Buttermilk is a whitish, slightly sour-tasting liquid that separates from cream during the production of butter. Somewhat creamy, buttermilk separates into two layers when left undisturbed; the relatively light top layer is comprised of lacto serum and the bottom layer consists of fine lumps of coagulated casein. The buttermilk sold today is not a by-product of the traditional butter-making process; adding a bacterial culture to skim, or partially skim, milk, makes it. This transforms a portion of the sugar naturally found in milk (lactose) into lactic acid, thus creating the sour taste associated with traditional buttermilk.
The nutritional value of buttermilk is similar to that of the skim, or partially skims, milk from which it is made. It is an excellent source of potassium, vitamin B12 calcium, and riboflavin, and a good source of phosphorus. It also contains zinc, magnesium, pantothenic acid, niacin, thiamine, folic acid, and vitamin B6. Low in fat, it is rich in lactic acid and nitrogen. It is often recommended for people with digestive problems.
Check the expiration date on the package to ensure that the buttermilk is fresh.
Unopened containers of buttermilk can be refrigerated for about 2 weeks. Once the container is opened, the buttermilk will remain fresh for about 1 week. Reseal the container tightly.
Buttermilk is a natural emulsifier that is often used to make baked goods, pastry, and ice cream; it is a very common ingredient in breads and cakes, especially in the form of a powder. Powdered buttermilk is an excellent emulsifier because it is rich in phospholipids, and it also has an appetizingly rich flavour. Buttermilk is added to soups and certain cheeses; it can also be blended with fruit to make delicious refreshing drinks or combined with fragrant herbs and lemon juice to make a cold sauce. Fresh milk to which vinegar has been added (2 teaspoons per cup) can replace buttermilk (and sour milk) in most recipes.