I like to experiement in the kitchen, and am sometime daring enough to try a little baking, which is generally less forgiving. Where I often get stuck is not knowing when to use baking soda, and when to use baking powder. It is clear enough when following a recipe, but when messing around, which should I use when? What is the difference?
I know that baking soda is a single compound – sodium bicarbonate – and that baking powder is a mixture which includes baking soda and some other things. But functionally, what is the difference?
According to pulykamell in this thread, baking powder is
“Sodium bicarbonate and cream of tartar. When moisture is added, the tartar forms an acid which reacts with the baking soda, forming bubbles which makes whatever you’re cooking rise. If what you’re making already has an acidic substance in it, usually only baking soda is called for, since your acid (beit lemon juice or whatever) will act as cream of tartar would.”
I’ver never heard the rise-up/spread-out distinction, but I do have a question: Most cookie recipes I’ve seen do use baking soda, but what acid is it reacting with? The only suspects I see are milk (not soured,though) and brown sugar (is this acidic)?
If you really want to get to the bottom of this I recommend that you have a look at On Food and Cooking, by Harold McGee. (that’s probably the fifth time I recommend that book this week.) He has a very good chapter on baking, where he describes what goes on in a dough as well as a batter, all the way from grinding the grain to the bread going stale.
Simply: a yeast-containing dough utilizes gelatinized starch, reinforced by gluten, to keep in the CO[sub]2[/sub] which the yeast generates over the hour-long ‘proving’. As the process takes rather long, the structure has to be rather sturdy and impermeable.
A baking powder/soda containing batter, on the other hand, doesn’t need the gluten, as the gasses are created much quicker, and the starch sets straight away. A lot of the gasses are produced while the cake is in the oven.
As pointed out earlier, baking powder is baking soda mixed with an acid, normally cream of tartar. The baking soda gives out CO[sub]2[/sub] when exposed to water and acid (and heat). If the batter is acidic enough, you might not need the 'powder. In fact almost all usual ingredients are acidic - but maybe not acidic enough. (In fact, the only alkaline things you’ll find in a kitchen are egg whites and baking soda.)
Again, Try to find that book. If you’re into ‘experimenting in the kitchen’, it’s worth its weight in, maybe not gold, but at least sugar.
Isn’t cocoa basic, also? I know that this is contrary to what MikeS said, but I think that was a typo (especially considering his statement that it can sometimes replace baking soda). And certainly cocoa tastes bitter. I didn’t know about the egg whites, though.
pulykamell, you may not have known this, but molasses is what makes brown sugar brown. So since molasses is acidic, so is brown sugar.
This is worth highlighting. Many people believe that brown sugar is somehow ‘more natural’, and less refined. In fact, nowadays, brown sugar is simply normal white sugar that has been flavoured with some molasses.
I’m out on a limb here, but I would have thought that (a solution of) sucrose (white sugar) by itself is slightly acidic. I can’t find any good reference right now though, so don’t quote me on that.
Chronos: No, I’m pretty sure that chocolate, at least, is acidic. Try melting a square of baker’s chocolate sometime and stirring in a quarter-teaspoon of baking soda; you’ll find that the chocolate becomes light and sponge-like. (I did this once while I was preparing a chocolate cake, and was surprised at the result.)
What I was driving at in my previous comment was that the only candidates for leavening in this particular cookie recipe are the cocoa and the baking soda; judging from the comments above, though, it may be that the 3/4 c of brown sugar in the recipe adds more acid than the 1/4 c of cocoa.