How many of your recipe books state that you shouldn't overmix your batter to avoid it becoming tough? I know all of mine do. So guess what...its experiment time!!!
To test my theory, I mixed up a standard butter cake batter, either mixing until just incorporated, mixing for 5 minutes, or a full 15 minutes before baking. When I took the cakes out of the oven, I was super surprised with the results, and you will be too.
Before I reveal my results, let’s get into the science of how toughening a cake works.
According to Google, all cakes exist with a balance of structure makers and structure weakeners.
Structure molecules refer to egg and dairy proteins, gluten and starches.
Weakening molecules include fats, sugars, liquids, acids and fibers.
If your recipe is out of whack and you have too many structural components and not enough weakeners, you will have a beautiful looking cake that is tall and fluffy, but it will likely be tough and chewy. On the other hand, an unbalanced recipe that is heavy on weakeners may taste great but can be short in height and fall apart easily when stacked or cut. Bakers are constantly tweaking recipes to find the perfect balance of ingredients that will result in the best texture and taste great at the same time.
Some of the structural elements in a cake batter are affected by how well and how long you mix. The proteins that form gluten, for example, are activated my mixing in the presence of water. If you mix a batter that contains flour and water for a long time with little fat or sugar you will end up with long strands of gluten and a tough, chewy cakey.
Fat and sugar in the cake batter counteract the formation of the gluten strands and in theory should minimize the gluten-forming effects of a long mix time. What surprised me in my experiment was the fact that mixing actually seemed to weaken the protein network of the cake. The least mixed cake was the strongest structurally and the 15 minute mixed cake was so fragile and tender that I could barely get it out of the pan without it breaking.
There are a number of factors that seem to come into play in this process;
1.The longer you mix the more fat distribution/protein coating occurs and consequently more protein weakening.
2.The longer mix time results in greater sugar dispersal and dissolving. The sugar reacts with proteins in the batter reducing their structural capabilities and hinders starch-mediated structural components as well. The thoroughly dissolved sugar in the long mixed cake also seems to effect browning processes, as seen in this top down view of the cakes.
3.An extended mixing will allow for more reaction of leavening agents, reducing the expansion of air pockets, leading to a “shorter” cake.
So, if you are baking a fat and sugar-rich cake (like a mud cake) the longer you mix the denser and weaker your cake structure will be, contradictory to the popular belief that it will lead to toughening of the cake. The 5 minute mix time resulted in a cake with a nice texture and moderately tender crumb. Anywhere between 2 and 6 minutes should suffice. The time necessary for mixing will vary with recipe but this should help give you with an estimate of mixing time.