15.3 What eggs do in a recipe

Eggs do many jobs at once, especially in the bakeshop. Once you know what each job is, you can change a formula with confidence. Most of the jobs come back to two facts: egg proteins set when they are heated, and the yolk carries fat. see chapter 7: Proteins set: coagulation

• Leavening. Eggs can carry many times their weight in other ingredients, because they form a network of tiny cells, alone or together with flour. The white is especially good at this: its protein builds a fine web that traps a great mass of cells.
  ▶ Watch
• Structure. Eggs bind with other ingredients, mostly flour, to build the frame that holds everything else up.
  ▶ Watch
• Moistening and binding. The fat in eggs keeps a product moist, and the proteins set when heated, holding the other ingredients together.
• Thickening. Eggs thicken custards and chiffon pie fillings.
  ▶ Watch
• Emulsifying. The yolk contains lecithin, a natural emulsifier that helps make batters smooth.
  ▶ Watch
• Tenderizing. Egg fat works like a shortening and makes a baked cake more tender.
  ▶ Watch
• Shelf life. The fat in the yolk helps a product keep longer.
• Appeal. Eggs add color and flavor and improve texture and grain.
• Nutrition. Eggs are a valuable food. About 4% of the fat in a yolk is cholesterol, which concerns some people; makers of poultry feed claim to have lowered or removed it.

Changing a formula

A few examples show how bakers adjust eggs to get a result:

• In French butter cream in summer, egg whites can replace whole eggs. The cream is more stable and resists bacteria, because egg white is alkaline, at pH 8.5.
• Working a yolk or two into a sweet short paste lets the dough stretch further before it tears.
• Extra yolks in the sponge for a jelly roll help it roll up without cracking.

If you swap some or all of the eggs for water, remember two things. An egg is about 25% solids, so use water equal to about 75% of the egg you take out. And the batter loses lift, so add chemical leavening to make up for it.

Points to keep in mind

• A blood spot comes from a small fragment of blood in the hen's ovary. The egg is safe to eat and can be used.
• Egg white dissolves in cold water. It sets at 70°C (158°F), and after that it will not dissolve again.
• Leftover whites or yolks go into the refrigerator, tightly covered. To stop yolks forming a crust, pour a little water over them or mix in 10% sugar.
• Never pour unused egg back into the main container, and always use a clean utensil to take egg product out of its container.