Question

To study the condition necessary for the growth of curd bacteria.
Under the guidance of your mother or elder at home make arrangement for the formation of curd. Write your experience in the form of paragraph.

Answer 1

Milk is converted into curd or yogurt by the process of fermentation. Milk consists of globular proteins called casein. The curd forms because of the chemical reaction between the lactic acid bacteria and casein. During fermentation, the bacteria use enzymes to produce energy (ATP) from lactose. The byproduct of ATP production is lactic acid. Lactic acid acts on the globular proteins present in the milk and denatures them. This denaturation destroys the tertiary and quaternary structures of proteins and the globular proteins are converted into fibrous proteins thus giving a thick texture to the milk due to coagulation of the proteins. The thick texture which is form is know as curd.

Answer 2

To prepare curd, my mother first boiled the milk. It was then allowed to cool. When the heat was quite normal my mother checked the heat of the milk to check whether it was warm. Then, she added a packet full of curd to the warm milk and left it aside without disturbing it for the whole night. In the morning, when we saw the vessel the milk was totally converted into the curd. It was a very exciting experience to do this work.