When you fry, roast, sear or grill, you subject food to temperatures higher than some cooking oils can withstand. The best high-temperature cooking oil balances thermal tolerance, cooking method and flavour. Chefs use a range of cooking oils in their kitchens and choose the best for various applications based on all these variables. Home cooks can build a similar collection of flavourful oils.
If you've ever smelled the choking odour of overheated cooking oil, you know something about smoke points. Oil exposed to heat begins to break down into its constituent glycerol and fatty acids well before reaching its boiling point. Free fatty acids burn at a lower temperature, forming acrid smoke; the temperature at which this happens is the oil's smoke point. You may see different smoke points listed for different oils, but consider the figures guidelines, not rules. Different samples of the same oil may vary in purity. Refined, unused oil has a higher smoke point than unrefined or reused oil. Change used cooking oil after two or three uses to avoid discovering your oil's lowered smoke point the hard way.
Safflowers are related to sunflowers. Like sunflowers, their oil has a faint but pleasantly nutty flavour when refined. Safflower oil has the highest listed smoke point at 266 degrees Celsius, but as with any oil, that smoke point drops if you're reusing it. Monounsaturated refined safflower oil works best for deep frying and pan searing as it imparts little flavour of its own to food.
Grapeseed oil was once just a byproduct of the winemaking industry; now it flavours everything from fried foods to salads. Its nutty flavour and high smoke point of 216 degrees C make it a good deep-frying oil for fish, poultry and vegetables. This oil is costly despite being a waste product of wine grapes, but its delicate taste won't overshadow subtle flavours. Heavily spiced foods such as barbecue and curry overpower grapeseed oil's light taste.
Along with canola, almost flavourless refined corn oil is the frying fat of choice for chain restaurants throughout North America. Cheap and plentiful corn oil imparts almost no taste of its own to food. With a smoke point of 232 degrees C, this oil holds up well to any cooking method and can be reused.
As the Canola Council of Canada asserts, canola is not rapeseed oil. A close relative of rapeseed, the canola plant's oil contains oleic acid instead of the less palatable erucic acid. Refined canola has almost no flavour and a high smoke point at 224 degrees C. Use it for deep frying and for roasting foods that have subtle flavours that you don't want to bury under a strongly flavoured oil.
This high-temperature cooking oil imparts a faint peanut flavour to food. Highly refined peanut oil has a smoke point of 227 degrees C, so it's suitable for deep frying, roasting and pan frying. Peanuts are a source of anxiety for people with peanut allergies, but the Food and Drug Administration reports in its "Approaches to Establish Thresholds for Major Food Allergens and for Gluten in Food" that highly refined oils from allergenic sources did not cause allergic reactions in the individuals studied. The Allergy Asthma and Immunology Society of Ontario also refers to refined peanut oil as "generally non-allergenic."
Refined Olive Oil
Olive oil's smoke point is a also a point of contention for chefs and scientists. Extra virgin olive oil -- the minimally processed first pressing from the olives -- has a low smoke point of 177 to 188 degrees C that makes it unsuitable for frying. However, highly refined olive oil, also called light olive oil, has a high smoke point of 460 degrees. Even refined olive oil has a characteristic resinous flavour; if you enjoy it, deep fry in refined olive oil. Save the extra virgin olive oil for topping bread or salads instead of high-temperature cooking.