Leavening
Baking soda, baking powder, and yeast all end up putting gas bubbles into your dough -- but by three completely different chemical routes, on three completely different timelines. Swap one for another without adjusting anything else and it will not behave the same way.
The kitchen answer
Your batter needs gas to rise, and something strong enough to hold that gas once it forms. Soda and powder make the gas by a quick chemical reaction; yeast makes it slowly, by being alive. None of them cause "rise" on their own -- they only supply the bubbles. Whether those bubbles turn into height depends on the rest of the batter too.
What's actually happening
Baking soda is pure sodium bicarbonate -- it needs an acid already in the recipe (buttermilk, brown sugar, cocoa, yogurt) to react with, and the reaction starts the moment it gets wet. That's single-acting: get it in the oven promptly, or the gas escapes before it can do any work.
Baking powder already contains its own acid alongside the bicarbonate -- usually two different acids, one that reacts as soon as it's wet and a second, slower one that only activates once the batter actually heats up in the oven. That's double-acting, and it's why baking powder is far more forgiving of batter sitting around before baking.
Yeast isn't a chemical reaction at all -- it's a living organism metabolizing sugars and releasing CO₂ as a byproduct, which is why it's slow, temperature-sensitive, and keeps working (fermenting, developing flavor) for as long as it's alive and fed.
What does that mean for your recipe
More baking soda isn't necessarily more lift. Soda only reacts with the acid actually present in the recipe -- add more soda than there's acid to consume, and the surplus just sits there unreacted, doing nothing for rise but leaving a distinctly soapy, metallic aftertaste (and, at high enough concentration, a noticeably alkaline environment that can interfere with how gluten and egg proteins behave elsewhere in the batter). If a recipe needs more lift, that calls for more total leavening capacity -- which usually means baking powder, not more soda.
What can go wrong
- Soapy or metallic taste: too much baking soda relative to the acid available -- the leftover unreacted soda is what you're tasting. Full breakdown →
- Flat despite following the recipe: not enough acid to react with all the soda in it, or the acid was accidentally left out (skipping the buttermilk, using regular milk instead).
- Batter that rose in the bowl, not the oven: soda-leavened batter left sitting too long before baking -- the reaction is single-acting and the gas has already escaped by the time it goes in.
- Dead, flat yeast dough: liquid mixed in too hot (above roughly 60°C), which kills the yeast outright rather than just slowing it down.
Try it yourself
One batter, one variable -- timing:
- Mix a simple pancake batter leavened only with baking soda (plus its acid, e.g. buttermilk).
- Cook half immediately.
- Let the other half sit on the counter for 20 minutes, then cook it.
- Compare height and bubble structure side by side.
Watch for: the rested batch rising noticeably less -- the reaction already happened while it sat, and those bubbles are gone before the pan ever gets hot. Repeat with baking-powder batter and the gap should mostly disappear.
Go deeper
The reaction itself is straightforward: sodium bicarbonate plus an acid produces carbon dioxide, water, and a salt of that acid (the exact salt depends on which acid is present). What's less obvious is that leftover, unreacted soda also raises the batter's pH -- and a higher pH measurably speeds up the Maillard reaction, the browning reaction responsible for crust color. That's the real reason recipes sometimes use a little baking soda alongside baking powder even when they don't strictly need the extra lift: it's there for color, not gas.
More on the way
Next for this section: a real yeast fermentation timeline recipe. (Curious why over-proofed dough itself collapses -- a related but different mechanism from why cakes collapse? That's now covered too.)