Determination of Fat in Milking
The price of milk fixed on its fat content.
To determine the fat level in milk by Gerber method.
Fat is the most important constituent of milk as it is used as a basis for fixing the
purchase and sale price of milk. It helps to detect adulteration like watering and skimming of
milk. Gerber’s method commonly used in Europe and in India.
Dr. N Gerber of Zurich Switzerland invented this method in the year 1892-1895. In this test H2SO4 is used to increase specific gravity of milk serum which makes greater difference between milk serum and fat globules. It also destroys stickiness of milk by dissolving all the SNF. The free fat globules rise to the surface by subsequent application of centrifugal force to this mixture and heat produced due to mixing of acid and milk, causing melting of fat. It facilitates the fat particles to come to the surface freely. The specific gravity of fat is 0.9 and that of acid milk mixtures is 1.43. This situation promotes complete separation of fat when proper centrifugal force is applied.
Due to application of centrifugal force lighter substances (Butter fat) are thrown towards centre and rest of serum portion that is heavier is thrown towards the pheriphen.
Addition of amyl alcohol helps for separation of fat from the milk acid mixture and also prevents the charging of fat and sugar by the H2SO4.
1. Carryout through mixing of milk before testing.
2. Amyl alcohol must be pure.
3. Sulphuric acid is to be added gently by the sides of the butyrometer without wetting the neck of the butyrometer. Avoid direct pouring of milk on acid.
4. The three fluids viz. Sulphuric acid, milk and amyl alcohol should be added gently, so that they form three distinct layers.
5. Rubber stopper should be dry, clean and without crack.
6. Before centrifuging the butyrometer, see that there is no curdy white material left undissolved.
7. The centrifugal machine must be properly balanced.
8. Always carry out the test in duplicate.
9. Butyrometer should be free from Na2Co3 (soda ash) if cleaned by Na2Co3 otherwise it lowers the specific gravity and strength of Sulphuric acid.
10. Use butyrometer stand for shaking of butyrometer contents to dissolve the SNF content of milk.
ii.Sulphuric acid (sp.gr..1.82)
iii.Amyl alcohol (sp.gr.0.82-0.83)
1. Milk sample bottle.
2.10 ml automatic tilt measure for H2SO4.
3. 1 ml automatic tilt measure for amyl alcohol.
4. 10.75 ml capacity milk pipette.
5. Dairy floating thermometer.
6. Hot water bath.
7. Gerber’s centrifuge machine (1100 rpm).
8. Gerber’s butyrometer plain neck with graduations from 0-10%.
9. Butyrometer stand.
10. Rubber stopper.
11. Guiding pin or key.
1. Put the clean and dry butyrometer in a butyrometer stand with open mouth upwards.
2. Run 10 ml of sulphuric acid with the tilt measure in the butyrometer.
3. Pipette out 10.75 ml of milk sample gently by the side of butyrometer, whose temperature is about 60-70 0 F.
4. Pour 1 ml. of amyl alcohol with tilt measure.
5. Stopper the butyrometer with the help of lock stopper using regulating pin/guiding pin.
6. The tube is well (mixed) shaken till mahogany red colour is obtained. Keep the butyrometer in hot water bath till it attains 60-70 0 F and the butyrometer are placed in the centrifuged machine that is revolved at 1100 rpm for 4 minutes.
7. Take out the butyrometer in an upright position with the stopper end down wards.
8. Keep the butyrometer in hot water bath a 149 0 F (600 C) for some time.
9. Adjust the fat column which will appear clear and yellowish within the graduation with the help of key.
10. Note the reading. Reading should be taken from bottom of the fat column to lower border of meniscus on the scale.