Buttermilk is essentially the liquid that is left over after milk has been churned; it's left over after the solid butter removed. It is often used in cooking for its light and tangy flavour. The name buttermilk is misleading as many assume that it is fattening. In actuality, it is fairly healthy as all the cream has been removed. If you don't happen to have any buttermilk on hand when a recipe calls for it, there are several substitutes you can use to achieve approximately the same taste.
Fake Your Own Buttermilk
You can make your own buttermilk by (safely) souring regular milk. Add one tablespoon of white vinegar or lemon juice to a one cup measuring cup. Slowly add regular milk until the measuring cup is full. Allow the mixture to sit for five to ten minutes before using. Discard any leftovers.
Sour cream may also be substituted for buttermilk in a baking recipe. Simply exchange one cup of the substitute for every one cup of buttermilk the recipe needs. Depending on the recipe, you may need to add a small amount of additional liquid to make sure the proper consistency is reached. Add milk or water by the tablespoon until it is correct.
Plain Yogurt and Milk
Buttermilk can also be faked by making a mixture of half plain yoghurt and half whole milk. Mix thoroughly and allow the mixture to sit for a few minutes to thicken. Whole milk is the best substitute in this case.