Why does milk curdle

There is one food we have to very careful about in summer and that is milk. We find the high atmospheric temperature causes the milk to curdle for some unexplainable reason. What we have to do then is to think of ways of using the paneer and whey we had not planned for. Actually it is not only the atmospheric high temperature that curdles the milk. Well, it is a different thing that we sometimes curdle milk on purpose to have a paneer dish at home. Milk curdles very easily once the right curdling agent is added. Let me explain why milk curdles. 

Milk as a substance is composed of many different “ingredients’. The main which we know is fat but there are also proteins in milk. These proteins float around in the milk, which is a colloidal system. A colloidal system is a mixture of two substances, one of which, called the colloid is uniformly distributed in a finely divided state through the second substance, called the dispersing medium. So when we have to make paneer and we add either lemon juice, or citric acid or vinegar, the water in which the proteins are floating becomes acidic and the proteins do not like this. They start to ‘flock’ together, because if they are curdled they have less surface which is in contact with the acidic water. This is the action which justifies the curdling of milk. 

The whey that separates when you curdle milk and drain off the paneer can be used in other preparations. It is nutritious and should not be discarded. It can also be used to curdle more milk to make more paneer.