What is Specific Gravity?
Specific Gravity is a way to measure the air added into cake batter. It shows the amount of aeration, or air movement, in specific batters, allowing bakers to determine if it is too dense or not.
It's the ratio of the weight of a cake batter in a container compared to the weight of water in the same container. This ratio will change depending on factors such as mixing times or temperatures, and affect the cake’s volume, texture and grain.1
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...