4.7.7 Comparaison avec la méthode absolue ........................................................................................................ 6

4.8 Notes sur le mode opératoire ..................................................................................................................................................... 6

4.9 Rapport d’essai ....................................................................................................................................................................................... 6

5 Méthode pratique sur grains entiers .............................................................................................................................................. 7

5.1 Principe ......................................................................................................................................................................................................... 7

5.2 Appareillage............................................................................................................................................................................................... 8

5.3 Échantillonnage ...................................................................................................................................................................................... 8

5.4 Mode opératoire .................................................................................................................................................................................... 8

5.4.1 Prise d’essai .......................................................................................................................................................................... 8

5.4.2 Séchage ..................................................................................................................................................................................... 8

5.4.3 Nombre de déterminations..................................................................................................................................... 8

5.5 Expression des résultats ................................................................................................................................................................. 9

5.5.1 Méthode de calcul et formules ............................................................................................................................. 9

5.5.2 Répétabilité .......................................................................................................................................................................... 9

5.5.3 Reproductibilité ................................................................................................................................................................ 9

5.5.4 Comparaison de deux groupes de mesures dans un laboratoire ........................................... 9

5.5.5 Comparaison de deux groupes de mesures dans deux laboratoires ................................10

5.5.6 Application des limites de fidélité..................................................................................................................10

5.6 Remarque .................................................................................................................................................................................................10

5.7 Rapport d’essai ....................................................................................................................................................................................10

Annexe A (informative) Méthode absolue ....................................................................................................................................................12

Annexe B (informative) Essai interlaboratoires ....................................................................................................................................19

Annexe C (informative) Application des données de fidélité pour la méthode sur des grains

entiers ...........................................................................................................................................................................................................................25

Bibliographie ...........................................................................................................................................................................................................................26

© ISO 2021 – Tous droits réservés iii
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ISO 6540:2021(F)
Avant-propos

L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes

nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est

en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude

a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,

gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.

L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui

concerne la normalisation électrotechnique.

Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont

décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents

critères d’approbation requis pour les différents types de documents ISO. Le présent document a été

rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir www

.iso .org/ directives).

L’attention est attirée sur le fait que certains des éléments du présent document peuvent faire l’objet de

droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable

de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant

les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de

l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de

brevets reçues par l’ISO (voir www .iso .org/ brevets).

Les appellations commerciales éventuellement mentionnées dans le présent document sont données

pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un

engagement.

Pour une explication de la nature volontaire des normes, la signification des termes et expressions

spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion

de l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles

techniques au commerce (OTC), voir le lien suivant: www .iso .org/ iso/ fr/ avant -propos .html.

Le présent document a été élaboré par le comité technique ISO/TC 34, Produits alimentaires, sous-

comité SC 4, Céréales et légumineuses, en collaboration avec le comité technique CEN/TC 338, Céréales

et produits céréaliers, du Comité européen de normalisation (CEN), conformément à l’Accord de

coopération technique entre l’ISO et le CEN (Accord de Vienne).

Cette deuxième édition annule et remplace la première édition (ISO 6540:1980), qui a fait l’objet d’une

révision technique. Les principales modifications par rapport à l’édition précédente sont les suivantes:

— Les Articles 7 à 10 et 17 à 20 (désormais renumérotés 4.5 à 4.9 et 5.4 à 5.7) et les annexes ont été

révisés.

Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent

document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes

se trouve à l’adresse www .iso .org/ fr/ members .html.
iv © ISO 2021 – Tous droits réservés
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ISO 6540:2021(F)
Introduction

La méthode de référence fondamentale et la méthode de référence pratique relatives aux céréales

(voir l’ISO 712) ne sont applicables qu’aux céréales autres que le maïs et aux produits céréaliers. Par

conséquent, le présent document a été élaboré en vue de spécifier les deux méthodes applicables au

[4]
maïs sur la base des travaux de recherche publiés en 1979 .

La méthode de référence fondamentale relative au maïs, appelée «méthode absolue», qui demande un

matériel particulier et un personnel expérimenté, ne peut être appliquée que dans des laboratoires

spécialisés.

Du fait des très hautes teneurs en eau pouvant être présentes dans les échantillons de maïs (parfois

supérieures à 40 % en fraction massique) et du fait de la dimension et de la texture des grains, le dosage

de l’eau dans le maïs pose des problèmes au niveau de son broyage et de son préséchage.

En conséquence, si l’on veut éviter ce préséchage et ce broyage, le présent document décrit également

une méthode pratique sur grains entiers qui est plus facile d’emploi et permet un travail en série.

