Whole grain cake is a sweet baked confection made from grains that have not been abraded to remove the bran. Most cakes of this type use wheat flour, but some also incorporate rice flour, buckwheat, or other grains. Whole grain flours tend to produce a slightly tougher, denser result than refined flour, and can require special handling or extra ingredients to produce quality cakes.
All grains naturally have an outer skin called bran, an embryo called the germ, and a starchy endosperm. Refined grains remove part or all of the bran and germ, leaving the fluffier but less nutritious endosperm. Enriching refined flour returns some of the nutrients lost in refining, but enriched flour is not equivalent to whole grain, and will not provide the same nutrition in baking. Many companies add bran and germ back into refined flour after processing instead of grinding the grain in one step. To use the label “whole grain” in many countries, the resulting flour must have about the same proportion of germ, bran, and endosperm as the original grain.
Though it comes in the same basic flavors as its refined-flour cousins, the extra bran in whole grain cake can produce a denser, drier, less-fluffy product. Cakes made with whole grain flour may also have a coarser texture, as it's difficult to grind the bran to the same fineness as the endosperm. Whole grain flours work best in cakes that are already meant to be dense and moist, such as fruit-based cakes, heavy chocolate cakes, and spice cakes. They work poorly for light baked goods like angel food cake, white cake, or sponge cake.
Ingredients such as sour cream, yogurt, and bananas can help to keep a whole grain cake moist and rich-tasting, as can using recipes high in butter, eggs, or oil. Bakers can also replace only part of the refined flour in a cake recipe with whole grain flour, producing a relatively light cake with more protein and vitamins. Leaving 50% or more of the refined flour in a recipe decreases the risk of an unappetizing product.
Flour quality can affect the success of whole grain cakes as well. Bakers should use whole grain cake or pastry flour, which contains less gluten and has a reduced risk of toughness. White whole wheat flour tends to produce a lighter taste and feel than the more common red variety, since its germ contains fewer tannins. Storing fresh flour in the freezer keeps the germ from going rancid and developing an unpleasant musty or earthy flavor.