How it works
Aeration occurs in batter during the mixing stage. While liquid and dry ingredients are mixed together, air is also added into the batter. The amount of air blended in depends on the method of blending and the order ingredients are added. Aeration also depends on plasticity, consistency, emulsification, and fats and oils properties.2
Specific gravity measures how much aeration takes place in the batter by comparing the weight of the batter to the volume it takes up.
Specific gravity = x/y, where x = the weight of batter in a container and y = the weight of water that fits in the same space inside that container.
For example, if the container holds 100 grams of water, and weighs 80 grams when filled with batter, the specific gravity is 80/100 or 0.80. With aeration, specific gravity is usually between 0.40 to 0.80. A specific gravity of close to 1.0 would indicate that batter had fewer air bubbles incorporated into it.
Why it matters
If it’s too high (insufficient volume of air cells and low batter viscosity), the cake will exhibit reduced volume and dense grain. On the other hand, if it’s too low (indicating that the batter has too much air cells and a high batter viscosity), then the cake will result in some tunneling, be fragile and have a crumbly crust.
Creaming helps reduce specific gravity. Creaming, or the conventional method of mixing fat and sugar together first, introduces large air cells into the batter. While the blending method mixes flour and shortening in one bowl while sugar and eggs are mixed separately before all are blended together with milk. This has less aeration, and a creates a finer grain.3
If a cake comes out of the oven with an open structure and is somewhat uneven, then the specific gravity should be adjusted. The easiest way to fix this is to change the mixing times. To test times, check the specific gravity every 2-3 minutes during a 10 minute last stage mixing. Refrigerating ingredients before mixing can also help with aeration. Emulsifier gels also help with air movement and lower specific gravity. 4
Depending on the type of cake, different specific gravities are recommended. Cake mixes usually list the best specific gravity, but below are some suggested ratios for cake type:5
- Chocolate Cake: 0.90
- Cream Cake: 0.85
- Pound Cake: 0.80
- White or Yellow Cake: 0.70
- Devil’s Food Cake: 0.70
- Sponge Cake: 0.50
- Angel Food Cake: 0.30
- Edoura-Gaena, Roch-Boris, Irène Allais, Gilles Trystram, and Jean-Bernard Gros. “Influence of Aeration Conditions on Physical and Sensory Properties of Aerated Cake Batter and Biscuits.” Journal of Food Engineering 79.3 (2007): 1020-032. Web.
- O’Brien, Richard D. Fats and Oils: Formulating and Processing for Applications. Boca Raton: CRC, 2009. Print.
- Desrochers, J.l., K.d. Seitz, and C.e. Walker. “CAKES | Chemistry of Baking.”Encyclopedia of Food Sciences and Nutrition (2003): 760-65. Web.
- Jyotsna, R., P. Prabhasankar, D. Indrani, and G. Venkateswara Rao. “Improvement of Rheological and Baking Properties of Cake Batters with Emulsifier Gels.” Journal of Food Science J Food Science 69.1 (2004): n. pag. Web.
- Suas, Michel. Advanced Bread and Pastry: A Professional Approach. Detroit: Delmar Cengage Learning, 2009. Print