Son temps de réponse est plus long, mais la charge de travail est moins importante en raison de

l’absence de broyage. Cependant, cette méthode pratique sur grains entiers comporte un biais positif

d’environ 0,30 % en fraction massique comparé à la méthode de référence.
© ISO 2021 – Tous droits réservés v
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NORME INTERNATIONALE ISO 6540:2021(F)
Maïs — Détermination de la teneur en eau (sur grains
broyés et sur grains entiers)
1 Domaine d’application
Le présent document spécifie deux méthodes:

— une méthode de référence pour la détermination de la teneur en eau des grains de maïs et de la

mouture de maïs entier, des gruaux et de la farine de maïs; voir l’Article 4;

— une méthode pratique pour l’évaluation de la teneur en eau des grains de maïs, en opérant sur les

grains entiers; voir l’Article 5.

Cette dernière ne convient ni pour des expertises ni pour l’étalonnage ou le contrôle des humidimètres

en raison de son biais important par rapport à la méthode de référence (voir le Tableau B.3).

2 Références normatives
Le présent document ne contient aucune référence normative.
3 Termes et définitions

Pour les besoins du présent document, les termes et définitions suivants s’appliquent.

L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en

normalisation, consultables aux adresses suivantes:

— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp

— IEC Electropedia: disponible à l’adresse http:// www .electropedia .org/
3.1
teneur en eau du maïs
perte de masse subie par un produit dans des conditions spécifiées
Note 1 à l'article: Elle est exprimée en pourcentage.
4 Méthode de référence
4.1 Principe

Broyage éventuel d’un échantillon, après conditionnement préalable si nécessaire. Séchage d’une prise

d’essai à une température comprise entre 130 °C et 133 °C, dans des conditions permettant d’obtenir un

résultat concordant avec celui qui est obtenu par la méthode absolue (voir l’Annexe A).

4.2 Appareillage

4.2.1 Balance analytique, permettant des pesées à ± 0,001 g près et ayant donc une précision

d’affichage de 0,000 1 g.

4.2.2 Balance analytique, permettant des pesées à ± 0,1 g près et ayant donc une précision d’affichage

de 0,01 g.
© ISO 2021 – Tous droits réservés 1
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ISO 6540:2021(F)
4.2.3 Broyeur, ayant les caractéristiques suivantes:
a) construit en matériau n’absorbant pas l’humidité;
b) facile à nettoyer et présentant un espace mort minimal;

c) permettant un broyage rapide et uniforme de 30 g de grains de maïs, sans provoquer d’échauffement

sensible et en évitant au maximum le contact avec l’air extérieur;

d) pouvant être réglé de façon à obtenir des dimensions de particules correspondant à celles indiquées

en 4.4.1.

4.2.4 Nacelle métallique, sans couvercle, ayant une surface utile permettant d’obtenir la répartition

de 100 g de grains de maïs en couche unique.

4.2.5 Capsule métallique, de dimensions appropriées, non attaquable dans les conditions de l’essai,

ou, à défaut, capsule en verre, munie d’un couvercle suffisamment étanche et ayant une surface utile

permettant d’obtenir une répartition de la prise d’essai d’au maximum 0,3 g par centimètre carré.

4.2.6 Étuve isotherme, à chauffage électrique, réglable entre 60 °C et 80 °C, et possédant une

ventilation suffisante.

4.2.7 Étuve isotherme, à chauffage électrique, réglable de façon que la température de l’air et des

plateaux porte-échantillons soit comprise entre 130 °C et 133 °C au voisinage des prises d’essai, en

condition de fonctionnement normal.

L’étuve doit avoir une capacité calorifique telle que, réglée préalablement à une température de 131 °C,

elle puisse atteindre à nouveau cette température moins de 45 min (de préférence, moins de 30 min)

après la mise en place du nombre maximal de prises d’essai pouvant sécher simultanément.

L’efficacité de la ventilation doit être déterminée en utilisant comme matériau d’essai une semoule de

blé dur ayant une dimension maximale de particules de 1 mm. La ventilation doit être telle qu’après

insertion du nombre maximal de prises d’essai que l’étuve peut recevoir et séchage à une température

comprise entre 130 °C et 133 °C, les résultats, après une période de chauffage des mêmes prises d’essai

durant 2 h puis durant 1 h supplémentaire, ne présentent pas entre eux d’écart supérieur à 0,15 g d’eau

par 100 g d’échantillon.
4.2.8 Dessiccateur, garni d’un agent déshydratant efficace.
4.3 Échantillonnage

L’échantillonnage ne fait pas partie de la méthode spécifiée dans le présent document. Une méthode

d’échantillonnage recommandée est indiquée dans l’ISO 24333.

Il convient que le laboratoire reçoive un échantillon réellement représentatif, dans un emballage

étanche, n’ayant pas été endommagé ou modifié lors du transport et de l’entreposage.

