Chicken piccata. [Photograph: Vicky Wasik. All other photographs: J. Kenji López-Alt]

Editor's Note: This article is adapted from my book, The Food Lab: Better Home Cooking Through Science. I hope you enjoy it. You can buy the book here and find more Food Lab content here. Visit my personal website and sign up for my newsletter to hear about my upcoming second book and live events.

Have you ever dropped a naked, skinless chicken breast into the deep fryer? I strongly advise against it. The moment it enters a vat full of 400°F oil, a couple of things start happening. First, the water content will rapidly convert to steam, bubbling out like a geyser, and the chicken's outer tissues become drier and drier. At the same time, the soft network of folded proteins in its musculature will begin to denature and tighten, firming its flesh and squeezing out juices. Pull it out a minute or two later, and you'll discover that it's become quite stiff, with a layer of desiccated meat a good quarter inch thick surrounding it. This is when you'll quite rightfully say to yourself, "Ah, I wish I had battered that first."

Batters are made by combining some sort of flour—usually wheat flour, though cornstarch and rice flour are not uncommon—with a liquid and optional leavening or binding ingredients, like eggs and baking powder. They coat foods in a thick, goopy layer. Breadings consist of multiple layers. Generally, a single layer of flour is applied directly to the food to ensure that its surface is dry and rough, so that the second layer—the liquid binder—will adhere properly. That layer generally consists of beaten eggs or a dairy product of some kind. The last layer gives the food texture. It can consist of a plain ground grain (like the flour or cornmeal in a traditional fried chicken breading), ground nuts, or any number of dry ground bread or bread-like products, such as bread crumbs, crackers, or breakfast cereals.

No matter how your breading or batter is constructed, it serves the same function: Adding a layer of "stuff" around the item being fried means the oil has a tough time coming in direct contact with it, and thus has a hard time transferring energy to it. All the energy being transferred to the food has to go through the medium of a thick, air-pocket-filled coating. Just as the air-filled insulation in your house helps mitigate the effects of harsh external conditions on the air temperature inside, so do batters and breadings help the food underneath cook more gently and evenly, rather than burning or becoming desiccated by the fiercely energetic oil.

Of course, while the food inside is gently cooking, the precise opposite is happening to the batter or breading: It's drying out, and its structure is getting firmer and firmer. Frying is essentially a drying process. Batters and breadings are formulated to dry out in a particularly graceful way. Rather than burning or turning leathery, a nice airy batter forms a delicately crisp, air-filled web of teeny-tiny bubbles—a solid foam that provides substance and crunch.

Breadings work similarly, though, rather than foamy in structure, they're craggy. The nooks and crannies in a good bread-crumb coating vastly increase the surface area of the food being fried, giving you more crunch in each bite. In the ideal world, a batter or breading becomes perfectly crisp just as the food inside—say, a slice of onion or a delicate piece of fish—approaches the ideal level of doneness. Achieving this balance is the mark of a good fry cook.

The Pros and Cons of 5 Common Breadings and Batters

Flour-Dredge Breading

Southern-style fried chicken.

• How It's Done: Brined or soaked (often in buttermilk) pieces of food are tossed in seasoned flour and fried.
• Pros: When done well, produces plenty of crunchy, dark brown crust.
• Cons: A little messy (you often end up breading your hands). Causes extremely rapid breakdown of oil.
• Classic Uses: Southern-style fried chicken, chicken-fried steak.
• Crispness Level (1 to 10, low to high): 8

Standard Bread-Crumb Breading

Chicken Parmesan.

• How It's Done: Food is dredged in flour, followed by beaten eggs, followed by dried bread crumbs.
• Pros: Very easy, though it requires a few pans for dredging. Achieves a very crisp, solid, airtight crust that absorbs sauces well.
• Cons: Bread crumbs can sometimes be too flavorful, obscuring the food they coat. Standard bread crumbs can get soft fairly rapidly. Causes fairly rapid breakdown of oil.
• Classic Uses: Chicken Parmesan, schnitzel.
• Crispness Level (1 to 10, low to high): 5

Panko Bread-Crumb Breading

Tonkatsu.

• How It's Done: As with standard bread crumbs, food is dredged in flour, followed by beaten eggs, followed by panko.
• Pros: Panko crumbs have tons of surface area, leading to exceptionally crisp coatings.
• Cons: Panko can occasionally be hard to find. A very thick coating means that the food underneath must be quite robust.
• Classic Uses: Traditionally, Japanese-style tonkatsu (fried chicken or pork cutlets).
• Crispness Level (1 to 10, low to high): 9

Beer Batter

Onion rings.

• How It's Done: Seasoned (sometimes leavened) flour is mixed with beer (and sometimes eggs) to create a thick, pancake-like batter. The beer promotes browning, while its bubbles help keep the batter light. Beer-battered items can be re-dredged in flour for increased crispness.
• Pros: Great flavor. It's thick, and thus good at protecting delicate foods like fish. Easy to make and relatively stable after mixing. Very slow oil breakdown if plain (no second flour dredge).
• Cons: Doesn't achieve the same crispness as some other batters. Quite a few ingredients are required. The batter must be used quickly after it's made. The coating can turn soft fairly rapidly if plain (no second flour dredge). Rapid oil breakdown if second flour dredge is applied.
• Classic Uses: Fried fish, onion rings.
• Crispness Level (1 to 10, low to high): 5

Cornstarch/Thin, Tempura-Style Batter

Korean-style fried chicken.

• How It's Done: High-starch/low-protein flour (such as a wheat flour/cornstarch mix) is combined with ice-cold water (sometimes soda water), or sometimes egg, and rapidly mixed, leaving the batter still lumpy. Foods are immediately dipped and fried briefly.
• Pros: Extremely crisp. High surface area means lots of crunchy bits. Low-protein batter means less browning, allowing flavor of delicate foods, like vegetables or shrimp, to come through. Moderately slow oil breakdown.
• Cons: Difficult to mix batter correctly (it's very easy to over- or under-mix). Batter must be used immediately.
• Classic Uses: Vegetables, shrimp, Korean-style fried chicken.
• Crispness Level (1 to 10, low to high): 8