homemade substitute HOMEMADE SUBSTITUTE FOR BAKING POWDER 2 tbsp. cream of tartar 1 tbsp. baking soda 1 tbsp. cornstarch Sift together. Store in airtight container. One teaspoon of this is equal to 1 teaspoon store bought baking powder. Source: www.cooks.com Baking powder has two active ingredients:
Cream of tartar (tartaric acid) and baking soda (sodium bicarbonate).

The reaction of these two creates a salt and a gas, (carbon dioxide) which, as it is larger in volume than the original ingredients, causes the food to fluff up, rise etc.

If the other ingredients in the recipe include an acid (say milk which has lactic acid) then the cream of tartar can be reduced or eliminated, as the baking soda will react with any acid. It is important to get the proportions correct or there can be not enough rising or a bad tasting result!

If too much of baking powder is used the resultant salt will also affect the taste of the food.

Other methods of creating lightening or rising involve incorporating air in the food that will expand during the cooking process, (beating and folding), or adding yeast that as is grows, exhales gas, (carbon dioxide again) creating more of those useful bubbles.

Foods that use rising require binders such as proteins, (examples are the gluten in some flours and the protein in egg whites,) as these are elastic enough to stop the bubbles bursting, but are fixed when dried out enough and the baking is complete.

That is why a cake or souffle will fall or flop if removed from the oven before it is done: the bubbles are still elastic and can be broken.