milk or buttermilk

Buttermilk is the acidic liquid byproduct traditionally obtained from churning butter, though modern commercial buttermilk is typically cultured by fermenting regular milk with lactic acid bacteria. Historically, traditional buttermilk was the thin, tangy liquid left behind after butter solids separated during churning; contemporary cultured buttermilk is created by inoculating pasteurized milk with Lactobacillus cultures, resulting in a thick, pourable liquid with a distinctive sour tang and probiotic properties. The fermentation process lowers the pH of the milk and creates lactic acid, which imparts a characteristic sourness and allows the milk to coagulate slightly. Buttermilk has a thinner consistency than yogurt, with a mild, creamy texture and slightly grainy appearance from the fermentation process.

Traditional buttermilk, still produced in some regions, is thinner and less acidic than cultured buttermilk, with a more subtle flavor and lower lactose content due to the partial removal of milk solids during butter-making. Cultured buttermilk, now the commercial standard, contains approximately 3.3% protein and around 0.9% fat, with full lactose content intact unless specified as reduced-lactose.

Buttermilk is essential in baking, where its acidity reacts with baking soda to produce lift and tenderness in pancakes, biscuits, waffles, and quick breads. It is used to marinate meats, particularly poultry, where the lactic acid breaks down proteins and creates a tender texture while imparting a subtle tang. In beverages, buttermilk is consumed as a drink in South Asian cuisine (chaach) and used to make lassi. Buttermilk also features in savory sauces, dressings, and as a base for marinades in Southern and Middle Eastern cuisines, where it brings acidity and richness without excessive fat. Its probiotic properties and lower lactose content make it suitable for those with mild lactose sensitivity.