How to test the purity of milk?

Generally, to test the purity of milk, an instrument called ‘lactometer’ is used. However, a lactometer is not a very feasible instrument for household use; also there are various types of milk products with varying fat and cream content. Thus, it becomes too hard to differentiate one product from the other. While testing milk, people generally look into certain issues.

General tests and their credibility

• A basic thing is to test the fat content. But customers could be easily fooled by the producers of milk, by adding other natural oils to it.

• Next is the protein content. There are several tests that can be performed to detect the presence of proteins but in this case too, manufacturers can add other proteins and chemicals, which would make their milk, clear the tests.

• Density is another thing that people test for, but in this case too, the test results can be manipulated.

• Visual conformation can be sought by using a microscope, but the process would be very time-consuming and, you may not even pick up the soluble.

• There are several methods to test for poisonous impurities like pesticides and other chemicals but this too would be time-consuming and expensive.

Thus, we can say that no particular instrument or test alone can testify the purity of milk. The only instrument that does all these is the lactometer.


The lactometer is a cylinder shaped glass vessel. One end of this vessel is of the shape of a bulb and is filled with mercury, and the other end is of the shape of a thin glass tube which remains sealed. The principle of lactometer is based on the density of pure milk. The ideal level upto which it should sink in pure milk is labeled by ‘M’. ‘W’ denotes the level of sinking of the instrument in water. Obviously, due to the difference in density of both the liquids (milk being more dense than water), ‘W’ is above ‘M’. The length between ‘W’ and ‘M’ gives the purity of milk. When the reading is closer to ‘M’, it means that the milk is relatively pure, while if the reading is closer to ‘W’ it would mean otherwise. Lactometer doesn’t give exact purity when tested with skimmed milk products.

Government standards and measures

There are certain standards put by the federal board with respect to different milk products and their content. Milk containing 2% fat is termed as ‘reduced-fat milk’ as the quantity of fat is less than 3 grams. Products containing about 18% fat is a ‘light cream’ product while the ‘heavy cream’ products contain more than 36% fat.

To kill germs and maintaining the ingredient levels, milk is passed through various treatments. Pasteurization involves heating and sudden cooling, which kill any bacteria that may be present. Homogenized milk has reduced-fat particle sizes so that the cream does not rise to the top. Vitamin fortified milk is one with added vitamins.
Depending on the quality of manufacturing milk is graded into categories A and B, the latter being less reliable for healthy consumption.

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    I am a in Chandigarh.I our city,dairies are not allowed.We buy milk from milkman.But i am not satisfied with that milk.How can i test milk at home?

    Shalini ji aap milk ki mlai se or lactometer se gravity check kare.sabse asaan trika apne anguthe (thumb) ke nail par ek bund milk ki dale if milk is pure to bund jaldi jaldi giregi nahi .agar pani mix hai to pani ki jaise beh jaigi.

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