The Baking Answer Book (14 page)

Q
What happens when egg whites are whipped?

A
Egg whites consist of tightly wound but separate strands of protein that uncoil and link together with each other during whipping, forming a weblike network that traps and holds air. It is crucial when making an egg white foam capable of raising a cake or soufflé not to overwhip the whites. You want them to stay soft, moist, and flexible, so they can stretch along with the trapped air as it heats in the oven. Overwhipping will separate the protein from the moisture in the egg whites, leaving you with lumpy whites made of dry, stiff, and set protein that’s been separated from the water molecules in the egg. When overwhipped egg whites are folded into a cake or soufflé batter, they do nothing to help the cake or soufflé rise, since they are incapable of expanding.

Q
What is the difference between “soft peaks” and “stiff peaks” and when is one preferable over the other?

A
The longer you beat whites, the more air you will incorporate into them and the more rigid the proteins will become. Egg whites whipped to soft peaks will flop over slightly when a whisk is pulled up from the bowl. Whipped to stiff peaks, the whites won’t flop over. Egg whites whipped to soft peaks are good in soufflés, where moisture and maximum flexibility are important. Whipped to stiff peaks, they are better in meringues, angel food cakes, and other recipes where maximum volume is desired.

Q
Why do recipes emphasize the need for a clean bowl and beaters when beating egg whites?

A
Oil or grease on the surface of an improperly cleaned bowl or beater will corrupt an egg white foam, coating the proteins and inhibiting their ability to link up with each other to form the 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 beaten
in 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 extremely crumbly, fragile texture.

The same denaturing process is at work in baked custards, but a little more caution must be used so that you wind up with a smooth rather than a cottage cheese–like result. In the case of crème anglaise, a mixture of milk, sugar, and eggs is gently heated until it thickens into a smooth sauce at about 160°F (71°C). Constant stirring is necessary to break up clumps of coagulating protein and care must be taken not to overheat the mixture or no amount of stirring will prevent the formation of clumps. In the case of a custard that isn’t stirred, like cheesecake or crème brûlée, it is especially important to heat the custard gently until it sets into a smooth mass. Custards are often baked in a water bath, which protects them from heating too quickly and to too high a temperature.

HOW FLOUR HELPS BAKED GOODS KEEP THEIR SHAPE

Gluten development is key to the structure and texture of baked goods, even those made without yeast. As when making bread dough, during the mixing of other doughs and batters, the proteins in flour organize themselves into a webbed cell structure made of gluten strands. Whichever method of leavening a recipe employs, this webbed cell structure works in a similar way to trap air. As the flexible walls of the cells expand to accommodate expanding gases, or water turning to steam, the baked goods rise.

Compare a slice of tender pound cake to a slice of chewy artisan bread. The differences in texture are significant, for two reasons: First, the cake calls for a low-protein cake flour. This type of flour will develop just enough gluten to support the cake, which will rise just enough to give it a light texture and delicate crumb. In contrast, high-protein bread flour will be able to produce much more gluten than cake flour, for an extremely strong and extensible dough that can support the bread’s lofty rise.

The way flour is handled also has a significant impact on a product’s structure and texture. Compare directions for mixing biscuits with mixing bread dough. For biscuits, the dough is handled as little as possible, mixed just until all dry ingredients are moistened, to avoid overdevelopment of the gluten, which can lead to toughness. For bread dough, the opposite is true. Vigorous, prolonged kneading is required to develop the gluten to its utmost, so it can support the dough as it rises in the oven.

Q
What happens to sugar when it caramelizes? Why does the crust of a bread or muffin taste so good?

A
Caramelization is a chemical reaction that occurs when sugar is heated until its molecules break apart and recombine into a variety of compounds with a diversity of flavors and aromas ranging from sweet to sour to bitter. These compounds account for the complex taste of caramel.

Q
How do baked goods get their caramelized crusts?

A
Sugar on the surface of baked goods, exposed to the heat of the oven, caramelizes. The resulting sweet crustiness provides a delicious contrast to the yielding interior of most cakes and pastries. Even breads with no added sugar can sport caramelized crusts, thanks to starches that convert into sugars in reaction to yeast during fermentation.

Q
Aside from sweetening, tenderizing, and browning, does sugar serve other functions in baking?

A
Sugar also raises the temperature at which a batter will change from fluid to solid by delaying the coagulation of proteins. A little sugar added to bread dough will have a similar effect, delaying protein coagulation and giving the gluten more time to stretch before it sets.

Q
What role does salt play in baking?

A
Primarily, salt plays the same role in baking that it does in cooking. It enhances the flavors of the other ingredients in the recipe, making brownies more chocolaty and corn muffins more redolent of corn. It brings out the earthy flavors of stone-ground whole wheat in bread. Without a pinch of salt, your cookies, cream puffs, and crème caramel will taste flat and bland. Salt even makes sugar cookies taste more pleasantly sweet than they would without salt. The proportion of salt to other ingredients is minute in most baked goods, and presents little risk to people trying to watch their salt intake. So unless you are on a strict no-salt diet, use the recommended amount of salt for optimum flavor results.

In addition to enhancing the flavor of bread, salt plays a crucial role in crafting tall and beautifully browned loaves. Salt strengthens gluten, tightening the webbing of proteins that give bread dough the structure to expand without collapsing. It also acts to slow fermentation in yeast breads. Slow fermentation prevents yeast breads from bubbling up too quickly, allowing gluten to develop as the dough rests, which contributes to a yeast dough’s high rise in the oven. In addition, when yeast is allowed to proliferate too quickly, it gobbles up all of the sugars in the dough, sugars that, ideally, caramelize and give the crust a rich brown color. Without enough salt, your bread may be dense and pale instead of tall and deliciously dark golden.

SEE ALSO:
Fermentation in yeast breads,
page 312

WHAT MAKES BAKED GOODS TENDER?

A rundown of basic baking ingredients and techniques will give you a good idea of how each one contributes to the tenderness of baked goods.

When flour is mixed with a liquid, a webbed network of proteins called gluten develops, which provides structure for all baked goods as they rise. Different types of flour contain different amounts of protein.

In general, the most tender baked goods are made from flour with a low protein content. Thus, yellow cake, biscuits, and madeleines often call for very soft cake flour, which will develop relatively little gluten and thus contribute to the tenderness of the finished product. Conversely, an abundance of gluten is desirable in items such as French bread, which has a bubbly and open crumb along with a thick, chewy crust. High protein bread flour makes sense in these recipes, where tenderness isn’t important but a strong structure is. Using cake flour in a baguette recipe would be a disaster, because the dough would lack the strong gluten structure to support it as it rose in the oven, resulting in a flat, soft bread with a close crumb.