DETERMINATION OF SPECIFIC GRAVITY OF MILK

What is specific gravity?

Specific gravity is the ratio between the weight of a certain volume of milk at a standard temperature of 15C and the weight of the same volume of water at the same temperature.

Avg. specific gravity of buffalo’s milk = 1.033

Avg. specific gravity of cow’s milk = 1.032

APPARATUS:

Lactometer, graduated glass cylinder (50 ml) and thermometer.

PROCEDURE:

The given sample of milk is poured into a glass cylinder. The lactometer is slowly lowered into the milk until it floats. The lactometer must not be allowed to touch the sides of cylinder or its bottom. When it becomes stationary one record:

(i)The scale reading and (ii) temperature.

If temperature is above or below the standard temperature (15C), then the lactometer reading is corrected according to the following rule:

Add 0.1 to the lactometer reading or 0.0001 to the specific gravity for each degree Fahrenheit above 60 F and subtract 0.1 from lactometer reading or 0.0001 from specific gravity for each degree Fahrenheit below 60 F.

          CALCULATION:

LAB EXAMPLE;

Lactometer reading = 14

Thermometer reading = 88 F

Standard temperature = 60 F

Formal factor = 0.1

Temperature difference = 88-60 = 28 F

= 28 x 0.1 = 2.8

Corrected lactometer reading (CLR) = 14 + 2.8 = 16.8

Specific gravity =   1 + CLR/1000

                                  

= 1 + 16.8

         1000

= 1 + 0.016 = 1.016

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