4.4 Préparation de l’échantillon pour essai
4.4.1 Produits ne nécessitant pas de broyage

Les produits qui ont des particules de dimensions inférieures ou égales à 1,7 mm, dont moins de 10 %

en fraction massique sont supérieures à 1 mm et plus de 50 % en fraction massique sont inférieures

à 0,5 mm, n’ont pas besoin d’être broyés avant la détermination.

Bien homogénéiser l’échantillon pour laboratoire avant de prélever la prise d’essai (voir 4.5.3).

2 © ISO 2021 – Tous droits réservés
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ISO 6540:2021(F)
4.4.2 Produits nécessitant un broyage
4.4.2.1 Généralités

Si l’échantillon pour laboratoire ne correspond pas aux caractéristiques granulométriques mentionnées

en 4.4.1, il est nécessaire de le broyer sans conditionnement préalable (4.4.2.2) ou avec conditionnement

préalable (4.4.2.3), selon le cas.
4.4.2.2 Broyage sans conditionnement préalable

Pour les produits qui ne risquent pas de subir des variations de teneur en eau au cours du broyage (en

général lorsque la teneur en eau est comprise entre 9,00 % et 15,00 % en fraction massique; voir 4.8),

effectuer le broyage sans conditionnement préalable.

Régler le broyeur (4.2.3) pour obtenir des particules ayant les dimensions indiquées en 4.4.1.

Broyer ensuite rapidement environ 30 g de l’échantillon pour laboratoire, puis homogénéiser au moyen

d’une spatule et opérer immédiatement conformément à 4.5.1.
4.4.2.3 Broyage avec conditionnement préalable

Les produits risquant de subir des variations de teneur en eau au cours du broyage (en général lorsque

la teneur en eau est supérieure à 15,00 % ou inférieure à 9,00 % en fraction massique) doivent être

préalablement conditionnés de façon à amener leur teneur en eau entre 9,00 % et 15,00 % en fraction

massique (voir 4.8), avant le broyage.

Si la teneur en eau est supérieure à 15,00 % en fraction massique (cas le plus fréquent), peser, à 0,1g

près, environ 100 g de l’échantillon pour laboratoire dans la nacelle métallique (4.2.4), placer celle-ci

dans l’étuve (4.2.7) réglée entre 60 °C et 80 °C, et l’y laisser séjourner le temps nécessaire pour ramener

la teneur en eau entre 9,00 % et 15,00 % en fraction massique. Retirer la nacelle de l’étuve et la laisser

reposer dans l’atmosphère du laboratoire le temps nécessaire (au moins 2 h) pour ramener l’échantillon

préconditionné à la température du laboratoire et obtenir une répartition de l’eau relativement

homogène. Pendant ce repos, il faut s’assurer qu’aucun matériau n’est ajouté ou retiré du contenu de

la nacelle. Si nécessaire, la recouvrir avec une feuille de papier, mais pas avec un couvercle, car cela

pourrait limiter l’échange d’humidité entre l’air et le grain.

Après conditionnement, peser l’échantillon à 0,1 g près, puis, en opérant rapidement, broyer environ 30 g

de ce produit. Homogénéiser au moyen d’une spatule.

Si la teneur en eau est inférieure à 9,00 % en fraction massique, placer environ 100 g de l’échantillon pour

laboratoire, pesés à 0,1 g près, dans une atmosphère appropriée (en général celle du laboratoire) et les y

laisser séjourner jusqu’à l’obtention d’une teneur en eau comprise dans les limites spécifiées ci-dessus.

4.5 Mode opératoire
4.5.1 Nombre de déterminations
Effectuer deux déterminations pour chaque échantillon pour laboratoire.

Effectuer une détermination sur chacune des deux prises d’essai broyées prélevées à partir de

l’échantillon pour laboratoire conformément à 4.5.2 à 4.5.4. Si la différence absolue entre les deux

résultats est supérieure à la limite de répétabilité indiquée en 4.7.2, répéter la détermination jusqu’à ce

que les exigences soient satisfaites.
4.5.2 Prise d’essai

Pour chaque échantillon, tarer à 0,001 g près deux capsules métalliques (4.2.5). Pour chaque capsule,

noter la tare t.
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ISO 6540:2021(F)

Peser rapidement, à 0,001 g près, environ (8 ± 1) g de l’échantillon pour essai (voir 4.4.1, 4.4.2.2

ou 4.4.2.3, selon le cas) dans la capsule. Noter la masse m′0.
4.5.3 Séchage

Introduire la capsule ouverte contenant la prise d’essai et son couvercle dans l’étuve (4.2.7) réglée entre

130 °C et 133 °C et les y laisser séjourner durant 4 h ± 5 min.

