Milk - Determination of freezing point - Thermistor cryoscope method (Reference method) (ISO 5764:2009)

ISO 5764|IDF 108:2009 specifies a reference method for the determination of the freezing point of raw bovine milk, heat-treated whole, reduced fat and skimmed bovine milk, as well as raw ovine and caprine milk, by using a thermistor cryoscope.
The freezing point can be used to estimate the proportion of extraneous water in milk. Calculation of the amount of extraneous water is subject to daily and seasonal variations, and is not within the scope of ISO 5764|IDF 108:2009.
Results obtained from samples with a titratable acidity exceeding 20 ml of 0,1 mol/l sodium hydroxide solution per 10 g of non-fat solids are not representative of the original milk.

Milch - Bestimmung des Gefrierpunktes - Thermistor-Kryoskop-Verfahren (Referenzverfahren) (ISO 5764:2009)

Diese Internationale Norm legt ein Referenzverfahren zur Bestimmung des Gefrierpunktes von roher Vollmilch,
hitzebehandelter Vollmilch, teilentrahmter und entrahmter Milch (Magermilch) sowie roher Schaf- und
Ziegenmilch mit einem Thermistor-Kryoskop fest.
Der Gefrierpunkt kann zur Abschätzung des Anteils von Fremdwasser in Milch verwendet werden. Die Berechnung
der Menge von Fremdwasser hängt von täglichen und saisonalen Schwankungen ab und liegt nicht
innerhalb des Anwendungsbereichs dieser Internationalen Norm.
Ergebnisse von Untersuchungsproben, deren titrierbare Acidität über 20 ml an 0,1 mol/l Natriumhydroxidlösung
je 10 g fettfreier Trockenmasse beträgt, sind für die Milch im Originalzustand als nicht repräsentativ
anzusehen.
ANMERKUNG 1 Sterilisation und Pasteurisierung im Vakuum können den Gefrierpunkt von Milch beeinflussen
(siehe [5]).
ANMERKUNG 2 Das Verfahren beinhaltet die Anwendung von plateau-zeitgesteuerten Messgeräten. Für Routinemessungen
können auch andere Thermistor-Kryoskop-Verfahren, d. h. Festzeit-Verfahren, angewendet werden. Ein Leitfaden
für die Anwendung anderer Verfahren ist in Anhang C angegeben.
ANMERKUNG 3 Die in Abschnitt 1 und 9.2 genannten Grenzwerte für die titrierbare Acidität beziehen sich auf Kuhmilch.
Es ist möglich, dass die Grenzwerte bei Schaf- und Ziegenmilch höher sind.

Lait - Détermination du point de congélation - Méthode au cryoscope à thermistance (Méthode de référence) (ISO 5764:2009)

L'ISO 5764|FIL 108:2009 spécifie une méthode de référence pour la détermination du point de congélation du lait entier cru de bovin, traité thermiquement, à matière grasse réduite, et du lait écrémé de bovin ainsi que du lait cru de brebis et de chèvre, utilisant un cryoscope à thermistance.
Le point de congélation peut être utilisé pour estimer la proportion d'eau étrangère dans le lait. Le calcul de la quantité d'eau étrangère est toutefois sujet à des variations journalières et saisonnières et ne fait pas partie du domaine d'application de l'ISO 5764|FIL 108:2009.
Les résultats obtenus à partir d'échantillons ayant une acidité supérieure à 20 ml d'une solution d'hydroxyde de sodium à 0,1 mol/l pour 10 g de solides non gras ne sont pas représentatifs du lait d'origine.

