DETERMINATION OF TOTAL SOLIDS AND SOLIDS NOT FAT IN MILK

DETERMINATION OF TOTAL SOLIDS AND

SOLIDS-NOT-FAT IN MILK

The entire residue left after complete evaporation of water from milk is put under the term ‘total solids’ or ‘dry matter’. The term includes fat, proteins, lactose and mineral matter of milk. These solid constituents of milk exist in a mechanical mixture. The amount of solid matter in milk varies within considerable limits. Much depends upon the fat content of milk; the higher the percentage of fat in milk, the higher is the amount of total solids. Depending upon the species of the dairy animals (buffalo or cow), total solids vary from eleven to twenty percent of the milk. The specific gravity of total solids of milk ranges between 1.3 to 1.4; milk richer in fat has solids of lower specific gravity. Total solids in milk, minus its butter fat, constitute the solids-not-fat (SNF) of milk. The proteins, sugar, mineral matter, etc., together make the solids-not-fat.

For purposes of detecting adulterations of milk especially of the nature of skimming, watering or both, the determination of the percentage of total solids is of special value when considered in conjunction with specific gravity and fat content. The estimation of milk solids is a fairly simple matter and may be carried out by the following methods:

1.                  By evaporation

2.                  By calculation

3.                  By an automatic reckoner (Richmond’s Sliding Rule)

BY EVAPORATION

Apparatus

●             Evaporating dishes (platinum, porcelain or silica dishes)

●             An analytical balance with weights

●             Pipette

●             Oven

●             Desiccators

●             Pair of tongs

Procedure

About 3 to 5 g of milk to be tested are placed in a previously weighed and thoroughly dried evaporating dish. This dish is transferred to the oven for evaporation of water. The skin formed on the surface of milk is broken with a needle from time to time. The temperature of the oven should not go beyond 100°C otherwise the solids will get charred. When dryness is complete transfer the dish with a pair of tongs to the desiccator. When cooled, weigh the dish. It is again placed in the oven for about 30 minutes for further evaporation, cooled in a desiccator and weighed. If the two weights agree or the difference in weights is within 2 mg, it indicates that water has all been driven off. The last weight minus the weight of the dish gives the weight of the total solids in the amount of milk taken in the dish, from which the percentage can be easily calculated.

Precautions

●             Weighings must be accurate.

●             The evaporating dish must be thoroughly clean and dried before use.

●             The temperature of the oven should not go beyond 100°C.

●             Use pair of tongs for transferring the dish from the oven to the desiccator.

●             Break the skin of milk occasionally with a fine needle.

●             Perform the test in duplicate.

●             In case mineral matter or ash in milk is to be determined, preserve the evaporating dish along with total solids for further use.

BY CALCULATIONS

The following formulae can be used for determining total solids and solids-not-fat in milk:

Percentage of total solids:			CLR		+ 1.2 x F
		4
Percentage of solids-not-fat:				CLR		+ 0.2 x F
		4
Where,
CLR	=	Lactometer (Quevenne) reading corrected to 60°F
F	=	Percentage of fat

EXERCISES

1.                  What is the normal content of total solids-not-fat in buffalo and cow milk?

The CLR and percentage of fat in a sample of buffalo milk are 30.4 and 5.9, respectively. Calculate the percentage of total solids by using the formula given in your practical manual.

Share: