I remember once asking my mother what the difference was between baking soda and baking powder (in my head, I knew it was that one was used for making volcanoes and the other one wasn’t). She was busy and distractedly told me that baking powder had baking soda in it and a bunch of other things, including salt. My mind skipped right over the “bunch of other things” and latched onto “salt”. So for years, I thought that baking powder was simply baking soda with salt (and maybe some other, non-important stuff) in it. This is completely wrong.
Recently, I decided to take a closer look at baking soda and baking powder since I began to suspect the difference hinged on a little more than just the presence/absence of salt. Turns out, salt doesn’t even play a role in the matter.
BAKING SODA – made of pure sodium bicarbonate. It reacts chemically with acidic ingredients (ex. chocolate, honey, molasses, buttermilk, etc.) to produce carbon dioxide bubbles. These bubbles expand during the baking process, creating a leavening effect. Because baking soda is alkaline, it speeds up the Maillard reaction (the browning that occurs when you bake/cook/burn something) and can add a nice touch of color to your pastries.
BAKING POWDER – made from sodium bicarbonate, starch (a drying agent), and cream of tartar (an acidifying agent). It can also contain sodium aluminum sulfate, another dry acid. Cornstarch helps prevent clumping, keeps the sodium bicarbonate and cream of tartar dry (to prevent them from reacting in the container), and bulks up the powder to facilitate measuring/standardization. There are two main types of baking powder: single-acting and double-acting.
Single-acting powder is set off by moisture (so reactions occur immediately). They differ based on the acids they include. Tartrate baking powders contain cream of tartar and tartaric acid; they react quickly with liquids, so batter containing them must be cooked immediately. Phosphate baking powders contain calcium phosphate or disodium pyrophosphate; they react a little slower, but most of the reaction still takes place before heating in the oven and should be cooked quickly. SAS baking powders contain sodium aluminum sulfate; they react little until heated, but have a bitter taste. SAS is often used in double-acting powders.
Double-acting powder reacts to moisture, also, but most of the reaction takes place during baking. The first reaction creates the initial bubbles, which are trapped while the dough cooks and forms solid structure during baking. Double-acting powder contains a dry acid as well as sodium bicarbonate (baking soda) which reacts when the powder comes into contact with liquid.
Whether a recipe calls for baking soda or baking powder depends on the other ingredients. Since baking soda is basic, it won’t react and leaven the dough unless it is combined with an acid ingredient. It will also create a bitter taste unless countered by an acidic ingredient. When combined with cocoa powder, it causes reddening. Baking soda is commonly used in cookie recipes. Baking powder is used when there is no acidic ingredient or in combination with neutral ingredients (ie. milk). Baking powder is commonly used in cakes and biscuit recipes.
If you have too much baking soda, you’ll get an end result with a soapy taste and a coarse, open crumb.
If you have too much baking powder, you’ll get a bitter tasting batter that will rise and collapse quickly (since the carbon dioxide bubbles become too big, they break and the dough falls). The end result will have a coarse, fragile crumb and a fallen center. Too little baking powder gives a flat, tough final product with a compact, dense crumb.
Baking powder –> Baking soda: Unless you find a way of separating the sodium bicarbonate from the dry acid and starch, this substitution doesn’t work.
Baking soda –> Baking powder: Combine 1/4 of the amount baking soda called for in the recipe with an equal measure of cornstarch and twice as much cream of tartar. It’s not a perfect substitution, however, and taste/texture may be affected.
*Generally, it’s best to keep your pantry stocked with both baking soda and baking powder
Baking soda reacts immediately, so bake recipes calling for it right away (or they’ll collapse and flatten).
Bake recipes calling for single-acting baking powder as soon as possible (or they’ll collapse and flatten).
Even though double-acting baking powder reacts twice, the initial liquid reaction is vital to your finished product (so bake right away, or your pastries will — what’s that? Yes, that’s right, collapse and flatten. Well, not really, but you can’t rely on the second reaction alone to do all your leavening)
*There is yet another type of leavening agent similar to baking soda and baking powder: ammonium bicarbonate/carbonate. Recipes that need a quick rise before the dough spreads in the oven (ie. cream puffs, some cookies, and eclairs) need the fast rate gas release provided by ammonium bicarbonate/carbonate. However, ammonium bicarbonate/carbonate aren’t usually used in household cooking since they don’t store well and lose their reacting ability quickly.