How milk turns in to curd?

Milk turns into curd due to a process called coagulation, which is triggered by the action of lactic acid bacteria (LAB) on the milk sugar, lactose. Here is a step-by-step explanation of how milk turns into curd:

1. Lactic Acid Bacteria (LAB) Growth:

- When milk is exposed to LAB, usually added as a starter culture or present naturally in raw milk, they begin to grow and multiply rapidly.

2. Lactose Fermentation:

- LAB converts the lactose in milk into lactic acid through the process of fermentation.

3. pH Change:

- As LAB produces lactic acid, the pH of milk starts to decrease, making the milk more acidic.

4. Protein Denaturation:

- The decrease in pH causes the casein proteins in milk to change their structure and form bonds with each other. This process is called protein denaturation.

5. Curd Formation:

- The denatured casein proteins form a network that traps water, fat, and other milk solids, resulting in the formation of curd. The curd is semisolid and separates from the liquid portion, which is whey.

6. Acidification Continues:

- LAB continues to produce lactic acid, further lowering the pH and causing more curd to form.

7. Enzyme Rennet (Optional):

- In certain curd-making processes, an enzyme called rennet may be added to accelerate the coagulation process. Rennet helps break down the casein proteins, making it easier for LAB to coagulate the milk.

8. Draining and Pressing:

- Once the desired level of coagulation is reached, the curds are separated from the whey by straining or draining. The curds may be further pressed to remove excess whey.

9. Curd Processing:

- Depending on the type of curd or cheese being produced, the curds may undergo additional processing steps such as heating, salting, and aging to develop their desired flavor and texture.

Overall, the transformation of milk into curd involves the fermentation of lactose by LAB, which leads to protein denaturation and the formation of a semi-solid curd network that separates from the whey.