Ne jamais introduire des produits humides dans une étuve contenant des prises d’essai en fin de

déshydratation, ni ouvrir la porte de l’étuve durant le séchage, ni introduire de nouveaux échantillons

pour essai humides avant de retirer les prises d’essai sèches, car cela aurait pour conséquence de les

réhydrater.

À la fin du temps de séchage et en opérant rapidement, retirer la capsule de l’étuve, la couvrir et la

placer dans le dessiccateur (4.2.8). Dans le cas d’essais en série simultanés, ne jamais superposer les

capsules dans le dessiccateur.
4.5.4 Pesée

Dès que la capsule est refroidie à la température du laboratoire (en général entre 30 min et 45 min

après la mise en place dans le dessiccateur), la peser à 0,001 g près. Noter la masse m′ .

4.6 Expression des résultats

La teneur en eau, w , exprimée en pourcentage en masse, du produit tel qu’il est reçu, est donnée par

H2O
les Formules (1) et (2):
a) sans conditionnement préalable:
100
wm=−m (1)
H200 1
m = m′ – t est la masse, en grammes, de la prise d’essai (voir 4.5.3);
0 0

m = m′ – t est la masse, en grammes, de la prise d’essai après séchage (voir 4.5.4);

1 1
t est la tare de la capsule, en grammes (voir 4.5.2).
b) avec conditionnement préalable:
 
m 100
wm=−m +−mm (2)
 
H200 1 23
 02
 
w =−100 1
 
H20
 02 
m et m ont la même signification qu’en a) ci-dessus;
0 1

m est la masse, en grammes, de l’échantillon avant conditionnement (voir 4.4.2.3);

m est la masse, en grammes, de l’échantillon après conditionnement (voir 4.4.2.3).

Prendre comme résultat la moyenne des deux valeurs obtenues, si les conditions de répétabilité

(voir 4.7.2) sont remplies. Dans le cas contraire, recommencer les déterminations.

4 © ISO 2021 – Tous droits réservés
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ISO 6540:2021(F)
Exprimer le résultat avec deux décimales.
4.7 Fidélité
4.7.1 Essai interlaboratoires

Les détails d’un essai interlaboratoires sur la fidélité de la méthode sont résumés dans l’Annexe B. Les

valeurs dérivées de cet essai ne sont applicables qu’à des plages de teneur en eau allant de 11,90 %

à 39,20 % et à la matrice étudiée (maïs).
4.7.2 Répétabilité

La différence absolue entre deux résultats d’essai individuels indépendants obtenus avec la même

méthode, sur le même matériau d’essai, dans le même laboratoire et par le même opérateur utilisant

le même équipement dans un court intervalle de temps, ne doit dépasser la limite de répétabilité r que

dans 5 % des cas au plus.
Pour le maïs avec une teneur en eau comprise entre 11,90 % et 39,20 %:
— r = 2,8 S
— r = 2,8 × 0,07 = 0,19
4.7.3 Reproductibilité

La reproductibilité est la différence absolue entre deux résultats d’essai individuels obtenus avec la

même méthode, sur le même matériau d’essai, dans des laboratoires différents, par des opérateurs

différents utilisant des équipements différents.

Dans la pratique, il n’est pas approprié de comparer les résultats de deux laboratoires si l’essai en

question impose des conditions de répétabilité.

L’outil de comparaison approprié est la différence critique telle que décrite en 4.7.5.

4.7.4 Comparaison de deux groupes de mesures dans un laboratoire

La différence critique (D ) est l’écart entre deux valeurs moyennées obtenues à partir de deux résultats

d’essai dans des conditions de répétabilité. Comme chaque résultat est la moyenne de deux valeurs

(voir 4.6), la comparaison des deux résultats de teneur en eau doit être effectuée à l’aide de la différence

critique.

La D entre deux valeurs moyennées obtenues chacune à partir de deux résultats d’essai dans des

conditions de répétabilité est donnée par la Formule (3):
1 1 1
DS=+28,,==28SS19,,80= 14 (3)
rr rr
2nn2 2
S est l’écart-type de répétabilité;

n et n correspondent au nombre de résultats d’essai pour chacune des valeurs moyennées.

1 2
© ISO 2021 – Tous droits réservés 5
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ISO 6540:2021(F)
4.7.5 Comparaison de deux groupes de mesures dans deux laboratoires

La différence critique (D ) entre deux valeurs moyennées obtenues dans deux laboratoires différents à

partir de deux résultats d’essai dans des conditions de répétabilité est donnée par la Formule (4):

 
1 1
22 22
DS=−28,,S 1−− =−28 SS05,,=068 (4)
 
RR rR r
2nn2
 12 
S est l’écart-type de répétabilité;
S est l’écart-type de reproductibilité;

n et n correspondent au nombre de résultats d’essai pour chacune des valeurs moyennées.

