Reader Dan, who is working on financiers this week, has a very interesting question about baking powder:
If you’re using [baking powder], why rest the mix in the fridge? Surely the [baking powder] is activated, and loses its potency before you actually come to baking?
It’s very reasonable to assume that, Dan. Conventional wisdom holds that whenever you get baking powder wet you need to hurry it into the oven so you don’t lose any volume. That actually isn’t the case. It’s certainly true that you get a gas-producing “pop” when the baking powder gets wet. That’s the first “action” of double-acting baking powder. The second action happens when the baking powder gets hot.
The question is: is that first action wasted if the batter isn’t in the oven when it occurs? The answer is: not really. Why not? Because that first action is by design the one that creates what you might call “seed bubbles”, little cells in the batter that will fill with gas and steam once the batter is heated. The creaming method does something similar, using granules of sugar to poke holes in solid fat. Those little cells get incorporated into a batter where they wait for heat to be applied.
So the message is: as long as the batter isn’t agitated a whole lot — which would pop the little bubbles — the first action will have done its job and its effects will be preserved. When the batter heats up later the second action will take place, more CO2 will be produced (along with plenty of steam) and the batter will inflate.
I once worked in a bakery where we made baking power-leavened muffin batters that held in the walk-in for a week. We just scooped them, plopped the scoops into forms and baked them up. No problem, and no discernible difference even after seven days. Great question, Dan!