Have you ever wondered how a baker can create a cake recipe from scratch and know that it will work? Unlike a savory chef, who can often use intuition to design a successful dish, a baker must work within defined parameters to produce a cake that will rise, set, and taste the way she wants. Experienced cake bakers would never dream of trying to bake a cake without first "doing the math" to make sure that the ingredients are in balance. Having the right proportions of flour, eggs, sugar, and fat makes all the difference.
Flour and eggs for structure, fat and sugar for tenderness
In cakes, the protein ingredients, which are the flour and eggs, are the major structure-builders. They're essentially what holds the cake together. Fat and sugar do the opposite; they actually wreck or soften the cake's structure, providing tenderness and moisture.
If you have too much of the structure-building flour and eggs, the cake will be tough and dry. If you have too much of the moistening, softening fats and sugars, the cake might not set. It could be a soupy mess or so tender that it falls apart.
Bakers have formulas that balance these ingredients so their cakes have the strength to hold together but are still tender and moist. These formulas don't have to be followed dead on, but if you stray by more than about 20 percent, you may have problems.
There are two sets of formulas: pound-cake (or lean-cake) formulas, which have less sugar than flour; and "high-ratio" formulas, which contain more sugar. The general rule is that high-ratio cakes require shortening, whose added emulsifiers help hold the cake together. You can, however, make successful high-ratio cakes with butter if you aerate the butter by creaming it and if you add emulsifiers in the form of egg yolks. Some bakers even make cakes with olive oil, which contains natural emulsifiers (mono- and diglycerides).
Here are the three formulas for the more popular, sweeter, high-ratio cakes:
Sugar = Flour
The sugar should weigh the same as, or slightly more than, the flour. Remember that this is weight, not volume. A cup of sugar weighs about 7 ounces, and a cup of all-purpose flour weighs about 4-1/2 ounces. So, if we're building a recipe with 1 cup sugar, we'll need about 1-1/2 cups flour (about 6-3/4 ounces).
The eggs should weigh about the same as, or slightly more than, the fat. One large egg (out of its shell) weighs about 1-3/4 ounces. If our developing recipe contains 4 ounces butter (or shortening), we could use two whole eggs (3-1/2 ounces). This is a little under, but remember that these rules are flexible, and we're still within 20%.