Before baking soda and baking powder were available, cooks often kept their baked goods from being heavy by using cream of tartar. This is the common name for potassium hydrogen tartrate and is essentially an acidic salt. It is manufactured by mixing potassium hydroxide with tartaric acid. For centuries, it has been formed from the sediment left over in barrels after the winemaking process.
Cream of tartar is found in some baking powder, and is often used to help stabilize egg whites and to produce creamy frostings and candy. If a cook is out of baking powder, he can substitute cream of tartar and baking soda, carefully, to mimic the action of baking powder, which is actually formed from these two compounds. However, homemade baking powder can pack a kick, so it should be substituted with great care. This is how most cooks made their baking powder before it became commercially available.
Cooks can often find cream of tartar in the spices or baking section of most grocery stores, and it's available from many spice retailers. Even a small container will last for some time, since very little is usually needed for the desired results. White vinegar or lemon juice can be substituted for cream of tartar, but it takes about three times more vinegar to produce the right amount of acidity.
Cream of tartar also has other household applications. It can be used to clean brass and copper cookware. It is also helpful in removing stains from sinks and bathtubs. Combined with hydrogen peroxide, it can remove even the most stubborn rust stains without scratching a delicate surface. Consumers should always test the solution in an inconspicuous area first, however, to ensure its suitability for use on that surface.
Recipes using cream of tartar are available online. When kept away from heat and light, its shelf life is indefinite, making it a good buy. This unassuming baking aid is a useful addition to any kitchen.