STIR-FRYING sounds like a simple way to cook food, but it is so easy to do it badly. Each ingredient should be cooked to the point of being done and no more. Meat is browned on the outside, but still tender. Vegetables retain a fresh flavour and crunchy texture, but their exteriors have developed that slightly smoky flavour that comes from high heat, without any parts being burnt.
Cantonese chefs call the flavour imparted by stir-frying in a wok “wok hei“. This means wok energy or, more poetically, wok breath. The exact source of wok hei is a matter of debate. Some of it no doubt comes from Maillard reactions, when sugars and amino acids react at high temperatures.
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Some chefs say that wok hei comes from the combustion of oil, particularly when food is tossed into the air over a flame and small droplets of oil ignite. Smoke from the wok may also contribute.
True wok hei comes from skilled chefs expertly marshalling the heat on professional burners that get much hotter than domestic hobs can. by researchers at Georgia Institute of Technology looked into the mechanics of wok tossing techniques used by professional chefs to make fried rice.
The chefs employed a see-saw motion, using the stove rim as a fulcrum, to toss the rice into the air and catch it in the wok. They consistently tossed at a frequency of 2.7 cycles per second, a rate determined by the time it takes for the rice to jump up to 20 centimetres into the air and fall back into the wok. This fast rate keeps the food moving constantly, allowing it to char in the high heat without any burning.
This technique is difficult to emulate at home, but you can still make a good stir-fry without powerful restaurant burners.
First, use a wok. Its high sides create lots of cooking surface and help you to keep food moving constantly without it escaping.
Chop your ingredients into evenly sized pieces that will cook quickly. Have everything prepared before you start cooking, so you don’t have to go looking for something midway through.
Turn up the heat as high as you can. Preheat the wok with nothing in it. Don’t be afraid if it gets smoky. Extractor fans and windows are your friends.
Once the wok is hot, add oil just before adding other foods, so it doesn’t decompose on the high heat. Use a flavourless oil like vegetable oil or peanut oil, which can reach high temperatures without breaking down.
Keep food moving constantly to ensure that it cooks evenly without burning. Don’t put too much food into the wok, or it will cool down too much. If you need to, cook in batches, then combine everything at the end.
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