Baking Powder vs. Baking Soda

Yesterday, I began my holiday biscotti baking marathon. I make 14 to 17 batches every year: orange-hazelnut, classic vanilla-almond, and anise pignoli.(See http://www.neighborhood-dish.org/ for recipes). I didn't manage to do any baking last year, so it took me a while to get back into the groove. One of the things I forgot to do was check on my ingredients, so while he first batch was baking the second time, I ran out to Stop & Shop to pick up more flour and eggs, and to replace my almost-expired baking powder. There was a choice of single-acting and double-acting. Afraid the double-acting would raise twice as high, I opted for the former. (This shows you my screwed-up sense of logic.)

That got me to wondering. I know I learned the difference between baking powder and baking soda in high school cooking classes, but 30+ years later, it's slipped my mind. But now, in 2010, we have the internet and a quick search online answered this question and then some. Here are some key points:

• Baking powder contains baking soda, which is simply sodium bicarbonate. Sodium bicarbonate is made by combining limestone and salt in ammonia. (Doesn't sound too appetizing, does it?)
• Baking soda needs an acid to form carbon dioxide, which is what makes the baked good rise. Baking powder contains cream of tartar, which provides the acid. Usually, it also contains some kind of starch. the one I bought contains cornstarch. Adding liquid activates leavening.
• Double-acting baking soda is so-called because it starts leavening when mixed with liquid and then again when it is heated. So when you use single-acting, you need to bake it right away, but when you use double-acting, you can wait a bit. So, I guess I should have opted for the double-acting!
• You can substitute baking powder for baking soda (adjusting quantities), but not vice versa. However, you can make baking powder by mixing baking soda (1 part) and cream of tartar (2 parts. I suppose you could add some cornstarch, too.
• Both baking soda and baking powder expire. I'd thought it was only baking powder. Use vinegar to test baking soda (1/4 t. baking soda to 1 t. vinegar), and hot water to test baking powder (1 t. baking powder to 1/2 c. hot water).

Well, those are the basics. I'd better go test my baking soda!

Happy Holidays and Best Wishes for the New Year!