Free The Baking Answer Book by Lauren Chattman Page B

flexible web needed to trap air bubbles.
    Q What happens if you accidentally spill a little bit of yolk into the bowl with your whites before whipping?
    A Egg yolks contain fat. Even a speck of yolk can prevent a bowl of egg whites from whipping properly, so if some yolk winds up in your whites you should discard the contents of the bowl, wash it scrupulously, and start again. To prevent waste and bother, separate your eggs one at a time in a small bowl, transferring each successfully separated white to a larger mixing bowl as you go. This way, if a little yolk gets into one of your whites as you work, you can simply throw away one white instead of discarding the whole bowl.
    Q Why do room-temperature whites whip better than cold ones?
    A The coiled proteins in egg whites will relax slightly as they warm up, so that whipping them will take less time. Egg whites straight out of the refrigerator can achieve the same volume, but it will take longer.
    Q Why are old egg whites better than very fresh ones for whipping?
    A Egg whites that are 3 or 4 days old whip to greater heights than very fresh ones because the coiled proteins will relax over the course of several days. If you are using eggs from the supermarket, they will most likely be at least a week old by the time you purchase them. But if you are lucky enough to have a source for fresh eggs, let them sit for a few days before whipping.
    Q Why is cream of tartar sometimes called for in recipes for whipping egg whites?
    A Cream of tartar or another acidic ingredient, such as lemon juice or vinegar, is often added to egg whites before whipping because the acid encourages the egg proteins to uncoil more quickly to trap air bubbles. It also strengthens the protein in whipped whites, making them more stable and less likely to deflate during baking. Similarly, whites beatenin a copper bowl are made more elastic due to their contact with the element, which makes the whites flexible so they can expand more in the oven.
    Q What is the effect of sugar on egg whites during whipping? When and how should sugar be added?
    A Sugar whipped along with egg whites dissolves and coats the proteins so they don’t dry out and harden. It creates a glossy, thick foam that is more stable and less likely to deflate than a foam made with egg whites alone. Sugar will slow down the incorporation of air into the mixture, so it’s best to whip the whites by themselves at least until they reach a foamy, almost-soft peak stage before adding the sugar. Then, add the sugar in a very slow stream as you whip the egg whites. Waiting too long to add the sugar is a mistake, the danger being that the egg whites will already have begun to dry out, and won’t be able to take advantage of sugar’s protective capabilities.
    Q How do baked goods keep their shape?
    A The short answer is just one word: protein. See the following pages for a longer explanation of the two different sources of protein — in eggs and in flour — that bakers rely on to keep their cakes and other creations from crumbling to pieces.
HOW EGG PROTEINS HELP BAKED GOODS KEEP THEIR SHAPE
    The protein in eggs and flour is what holds baked goods together. Eggs, both the yolks and the whites, are high in protein, which goes from liquid to solid as it cooks. Anyone who has scrambled an egg knows this.
Here is how it happens: Uncooked protein consists of small, individual, tightly coiled strands. Heating these proteins causes them to unravel (or denature) and then link together with each other, forming a solid mass, or, more precisely, separate solid curds. If you stir uncooked eggs into a cake batter, the proteins will do the same thing, linking up with each other to hold your cake together and give it a solid structure.

Eggs work the same way in cookies. Think about the difference in texture between a chocolate chip cookie, which contains eggs and becomes a solid, chewy mass when baked, and a shortbread cookie, which contains no egg and has an