Definition

• Cream of tartar is another name for potassium hydrogen tartrate, and it's a byproduct of the winemaking industry. Grapes contain tartaric acid, which gathers as sediment at the bottom of wine barrels. When processed and dried, this tartaric acid becomes cream of tartar, an acid salt that helps stabilize egg whites and also keeps sugar from crystallizing in candies. Commercially, cream of tartar is used in soft drinks, candies and desserts. It is also sometimes added to baking powder.

Shelf-Life

• White, odorless cream of tartar is typically packaged in small bottles containing 1 ounce or less of the product. When stored in a cool, dark, dry pantry, it will last at least two years, and perhaps indefinitely. In hot, humid climates, though, it may clump or lose its effectiveness. Discard any cream of tartar that has an off-color or odor, or has been mixed with other ingredients that may spoil.

Use

• Although cream of tartar has a long shelf-life and isn't likely to spoil, you should cook any baked products made with it immediately. When used in snickerdoodles, for example, cream of tartar provides the acid that activates the bubbles in baking soda. These bubbles give baking soda its leavening power. As the cookies bake in the oven, they become puffy and golden brown. If you don't cook the cookies promptly, the bubbles dissipate, resulting in flatter cookies.

Substititions

• In most cases, the cream of tartar in your pantry should work just fine. But if it's become wet or lumpy, you might need a substitute. In baked goods, such as snickerdoodles, substitute baking powder at a rate of 1 teaspoon baking powder for each 1/4 teaspoon baking soda and 5/8 teaspoon cream of tartar. Baking powder won't give snickerdoodles their characteristic tangy flavor, but it works in a pinch. To whisk egg whites successfully without cream of tartar, start with a very clean, dry metal or glass bowl and cold, fresh eggs. Don't use plastic bowls for whisking eggs.