The rules for low-fat baking are completely different from those for traditional full-fat baking. Reduced- and low-fat batters are more sensitive to overmixing, overbaking, ingredient substitutions, improper measuring, oven temperatures, and choice of baking pans. Practically every baked good, traditional or reduced-fat, is created from a balance of many components. A recipe is a culinary formula. Each component has a role to play in the formula and the success of the final result. It is important that the baker understands how these ingredients work, and why they require different mixing and baking methods than the ones my mom taught me when I was first learning my way around the kitchen.
For example, most of Mom's recipes start with a large amount of butter, which through creaming with crystalline sugar, creates and traps air and moisture in the batter. In reduced-fat baking, the butter is significantly reduced or eliminated altogether, and the fat is often replaced by a fruit puree and other ingredients. If butter is used at all, it is as a flavoring.
Here are the basic components that you'll find in almost every recipe for any baked good.
Wheat flours and egg whites contain proteins that provide strength for a batter or dough so it will rise and not collapse when baked. When wheat flour is moistened and stirred, two proteins in the flour, glutenin and gliadin, connect and cross-connect to form strands of gluten, which help give structure to the baked good. Wheat is the only grain with significant amounts of gluten-forming potential. Other grains like corn and oats, and therefore products like cornmeal and oatmeal, do not create gluten in a batter. They provide only flavor and bulk, and must be mixed with wheat flour for strength.
Depending on the type of wheat and where and when it was planted, the resulting flour can be high-gluten (milled from hard winter wheat), low-gluten (from soft spring wheat), or moderate (a combination of the two). Baked goods made from high-gluten flours have a firm crumb; low-gluten flours give more tender results, and goods made from flours with a moderate gluten content fall somewhere in between.
The more a batter is stirred, the stronger the gluten becomes. Fat, which is not present in reduced-fat baking in traditional amounts, plays an important role in coating the proteins in flour, minimizing their contact with moisture, and shortening the gluten's development. Without the fat lubricator, the gluten strands form more readily. That is why it is very important to never overmix a reduced-fat batter. You'll see the phrase "Do not overmix" in practically every recipe in my book.
I often use unbleached all-purpose flour, which has a moderate gluten content. For a lower gluten content with a more tender outcome, I use whole wheat pastry flour or cake flour. In a few cases, I also use high-gluten, regular whole wheat flour. Each recipe is written with a specific flour in mind to give the best results.
Most bakers are very familiar with traditional shortenings such as butter, margarine, and vegetable shortening. Shortenings coat the flour proteins, reducing their contact with the moisture in the recipe, and shortening the length of the gluten strands when the flour is stirred with that moisture (that's why they're called "shortenings"). In traditional baking, where solid fats are creamed with crystalline sugar, tiny air cells are whipped into the batter, so the baked good will have a fine, aerated texture. When a shortener is removed or reduced, it increases the chances that the end product will lack flavor and be tough and full of tunnels. The new mixing methods in this book reduce this possibility.
Butter makes a very important flavor contribution, whereas margarine does not have as fine a texture and taste, so when choosing a shortening, I always go for the butter, but in the small amounts that are needed to retain a great taste and aroma. If you have dietary restrictions that make it necessary for you to reduce saturated fats in your diet, you can substitute a butter-margarine blend. The recipe won't taste the same if you use margarine. Vegetable oil does not act as a shortener because it is a liquid and won't cream with crystalline sugar in the same way as a solid fat. It reduces dryness and enhances flavor, so I use it sparingly because it has the same number of calories and fat grams as butter, even though it has less saturated fat.