Sour milk is characterized by a high presence of which acid?

Sour milk is primarily characterized by a high presence of lactic acid. This acid is produced during the fermentation process when lactose, the sugar found in milk, is converted into lactic acid by lactic acid bacteria. This fermentation process not only changes the flavor of the milk, giving it a sour taste, but also impacts its texture and preservation properties.

Lactic acid is a key component in the production of various dairy products, including yogurt and cheese, where the sourness is a desirable trait. The increase in lactic acid lowers the pH of the milk, which can help inhibit the growth of spoilage-causing bacteria, thereby extending shelf life to some extent.

While acetic acid, citric acid, and butyric acid are associated with other processes and flavors in dairy or fermented products, they do not play a primary role in the souring of milk. Acetic acid is most known for its presence in vinegar, citric acid is commonly found in citrus fruits, and butyric acid is typically associated with rancid butter or certain fermented foods, making lactic acid the distinctive compound responsible for the sour taste in fermented milk.