Cream of tartar is one of those household products that most people have probably heard of, but many are completely in the dark about what to do with. You may be able to find a little jar of it in the back of your pantry, and in some cases it may still be unopened. It sounds like a baking ingredient, but it's much more versatile than that.
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It Isn't Really a Cream
That jar of cream of tartar you aren't sure what to do with is actually potassium hydrogen tartrate. This is an acidic salt that has both culinary and household uses. The only natural place you're going to find a significant amount of tartaric acid is in grapes, which is why cream of tartar is created after the winemaking process has completed. It is also known as potassium bitartrate, and it is removed from fermentation tanks in crystal form to make cream of tartar, which is sold as a bright white powder.
In the culinary world, cream of tartar is not a suitable substitution for thickening agents in desserts or sauces, but it is used for stabilizing and adding volume to egg whites. This is particularly useful when making meringue for pies or other desserts. Cream of tartar also can be used to stop the crystallization process if you're making candy, icing or syrups. When sugar reaches the crystallization stage, the candy is often ruined, so for this purpose cream of tartar is particularly useful. When cream of tartar and baking soda are added to a liquid together, the resulting carbon dioxide bubbles that are formed cause baked goods like cakes and cookies to rise and be tender.
Doesn't Measure Up
When compared with starch-based thickeners such as arrowroot, tapioca or cornstarch, cream of tartar just doesn't have the same ability to dissolve in a liquid, such as a soup, gravy, sauce or pie filling, and create the process known as gelation. Cream of tartar is an acidic powder, and as such, gives off a slightly acidic, sour taste. Most starch thickeners don't affect the taste of the liquid they are added to.
Storage and Substitution
When you get the cream of tartar home, aim for a cool and dry place like your pantry so it is away from humidity. You probably won't be using it often, so keep it in good shape for when you do. If it is stored in a humid place, the powder may clump together. Replace your cream of tartar annually to ensure it's in good working condition. If you don't have any cream of tartar and a recipe needs it and baking soda, you can substitute with an equal amount of regular baking powder, since it is a combination of the two.
Cream of tartar is also useful in non-culinary roles. When mixed with varying amounts of water, it makes an effective cleaner and polish for items like aluminum pans and stainless steel appliances, or a paste to remove scratches from dishes. Cream of tartar and lemon juice can clean copper, and cream of tartar with hydrogen peroxide removes a bathtub ring.