Buttermilk is a fermented dairy product produced from cow's milk with a characteristically sour taste. The product is made in one of two ways. Originally, buttermilk was the liquid left over from churning butter from cream. Today, this is called traditional buttermilk. Buttermilk also refers to cultured buttermilk, a product where lactic acid bacteria have been added to milk. Whether traditional or cultured, the tartness of buttermilk is due to the presence of acid in the milk.
In the early 1900's, cultured buttermilk was labeled artificial buttermilk, to differentiate it from traditional buttermilk, which was also known as natural or ordinary buttermilk.
For recipes, a substitute for buttermilk can be made by adding 1 tablespoon of lemon juice or white wine vinegar or 1.75 teaspoons cream of tartar to each cup of regular milk. The soured milkshould be allowed to sit for ten minutes before being used.
Another combination that would produce a thick buttermilk substitute is to mix equal parts full-fat milk and thick Greek natural yogurt such as Total.