Mleko - Določevanje ledišča - Metoda Thermistor cryoscope (referenčna metoda) (ISO 5764:2009)

General Information

Status
Withdrawn
Publication Date
30-Aug-2009
Withdrawal Date
29-Nov-2009
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Start Date
01-May-2009
Completion Date
01-May-2009

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SLOVENSKI STANDARD
SIST EN ISO 5764:2009
1DGRPHãþD
SIST EN ISO 5764:2002
0OHNR'RORþHYDQMHOHGLãþD0HWRGD7KHUPLVWRUFU\RVFRSH UHIHUHQþQDPHWRGD
,62
Milk - Determination of freezing point - Thermistor cryoscope method (Reference
method) (ISO 5764:2009)
Milch - Bestimmung des Gefrierpunktes - Thermistor-Kryoskop-Verfahren
(Referenzverfahren) (ISO 5764:2009)

Lait - Détermination du point de congélation - Méthode au cryoscope à thermistance

(Méthode de référence) (ISO 5764:2009)
Ta slovenski standard je istoveten z: EN ISO 5764:2009
ICS:
67.100.10 0OHNRLQSUHGHODQLPOHþQL Milk and processed milk
SURL]YRGL products
SIST EN ISO 5764:2009 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 5764:2009
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SIST EN ISO 5764:2009
EUROPEAN STANDARD
EN ISO 5764
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2009
ICS 67.100.10 Supersedes EN ISO 5764:2002
English Version
Milk - Determination of freezing point - Thermistor cryoscope
method (Reference method) (ISO 5764:2009)

Lait - Détermination du point de congélation - Méthode au Milch - Bestimmung des Gefrierpunktes - Thermistor-

cryoscope à thermistance (Méthode de référence) (ISO Kryoskop-Verfahren (Referenzverfahren) (ISO 5764:2009)

5764:2009)
This European Standard was approved by CEN on 13 April 2009.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the CEN Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the

official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,

Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2009 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 5764:2009: E

worldwide for CEN national Members.
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SIST EN ISO 5764:2009
EN ISO 5764:2009 (E)
Contents Page

Foreword ..............................................................................................................................................................3

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SIST EN ISO 5764:2009
EN ISO 5764:2009 (E)
Foreword

This document (EN ISO 5764:2009) has been prepared by Technical Committee ISO/TC 34 "Agricultural food

products" in collaboration with Technical Committee CEN/TC 302 “Milk and milk products - Methods of

sampling and analysis” the secretariat of which is held by NEN.

This European Standard shall be given the status of a national standard, either by publication of an identical

text or by endorsement, at the latest by November 2009, and conflicting national standards shall be withdrawn

at the latest by November 2009.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 5764:2002.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following

countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech

Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,

Sweden, Switzerland and the United Kingdom.
Endorsement notice

The text of ISO 5764:2009 has been approved by CEN as a EN ISO 5764:2009 without any modification.

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SIST EN ISO 5764:2009
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SIST EN ISO 5764:2009
INTERNATIONAL ISO
STANDARD 5764
IDF
108
Third edition
2009-05-01
Milk — Determination of freezing point —
Thermistor cryoscope method (Reference
method)
Lait — Détermination du point de congélation — Méthode au cryoscope
à thermistance (Méthode de référence)
Reference numbers
ISO 5764:2009(E)
IDF 108:2009(E)
ISO and IDF 2009
---------------------- Page: 7 ----------------------
SIST EN ISO 5764:2009
ISO 5764:2009(E)
IDF 108:2009(E)
PDF disclaimer

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COPYRIGHT PROTECTED DOCUMENT
© ISO and IDF 2009

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 either ISO or IDF at the respective

address below.
ISO copyright office International Dairy Federation

Case postale 56 • CH-1211 Geneva 20 Diamant Building • Boulevard Auguste Reyers 80 • B-1030 Brussels

Tel. + 41 22 749 01 11 Tel. + 32 2 733 98 88
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Web www.iso.org Web www.fil-idf.org
Published in Switzerland
ii © ISO and IDF 2009 – All rights reserved
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SIST EN ISO 5764:2009
ISO 5764:2009(E)
IDF 108:2009(E)
Contents Page

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

Foreword............................................................................................................................................................. v

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

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

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

4 Principle..................................................................................................................................................2

5 Reagents.................................................................................................................................................2

6 Apparatus ...............................................................................................................................................3

7 Sampling.................................................................................................................................................4

8 Calibration of the thermistor cryoscope .............................................................................................4

9 Preparation of test sample....................................................................................................................5

9.1 Preparation .............................................................................................................................................5

9.2 Sample condition...................................................................................................................................6

10 Procedure ...............................................................................................................................................6

10.1 Preliminary checks ................................................................................................................................6

10.2 Routine calibration check .....................................................................................................................6

10.3 Determination.........................................................................................................................................6

11 Calculation and expression of results.................................................................................................7

11.1 Calculation..............................................................................................................................................7

11.2 Expression of results ............................................................................................................................7

12 Precision.................................................................................................................................................7

12.1 Interlaboratory test ................................................................................................................................7

12.2 Repeatability...........................................................................................................................................7

12.3 Reproducibility.......................................................................................................................................7

13 Test report ..............................................................................................................................................8

Annex A (informative) Interlaboratory trial on bovine milk.............................................................................9

Annex B (informative) Interlaboratory trial on raw ovine and caprine milk ................................................11

Annex C (informative) Guidelines for the application of routine thermistor cryoscope methods ...........13

Annex D (informative) Adjustment of the freezing point value used as the reference for genuine

milk........................................................................................................................................................16

Bibliography ......................................................................................................................................................17

© ISO and IDF 2009 – All rights reserved iii
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SIST EN ISO 5764:2009
ISO 5764:2009(E)
IDF 108:2009(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.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. 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.

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.

International Standard ISO 5764⎪IDF 108 was prepared by Technical Committee ISO/TC 34, Food products,

Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF). It is being published

jointly by ISO and IDF.

This third edition of ISO 5764⎪IDF 108 cancels and replaces the second edition (ISO 5764⎪IDF 108:2002), the

scope of which has been technically revised.
iv © ISO and IDF 2009 – All rights reserved
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SIST EN ISO 5764:2009
ISO 5764:2009(E)
IDF 108:2009(E)
Foreword

IDF (the International Dairy Federation) is a non-profit organization representing the dairy sector worldwide.

IDF membership comprises National Committees in every member country as well as regional dairy

associations having signed a formal agreement on cooperation with IDF. All members of IDF have the right to

be represented on the IDF Standing Committees carrying out the technical work. IDF collaborates with ISO in

the development of standard methods of analysis and sampling for milk and milk products.

Draft International Standards adopted by the Action Teams and Standing Committees are circulated to the

National Committees for voting. Publication as an International Standard requires approval by at least 50 % of

the IDF National Committees casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. IDF shall not be held responsible for identifying any or all such patent rights.

International Standard ISO 5764⎪IDF 108 was prepared by Technical Committee ISO/TC 34, Food products,

Subcommittee SC 5, Milk and milk products, and the International Dairy Federation (IDF). It is being published

jointly by ISO and IDF.

All work was carried out by the Joint IDF-ISO Action Team on Water, of the Standing Committee on Main

components in milk, under the aegis of its project leader, Mrs. S. Orlandini (IT).

This edition of ISO 5764⎪IDF 108 cancels and replaces ISO 5764⎪IDF 108:2002, the scope of which has been

technically revised.
© ISO and IDF 2009 – All rights reserved v
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SIST EN ISO 5764:2009
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SIST EN ISO 5764:2009
ISO 5764:2009(E)
INTERNATIONAL STANDARD
IDF 108:2009(E)
Milk — Determination of freezing point — Thermistor cryoscope
method (Reference method)
1 Scope

This International Standard specifies a reference method for the determination of the freezing point of raw

bovine milk, heat-treated whole, reduced fat and skimmed bovine milk, as well as raw ovine and caprine milk,

by using a thermistor cryoscope.

The freezing point can be used to estimate the proportion of extraneous water in milk. Calculation of the

amount of extraneous water is subject to daily and seasonal variations, and is not within the scope of this

International Standard.

Results obtained from samples with a titratable acidity exceeding 20 ml of 0,1 mol/l sodium hydroxide solution

per 10 g of non-fat solids are not representative of the original milk.

NOTE 1 Sterilization and vacuum pasteurization can affect the freezing point of milk (see Reference [5]).

NOTE 2 The method uses plateau-timed instruments. For routine measurements, other thermistor cryoscope methods,

i.e. fixed time procedures, can be used. Guidelines for the application of other procedures are given in Annex C.