1 2
4.7.6 Incertitude

Il est possible d’évaluer les incertitudes de mesure en utilisant des données obtenues à partir

d’études menées conformément à l’ISO 5725-2. L’écart-type de reproductibilité obtenu lors d’un

essai interlaboratoires est une base valide pour évaluer l’incertitude de mesure, car, par définition,

l’incertitude caractérise la dispersion des valeurs pouvant raisonnablement être attribuée à ce

paramètre.

Il convient que l’incertitude-type élargie calculée soit ≤ ± 2 écarts-types de reproductibilité

(voir l’Annexe B).
4.7.7 Comparaison avec la méthode absolue

Par rapport à ceux de la méthode absolue (voir l’Annexe A), les résultats diffèrent en général de moins

de 0,15 g d’eau pour 100 g d’échantillon.
4.8 Notes sur le mode opératoire

4.8.1 La plage de teneur en eau pour laquelle le conditionnement des produits avant broyage doit être

réalisé correspond, dans le laboratoire, à une température de (20 ± 2) °C et une humidité relative de 45 %

à 75 %. Il convient de la modifier pour des conditions atmosphériques différentes.

4.8.2 Le conditionnement et le broyage effectués respectivement sur 100 g et 30 g, pour une prise

d’essai de 8 g, ont pour but l’obte
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 6540
ISO/TC 34/SC 4
Maize — Determination of moisture
Secretariat: SAC
content (on milled grains and on
Voting begins on:
2020­11­17 whole grains)
Voting terminates on:
Maïs — Détermination de la teneur en eau (sur grains broyés et sur
2021­01­12
grains entiers)
ISO/CEN PARALLEL PROCESSING
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 6540:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 6540:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

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
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Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 6540:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Reference method ............................................................................................................................................................................................... 1

4.1 Principle ........................................................................................................................................................................................................ 1

4.2 Apparatus .................................................................................................................................................................................................... 1

4.3 Sampling ....................................................................................................................................................................................................... 2

4.4 Preparation of the test sample .................................................................................................................................................. 2

4.4.1 Products not requiring to be ground .............................................................................................................. 2

4.4.2 Products requiring to be ground ........................................................................................................................ 3

4.5 Procedure .................................................................................................................................................................................................... 3

4.5.1 Number of determinations...................................................................................................................................... 3

4.5.2 Test portion .......................................................................................................................................................................... 3

4.5.3 Drying ........................................................................................................................................................................................ 4

4.5.4 Weighing ................................................................................................................................................................................. 4

4.6 Expression of results .......................................................................................................................................................................... 4

4.7 Precision ....................................................................................................................................................................................................... 5

4.7.1 Interlaboratories test ................................................................................................................................................... 5

4.7.2 Repeatability ....................................................................................................................................................................... 5

4.7.3 Reproducibility .................................................................................................................................................................. 5

4.7.4 Comparison of two groups of measurements in a laboratory .................................................. 5

4.7.5 Comparison of two groups of measurements in two laboratories ....................................... 5

4.7.6 Uncertainty ........................................................................................................................................................................... 6

4.7.7 Comparison with the absolute method ........................................................................................................ 6

4.8 Notes on procedure ............................................................................................................................................................................. 6

4.9 Test report ................................................................................................................................................................................................... 6

5 Routine method on whole grains ........................................................................................................................................................ 7

5.1 Principle ........................................................................................................................................................................................................ 7

5.2 Apparatus .................................................................................................................................................................................................... 8

5.3 Sampling ....................................................................................................................................................................................................... 8

5.4 Procedure .................................................................................................................................................................................................... 8

5.4.1 Test portion .......................................................................................................................................................................... 8

5.4.2 Drying ........................................................................................................................................................................................ 8

5.4.3 Number of determinations...................................................................................................................................... 8

5.5 Expression of results .......................................................................................................................................................................... 9

5.5.1 Method of calculation and formulae ............................................................................................................... 9

5.5.2 Repeatability ....................................................................................................................................................................... 9

5.5.3 Reproducibility .................................................................................................................................................................. 9

5.5.4 Comparison of two groups of measurements in a laboratory .................................................. 9

5.5.5 Comparison of two groups of measurements in two laboratories ....................................10

5.5.6 Application of fidelity limits................................................................................................................................10

5.6 Remark ........................................................................................................................................................................................................10

5.7 Test report ................................................................................................................................................................................................10

Annex A (informative) Absolute method .......................................................................................................................................................11

Annex B (informative) Interlaboratories test results ......................................................................................................................18

Annex C (informative) Application of fidelity data for the whole grains method ...............................................24

Bibliography .............................................................................................................................................................................................................................25

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ISO/FDIS 6540:2020(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 non­governmental, 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 Technical Committee ISO/TC 34, Food products, Subcommittee SC 4,

Cereals and pulses, in collaboration with the European Committee for Standardization (CEN) Technical

Committee CEN/TC 338, Cereal and cereal products, in accordance with the Agreement on technical

cooperation between ISO and CEN (Vienna Agreement).

