when to use baking powder vs baking soda?
when should i use one over the other? in some quick bread/muffin/cake recipes i've used, both are needed in differing quantities. i've experimented with using more of one vs the other, but haven't figure out what the difference is. does one have a better rise? more acidity? does the usage depend on the other ingredients?
First, baking powder contains cream of tartar -- it's sodium bicarbonate plus tartaric acid, so it's used in baking when "sweet" as opposed to acidic or "sour" liquids are added to the dry ingredients. Baking soda does not contain acid -- it's just plain sodium bicarbonate, so it's used when the liquids are acidic -- e.g. sour cream, buttermilk, orange juice. The acids mix with the sodium bicarbonate to create carbon dioxide and thus leaven the product.
Second, many baking powders are "double-acting" -- they work first when mixed with the liquid and give a second boost when heated. Therefore, many recipes for items like quick breads call for baking powder so that they will get that oven boost and thus be lighter. Often a bread or cake that has a sour liquid like buttermilk or sour cream in it will call for a combination of some baking soda to work with the acid and some baking powder to provide the boost.
Fiddling with bp and bs quantities isn't a good idea unless you are willing to accept some failures.
Ideally the amount of baking soda should match the amount of acid (e.g. buttermilk). Baking powder is already a balance of baking soda and its own acid. So you have, in theory, the freedom of adjusting that up or down. So if I had to make an adjustment, I'd leave the baking soda amount the same, and just lower the baking powder.
Baking powder (the "double acting" kind you usually get in supermarkets) contains ingredients which react with each other in the presence of first moisture and then heat to provide leavening power.
Baking soda, on the other hand, needs something acidic (e.g., buttermilk, yogurt, sour cream, molasses etc) to react with. Baking soda is actually a component of baking powder. Since baking soda's reaction is triggered in the mixing bowl, it's important to get the dough into the oven quickly.