What is buttermilk?

There are numerous different types of buttermilk; traditional and cultured being the primary two. Traditional buttermilk is a by-product of butter production. It is the remaining liquid portion following the churning of butter out of cream. Cultured buttermilk is produced from low-fat/skimmed milk to which lactic acid bacteria has been introduced. Buttermilk is primarily a drinking product, but is also commonly used in cooking and baking.