NOTE 3 The limit value mentioned for the titratable acidity in Clause 1 and 9.2 applies to bovine milk. It is possible that

the limit values for ovine and caprine milk are higher.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 6091, Dried milk — Determination of titratable acidity (Reference method)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
freezing point of milk

temperature value obtained using the method specified in this International Standard

NOTE The freezing point is expressed in millidegrees Celsius.
1) Equivalent to IDF 86.
© ISO and IDF 2009 – All rights reserved 1
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SIST EN ISO 5764:2009
ISO 5764:2009(E)
IDF 108:2009(E)
4 Principle

A test sample of milk is supercooled to an appropriate temperature. Crystallization is induced by means

sufficient to cause an instantaneous release of heat with an accompanying warming of the sample to a

temperature plateau. The plateau is reached when the temperature rise has not exceeded 0,5 m°C over the

previous 20 s. The temperature thus attained corresponds to the freezing point of the test sample.

The instrument is calibrated by adjusting it to give the correct readings for two sodium chloride standard solutions,

using the same procedure as for test portions of milk.
5 Reagents

During the analysis, unless otherwise stated, use only reagents of recognized analytical grade.

5.1 Water, in accordance with ISO 3696 grade 2 or water of equivalent quality distilled from borosilicate

glass apparatus.
Boil the water and cool it to 20 °C ± 2 °C shortly before use.

5.2 Sodium chloride (NaCl), finely ground, dried in the electric furnace (6.7) at 300 °C ± 25 °C for 5 h or,

alternatively, dried in the drying oven (6.8) at 130 °C ± 2 °C for at least 24 h, then cooled to room temperature

in a desiccator (6.9).
5.3 Sodium chloride standard solutions.

Preferably, make up the sodium chloride standard solution on a gram per kilogram basis (see Table 1,

leftmost column) by weighing the required amount of prepared dry sodium chloride (5.2) to the nearest 0,1 mg

and dissolving it in 1 000 g ± 0,1 g of water (5.1). Store standard solutions at about 5 °C in well-stoppered

polyethylene bottles (6.10) of capacity not greater than 250 ml.

Alternatively, weigh, to the nearest 0,1 mg, the appropriate amount (see Table 1, middle column) of prepared

dry sodium chloride (5.2) in a weighing bottle (6.5). Dissolve in water (5.1) and transfer quantitatively to a

1 000 ml one-mark volumetric flask (6.6). Dilute to the 1 000 ml mark with water (5.1) at 20 °C ± 2 °C and mix.

Table 1 — Freezing point of sodium chloride standard solutions
NaCl solution NaCl solution at 20 °C Freezing point
g/kg g/l m°C
6,763 6,731 −400,0
6,901 6,868 −408,0
7,625 7,587 −450,0
8,489 8,444 −500,0
8,662 8,615 −510,0
8,697 8,650 −512,0
8,835 8,787 −520,0
9,008 8,959 −530,0
9,181 9,130 −540,0
9,354 9,302 −550,0
9,475 9,422 −557,0
10,220 10,161 −600,0
2 © ISO and IDF 2009 – All rights reserved
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SIST EN ISO 5764:2009
ISO 5764:2009(E)
IDF 108:2009(E)

Before using a standard solution, gently invert and rotate the bottle several times to mix its contents

thoroughly.

Do not agitate the standard solution violently at any time, as this can lead to incorporation of air. Pour samples

of standard solutions from the bottles; never use pipettes for this purpose. Do not use standard solutions from

bottles less than one-quarter full, or more than 2 months old, or containing visible moulds.

Only use unpreserved sodium chloride standard solutions for this reference method. For routine methods,

sodium chloride standard solutions with a fungicidal or fungistatic agent may be used. For guidance, see

Annex C.
6 Apparatus
Usual laboratory apparatus and, in particular, the following.

6.1 Cryoscope, consisting of a thermostatically controlled cooling device, a thermistor probe with

associated circuit, a read-out device, a sample agitator and a crystallization device (see Figure 1).

