EN ISO 7208:1999
(Main)Skimmed milk, whey and buttermilk - Determination of fat content - Gravimetric method (Reference method) (ISO 7208:1999)
Skimmed milk, whey and buttermilk - Determination of fat content - Gravimetric method (Reference method) (ISO 7208:1999)
Migrated from Progress Sheet (TC Comment) (2000-07-10): Shall be // at formal vote level glg/98_02_06
Magermilch, Molke und Buttermilch - Bestimmung des Fettgehaltes - Gravimetrisches Verfahren (Referenzverfahren) (ISO 7208:1999)
Diese Internationale Norm legt das Referenzverfahren für die Bestimmung des Fettgehaltes von flüssiger Magermilch, Molke und Buttermilch fest. Dabei handelt es sich um ein besonders genaues gravimetrisches Verfahren, insbesondere um die Wirksamkeit von Rahmseparatoren festzustellen. Diese Internationale Norm legt außerdem das Referenzverfahren zum Erstellen von Korrekturtabellen für Bestimmungen mit Magermilch-Butyrometern fest. ANMERKUNG: Falls eine hohe Bestimmungsgenauigkeit nicht erforderlich ist, kann das in ISO 1211 festgelegte Verfahren verwendet werden.
Lait écrémé, sérum et babeurre - Détermination de la teneur en matière grasse - Méthode gravimétrique (Méthode de référence) (ISO 7208:1999)
Posneto mleko, sirotka in pinjenec - Določevanje maščobe - Gravimetrijska metoda (Referenčna metoda) (ISO 7208:1999)
General Information
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Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 7208:2000
01-maj-2000
3RVQHWRPOHNRVLURWNDLQSLQMHQHF'RORþHYDQMHPDãþREH*UDYLPHWULMVND
PHWRGD 5HIHUHQþQDPHWRGD ,62
Skimmed milk, whey and buttermilk - Determination of fat content - Gravimetric method
(Reference method) (ISO 7208:1999)
Magermilch, Molke und Buttermilch - Bestimmung des Fettgehaltes - Gravimetrisches
Verfahren (Referenzverfahren) (ISO 7208:1999)
Lait écrémé, sérum et babeurre - Détermination de la teneur en matiere grasse -
Méthode gravimétrique (Méthode de référence) (ISO 7208:1999)
Ta slovenski standard je istoveten z: EN ISO 7208:1999
ICS:
67.100.10 0OHNRLQSUHGHODQLPOHþQL Milk and processed milk
SURL]YRGL products
SIST EN ISO 7208:2000 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 7208:2000
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SIST EN ISO 7208:2000
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SIST EN ISO 7208:2000
INTERNATIONAL ISO
STANDARD 7208
Second edition
1999-11-15
Skimmed milk, whey and buttermilk —
Determination of fat content — Gravimetric
method (Reference method)
Lait écrémé, sérum et babeurre — Détermination de la teneur en matière
grasse — Méthode gravimétrique (Méthode de référence)
A
Reference number
ISO 7208:1999(E)
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ISO 7208:1999(E)
Contents
1 Scope .1
2 Normative reference .1
3 Term and definition .1
4 Principle.1
5 Reagents.2
6 Apparatus .2
7 Sampling.3
8 Preparation of test sample.3
9 Procedure .4
9.1 Test portion .4
9.2 Blank tests.4
9.3 Preparation of fat-collecting vessel .4
9.4 Determination.5
10 Calculation and expression of results.7
10.1 Calculation.7
10.2 Expression of results .7
11 Precision.7
11.1 Interlaboratory test .7
11.2 Repeatability.7
11.3 Reproducibility.7
12 Test report .8
Annex A (informative) Notes on procedures .9
Annex B (informative) Alternative procedure using fat-extraction tubes with siphon or wash-bottle fittings 11
Bibliograhy .14
© ISO 1999
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
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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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.
International Standard ISO 7208 was prepared by Technical Committee ISO/TC 34, Agricultural food products,
Subcommittee SC 5, Milk and milk products, in collaboration with the International Dairy Federation (IDF) and
AOAC International, and will also be published by these organizations.
This second edition cancels and replaces the first edition (ISO 7208:1984), which has been technically revised.
Annexes A and B of this International Standard are for information only.
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SIST EN ISO 7208:2000
INTERNATIONAL STANDARD © ISO ISO 7208:1999(E)
Skimmed milk, whey and buttermilk — Determination of fat
content — Gravimetric method (Reference method)
WARNING — The use of this International Standard may involve hazardous materials, operations and
equipment. This standard does not purport to address all the safety problems associated with its use. It is
the responsibility of the user of this standard to establish safety and health practices and determine the
applicability of regulatory limitations prior to use.
1 Scope
This International Standard specifies the reference method for the determination of the fat content of liquid skimmed
milk, whey and buttermilk. It is a particularly accurate gravimetric method especially for the purpose of establishing
the operating efficiency of cream separators.
This International Standard also specifies the reference method for establishing correction tables for procedures
with skimmed milk butyrometers.
NOTE When a high accuracy of determination is not required, the method specified in ISO 1211 may be used.
