Buttermilk is primarily due to lactic acid produced by lactic acid bacteria while fermenting lactose, the primary sugar in milk. As the bacteria produce lactic acid, the pH of the milk decreases and casein, the primary milk protein, precipitates, causing the curdling or clabbering of milk. This process makes buttermilk thicker than plain milk. While both traditional and cultured buttermilk contain lactic acid, traditional buttermilk tends to be less viscous, whereas cultured buttermilk is more viscous. Buttermilk can be drunk straight, and it can also be used in cooking. Soda bread is a bread in which the acid in buttermilk reacts
Buttermilk as "cultured buttermilk", is produced from cow's milk and has a characteristically intense sour taste caused by lactic acid bacteria. This variant is made using one of two species of bacteria—either "Lactococcus lactis" or "Lactobacillus bulgaricus", which creates more tartness. A quick version of buttermilk, known as "acidified buttermilk", is used to make paneer. This version is simply cow's milk with a food-grade acid like lemon juice or vinegar added and left to sit for at least 10 minutes. That is when the milk has curdled. The tartness of buttermilk is due to acid in the milk. The increased acidity