Friday, October 2, 2009

Food Science Friday: Baking Soda vs. Baking Powder

Baking soda and baking powder . . . they have similar names and both are a part of helping things rise. But what's the difference?

Leavening is a result of a simple chemical reaction: acid + base = CO2 gas (bubbles).

Baking soda is sodium bicarbonate, a base. When used with other acidic ingredients in recipes (cream of tartar, lemon juice, etc.) it can react to create CO2 bubbles thereby raising the batter or dough.

Baking powder contains both the acid and the base, usually blended with cornstarch to keep the acid and base from reacting quickly on your shelf. It is made of baking soda (sodium bicarbonate) and acids like sodium aluminum sulfate (SAS), sodium aluminum pyrophosphate (SAPP), and monocalcium phosphate (MCP). Each of these acids can give the leavening system different properties depending on how the acids are free to react. You may see baking powders with descriptive names:

• Single-acting: One type of acid is present--either slow or fast. Slow-acting acids react slower, sometimes because they are only active with high heat, and release more gas during baking, frying or cooking on a griddle. Fast-acting acids react quickly when simply moistened in the batter or dough.

• Double-acting: This refers to a combination of at least two acids--slow and fast. One of the acids reacts in when moistened during mixing and the other during heating in the oven.

For more in-depth details on specific acids, click here.

Food scientists don't necessarily use standard retail baking powders, but instead select specific acids to mix with sodium bicarbonate when they are formulating baked goods. For a full technical chart of the different types of acids, click here. Sometimes the acids and/or bases can be even be encapsulated (coated in fat or maltodextrins) to further control their release properties. The end of shelf life for a formulated cake mix type product can often be due to the leavening having slowly reacted over time thus resulting in a under-leavened cake without the volume and lightness expected.

So what does all of this mean for you?

1. Don't simply substitute baking powder or baking soda for each other.
2. Don't forget to check the expiration date on the baking soda or powder box. Their efficacy diminishes over time and no one wants to have a cake that doesn't rise!