LPT 311: Milk and Milk Products Technology (1+1)

GERBER'S METHOD

The normal methods commercially followed are 

• Gerber’s method and   
• Babcok’s method

Apparatus required 

• Milk butyrometer 
• Acid pipette with safety bulb (10 ml)
• Milk pipette 
• 1 ml pipette      
• Lock stopper 
• Regulating pin
• Gerber’s centrifuge

Reagents prepared

• Gerber’s acid :  (91-92% of con. sulphuric acid with a specific gravity of 1.8 - 1.825 at 15^oC)
• Amyl alcohol (specific gravity 0.815-0.818)

Procedure

• In this method fat alone is separated from milk by subjecting the milk to digestion by the addition concentrated sulphuric acid and by the process of centrifugation the fat is separated and measured
• Dr. Gerber devised this method. This is also known as ‘Fucoma test’
• Special milk bottles called Gerber’s butyrometer are used in this method. A Gerber’s butyrometer is made up of glass of length 195 mm and diameter 23 mm at the cylindrical part. It is graduated from 0-10%. Different butyrometers are used for skim milk, cream, cheese and butter. The tube with large diameter at the flattened end is preferred because it is resistant to leakage and also the fat column will be well defined.
• The graduation of 1% in the butyrometer has an internal volume of 0.125 ml. Assuming the specific gravity of fat the weight represented by 1% in the butyrometer, will be 0.125x0.9=0.1125 gms. If 1% contains 0.1125 gm, 100% will contain 0.1125 x100=11.25 gm. Assuming the specific gravity of milk to be 1.032, the volume of milk represented by 11.25 gm will be 11.25/1.032 =10.9 ml.  But, since large variations in the specific gravity for the various samples of milk are found, it is preferred to use of pipette, which will measure only 10.75 ml. So, in Gerber’s method only 10.75 ml of milk is used instead of 10.9 ml.1.25 gms of fat we can declare that the

Gerber’s acid serves the following purposes

• It digests the casein and other organic constituents and renders the separation of fat in an easy way.
• Since there will be a great difference in specific gravity of fat and other portion of liquid in the butyrometer, usage of this acid will help in separating the fat easily during centrifuging.
• The heat produced during the mixing of acid and milk reduced the viscosity, which helps in an easier separation of fat.
• The heat thus produced will also help the fat to remain in fluid condition.

If the acid used is of higher or lower specific gravity then heat produced will affect the other effects.

Amyl alcohol of specific gravity is 0.815-0.818 is used in this experiment. Addition of amyl alcohol prevents the partial charring of sugar and fat.

10 ml of Gerber’s acid is pipetted out into butyrometer carefully along the side. Then 10.75 ml of well-mixed milk is pipetted out and layered over the acid carefully so that there are two separate layers. Finally 1 ml of amyl alcohol is added. The pipette should not be blown are shaken to discharge the last drop. A dry rubber lock stopper without any crack should be used to close the butyrometer using regulating pin. The tube is then inverted several times, So that the acid in the stem and in the bulb are thoroughly mixed with the milk. The tube is then placed in water bath at 65^oC for 5minutes. The butyrometer is then placed in the centrifuge with the stem towards the centre and the centrifuge is kept well balanced. Centrifuging is done at 1100 RPM for 5 minutes and removed from the centrifuge. The tube is placed in water bath at 65^oC for 5 minutes. The stopper is adjusted to bring the lower meniscus of the fat column against ‘o’ unit graduation. The lower meniscus of the surface of the fat column is noted without any parallelex error, which gives the fat percentage.

Latest methods include use of electronic devices such as Milko tester or Milkoscan or Infrared milk analyzer (IRMA). In these equipments the milk is a chemically modified and light ray of different wavelength / frequency capacities are passed through the sample. Their resultant effect are electronically gauged by light sensitive gadgets and converted to required units of measurements.

Result

• The fat percentage in the given sample of cream is = -----------