Baking soda is basically used as a leavener but needs the power of an
acidic ingredient and a liquid to be activated. Acids that can activate the
baking soda include yogurt, sour cream, buttermilk, citrus juice and cream
of tartar. Baking powder is composed of bicarbonate of soda (baking soda),
some form of acid like acid phosphate of calcium, sodium sulfate and
cornstarch. When these elements are combined, carbon dioxide is released,
creating air bubbles that if all goes well will cause your baked goods to rise.
Baking soda begins to release carbon dioxide when it is combined with
moisture, meaning that your wet and dry ingredients should be combined at
the last minute and promptly put in the oven. The baking powder sold here
in the US is all pretty much double-acting, which means that one of the
acids it is made up of reacts to moisture and the other to heat.
There is also the issue of aluminum being added to baking powder. An
aluminum-free product (which I think is preferable) is sold at many health
food stores. You can also make your own baking powder by combining 1/4 tsp.
baking soda, 1/2 tsp. cream of tartar and 1/2 tsp. corn- starch. I would
make this in small quantities as it will not keep as well as store-bought.
Finally, baking soda can be substituted for baking powder at a 1:4 ratio.
(1 tsp. soda = 4 tsp. powder).
A long answer to a short question. Hope this helps, Ivana.
Cheryl