I appear to be in a question answering phase. A number of people have asked me questions as they relate to baking soda and baking powder lately. In recipes, they are both what I refer to as leaveners. Chemicals which help to make baked goods rise. Yeast is a whole other subject.
At home I buy Rumford. My mouth has a sensitivity to baking powder, and this one seems to be the most low-lying in terms of outright flavour, metallic taste or bitterness. Baked goods high in baking powder include biscuits, cakes, scones, muffins, quick breads and coffee cake. I generally avoid these items unless I make them myself, or can have a little taste to see how my tongue reacts.
In America we tend to associate a high rise with excellence. It's why much of our baked goods are way too big. My feeling has always been that I want to achieve a wonderful crumb, but not to the detriment of taste. Call it comfort alongside fashion, if you will.
When doubling and tripling (or more) recipes, the baking powder does not increase equally. Also, a high proportion of baking powder will stale a baked good faster. This leavener will also attract color in the oven. I hear a lot of people say they took a cake out of the oven because it was getting too dark, but it was still under-baked. Fat, acid, sugar and baking powder will add to the darkening of a baked good, so it's important to read a recipe like a map. Where will this amalgamation of ingredients bring me?
I worked at a place a few years ago where the owner insisted we make our own baking powder. Although the homemade version is not nearly as powerful as a commercially made brand, the difference in taste was marked.
HOMEMADE BAKING POWDER
Cream of Tartar 1/4 Cup
Baking Soda 2 Tablespoons
*Cornstarch 1 Tablespoon
Sift ingredients. Twice if they began lumpy. Transfer to a clean, dry, tight sealing glass jar. Sore at room temperature, for up to 6 weeks.
Baking powder, even one bought in a store, will not last much longer than a year. It looses it's fizz.