Britannica Sources used in this answer

How does a gas-forming reaction make cake batter rise?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

combustion — chemical reaction Log burning in a fire. Burning wood is an example of a chemical reaction in which wood in the presence of heat and oxygen is transformed into carbon dioxide, water vapor, and ash.

Cake batter rises due to a gas-forming chemical reaction that releases carbon dioxide gas, which creates a porous structure within the mixture.12

This process typically involves baking soda (sodium bicarbonate) reacting with an acid, such as tartaric acid or other acidic ingredients like sour cream or molasses. When baking powder—a mixture of a base and an acid stabilized by starch—is added to moist batter, the components dissolve and react to produce gas.123

The chemical equation for the reaction between tartaric acid and sodium bicarbonate is:
$C_{4} H_{6} O_{6} (a q) + N a H C O_{3} (a q) \to N a C_{4} H_{5} O_{6} (a q) + H_{2} O (l) + C O_{2} (g)$

Many modern baking powders are "double-acting," meaning they release a small amount of gas during initial mixing and the remainder when the batter is heated in the oven, ensuring the cake rises effectively during the baking process.13