Baking powder consists of baking soda, one or more acid salts (cream of tartar and sodium aluminum sulfate) plus cornstarch to absorb any moisture so a reaction does not take place until a liquid is added to the batter. Most baking powder used today is double-acting which means it reacts to liquid and heat and happens in two stages. The first reaction takes place when you add the baking powder to the batter and it is moistened. One of the acid salts reacts with the baking soda and produces carbon dioxide gas. The second reaction takes place when the batter is placed in the oven. The gas cells expand causing the batter to rise. Because of the two stages, baking of the batter can be delayed for about 15-20 minutes without it losing its leavening power.

Too much baking powder can cause the batter to be bitter tasting. It can also cause the batter to rise rapidly and then collapse. (i.e. The air bubbles in the batter grow too large and break causing the batter to fall.) Cakes will have a coarse, fragile crumb with a fallen center. Too little baking powder results in a tough cake that has poor volume and a compact crumb.

Baking soda, also known as sodium bicarbonate or bicarbonate of soda (alkali) is about four times as strong as baking powder. It is used in recipes that contain an acidic ingredient (e.g. vinegar, citrus juice, sour cream, yogurt, buttermilk, chocolate, cocoa (not Dutch-processed), honey, molasses (also brown sugar), fruits and maple syrup). Baking soda starts to react and release carbon dioxide gas as soon as it is added to the batter and moistened. Make sure to bake the batter immediately.

Baking soda has an indefinite shelf life if stored in a sealed container in a cool dry place. Too much baking soda will result in a soapy taste with a coarse, open crumb. Baking soda causes reddening of cocoa powder when baked, hence the name Devil's Food Cake.