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I've always wondered that about my madeleine batter.

I thought it might also have to do with the rising agents. Eg., resting cornbread batter gives the baking powder time to start doing its business, since it bakes so quickly once in the oven.

An old man who lived next door to me told me this was the secret to great pancakes and I've always done it ever since--and it's true! Glad to know the science behind it. I suspected it was similar to what they said about letting cookie dough rest.

“This resting step ensures a thin and uniform structure to the finished baked good, as with the hollow shells of popovers or the paper-thin quality of crêpes.”

This is exactly the wrong step for popovers. You don't want to let the batter rest because resting helps develop gluten, just like it does in no-knead bread when it rests/rises for such a long period of time. Too much gluten traps the air in the popover batter throughout the structure, and you get a popover that doesn't "pop." You get an eggy unrisen muffin.

You also definitely do not want to let the air bubbles slowly work out of a popover batter, because they're what make the popover rise! You want plenty of air bubbles and to get the batter into the oven absolutely as soon as possible after vigorous mixing.

I commented about this in detail at King Arthur Flour's site a couple of months ago; you can read that here. It includes references to Alton Brown and other food science.

Resting a batter with baking powder is a double-edged sword. Baking powder includes both baking soda and an acid to react with it (cream of tartar), and when it gets wet, they react and start producing bubbles. If you let that rest, those bubbles can "work their way out," and you don't get as much benefit as you might otherwise, especially in a thin batter.

If the batter has only baking soda plus an acidic ingredient like buttermilk, or if you use single-action baking powder as I do (because I have a sodium-restricted diet), this first bubble reaction is all you get. Double-acting baking powder gives you some insurance, with new bubbles forming when the temperature hits about 120°F or so, but letting these batters rest is letting the air bubbles dissipate, and creating those bubbles is why you put the baking powder or soda in the batter in the first place.

Now, what resting it does do is let the flours hydrate fully, which can take a while in a relatively thick batter, especially if you don't mix it a lot because you don't want much gluten. It's a workaround that lets you avoid the best solution, which is using a lower-protein flour for batters that shouldn't have much gluten but need to be thoroughly mixed.

Most of us just don't have many flour choices in the grocery store, falling from all-purpose flour (which can be anything from 10.5% protein to 11.7% protein, depending on your part of the country) to cake flour (which is bleached, to reduce gluten, and only about 8% protein or less). It can be hard to find pastry flours with 9-10% protein that might be better in some of these applications.

As for resting pancake batter, Alton Brown says it'll be OK if you use double-acting baking powder. The batter gets too thick if it rests, but you can dilute it with buttermilk to the right consistency, and the second action of the baking powder gives you some lift—but not as much as if you put the batter on the grill immediately. I don't know when Food Network will air the Good Eats pancake show again, but you can read the full transcript here.

Hope this helps.

For really liquidy batters (crepe, popover, dutch pancake), I've had good luck skipping the resting step and using my immersion blender to do the mixing. I'm pretty sure I got that idea from an old Fine Cooking, and it works well (and is great for those of us with no cooking forethought, or patience).

mdeatherage - Thanks for your long comment and many insights! You've given me a lot of fodder for future food science posts! I need to do a little research to be sure of all the facts, but I just wanted to quickly comment on a few of the points you made.

This food science stuff can all get a little tricky - there's still quite a bit of gray area! Based on my culinary training, it's my understanding that resting batters and doughs relaxes gluten that's already there. It doesn't actually create gluten, which is developed through a combination of liquid and mechanical action (ie, stirring flour and water together).

I'm not 100% sure about the no-knead bread (again - this is where I need to do some more research to get my facts straight) but I think the gluten there is developed through the long rise - the batter rises and falls several times, which is the mechanical action needed to create the gluten.

When making things like crepes, popovers, and quick breads, you don't have to worry about any rising and falling creating gluten because a) the resting period is typically very short and b) these batters generally don't use yeast (which causes the repeated rising and falling; chemical leaveners would only make it rise once before going the oven).

Also, whether or not you want air bubbles can be a matter of the recipe and also of personal preference. Popovers and our big pancake recipe rise primarily due to steam, which is created when the liquid in the batter starts to evaporate in the heat of the oven. The steam will cause any pockets of air to expand during baking, which makes the batter/dough rise (or "expand" might be a better term).

If your batter has a lot of air bubbles, your resulting baked good will tend to have a more honey-comb-like structure. If your batter doesn't have a lot of air bubbles, it will have a more hollow structure with a uniform crumb. Definitely personal preference on this one, but traditionally things like crepes, popovers, and dutch babies had a relatively uniform, un-airy crumb (and with large hollow interiors, in the case of popovers and dutch babies).

I totally agree with you on the dangers of letting a batter with baking soda or powder sit for too long. Sit just a bit, and you get the bubbles in the batter from the first reaction as well as the lift once it hits the heat of the oven. But let it sit too long and the batter deflates, giving you less rise in the oven. I think the key in situations these is to follow the recipe as closely as possible. If it doesn't work, you can try shortening the resting period next time.

I'll check out the Alton Brown episode tonight to get his scoop. I generally agree with his testing and logic, so it will be interesting to see what he has to say!