We know that density is defined as mass per unit volume. It is expressed in gm/ml at a given temperature.
Density = weight/volume
Density is a characteristic property of milk. Though the composition of milk is variable but the density of milk remain within a very short range. Same is true for various constituents of milk e.g. milk fat. Density is an absolute value i.e. absolute density. When density is related with a standard material e.g. water it is termed as specific gravity (sp.gr).
Specific gravity=density of substance/density of water Generally density of water at 4 0 C is used as the standard for specific gravity for liquid and solids. Since the absolute value of water at 4 0 C is unity, the numerical values for absolute density and sp.gr. are identical. The density of any substance including water varies with temperature, it is therefore necessary to specify the temperature when reporting density or specific gravity.
Determination of Density of Fluid milk: Density of milk is determined by the following methods:
i)Pycnometer/ Specific gravity bottle: Pycnometer is a simplified form of specific gravity bottle. Density is determined by weighing milk in the pycnometer with a specific volume generally at 20 0 C.
ii) Lactometer: Lactometer is used as an instrument for rapid determination of density of milk. The density is determined with a glass instrument called lactometer. It is based on the principle of floatation which displaces specific volume of milk on floatation. The lactometer is graduated in such a manner where each graduation is called as lactometer reading of the scale. Each division is graduated as lactometer degree. The average lactometer reading for normal cow whole milk is between 26-30. For buffalo milk the range is between 28-32. The lactometer reading can be changed to sp. gr. by prefexing 1.0. Thus a reading of 32 indicates a sp.gr. of 1.032. The specific gravity of cow milk ranges from 1.028 to 1.032 and that of buffalo milk from 1.030 to 1.034. Skim milk ranges from 1.034 to 1.036.
Density = weight/volume
Density is a characteristic property of milk. Though the composition of milk is variable but the density of milk remain within a very short range. Same is true for various constituents of milk e.g. milk fat. Density is an absolute value i.e. absolute density. When density is related with a standard material e.g. water it is termed as specific gravity (sp.gr).
Specific gravity=density of substance/density of water Generally density of water at 4 0 C is used as the standard for specific gravity for liquid and solids. Since the absolute value of water at 4 0 C is unity, the numerical values for absolute density and sp.gr. are identical. The density of any substance including water varies with temperature, it is therefore necessary to specify the temperature when reporting density or specific gravity.
Determination of Density of Fluid milk: Density of milk is determined by the following methods:
i)Pycnometer/ Specific gravity bottle: Pycnometer is a simplified form of specific gravity bottle. Density is determined by weighing milk in the pycnometer with a specific volume generally at 20 0 C.
ii) Lactometer: Lactometer is used as an instrument for rapid determination of density of milk. The density is determined with a glass instrument called lactometer. It is based on the principle of floatation which displaces specific volume of milk on floatation. The lactometer is graduated in such a manner where each graduation is called as lactometer reading of the scale. Each division is graduated as lactometer degree. The average lactometer reading for normal cow whole milk is between 26-30. For buffalo milk the range is between 28-32. The lactometer reading can be changed to sp. gr. by prefexing 1.0. Thus a reading of 32 indicates a sp.gr. of 1.032. The specific gravity of cow milk ranges from 1.028 to 1.032 and that of buffalo milk from 1.030 to 1.034. Skim milk ranges from 1.034 to 1.036.
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