Learn: Cream of tartar is the culinary name for potassium bitartrate, a by-product of winemaking. Potassium bitartrate crystallizes and collects in fermentation tanks, and is removed and purified to make the bright white powder.
Purchase: You'll find cream of tartar near the baking powder and baking soda in your local market. It's sold in small plastic bottles.
Store: Humidity can cause cream of tartar to clump, so store in a cool, dry place like a cabinet or pantry, and replace annually.
Use: Cream of tartar has a number of culinary uses. Many chefs add about 1/8 teaspoon of cream of tartar per egg when beating whites to make meringue―this keeps them stable and adds volume. It also prevents sugar from crystallizing, so mix in a small amount to create smooth icings, syrups, and caramels. Cream of tartar is also a common ingredient in baking powder. If in a pinch, make your own baking powder by combining two parts cream of tartar with one part each baking soda and cornstarch (when dissolved in water, cream of tartar becomes acidic and activates the baking soda, causing baked goods to rise).