LOVE, that question, reader Jason. It seems like every food writer out there loves talking about “smoke points”, a.k.a. the temperature at which an oil starts to give off wisps of blue-black smoke. It’s the tell-tale sign that the fat molecules in the oil are breaking apart at an accelerated rate, which compromises both the oil’s flavor and its performance, to say nothing of its safety (since smoke is often a precursor to the oil’s surface catching fire).
But how important is it to know your oil’s precise smoke point? If you’re deep frying it’s not important at all in my view, provided you routinely deep fry at or below 375 degrees Fahrenheit, and frankly I can’t think of a reason for frying at a higher temperature. All a home fry jockey needs to know are four words: vegetable, canola, peanut, corn. These are the oils in your supermarket that are best suited for deep frying (vegetable and canola have the most neutral flavor). Solid fats like shortening and lard are also very good, though there you’ll need to fry slightly lower, about 360 F.
Something that’s lost in all the sagely advice about smoke points is that smoke points are highly variable. As you use an oil its smoke point drops as the fats in it break down through exposure to heat and air. Very old oil will smoke at a much lower temperature than fresh oil will, a sign that it’s time for a change. Does that mean you should always deep fry in perfectly fresh, new oil? By no means. Slightly-to-semi-used oils are often ideal for deep frying for reasons I go to some length explaining here.
For cooks who like to sauté foods in exotic oils (mustard, avocado, macadamia, things like that) a knowledge of smoke points is handy, and may well be essential. For a home cook who simply wants to deep fry some doughnuts, other than watching your temperature and staying alert for smoke, ignorance is bliss.