There is not one single type of oil that should be used in a wok. Since wok cooking generally involves very high heat, however, the best type of wok oil should be one that can withstand high temperatures without breaking down and smoking. Oils with high smoke points include peanut oil, safflower oil, and grapeseed oil, among others. Special wok oils are also usually found in the Asian food section of most supermarkets, and these are often flavored.
A wok is a bowl-shaped Asian cooking vessel, and some classic wok dishes include stir fry and fried rice. Traditional woks are made from cast iron, while more modern woks may be made from carbon steel. Both of these types of woks can withstand the high heat of wok cooking, but they also require oil to prevent food from sticking.
When many oils are exposed to high temperatures, they begin to break down. This is what causes the oil to smoke. Different oils break down and smoke at different temperatures, and the temperature at which an oil starts to smoke is referred to as its smoke point.
Since high heat is usually necessary when using a wok, wok oil should have a very high smoke point. Peanut oil is traditionally used as wok oil, since it is able to handle high cooking temperatures. This type of oil also adds a somewhat nutty flavor to some dishes, and it is often used to cook such dishes as peanut chicken.
Peanut oil, however, is not the only type of oil that can be used in wok cooking. Refined safflower oil, for example, has an even higher smoke point than peanut oil, which makes it an excellent wok oil. Refined corn oil and refined sesame oil are also acceptable oils to use while cooking in a wok. Although their smoke points are slightly lower than the previously mentioned types of cooking oil, cottonseed, almond, and grapeseed oils can be used as well.
Although it is a very popular oil, most Asian chefs generally discourage the use of olive oil as a wok oil. This is especially true for extra virgin olive oil, which has a very low smoke point. Extra light olive oil, however, is usually acceptable to use, since it has a higher smoke point than other types of olive oil.
Specialty wok oils are also available. These are basically just a type of oil that has been flavored. Although it is not absolutely necessary when cooking in a wok, the extra flavor is appealing to many people.