Baking the perfect cake is both an art and a science. Red velvet is no exception. A confection that ignites the senses through striking visual appeal, a fine crumb texture and a hint of cocoa flavor, red velvet cake has captured the eyes and tastebuds of many. There has long been a sense of mystery and controversy surrounding the origins of the deep red cake. Its popularity grew significantly after the film Steel Magnolias featured a red velvet armadillo groom's cake in 1989. With the cupcake craze sweeping our nation, red velvet is now commonplace on menus around the country. No matter how the crimson hue is achieved, the recipes are nothing short of a good old-fashioned science experiment.
Red from anthocyanins
Largely unreplicated by today's bakers, traditional recipes from the early 1900s were believed to produce a reddish hue through a reaction between natural cocoa powder and acidic buttermilk or vinegar. Natural cocoa powder contains anthocyanins - antioxidants that are also found in red cabbage, pomegranate and many other species. In the presence of acid, anthocyanins exude a reddish hue. They're purple in neutral conditions and turn yellow-green in alkaline environments.
The darker Dutch process cocoa on the left won't do much to make red velvet cake red.
Today, Dutch (or alkali) processed cocoa powder is more common on grocery shelves than natural cocoa. The incorporation of Dutch processed cocoa causes a shift in the pH of the recipe and thus an undesired color change resulting in a brown cake. While this is interesting from a chemistry standpoint, it's highly unlikely that the quantity of cocoa powder (1/4 c. or less in most recipes) was ever enough to achieve the bright red color that we've come to associate with today's popular dessert. Another theory is that the cake was never actually red at all. Most red velvet recipes call for brown sugar, historically referred to as "red" sugar, which could have been responsible for the name.
Red from betalains
Another popular option for achieving a bright red cake is through the addition of beets, which serve to add both nutrients and moisture. Unlike cocoa, beets get their red pigmentation from betalains. Anthocyanins and betalains are two of the primary red pigments found in plants. Interestingly, these two plant compounds rarely, if ever, occur together in the same species. Like anthocyanins, betalains are highly pH sensitive, with acidic conditions favoring the desired red color.
Beet red velvet recipes have also frustrated bakers as a result of the many variables that affect betalain pigmentation, some of which include water content and temperature. In my experience, incorporating lemon juice, buttermilk and/or vinegar the recipe helps maintain a red cake. (If you would like to try a beet red velvet cake, visit my blog for a recipe).
Red from azo dyes
The most reproducible method for obtaining a deep shade of crimson in today's red velvet cake is to add food coloring - many recipes call for an entire 1 oz bottle. In these recipes, acidic ingredients are not needed, but most recipes retain buttermilk or vinegar out of tradition.
The ingredients listed on grocery store food coloring are FD&C Red # 40 and Red # 3 with a few preservatives and additives to keep everything solution. These red compounds, or azo dyes, are a specialty refined petroleum product. Red food coloring does little for the flavor, nutrition or texture of the cake, but it results in an unmistakable shade of red. Bakers and consumers have come to identify the confection by the bright pigmentation achieved with azo dyes.
No matter which approach you take to putting the red in red celvet cake, part of the fun is the science behind it. Why not try one of each and see which you prefer?