6.1.1 Cooling device.
Several types of thermostatically controlled cooling devices can be used, e.g.:
a) immersion type: a cooling bath with a suitable buffer capacity;

b) circulation type: a continuous stream of cooling liquid around the sample tube;

c) cooling block type: a cooling block with a small amount of cooling liquid.

After the initiation of freezing, keep the temperature of the cooling liquid around the sample tube constant at

−7,0 °C ± 0,5 °C.

NOTE A suitable cooling liquid is a 33 % (volume fraction) aqueous solution of propylene glycol.

6.1.2 Measuring device, associated circuitry and read-out device.

The thermistor shall be of the glass probe type with diameter of 1,60 mm ± 0,4 mm and an electrical

resistance of between 3 Ω and 30 kΩ at 0 °C.

The type and dimensions of the shank material (including a possible filler) shall not allow a heat transfer into

the sample greater than 2,5 × 10 J/s, under operating conditions.

When the probe is in measurement position, the thermistor bead shall lie on the axis of the sample tube and at

equal distances from the inner walls and the inner bottom of the tube (see Figure 1).

The thermistor and the associated circuitry shall show a discrimination of 1 m°C or better over a range of

−400 m°C to −600 m°C.

The linearity of the circuit shall be such that no error greater than 1 m°C is introduced at any point within the

range of −400 m°C to −600 m°C when the instrument is correctly operated.

The read-out device shall provide a discrimination of 1 m°C or better over a range of at least 0 m°C to

−1 000 m°C.

6.1.3 Stirring wire, inert to milk, used to stir the test portion during cooling.

The stirring wire shall be adjustable for amplitude and mounted vertically in accordance with the

manufacturer's instructions. The wire shall vibrate laterally with an amplitude of 2 mm to 3 mm to ensure that

the temperature within the test portion remains uniform during cooling. At no time during its normal stirring

operation shall the wire strike the glass probe or the wall of the tube.
© ISO and IDF 2009 – All rights reserved 3
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SIST EN ISO 5764:2009
ISO 5764:2009(E)
IDF 108:2009(E)

6.1.4 Device for initiating freezing, that, when operated, instantaneously initiates freezing of the test

portion when reaching −3,0 °C.

The stirring wire (6.1.3) may be used for this purpose. One method is to increase the amplitude of vibration for

1 s to 2 s such that the stirring wire strikes the wall of the sample tube (6.2).

6.2 Sample tubes, symmetrical, made of borosilicate glass, of length 50,5 mm ± 0,2 mm, of external

diameter 16,0 mm ± 0,2 mm and of internal diameter 13,7 mm ± 0,3 mm (see Figure 1).

The wall thickness throughout the tube shall not vary by more than 0,1 mm.

The tubes shall be equally shaped so that equal freezing points are obtained for equal volumes of the same

solution. Check on equality before using the tubes.

6.3 Main power supply, capable of operating within the manufacturer’s specifications.

6.4 Analytical balance, capable of weighing to the nearest 0,1 mg.
6.5 Weighing bottle.
[2]
6.6 One-mark volumetric flasks, capacity 1 000 ml, ISO 1042 class A.
6.7 Electric furnace, capable of being maintained at 300 °C ± 25 °C; or
6.8 Drying oven, capable of being maintained at 130 °C ± 2 °C.
6.9 Desiccator, containing silica gel with hygrometer indicator.
6.10 Polyethylene bottles, of maximum capacity 250 ml, with a suitable stopper.
7 Sampling

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

[1]
is given in ISO 707⎪IDF 50 .

It is important that the laboratory receive a sample that is truly representative and that has not been damaged

or changed during transport or storage.

Preferably, test samples immediately upon arrival at the laboratory. Provided it remains in a representative

state, a test sample of raw milk may be stored at a temperature of between 0 °C and 6 °C for up to 48 h after

sampling. For a test sample of processed milk, respect its shelf life.
8 Calibration of the thermistor cryoscope

Ensure that the cryoscope (6.1) is in working condition in accordance with the manufacturer's instructions.

