Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd?

As milk turns into curd, the pH will decrease. Milk contains lactose, a sugar. Bacteria such as Lactobacillus ferment lactose, converting it into lactic acid. Lactic acid is a weak acid, and its production lowers the pH of the milk, making it more acidic. This decrease in pH causes the milk proteins to denature and coagulate, resulting in the formation of curd. The final pH of curd is typically in the range of 4.0 to 4.5.