What is the difference between cultured and old-fashioned buttermilk?
Maria Presley, Durham, CT
Cary Frye replies: What we call old-fashioned, or churned, buttermilk is very different from cultured buttermilk. It is the thin, slightly acidic liquid left over after churning butter from full-cream milk. It is drunk or used in soups and sauces in northern Europe and South Asia but is not available commercially in the United States.
The buttermilk sold in supermarkets here is cultured, created by fermenting pasteurized low-fat or nonfat milk so the milk sugars turn into lactic acid. It is thick and tart, a result of its increased acidity, which keeps the milk protein casein from being soluble and results in clabbering or curdling. (That is why you can make a stand-in for buttermilk by adding a tablespoon of lemon juice or white vinegar to a cup of milk, increasing the acidity and curdling the milk.)
Old-fashioned and cultured buttermilk cannot be used interchangeably. Cultured buttermilk is used in pancakes, scones, biscuits, and other baked products because of the tangy flavor and tender texture it imparts.