Introduction:
One of the key bacteria responsible for turning milk into curd is Lactobacillus.

Role of Lactobacillus:
- Lactobacillus is a type of lactic acid bacteria that plays a crucial role in the fermentation process of milk into curd.
- This bacteria helps in converting lactose (milk sugar) into lactic acid through the process of fermentation.
- The lactic acid produced by Lactobacillus lowers the pH of the milk, causing it to coagulate and form curd.

Process of Curd Formation:
- When Lactobacillus is added to milk, it begins to multiply and produce lactic acid.
- The lactic acid lowers the pH of the milk, which denatures the milk proteins, causing them to coagulate and form a gel-like substance, which is curd.
- The curd also contains whey, a liquid that separates from the solid curd.

Benefits of Lactobacillus:
- Apart from its role in curd formation, Lactobacillus is also known for its probiotic properties.
- It helps in maintaining a healthy gut flora and aids in digestion.
- Consuming foods like curd, which contain Lactobacillus, can promote gut health and boost immunity.

Conclusion:
In conclusion, Lactobacillus is the key bacteria that turns milk into curd through the process of fermentation. It plays a vital role in curd formation and has various health benefits when consumed.