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 cultured buttermilk to simulate residual flecks of butter that can be left over from the churning process of traditional buttermilk. Cultured buttermilk, often known simply as "buttermilk" now, was first commercially introduced in the United States in the 1920s. It was popular among immigrants, and viewed as a food that could slow aging. It reached peak annual sales of in 1960. Buttermilk's popularity has declined since then, despite an increasing population, and annual sales in 2012 reached less than half that number. Condensed buttermilk and dried buttermilk have increased in importance in the food industry. Buttermilk solids are used in