SOP: Determination of Fat in Milk Powder by Gerber Method (Routine Method)

GIFSQ — Global Institute for Food Safety & Quality

Scope

This method is applicable to all types of milk powders.

1. Principle

The Gerber method for determination of fat in milk and milk products depends on the liberation of the fat by the action of sulphuric acid on milk or milk products in specifically shaped, calibrated glass containers, called butyrometers, which are then centrifuged to aid the separation of fat, the volume of which is finally read off against the percentage scale etched on the butyrometer.

2. Apparatus

a. Gerber butyrometer, 10% (ISI marked)

b. Lock stoppers and key

c. Gerber centrifuge

d. Water bath with temperature control

e. Dispenser for delivering 1 mL iso-amyl alcohol

f. Dispenser for delivering 10 mL of sulphuric acid

g. Weighing balance — suitable for weighing to 0.01 g

h. Small scoop with a counterpoise

i. Stemless or short stemmed funnel

j. Glass rod

3. Reagents

a. Sulphuric acid with a density of 1.807 to 1.812 g/mL at 27°C, corresponding to a concentration of sulphuric acid from 90–91% by weight

b. Amyl alcohol for milk testing (furfural free)

4. Procedure

Mix the sample thoroughly, and weigh 1.69 ± 0.01 g of milk powder into the counterpoised scoop

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Transfer 10 mL of sulphuric acid into the butyrometer by means of the automatic dispenser, taking care not to wet the neck of the butyrometer with the sulphuric acid

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Add gently from the wash bottle sufficient cold water to form a layer about 6 mm deep on top of the acid, allowing the water to flow down the side of the bulb

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Insert the narrow end of the stemless or short stem funnel into the neck of the butyrometer

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Transfer the contents of the scoop to the funnel quantitatively and remove the funnel

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Measure 1 mL of amyl alcohol into the butyrometer by means of the automatic dispenser. Do not wet the neck of the butyrometer with alcohol

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Add hot water (70°C) from the wash bottle until the butyrometer is filled to about 1 mm below the shoulder, allowing all air entrained in the powder to escape

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Close the neck of the butyrometer firmly with the stopper without disturbing the contents

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Shake the butyrometer carefully, without inverting it, until the contents are thoroughly mixed, the curd is dissolved and no white particles are seen in the liquid

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Then invert the butyrometer a few times to mix the contents thoroughly, and proceed as in the Gerber method for milk (water bath at 65 ± 2°C, centrifuge, read)

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Read the butyrometer to the nearest 0.05 percent. Multiply the scale reading of the butyrometer by the factor 20/3 to obtain the percentage of fat in milk powder

References

IS 1224 (Part II) — 1977, RA 2008.