buttermilk

Buttermilk is a dairy product traditionally the liquid left after churning butter from cream. In modern food production it is typically a cultured dairy product produced by fermenting low-fat milk with lactic acid bacteria, creating a tangy, slightly thick liquid.

Traditional buttermilk, derived from the churning process, is not deliberately fermented and its acidity arises from natural microorganisms; cultured buttermilk uses specific starter cultures. Modern versions are typically made from skim or low-fat milk and cultured with bacteria such as Lactococcus lactis and Leuconostoc species, sometimes with Streptococcus thermophilus.

The taste is tangy and mildly acidic with a smooth, pourable texture. It is used in baking to activate chemical leaveners, in dressings and marinades, in soups, and as a beverage or ingredient in pancakes, biscuits, and cake recipes.

Nutritionally, buttermilk is usually low in fat and calories, while providing calcium. Cultured versions may contain live bacteria that contribute probiotic-like benefits, though pasteurization can reduce viable cultures. It naturally contains lactose, but fermentation lowers sugar content somewhat. It should be refrigerated and kept sealed; typical shelf life is one to two weeks, and separation into watery whey may occur—shake before use.

Substitutes exist for recipes that call for buttermilk; a common method is to add one tablespoon of lemon juice or vinegar per cup of milk and let it stand a few minutes to sour.