This second edition cancels and replaces the first edition (ISO 6540:1980), which has been technically

revised. The main changes compared with the previous edition are as follows:

— Clauses 7 to 10 and 17 to 20 (now 4.5 to 4.9 and 5.4 to 5.7) and the annexes have been revised.

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.
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ISO/FDIS 6540:2020(E)
Introduction

The basic reference method and the routine reference method relating to cereals (see ISO 712) are

only applicable to other cereals than maize and cereal products. Therefore, this document has been

[4]

developed to specify the two methods for maize on the basis of research works published in 1979 .

The basic reference method for maize, which is called the “absolute method”, requires special equipment

and experienced personnel, and can only be applied in specialized laboratories.

Due to the very high moisture content that can be present in samples of maize (sometimes greater than

a mass fraction of 40 %) and because of the size and texture of the grains, the determination of the

moisture in maize raises problems with regard to its grinding and pre-drying.

Consequently, to allow the pre-drying and grinding to be avoided, this document also describes a

routine method for whole grains. which is easier to use and allows working in series. Its response time

is longer but the workload is lower, because of the absence of grinding. However, this practical whole

grain method has a positive bias of about a mass fraction of 0, 30 % compared to the reference method.

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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 6540:2020(E)
Maize — Determination of moisture content (on milled
grains and on whole grains)
1 Scope
This document specifies two methods:

— a reference method for the determination of the moisture content of maize grains and ground whole

maize, groats, grits and maize flour, see Clause 4;

— a routine method for the evaluation of the moisture content of maize in whole grains, see Clause 5.

The latter is not suitable for use for experts’ reports, or for calibration or checking of humidity meters,

because of its significant bias to the reference method (see Table B.3).
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
moisture content of maize
loss in mass undergone by a product under specified conditions
Note 1 to entry: It is expressed as a percentage.
4 Reference method
4.1 Principle

If necessary, grinding of a sample, after pre-conditioning, if required. Drying of a test portion at a

temperature between 130 °C and 133 °C, under conditions that enable a result to be obtained in

agreement with that obtained by the absolute method (see Annex A).
4.2 Apparatus

4.2.1 Analytical balance, able to weight with an accuracy of ±0,001 g and therefore having a display

accuracy of 0,000 1 g.

4.2.2 Analytical balance, able to weight with an accuracy of ±0,1 g and therefore having a display

accuracy of 0,1 g.
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ISO/FDIS 6540:2020(E)
4.2.3 Grinding mill, having the following characteristics:
a) made of material that does not absorb moisture;
b) easy to clean and having as little dead space as possible;

c) enabling grinding of 30 g of maize grains to be carried out rapidly and uniformly, without

appreciable development of heat and, as far as possible, without contact with the outside air;

d) adjustable so as to obtain particles of the dimensions indicated in 4.4.1.

4.2.4 Metal boat, without lid, with an effective surface area enabling 100 g of maize grains to be

distributed in a single layer.

4.2.5 Metal capsule, of suitable dimensions, non­corrodible under the test conditions, or, failing this,

a glass dish, with a sufficiently tight-fitting lid, and having an effective surface area such as to allow

distribution of the test portion with no more than 0,3 g per square centimetre.

4.2.6 Constant-temperature oven, electrically heated, adjustable between 60 °C and 80 °C, and with

adequate ventilation.

4.2.7 Constant-temperature oven, electrically heated, capable of being controlled in such a way that

the temperature of the air and of the shelves carrying the test portions is within the range of 130 °C to

133 °C in the neighbourhood of the test portions, in normal working condition.

The oven shall have a heat capacity such that, when initially adjusted to a temperature of 131 °C, it can

again reach this temperature in less than 45 min (preferably in less than 30 min) after insertion of the

maximum number of test portions that can be dried simultaneously.

The effectiveness of the ventilation shall be determined using durum wheat semolina, with a maximum

particle size of 1 mm, as the test material. The ventilation shall be such that, after inserting all the test

portions that the oven can hold and drying at a temperature of 130 °C to 133 °C, the results after a heating

period of 2 h and then a further 1 h will not differ by more than 0,15 g of moisture per 100 g of sample.

