If you’ve ever put some oil in a skillet to heat and then gotten distracted by a phone call or something on TV, you very likely ended up with a kitchen full of acrid black smoke and a wailing smoke alarm. Of course, you never want to let oil get so hot that it starts smoking. Not only is the oil then unusable, but the smoke that’s produced when oil is overheated contains harmful chemicals that you don’t want to be breathing in.
Ideally you don’t even want it to get hot enough to start changing color, because that is an indication that the oil has started to chemically degrade. When oil starts to break down, free radicals form, along with other harmful compounds.
That’s why it’s important to choose a cooking oil with a high smoke point. The smoke point is determined in part by the type of oil. Walnut oil, for example, starts to smoke when it reaches about 320°F, but grapeseed oil can be heated to 475°F before it begins to smoke. The type of oil is just one factor, however.
The refining process, which removes impurities from oil, also raises the smoke point. For example, extra virgin olive oil may smoke at 325°F, but refined (or “light”) olive oil can usually be heated to 450°F or higher. So, here’s a tip that will make your cooking healthier and save you money at the same time: Save your extra virgin olive oil for off-heat uses such as salad dressings and choose a refined olive oil for sautéing vegetables.