I’ve talked about the pros and cons of various oils and how to store oils in previous articles but several of you have asked me to talk more specifically about what happens to oils when you heat them up and which ones are safest to cook with. In fact, a few different things can go wrong when cooking with oil.
Which Oils Are Best for Cooking?
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. That is bad. Not only is the oil unusable but the smoke that’s produced when oil is overheated contains harmful chemicals that you don’t want to be breathing in.
What Happens When Oil Gets Too Hot?
Not only do you not want your oil to smoke, 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.
Different oils have different smoke points, of course. Some oils will start to smoke at just slightly over 200 degrees Fahrenheit; others hold steady past 500 degrees. Obviously, if you’re going to be cooking at high temperatures, you want an oil with a higher smoke point.
What Determines the Smoke Point of Oil?
Contrary to popular belief, the amount of saturated or unsaturated fat in a cooking oil is not a very good indicator of its smoke point. Grapeseed oil, for example, is very high in polyunsaturated fat and has a very high smoke point, whereas soybean oil, which is also quite high in polyunsaturated fat, has a fairly low smoke point. And coconut oil, which is among the highest in saturated fat, is in the middle of the pack in terms of smoke point.
See Resources, below, for a link to fatty acids in common cooking oils.
The Difference Between Refined and Unrefined Oils
How pure, or refined, the oil is plays a much bigger role in determining the smoke point. The refining process removes impurities from oil, which generally increases the smoke point. Unrefined (or extra virgin) olive oil, for example, has a smoke point of about 375 degrees F. Refined (or light) olive oil has a smoke point of 465 degrees F or so. Quick and Dirty Tip: Cheaper oils are refined using a chemical process. For a bit more money, you can buy oils that are refined without chemicals and these will be your best bet.
See Resources, below, for a link to smoke points of common cooking oils. Quick and Dirty Tip: Once an oil has been heated, its smoke point will be lower.