4.2.8 Desiccator, containing an efficient desiccant.
4.3 Sampling

Sampling is not part of the method specified in this document. A recommended sampling method is

given in ISO 24333.

The laboratory should be provided with a truly representative sample, in a sealed package, that is

undamaged and unmodified during transport and storage.
4.4 Preparation of the test sample
4.4.1 Products not requiring to be ground

Products that have particles of sizes less than or equal to 1,7 mm, less than a mass fraction of 10 %

being over 1 mm and more than a mass fraction of 50 % being less than 0,5 mm, do not need to be

ground before the determination.
Mix the laboratory sample thoroughly before taking the test portion (see 4.5.3).
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ISO/FDIS 6540:2020(E)
4.4.2 Products requiring to be ground
4.4.2.1 General

If the laboratory sample does not have the particle size characteristics mentioned in 4.4.1, it shall be

ground either without pre­conditioning (4.4.2.2) or with pre­conditioning (4.4.2.3) as required.

4.4.2.2 Grinding without pre-conditioning

For products that are not likely to undergo variations in moisture content in the course of grinding

(in general, products with a moisture content between a mass fraction of 9,00 % and 15,00 %, see

Clause 11), carry out grinding without pre-conditioning.

Adjust the grinding mill (4.2.3) to obtain particles of the dimensions indicated in 4.4.1.

Then quickly grind about 30 g of the laboratory sample, mix with a spatula and proceed immediately as

specified in 4.5.1.
4.4.2.3 Grinding with pre-conditioning

Products that are likely to undergo changes in moisture content in the course of grinding (in general,

products with a moisture content more than a mass fraction of 15,00 % or less than a mass fraction of

9,00 %) shall be pre­conditioned to bring their moisture content to between a mass fraction of 9,00 %

and 15,00 %, see 4.8) before grinding.

If the moisture content is greater than a mass fraction of 15,00 % (which is the more frequent case),

weigh, to the nearest 0,1g, about 100 g of the laboratory sample in the metal boat (4.2.4), place this

in the oven (4.2.7) controlled at between 60 °C and 80 °C, and leave it for the time necessary to bring

the moisture content to between a mass fraction of 9,00 % and 15,00 %. Take the boat out of the oven

and allow it to stand in the laboratory atmosphere for the time necessary (at least 2 h) for the pre-

conditioned sample to return to the laboratory temperature and for the moisture distribution to be

relatively uniform. During this rest, it shall be ensured that no addition or withdrawal of material is

made to the contents of the boat. If necessary, cover it with a sheet of paper but not with a lid, since this

could limit the exchange of moisture between the air and the grain.

After conditioning, weigh the sample to the nearest 0,01 g, then, proceeding rapidly, grind about 30 g of

this product. Mix using a spatula.

If the moisture content is less than a mass fraction of 9,00 %, place about 100 g of the laboratory sample,

weighed to the nearest 0,01 g, in a suitable atmosphere (usually that of the laboratory) and leave it until

a moisture content within the limits specified above is obtained.
4.5 Procedure
4.5.1 Number of determinations
For each laboratory sample, carry out the determination in duplicate.

Carry out one determination on each of the two ground test portions taken from the laboratory sample,

in accordance with 4.5.2 to 4.5.5. If the absolute difference between the two results is greater than the

repeatability limit given in 4.7.2, repeat the determination until the requirements are met.

4.5.2 Test portion

For each sample, tare to the nearest 0,001 g two metal capsules (4.2.5) beforehand. For each capsule,

note the tare t.

Weigh rapidly, to the nearest 0,001 g, approximately (8 ± 1) g of the test sample (see 4.4.1, 4.4.2.2 or

4.4.2.3, as appropriate) into the capsule. Note the mass m′ .
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ISO/FDIS 6540:2020(E)
4.5.3 Drying

Place the open capsule containing the test portion, and the lid, in the oven (4.2.7) controlled between

130 °C and 133 °C and leave it for 4 h ± 5 min.

Never place moist products in an oven containing test portions at the end of dehydration, nor open the

oven door during drying, nor introduce new wet test samples before removing the dry test portions as

this would rehydrate them.

At the end of the drying time and, proceeding rapidly, take the dish out of the oven, cover it and place it

in the desiccator (4.2.8). When several tests are being carried out simultaneously, never place dishes on

top of one another in the desiccator.
4.5.4 Weighing

When the dish has cooled to laboratory temperature (generally between 30 min and 45 min after it has

been placed in the desiccator), weigh it to the nearest 0,001 g. Note the mass m′ .

