What Are the Functions of Cream of Tartar?

Cream of tartar, potassium acid tartrate, is a byproduct of the wine-making industry. Grapes are the only important natural source of tartaric acid, and after fermentation they leave behind a deposit of tartaric acid crystals on the inside of wine barrels. This residue, mixed with potassium hydroxide, creates an acidic, usable salt called cream of tartar.

Uses--Alone

Cream of tartar is primarily used in home baking. Muffins, cakes and cookies all need some kind of leavening agent that works faster than yeast. Baking soda is that agent, but baking soda needs an acid to mix with, in order to produce the little gas bubbles that lighten and raise a batter. Cream of tartar is a convenient dry acid. Mixed two parts to one with baking soda, it creates what old-fashioned cooks would know as single-acting baking powder. This is a baking powder that begins to leaven as soon as a batter is moistened.

Uses--Baking Powder

Baking soda mixed with cream of tartar plus corn or other starches make a new product. The soda with its acidic partner will still leaven batter, but the starches will help keep both chemicals dry enough that they can raise a batter twice--once when it is moistened, and again when it goes into the oven to bake. This is double-acting baking powder, an American invention of the early 19th century.

Uses--Kitchen and Commercial

Cream of tartar has anti-caking, stabilizing and thickening properties. Home cooks use it to lend volume to beaten egg whites and to keep frostings smooth. Food manufacturers use it to keep a creamy texture in gelatins and candies, and to prevent crystal formation in sugary desserts or frostings.

Cleaning

Cream of tartar, mixed with water to form a paste, cleans brass and copper. In the 19th century, cream of tartar also served as a soak to whiten clothes. Its antimicrobial properties added to its value in the old-fashioned laundry business.

Careful in the kitchen

The interlocking uses of cream of tartar, baking soda and baking powder may confuse home cooks, especially where recipe substitutions are concerned. Cream of tartar, alone, will not leaven anything. It is already in baking powder, so if your recipe calls for that you are fine. You may substitute baking powder for baking soda, but you may need a lot more and the taste of your baked goods may change. If you don't have baking powder, you can make it, but you will need both cream of tartar and baking soda. And baking soda alone will not leaven anything. It needs an acid, whether a liquid one like orange juice or buttermilk, or the dry one--cream of tartar.

Resources

• What is cream of tartar?