At his sous vide seminar in Aspen, Momofuku chef David Chang urged us not to fear the buttermilk. "Buttermilk is just cultured milk!" he exclaimed — at which point I realized that I knew very little about the stuff.
Although they are both rich, creamy dairy items, the term buttermilk refers to two different products. There's old-fashioned buttermilk, which is the thin liquid left over after the natural process of butter being churned. It's acidic and often has flakes of butter still floating in it. Then there's cultured buttermilk, the thick and creamy fermented milk product that Chang was referring to, and what's typically seen sold in cartons at the supermarket. Sometimes called artificial buttermilk, it contains no butter. It is created by adding a lactic acid bacterial culture to dairy to ferment it, resulting in a tangy flavor and a thicker consistency.
Buttermilk is a popular ingredient in biscuits, scones, and fried chicken batter. (Chang likes to make a buttermilk dressing.) Since it typically has a longer shelf life than regular milk, buttermilk can be a good investment. However, in a pinch, one can make acidified buttermilk, a product made by adding acid such as lemon juice to regular milk. Do you use buttermilk?
Source: Flickr User jeffreyw