Let’s for the sake of discussion say that we have all put a little oil in the pan while prepping the garlic or onions to fry and then suddenly noticed that the pan was smoking. Eureka! If we had a thermometer we would have just discovered the temperature
at which the oil has changed, otherwise known as its smoke point. Not good.
Oils breaks down at set temperatures, called smoke point, which sounds like the name of a fake bar used in an 80’s romantic comedy but is actually the temperature limit up to which that cooking oil can be used. The oil loses some of its nutritional value when it starts to smoke because it is breaking down. It’s great when we can see this smoke because the degradation of the oil is obvious, but often we cannot, like when we did not prepare the food or when oven frying.
The smoke is a visual indication of the change in chemical composition of the oil, letting you know that the double bond is breaking, releasing the hydrogen and turning the oil into one that is partially hydrogenated. You have probably heard this term often in relation to trans fats. This release of the hydrogen through the breaking of the bond makes the oil a trans fat, which is not good. These trans fats behave like solids in your body because they have a higher melting point. Gross.
Recently I replaced pan-frying with olive oil, which has a fairly low smoke point at 375∞F - 400∞F, with grapeseed oil, which has a smoke point of 420∞F. The extra 20∞F makes a slight difference in its stability, although if you really want to stir-fry or require cooking at sustained high temperature, sesame oil, which has a smoke point of 450∞F, may be the best choice. The worst choice came as a big surprise to me: coconut oil, which breaks down at just 350 ∞F, essentially the temperature of a warm oven. Bummer.
Unsaturated fats are good for us but maybe not good for frying. Avocado, soybean oil, canola oil, olive oil, sunflower oil, fish oils, walnuts, flax, and red meats are all unsaturated fats. Unsaturated fats increase High-Density Lipoprotein (HDL or good cholesterol) and decrease Low Density Lipoprotein (LDL or bad cholesterol). Additional sources of HDL include onions, Omega-3 fatty acids, and foods rich in fiber, like grains. Unsaturated fats are considered good to eat if you are watching your cholesterol and are also considered high in antioxidants. Avocado, walnut, and flax oils are all excellent choices for salad dressing, but not for high temperatures.
Livestrong.com provides some simple rules to follow to prevent smoking:
“To keep olive oil from reaching its smoke point, do not reuse the oil. Store olive oil in a dark place. Do not overcook foods or fry them for long periods. Choose high-quality oils; although they are more expensive, they have a higher smoke point and will hold up better during frying.”
In short, the only thing you want to be smoking hot in your kitchen is you.