Check the position of the probe, the amplitude of vibration of the stirring wire, and the temperature of the

cooling device (6.1.1).

Select two sodium chloride standard solutions (see Table 1) which closely bracket the expected value of the

freezing point of the milk to be tested. The difference in the freezing points between the two selected sodium

chloride standard solutions shall not be less than 100 m°C. Ensure that the temperatures of the selected

sodium chloride standard solutions and that of the test sample are similar.

Pour 2,5 ml ± 0,1 ml of the sodium chloride standard solutions into clean, dry sample tubes (6.2) and calibrate

the instrument as indicated by the manufacturer. Use sample tubes (6.2) of the same type as those being

used during testing of the sample. Thereafter, the thermistor cryoscope is ready for use.

4 © ISO and IDF 2009 – All rights reserved
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SIST EN ISO 5764:2009
ISO 5764:2009(E)
IDF 108:2009(E)
Dimensions in millimetres
Key
1 mandrel
2 sample tube
3 stirring wire
4 thermistor bead
Figure 1 — Details of sample tube, thermistor probe, and stirring wire
9 Preparation of test sample
9.1 Preparation

If necessary, remove any visible foreign bodies or solid butterfat from the test sample by filtering into a clean,

dry vessel. Mix the sample gently. Use a filter that is inert to milk and effective when used at laboratory

temperature.

Test the samples at their storage temperature or after having reached the laboratory temperature before

commencing the determination. The test samples and the sodium chloride standard solutions shall have

similar temperatures when commencing the determination (see also Clause 8).
© ISO and IDF 2009 – All rights reserved 5
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SIST EN ISO 5764:2009
ISO 5764:2009(E)
IDF 108:2009(E)
9.2 Sample condition

If doubts exist about the sample condition, determine the titratable acidity of the test sample by the method

specified in ISO 6091 as far as possible at the same time as determining the freezing point.

Results obtained from test samples with a titratable acidity exceeding 20 ml of 0,1 mol/l sodium hydroxide

solution per 10 g of non-fat solids are not representative of the original milk (see Clause 1, Note 3).

10 Procedure
10.1 Preliminary checks

Carry out preliminary instrument checks in accordance with the manufacturer's instructions.

10.2 Routine calibration check

Before each series of determinations, measure the freezing point of a sodium chloride standard solution (5.3)

(e.g. a solution with a freezing point of −512 m°C) until the values obtained in two consecutive determinations

do not differ by more than 1 m°C.

If the arithmetic mean of the two results differs from the freezing point of the sodium chloride standard solution

used by more than 2 m°C, recalibrate the cryoscope as specified in Clause 8.

If the cryoscope is in continuous use, carry out a routine calibration check at least once every hour.

10.3 Determination

Gently invert and rotate the sample container several times to mix its contents, thereby avoiding the

incorporation of air.

Using a pipette, transfer a test portion of 2,5 ml ± 0,1 ml of the prepared test sample (9.1) into a clean and dry

sample tube (6.2).

Ensure that the probe and the stirring wire (6.1.3) are clean and dry. If necessary, wipe them carefully with a

soft, clean, and lintless tissue.

Insert the sample tube into the calibrated cryoscope (6.1) according to the manufacturer's instructions. Start

the instrument to cool the test portion and initiate freezing at −3,0 °C ± 0,1 °C.

The plateau is reached when the temperature rise over the previous 20 s has not exceeded 0,5 m°C. For

instruments with a resolution not better than 1 m°C, the plateau is reached as soon as the temperature has

remained constant for 20 s. Record this temperature.

If, for any reason, freezing is initiated before reaching a temperature of −3,0 °C ± 0,1 °C, abandon the test.

Repeat the determination with another test portion of 2,5 ml.

If this second test portion also freezes too early, warm the remaining test sample (or part of it) in a closed

container at 40 °C ± 2 °C for 5 min in order to melt any crystalline fat. Cool the thus re-prepared test sample

(or part of it) to the laboratory temperature (see also 9.1) and immediately repeat the test on a test portion

of 2,5 ml.
NOTE The time between the initiation of freez
...

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