2 Normative reference
The following normative document contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, this publication do
not apply. However, parties to agreement based on this International Standard are encouraged to investigate the
possibility of applying the most recent edition of the normative document indicated below. For undated references,
the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of
currently valid International Standards.
ISO 3889, Milk and milk products — Determination of fat content — Mojonnier-type fat extraction flasks.
3 Term and definition
For the purposes of this International Standard, the following term and definition apply.
3.1
fat content of skimmed milk, whey and buttermilk
mass fraction of substances determined by the procedure specified in this International Standard
NOTE The fat content is expressed as a mass fraction, in percent [formerly given as % (m/m)].
4 Principle
An ammoniacal ethanolic solution of a test portion is extracted with diethyl ether and light petroleum. The solvents
are removed by distillation or evaporation. The mass of the substances extracted is determined.
NOTE This is usually known as the Röse-Gottlieb principle.
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5 Reagents
Use only reagents of recognized analytical grade, unless otherwise specified, and distilled or demineralized water or
water of equivalent purity.
The reagents shall leave no appreciable residue when the determination is carried out by the method specified
(see 9.2.2).
5.1 Ammonia solution, containing a mass fraction of NH of approximately 25 % (r = 910 g/l).
3 20
NOTE If ammonia solution of this concentration is not available, a more concentrated solution of known concentration may
be used (see 9.4.2).
5.2 Ethanol (C H OH), or ethanol denatured by methanol, containing a volume fraction of ethanol of at least 94 %.
2 5
(See A.5.)
5.3 Congo red solution
Dissolve 1 g of Congo red in water in a 100 ml one-mark volumetric flask (6.14). Dilute to the mark with water.
NOTE The use of this solution, which allows the interface between the solvent and aqueous layers to be seen more
clearly, is optional (see 9.4.3). Other aqueous colour solutions may be used provided that they do not affect the result of the
determination.
5.4 Diethyl ether (C H OC H ), free from peroxides (see A.3), containing no more than 2 mg/kg of antioxidants,
2 5 2 5
and complying with the requirements for the blank test (see 9.2.2, A.1 and A.4).
NOTE The use of diethyl ether could lead to hazardous situations. Due to expected changes in safety regulations studies
are ongoing to replace diethyl ether by another reagent provided that it does not affect the end result of the determination.
5.5 Light petroleum, with any boiling range between 30 °C and 60 °C or, as equivalent, pentane (CH [CH ] CH )
3 2 3 3
with a boiling point of 36 °C and complying with the requirements for the blank test (see 9.2.2, A.1 and A.4).
NOTE The use of pentane is recommended because of its higher purity and constant quality.
5.6 Mixed solvent
Mix shortly before use equal volumes of diethyl ether (5.4) and light petroleum (5.5).
6 Apparatus
WARNING — Since the determination involves the use of volatile flammable solvents, all electrical
apparatus employed shall comply with legislation relating to the hazards in using such solvents.
Usual laboratory equipment and, in particular, the following.
6.1 Analytical balance, capable of weighing to the nearest 1 mg, with a readability of 0,1 mg.
6.2 Centrifuge, capable of holding the fat-extraction flasks or tubes (6.6) and capable of spinning at a rotational
–1 –1
frequency of 500 min to 600 min to produce a radial acceleration of 80 g to 90 g at the outer end of the flasks or
tubes.
NOTE The use of the centrifuge is optional but recommended (see 9.4.6).
6.3 Distillation or evaporation apparatus, for distilling the solvents and ethanol from the boiling or conical flasks,
or evaporating from beakers and dishes (see 9.4.13) at a temperature not exceeding 100 °C.
6.4 Drying oven, electrically heated, with ventilation port(s) fully open, capable of being maintained at a
temperature of 102 °C ± 2 °C throughout its working space.
The oven shall be fitted with a suitable thermometer.
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, capable of being maintained at a temperature of between 35 °C and 40 °C.
6.5 Water bath
6.6 Mojonnier-type fat extraction flasks, as specified in ISO 3889.
NOTE It is also possible to use fat-extraction tubes, with siphon or wash-bottle fittings, but then the procedure is different.
The alternative procedure is given in annex B.
The fat-extraction flasks shall be provided with good quality bark corks or stoppers of other material [e.g. silicone
rubber or polytetrafluoroethylene (PTFE)] unaffected by the reagents used. Bark corks shall be extracted with the
diethyl ether (5.4), kept in water at a temperature of 60 °C or more for at least 15 min, and shall then be allowed to
cool in the water so that they are saturated when used.
6.7 Rack, for holding the fat-extraction flasks (or tubes) (6.6).
6.8 Wash bottle, suitable for use with the mixed solvent (5.6).
A plastics wash bottle shall not be used.
6.9 Fat-collecting vessels, such as boiling flasks (flat-bottomed), of capacities 125 ml to 250 ml, conical flasks, of
capacity 250 ml, or metal dishes.
If metal dishes are used, they shall be of stainless steel, flat-bottomed with a diameter of 80 mm to 100 mm and a
height of approximately 50 mm.
