Q.  What is baking powder and how is it different than baking soda?

A.   Baking powder is a leavening containing a combination of baking soda, an acid (such as cream of tartar) and a moisture-absorber (such as cornstarch). When mixed with liquid, baking powder releases bubbles that cause a bread or cake to rise. The most common type of baking powder is double acting, which releases some gas when it becomes wet and the rest when exposed to oven heat. Because it's perishable, baking powder should be kept in a cool, dry place. Always check the date on the bottom of a baking-powder can before purchasing it. To test if a baking powder still packs a punch, combine 1 teaspoon of it with 1/3 cup hot water. If it bubbles enthusiastically, it's fine.

Baking soda is also known as bicarbonate of soda. When combined with an acid ingredient such as buttermilk, yogurt or molasses, baking soda produces bubbles, thereby causing a dough or batter to rise. Because it reacts immediately when moistened, it should always be mixed with the other dry ingredients before adding any liquid; the resulting batter should be placed in the oven immediately.

Definitions of other cooking terms can be located in the Oriental Foods And Recipes glossary.

Q.  What can I substitute for self-rising flour?

A.  To substitute for self-rising flour, use 1 cup all-purpose flour plus 1 1/2 teaspoons baking powder plus 1/2 teaspoon salt.

Q.  Can I substitute all-purpose flour for cake flour?

A.  Cake flour is fine-textured, soft-wheat flour with high starch content. It makes particularly tender cakes and pastries. Because of these qualities, it is generally not recommended that you substitute all-purpose flour for the cake flour called for in a recipe. If cake flour is called for, it means that all of the other recipe ingredients and amounts have compensated for the finer texture of this flour, and to substitute something else would most likely not give the intended results. More information about flour can be found in the article All About Flour .

Q.  What is shortening?

A.  The term "shortening" on our site refers to vegetable shortening, a solid fat made from vegetable oils, such as soybean and cottonseed. Vegetable shortening is virtually flavorless and may be substituted for other fats in baking and cooking. Bakers sometimes prefer shortening because it does create a slightly higher, fluffier cake but there is no reason why you should not be able to use butter instead.

Q.  Why do my cakes fall?

A.  There could be a number of reasons your butter cakes are falling; a butter cake is one made with shortening or butter. Among the more common reasons is the addition of too much baking powder or soda, over beating the egg whites, or removing the cake from the oven before it is done. 

Q.  My cakes do not rise evenly - they are tall in the middle, and slope down to the sides. What am I doing wrong?

A.  The most likely cause is that the oven is too hot. Check your oven with an oven thermometer to insure that you are baking at the correct temperature.

Q.  Can I freeze a cheesecake?

A.  You can freeze a cheesecake successfully for later use. First, allow the cheesecake to cool completely in the refrigerator. Wrap it in plastic, as airtight as possible to ward off freezer burn. Place the cheesecake in a safe spot in the freezer where it won't be bumped or otherwise contaminated. It's important that the cheesecake remain frozen for the duration of storage, and not be defrosted or thawed, then re-frozen. Thaw your cheesecake in the refrigerator before serving. Bear in mind that cheesecakes are made with dairy products and eggs, and shouldn't be left at room temperature. It will probably take about 12 hours to thaw. You can expect some moisture to collect on top of the cake due to condensation - this can be dabbed off with a paper towel. If you are planning to decorate the cheesecake or use a topping, it's best to do this after the cheesecake has thawed.

Q.  What about freezing a plain cake?

A.  For best results, don't freeze the cake after decorating with frosting. The cake expands faster than the frosting, causing it to crack while thawing. You can assemble the cake and apply a thin "crumb coat" of frosting, then finish decorating after the cake is thawed. Allow the frosting to firm up in the refrigerator or freezer, then wrap tightly in plastic. Place the cake in a safe spot in the freezer where it won't be bumped or otherwise contaminated. Defrost the cake gradually. Unwrap the cake and place in the refrigerator for 8 hours. To avoid absorbing odors from the refrigerator, place the cake in a cake carrier.

You can freeze undecorated cake layers for up to a month before using. Be sure to wrap them as airtight as possible, or they will dry out in the freezer.

Q.  I often find myself adjusting recipes in order to make enough for my family, but it doesn't quite work for some recipes. Do you have any advice for me?

A.  Changing recipes in order to make more or less servings is called "recipe scaling." Whenever you alter the amounts of ingredients for a given recipe, you may also need to adjust the cooking temperature, cooking time, pan size and seasonings. But for food chemistry reasons, recipe scaling simply does not work well for some dishes: delicate foods such as soufflés, baked items requiring yeast such as breads, and recipes for a single large item that is meant to be later divided into smaller portions such as cakes, pies, breads and whole turkey.