Science turned sweet with cupcake chemistry

You've cleared away a spot on the kitchen counter and scrounged together bowls, spoons and a measuring cup. (You don't really need a mixer, right?) You're totally prepared to try that great new recipe from the News-Letter.

Too late, you realize you are out of eggs and the baking soda is spilled inside the fridge, missing everything except taco shells and ketchup. Your roommate passes by, shaking salt into his Easy-Mac, appearing perplexed. The shaker is empty.

Have your baking dreams already been whisked away? Not if you understand how your ingredients work. And that's all science.

The most important ingredient in baking is the leavening agent. A typical leavener uses a chemical reaction between an acid and a base that causes the batter to rise. In a recipe, this is usually baking powder or baking soda. What is the difference?

Baking soda, or sodium bicarbonate, is simply a base. It is used to neutralize other acidic ingredients, such as vinegar, brown sugar or honey. Baking soda releases bubbles of carbon dioxide when mixed into the moist batter. These bubbles cause the batter to rise.

Baking powder, on the other hand, is a dry mixture containing baking soda, some acid salts and cornstarch. The baking soda reacts with the acid salts in the powder, in addition to any other acidic ingredients, only when the mixture is moistened. To prevent the reaction from occuring before it is added, baking powder includes cornstarch as a drying agent.

Hold on - baking powder already contains baking soda? Then why would a recipe call for both ingredients?

In this case, baking powder is doing most of the leavening of the batter, while the baking soda is present to neutralize the rest of the acids. By itself, baking soda produces the strong base sodium carbonate along with carbon dioxide, which causes the entire mixture to be slightly too basic and can result in a stomachache for whoever eats the baked goods.

Even though baking soda is about four times as strong as baking powder, the production of this extra base means it is less efficient at making carbon dioxide and therefore at leavening the batter.

Double-acting baking powder reacts in two stages - when moistened and when heated. This lets the batter start to react when mixed in the bowl and to rise further while baking in the oven. Most powder on the shelves today is double-acting.

What if the recipe needs baking powder, but all you have is baking soda?

There are a couple of ways to easily make this substitution. The most common directions say to mix a quarter teaspoon of baking soda, half a teaspoon of cream of tartar and a quarter teaspoon of cornstarch to make one teaspoon of baking powder.

If you don't have the other ingredients though, you can just mix a fourth of a teaspoon of baking soda with half a cup of another acidic ingredient, which allows the basic soda to react to produce carbon dioxide. Sour milk or yogurt work well, according to http://www.JoyofBaking.com.

The rest of baking's staple ingredients are not so complicated.

Flour forms the main structure of most baked goods. Its key component is gluten, a class of proteins that are able to expand to many times their original volume while remaining airy in texture, as is apparent in any tall, fluffy cake.

Sugar not only adds flavor, but is involved in browning reactions above 160?C (322?F), which make the top of a blueberry pie or the edges of a scone so appealing.

Eggs act like glue in the batter, holding the other ingredients together. In an interesting process, they also keep the batter from collapsing when baked.

The protein lecithin, found in egg whites, lines and protects the outside edges of the carbon dioxide bubbles formed by baking powder or soda. This makes them more durable in the oven, allowing the batter to stay risen.

Salt is multifaceted. It adds its own flavor, and it brings out other flavors by making them more potent. Furthermore, it toughens and tightens the batter and slows down the chemical reactions of leavening.

This last quality is important because when the batter rises too quickly, it is more likely to collapse.

Fat, found in various baking ingredients including butter, also has more than one function. Besides adding flavor, fat helps break down gluten networks in the flour to give a softer texture to the final product. When mixed, many air bubbles end up trapped in droplets of fat which preserve them in the oven where they can rise - a very important point for cake-makers.

Recipes are really only guidelines based on this set of principles. If you understand a little bit of science, you can bake almost anything. The rest is just a matter of flavor, preference and finesse.