Buttermilk is the liquid left over after producing butter from full-cream milk by the churning process. It has a slightly sour taste. Buttermilk may contain amounts of calcium from its dairy products, such as non-fat dry-milk powder.
Cultured buttermilk is buttermilk that has been fermented with lactic acid bacteria, much like yoghurt, giving it a tart (sour) taste. It is quite popular as a refreshment in India, made into a drink known as lassi.
Buttermilk is often used as an ingredient in baked goods. Some recipes using buttermilk are: