Baking powder does not contain any problematic ingredients, but as with any commercial product, baking powder should only be used if it has reliable kosher-for-Passover certification.

In order to understand why sodium bicarbonate (baking powder, baking soda) is not chametz, let’s clear up a common misconception about yeast. Yeast itself isn’t necessarily chametz either (no that isn’t a typo).

On Passover, it is forbidden to own or eat chametz—any food product made from one of the five grains (wheat, barley, rye, oat, spelt) that came into contact with water and was allowed to ferment and “rise.” No leavening agent is necessary for this to happen. This is because even the air we breathe contains some “yeast”—yeast being a living microorganism which converts some of the flour into carbon dioxide causing it to rise. Thus, there is a common saying that “matzah is the closest thing to chametz,” since leaving the dough for just a bit too long before baking can render it chametz.

Now, in addition to chametz, the Torah also prohibits se’or. However, while se’or (sourdough) may be yeast, yeast itself isn’t necessarily se’or.

Although it is true that the air we breathe contains yeast, most people don’t sit around waiting for their bread to rise by itself. Instead, they add a leavening agent. What people used to (and some still) do, is leave a piece of dough out, enabling the yeast in the dough to multiply to such an extent that that the batter turns sour and inedible. This ball of concentrated yeast is added to the next day’s dough to help it rise.This concentrated yeast-ball is called se’or (i.e. “sourdough,” due to its sour taste), which the Torah prohibits on Passover (despite it being inedible, which normally may render something permissible on Passover—a separate discussion).

One can, however, produce yeast using certain plants instead of sourdough. Such yeast, as long as it doesn’t otherwise contain chametz from the five grains, is not chametz despite the fact that it shares the same characteristics as se’or (sourdough), and therefore one may technically own and use it on Passover.

In light of the above, as long as the baking soda or powder (sodium bicarbonate) has a reliable kosher-for-Passover certification, it may be used on Passover.