6.10 Boiling aids, fat-free, of non-porous porcelain or silicon carbide (optional when metal dishes are used).
6.11 Measuring cylinders, of capacities 5 ml and 25 ml, or any other apparatus suitable for the product
concerned.
6.12 Pipettes, graduated, of capacity 10 ml.
6.13 Tongs, made of metal, for holding flasks, beakers or dishes.
6.14 Volumetric flask, one-mark, of capacity 100 ml.
7 Sampling
Sampling is not part of the method specified in this International Standard. A recommended sampling method is
given in ISO 707.
It is important that the laboratory receive a sample which is truly representative and has not been damaged or
changed during transport or storage.
Store the samples at a temperature of between 2 °C and 6 °C from the time of sampling.
8 Preparation of test sample
Warm the test sample to a temperature of between 35 °C and 40 °C by means of the water bath (6.5), if necessary.
Gently mix the test sample thoroughly by repeatedly inverting the sample bottle without causing frothing or churning.
Cool the test sample quickly to approximately 20 °C.
NOTE A reliable value for the fat content cannot be expected:
a) if the milk is churned;
b) when a distinct smell of free fatty acids is perceptible;
c) if during or after preparation of the test sample, white particles are visible on the walls of the sample bottle or fat droplets
float on the surface of the sample.
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9 Procedure
NOTE 1 In the determination, two test portions (9.1) are extracted in two Mojonnier-type fat-extraction flasks (6.6). The
extracts of the two flasks are poured into one prepared fat-collecting vessel (9.3).
NOTE 2 If it is required to check whether the repeatability limit (11.2) is met, carry out two single determinations in
accordance with 9.1 to 9.4.
NOTE 3 An alternative procedure using fat-extraction tubes with siphon or wash-bottle fittings (see note in 6.6) is given in
annex B.
9.1 Test portion
Mix the test sample (clause 8) by gently inverting the bottle three or four times. Immediately weigh, to the nearest
1 mg, 10 g to 11 g of the test sample, directly or by difference, in each of two fat-extraction flask (6.6).
Transfer the test portion as completely as possible into the lower (small) bulb of the fat-extraction flask.
9.2 Blank tests
9.2.1 Blank test for method
Carry out a blank test simultaneously with the determination using the same procedure and same reagents, but
replacing the test portion by 10 ml of water (see A.2).
If the value obtained in the blank test regularly exceeds 1,0 mg, check the reagents if this has not been recently
done (9.2.2). Corrections of more than 2,5 mg should be mentioned in the test report.
9.2.2 Blank test for reagents
To test the quality of the reagents, carry out a blank test as specified in 9.2.1. Additionally use an empty fat-
collecting vessel, prepared as specified in 9.3, for mass control purposes. The reagents shall leave no residue
greater than 1,0 mg (see A.1).
If the residue of the complete reagent blank test is greater than 1,0 mg, determine the residue of the solvents
separately by distilling 100 ml of the diethyl ether and light petroleum, respectively. Use an empty fat-collecting
vessel, prepared for control purposes as described above, to obtain the real mass of residue which shall not exceed
1,0 mg.
Very occasionally, the solvents may contain volatile matter which is strongly retained in fat. If there are indications of
the presence of such substances, carry out blank tests on all the reagents and for each solvent using a fat-
collecting vessel with about 1 g of anhydrous butterfat. If necessary, redistil solvents in the presence of 1 g of
anhydrous butterfat per 100 ml of solvent. Use the solvents only shortly after the redistillation.
Replace unsatisfactory reagents and solvents, or redistil solvents.
9.3 Preparation of fat-collecting vessel
Dry a fat-collecting vessel (6.9) with a few boiling aids (6.10) in the oven (6.4) set at 102 °C for 1 h.
NOTE 1 Boiling aids are desirable to promote gentle boiling during the subsequent removal of solvents, especially when
using glass fat-collecting vessels; their use is optional with metal dishes.
Protect the fat-collecting vessel from dust and allow it to cool to the temperature of the weighing room (glass fat-
collecting vessel for at least 1 h, metal dish for at least 30 min).
NOTE 2 To avoid insufficient cooling or unduly long cooling times, the fat-collecting vessel should not be placed in a
desiccator.
Use tongs to place the fat-collecting vessel on the balance. Weigh the fat-collecting vessel to the nearest 1,0 mg.
NOTE 3 Tongs should preferably be used to avoid, in particular, temperature variations.
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9.4 Determination
Carry out the determination without delay.
9.4.1
Carry out the operations described in 9.4.2 to 9.4.13 on both pre-treated test portions (9.1).
9.4.2 Add 2 ml of ammonia solution (5.1) to the two test portions in the fat-extraction flasks (9.1), or an equivalent
volume of a more concentrated ammonia solution (see note in 5.1). Mix thoroughly with the test portion in the small
bulb of each of the two fat-extraction flasks.
9.4.3 Add 10 ml of ethanol (5.2). Mix gently but thoroughly by allowing the contents of the two fat-extraction flasks
to flow backwards and forwards between the small and large bulb. Avoid bringing the liquid too near to the necks of
the flasks. If desired, add 2 drops of the
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