Boil the milk on low flame for 2-3 hours till it becomes thick with hardening. If it looks oily it means that it is of good quality.
If your milk vendor has added starch to the milk, you can get 5 ml of milk mixed with two tablespoons of salt (iodine). The mixture will turn blue if the milk is impure, otherwise, it will remain intact.
One of the most common types of adulteration in milk is urea admixture, as it does not change the taste and is difficult to find.
To test urea in milk, mix half a tablespoon of milk and soybean (or tur) powder together and stir well. After five minutes, dip the litmus paper for thirty seconds and if there is any colour modification from red to blue it means that the milk contains urea.
Synthetic milk is made by adding chemicals and soaps to natural milk. Synthetic milk can only be known by its bad taste. It feels like soap when rubbed and turns yellow on heating.
The water in milk may not be dangerous for your health but can be costly for your pocket. To check, place a drop of milk on your toes or an inclined surface and let it flow down. If the milk leaves a way, it is not pure, otherwise, it is good.
You should do these checks from time to time to make sure that there is no adulteration in the milk you buy.