Cook Your Vegetables in Hot Oil, But Not Always

Last week, our Test Kitchen Manager Josh Cohen made extra-crispy, French's-style fried shallots by starting very thinly sliced pieces in room temperature oil.

Room temperature oil?! What was behind this madness?

Almost every recipe for or incorporating sautéed vegetables instructs you to heat the oil until it's shimmering-hot.

But was Josh onto something? Should we be starting more vegetables in room temperature oil to achieve similarly pleasing textural properties? Was I living a lie? Were we all duped by a cooking myth?

Confused, I turned to Chris Young, the CEO and cofounder of ChefSteps, a Seattle-based company dedicated to helping people cook smarter. He also wrote extensively on the subject of frying in Modernist Cuisine.

As “a general rule of thumb,” said Chris, "when you’re making a quick side of vegetables, like sautéed carrots, starting in very hot oil is what most chefs do, and for very good reason.”

Typically, your goal is to prepare something fresh-tasting yet flavorful, tender-but-not-oil-saturated. And to achieve those results, “you’re trying to bring heat to the surface [of the food] really fast.”

You want to blister and quickly cook the surface, and avoid drying out the inside of the vegetable (which will ultimately lead to more oil absorption and greasy-feeling food). Plus, less cooking time means less natural sugar loss, which, in turn, translates to sweeter, more flavorful vegetables.

So hot oil is the rule—but here's the exception: If you're aiming to dehydrate the vegetables, you want to start with the oil at room temperature.

The shallots are a perfect example: The goal was to get rid of all the water inside the pieces as they fried (in Chris's words, "dehydration inside liquid oil")—to cook the vegetable slowly, so that the water exits the inside and outside of the food at the same rate. You're aiming to coax out all the water deep within, without creating a leathery or burnt outside and a mushy inside.

Put your food in the pan, with enough oil to shallow- or deep-fry, then heat the oil. Hold it just above the boiling point of water (212° F), and wait for the bubbles—evidence of the water leaving the food as steam—to subside. When the inside and outside of the pieces cook at the same rate, you get an even dehydration—which means consistent color and crispness.

Think about it like this: When you're deciding between starting in hot oil and room temperature oil, ask yourself this: "Am I trying to dehydrate this vegetable (or fruit)?"

If the answer is no: Start in hot oil—as hot as is possible and safe without burning the food.

If the answer is yes: Start in room temperature oil. It shouldn’t get much hotter than the temperature of boiling water. (Since the water inside the food can't exceed 212° F, cooking in oil above this temperature will mean the surface of the food will get much hotter than center and you will get a tough outside and a squishy inside.)

You may not be taking the temperature of your oil (I'm not either), but if your food starts to brown quickly or unevenly, or if the oil sputters or smokes, it's too hot. (You can also test the heat of the pan before adding the oil: Drop a few water droplets on the surface; if they evaporate into steam immediately, your pan is already at or above 212° F.)

Besides shallots, what else makes sense to begin in room temperature oil?

• Tomatoes, if you're trying to achieve a confit of sorts with a sun-dried, chewy-ish texture. Cover them in oil and cook at a low temperature, just like the shallots. Here, you're draining the water out of the center of the tomato without drying out the surface. When you sauté chopped tomato, on the other hand, you want really hot oil—you're not trying to dry out the center, just to break down the surface.
• Same goes for garlic confit as opposed to sautéed garlic.
• Fruit, if you're looking to dehydrate it and achieve either a chewy or crispy texture, which is determined on how long you let the pieces cook for. In both cases, start very thin slices of fruit (try mango or pineapple) in cold oil and turn the temperature up. The texture difference is based on when you take the fruit out: If you want something crisp (like a fruit chip), take it out when all of the bubbles have stopped (that is, all the water has evaporated); if you want something soft and chewy, periodically take a peek at your slices; when bubbles start to slow, take out a piece and bite into it, removing the rest when you've achieved the intended texture.

One last tip: Be sure to blot off the oil as soon as the fruit comes out of the frying pan. One of the biggest misconceptions about frying food is that oil is absorbed as the food cooks.

"What most people don’t understand is that oil doesn’t go into food while it’s cooking." As lipophobic (oil-fearing) water exits the food, it actually repels the oil. But once the food is out of the fryer, oil will begin leaching into any parts of the food that have become really dry. By wicking away the oil immediately after the food comes out with a paper towel, you minimize the oil absorption. It's not submerging the food in oil that makes it greasy—it’s what you do after that makes a difference.

Are there any vegetables that you always start in room temperature oil? Share your cooking prowess in the comments!