Question

Write the process of making curd from milk. Explain the changes that take place in the milk.

Answer 1

Hint: Curd is prepared from milk by following a few simple steps. It can be prepared at home easily. The process by which milk is converted into curd is known as fermentation.

Complete answer:
Curd is generally prepared from the milk. The process of making curd from milk is actually simple. It requires the following steps:
* First, the milk is heated to boil for a few minutes. In this process, the extra water present in the milk gets evaporated and the milk gets thickened a bit.
* Then, the milk is allowed to cool to the room temperature.
* Then one spoon of curd is added to the milk and mixed very well. This curd acts as a precursor.
* Then, it is kept overnight so that the entire milk is converted into curd.
Now, a very important chemical change occurs during this conversion process. This is an irreversible chemical change because once the milk is converted into curd, the curd cannot be transformed back into milk.
The process by which the milk is converted into curd is called fermentation.
* Curd contains bacteria called ‘lactobacillus’. When one spoon of curd is added to the milk (the precursor curd), the lactobacillus multiplies itself inside the milk.
* Now, milk has two major types of proteins: whey protein and casein protein. When cheese is prepared from milk, the whey protein is found in the water part and the casein protein is found in the cheese part. The casein protein is the globular form of protein of milk.
* During the process of fermentation, a chemical reaction occurs between the lactic acid bacteria and the casein protein of the milk.
* At first, the lactobacillus bacteria utilize their enzymes to produce ATP from lactose. During this process, lactic acid is generated as a by-product.
* Now, the lactic acid reacts with the casein protein of milk and denatures the protein. As a result, the tertiary and quaternary structures of the globular protein are broken and the globular protein is converted into a fibrous protein (simple chain protein).
* This fibrous protein starts providing a thick texture to the milk and coagulation of the protein occurs as well. As a result, the milk is converted into curd.

Note: In order to convert milk into curd, a small amount of curd should be added, which is designated as precursor curd. It will provide the required lactobacillus to the milk. Without it, the fermentation process will not take place.