Flour is the backbone of your cake. It adds body, texture and is what holds everything together. But, flour can also be the worse enemy of your cake -- if it's over-mixed. Finding the right balance between incorporating your flour and not over-mixing it comes down to the type of flour and cake recipe you're using.
Flour's Purpose in Your Cake
Flour contributes to the structure and body of your cake, but it also adds flavor. Without flour, your ingredients would deflate and you would have a flat, dense cake. Within flour there is a protein, and when it's mixed with water and introduced to heat that protein it produces gluten, the material that adds strength and elasticity to your cake. Your recipe is likely to call for either all-purpose flour or cake flour, and the main difference between the two is their protein content. Cake flour contains 6 to 8 percent protein and is made from soft wheat flour, while all-purpose has a 10 to 12 percent protein content and is made from a blend of soft and hard wheat flours. Cake flour yields a velvety, smoother texture than all-purpose flour.
Mixing With the Alternating Method
Alternating methods have you add your dry ingredients to your butter-sugar mixture by alternating the dry with the liquid -- which is usually milk. Use the low speed setting on your mixer and add in a small amount of dry, following up with an equal amount of wet. Continue the process until all of the ingredients are added. Mix only until the ingredients are combined. You shouldn't see any flour or dry ingredients resting on top of the batter or on the sides of the bowl. The alternating method ensures flour is mixed thoroughly, but helps prevent you from over-mixing the batter.
Mixing With the Folding Method
Some recipes require you to fold whipped egg whites in with your butter, sugar and dry ingredients. Place the egg whites on top of the prepared batter. Use a large, flexible spatula and fold from the bottom up to the sides, slowly turn the bowl and repeat until everything is incorporated. Don't mix or stir. Small lumps of whipped egg whites in the batter is normal, but you should fold until you no longer see liquid cake batter pooling at the bottom of the bowl.
Signs You've Overmixed
If you've overmixed your ingredients, your baked cake might have a domed or cracked surface once it's done baking. Inside the cake you might notice tunnels, pits or holes, which is a sign that you produced too much gluten. Your cake may also be chewy and dense, similar to a bread. Although you cannot fix this once a cake batter is already prepared, you can reduce the amount of time you mix on the next batter to correct the issue.
Tips for Success
Before you mix your flour with the liquid or wet ingredients of your recipe, you should sift or gently whisk all dry ingredients together. This helps evenly distribute your dry ingredients once they're mixed into the wet -- and reduces the amount of time you must mix them together.