Here's another exclusive excerpt from my book, The Food Lab: Better Home Cooking Through Science. I hope you enjoy it.
At their physical core, onion rings couldn't be more different from fried fish. But at their philosophical core, they are one and the same. In each case, the goal is to prevent the browning and toughening of the main ingredient being fried (that would be the onions or the cod) while simultaneously adding textural contrast and flavor to the exterior.
It's always difficult to decide whether to get onion rings or fries (get a combo if they'll let you!). Proper beer-battered onion rings, with a substantial crisp crust covering a sweet, tender, thick ring of onion, are one of life's three greatest pleasures (and the only one that can be enjoyed legally, incidentally), but how often do you get perfect rings? These are the four most common ways that a good beer-battered onion ring turns into a bad one:
- Not enough batter. When there's too little batter, the onion is exposed to the full ravaging power of the oil. Its sugars rapidly caramelize and then burn, while tissues dry out, turning papery and tough.
- Too much batter. This is almost worse than having batter that's too thin. Instead of staying light and crisp, an onion ring with too much batter will retain too much internal moisture, and as soon as it comes out of the oil, the batter starts getting soggy.
- The "split shell." This occurs when everything appears to be going fine until all of a sudden, through some as-yet-undiscovered mechanism, the batter crust spontaneously splits in half. Oil rushes into the gap, rendering the onion leathery and burnt.
- The dreaded worm. This is the most heinous of onion ring crimes. It occurs when the onions aren't cooked thoroughly, so that rather than breaking off cleanly with each bite, you're left with a long worm of onion in your mouth and the hollow shell left behind in your hand.
Dealing with the batter problems is a snap—we've already got an awesome recipe for light, crisp, lacy, just-thick-enough batter for our fried cod. But what about splitting and worming? Splitting was a tough case to crack. What could cause the batter shell to break open like that? To figure it out, I carefully dissected an afflicted ring with a set of tweezers and discovered that it's not the batter that's the problem, it's the onion. Every layer inside an onion is separated from the next by a thin, papery membrane—you can quite easily see it if you rub the inside of a raw onion ring—the membrane will slip off.
Because of their thinness and lack of structure, these membranes shrink much more than the ring itself during cooking and it's this shrinkage that tears a hole in the partially set batter, allowing oil to rush inside. Removing the membranes before battering solved the problem, but it was a tedious process—about as much fun as trying to brush my dog's teeth, and much less cute. Soaking the rings in water for half an hour before attempting the separation helped, but I found it was far better to place the onion rings in the freezer. When vegetables are frozen, their water content crystallizes into large, jagged shards of ice, puncturing cells, which results in limp vegetables. In most cases, this is a bad thing—that's why frozen vegetables are almost never as good as fresh. With onions destined for￼￼ the batter, however, this is not a defect—indeed, aside from making the inner membranes easier to remove, freezing tenderized the rings to the point that they could be broken quite easily when bitten; I'd inadvertently ended up solving my worming problem as well!
I was so ecstatic at the breakthrough that the only logical course of action was to commemorate the discovery with a celebratory batch of perfectly crisp, perfectly tender, worm- and crack-free, golden brown, beer-scented, sweet-and-salty onion rings.
￼EXPERIMENT: Gluten Development in Batter
Just as in a kneaded bread dough, gluten—the network of interconnected flour proteins—can form in a heavily mixed batter. Need proof? Try this little test.
See ingredients list for Foolproof Onion Rings.
Follow the recipe through step 3. Divide the batter in half and whisk one half of it for an extra minute. Proceed with the recipe as directed, using regular batter and the overmixed batter, and making sure to keep the rings separate from each when you fry them.
Taste the rings side by side. You'll find that the rings with the regular batter are light and crisp, while the rings with the overwhisked batter are chewier, denser, and doughier.
As you continue to whisk a batter, protein molecules in the flour (gliadin and glutenin) form tighter and tighter bonds with each other. Eventually those bonds are so tight that even the leavening power of baking powder is not enough to lighten and leaven the batter—it stays dense. Interconnected proteins also turn the texture leathery instead of crisp and tender. Lesson learned: do not overmix batter.
–Reprinted from The Food Lab: Better Home Cooking Through Science with permission from W.W. Norton