Cream of Tartar and Tartaric Acid

Cream of tartar is obtained when the acid in tartaric acid is half neutralized with potassium hydroxide, transforming it into a salt (hence it's other catchy names: potassium bitartrate and potassium hydrogen tartrate). Cream of tartar is therefore an offspring of tartaric acid. Grapes are the only significant natural source of tartaric acid, and cream of tartar is obtained from sediment produced in the process of making wine.

Cream of tartar is best known in our kitchens for helping stabilize and give more volume to beaten egg whites. It is the acidic ingredient in some brands of baking powder. It is also used to produce a creamier texture in sugary desserts such as candy and frosting, because it inhibits the formation of crystals. It is used commercially in some soft drinks, candies, bakery products, gelatin desserts, and photography products. Cream of tartar can also be used to clean brass and copper cookware.

Substitution: If you are beating eggs whites and don't have cream of tartar, you can substitute white vinegar (in the same ratio as cream of tartar, generally 1/8 teaspoon per egg white). It is a little more problematic to find a substitute for cream of tartar in baking projects. White vinegar or lemon juice, in the ratio of 3 times the amount of cream of tartar called for, will provide the right amount of acid for most recipes. But that amount of liquid may cause other problems in the recipe, and bakers have found that cakes made with vinegar or lemon juice have a coarser grain and are more prone to shrinking than those made with cream of tartar.

Tartaric acid is not called for very often in the home kitchen – when it is, it is primarily to provide extra tartness to foods, for instance, to give flatbread a little extra zing. If you don't have tartaric acid on hand (which is much harder to find and more expensive than cream of tartar (which itself can be hard to find)), you could probably use two teaspoons of cream of tartar in place of one teaspoon of cream of tartar and one of tartaric acid.