4.6 Expression of results

The moisture content, w , expressed as a percentage by mass of the product as received, is given by

H2O
Formulae (1) and (2):
a) without pre­conditioning:
100
w = mm− (1)
H200 1
where
m = m′ – t is the mass, in grams, of the test portion (see 4.5.3);
0 0
m = m′ – t is the mass, in grams, of the test portion after drying (see 4.5.5);
1 1
T is the tare of the capsule, in grams (see 4.5.2).
b) with pre­conditioning:
 
100
wm= −m +−mm (2)
 
H20 01 23
m m
 0  2
 mm 
w =100 1−
 
H20
 
where
m and m have the same signification as in a) above;
0 1
m is the mass, in grams, of the sample before conditioning (see 4.4.2.3);
m is the mass, in grams, of the sample after conditioning (see 4.4.2.3).

Take as the result the average of the two values obtained, provided that the requirement for repeatability

(see 4.7.2) is satisfied. If it is not, repeat the determinations.
Express the result to the second decimal place.
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ISO/FDIS 6540:2020(E)
4.7 Precision
4.7.1 Interlaboratories test

The details of an interlaboratories test relating to the precision of the method are summarized in

Annex B. Values from this test can only be applied to water content ranges from 11,90 % to 39,20 % and

the studied matrix (maize).
4.7.2 Repeatability

The absolute difference between two independent individual test results, obtained using the same

method on identical material tested in the same laboratory by the same operator using the same

apparatus and within a short time interval, shall be exceed in no more than 5 % of cases the repeatability

limit r.
For maize with water content between 11,90 % and 39,20 %:
— r = 2,8 S
— r = 2,8 × 0,07 = 0,19
4.7.3 Reproducibility

Reproducibility is the absolute difference between two individual test results, obtained with the same

method on identical material tested in different laboratories by different operators using different

equipment.

In practice, it is not appropriate to compare the results of two laboratories if the related test imposes

repeatability conditions.

The appropriate comparison tool is the critical difference as described in 4.7.5.

4.7.4 Comparison of two groups of measurements in a laboratory

The critical difference (D ) is the difference between two averaged values obtained from two test results

under repeatability conditions. Since each result is the average of two values (see 4.6), the comparison

of the two water content results shall be done using the critical difference.

The D between two averaged values each obtained from two test results under repeatability conditions

is shown by Formula (3):
1 1 1
DS=+28,,==28SS19,,80= 14 (3)
rr rr
2nn2 2
where
S is the standard deviation of repeatability;
n and n are the number of test results corresponding to each averaged values.
1 2
4.7.5 Comparison of two groups of measurements in two laboratories

The critical difference (D ) between two averaged values each obtained in two different laboratories

from two test results under repeatability conditions is shown by Formula (4):
1 1
22 22
DS=−28,(S 1−− ),=−28 SS05,,=068 (4)
RR rR r
2nn2
where
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ISO/FDIS 6540:2020(E)
S is the standard deviation of repeatability;
S is the standard deviation of reproducibility;
n and n are the number of test results corresponding to each averaged values.
1 2
4.7.6 Uncertainty

It is possible to evaluate measurement uncertainties using data obtained from studies carried

out in accordance with ISO 5725-2. The reproducibility standard deviation obtained during an

interlaboratories test is a valid basis to assess measurement uncertainty because, by definition,

uncertainty characterizes the dispersion of values that can be reasonably attributed to the parameter.

The calculated expanded standard uncertainty should be ≤ ±2 reproducibility standard deviations (see

Annex B).
4.7.7 Comparison with the absolute method

Compared to the absolute method (see Annex A), the results generally differ from less than 0,15 g of

water per 100 g of samples.
4.8 Notes on procedure

4.8.1 The range of moisture contents for which the conditioning of the products before grinding is to

be carried out corresponds, in the laboratory, to a temperature of (20 ± 2) °C and a relative humidity of

45 % to 75 %. It should be modified for different atmospheric conditions.

4.8.2 The conditioning and grinding carried out on 100 g and 30 g, respectively, for a test portion of 8 g

are intended to provide a more representative sample. A direct sampling for grinding of only 8 g would

correspond to an insufficient quantity of initial product to be representative and would lead to too great

a dispersion of the results.
4.9 Test report
The test report shall contain at least the following information:

a) all the information necessary for the identification of the sample (type of sample, origin and

designation of the sample);
b) a reference to this document, i.e. ISO 6540;
c) the date and type of sampling procedure (if known);
d) the date of receipt;
e) the date of the test;
f) the test results and the units in which they have been expressed;

g) any operation not specified in the method or regarded as optional which might have affected

the result.
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a) Without conditioning b) With conditioning
NOTE The weighing operations are boxed.

Figure 1 — Diagram of the two possible procedures for products requiring to be ground

5 Routine method on whole grains
5.1 Principle
Drying of whole grains for 38 h at a temperature between 130 °C and 133 °C.
© ISO 2020 – All
...

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