19.3 Cooking oils and smoke points

Cooking oils are refined from seeds, plants and vegetables. When you buy one, weigh four things:

• what it is for;
• its smoke point;
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• its flavor;
• its price.

Smoke point and flash point

Heat breaks a fat down, and each fat has its own limit. As it breaks down, its triglycerides come apart into separate fatty acids. These give the fat an off taste, and that taste passes into the food. The smoke point is the temperature where this breakdown begins and the fat starts to smoke. Higher still is the flash point, where the fat catches and small flames show on its surface. For hot work such as deep-frying and sautéing, choose a fat with a high smoke point.

For frying temperatures, the fire point and safe handling of a fryer, see chapter 8: Deep-fryer safety

Flavor against price

Cost and taste pull against each other. A salad dressing could be made with corn oil or with walnut oil. Corn oil is cheaper; walnut oil tastes stronger and more of itself. The choice weighs one against the other.

The kinds of oil

Vegetable oils are drawn from plants such as soybeans, corn, peanuts, sesame seeds, cottonseed and grape seeds, either by pressing or with chemical solvents. They are then refined to take out unwanted color, smell and taste. The result has almost no smell and a neutral flavor, and since no animal product is involved, no cholesterol. Labels tell you what is in the bottle:

• Pure, as in "pure corn oil": one oil only.
• Vegetable oil: a blend of oils from several plants.
• Salad oil: a highly refined blend of vegetable oils.

Canola oil is made from rapeseed. It has no flavor, no cholesterol, a high share of monounsaturated fat and a high smoke point, so it is a good oil for frying and for cooking in general.

Nut oils, such as walnut and hazelnut, are almost always sold pure rather than blended, and a good one smells and tastes strongly of its nut. Use them to flavor dressings, marinades and finished dishes. Heat dulls their flavor, so they are not for frying or baking. They turn rancid quickly, which is why they come in small bottles.

Olive oil

Olive oil is pressed from a fruit, the olive, rather than from a seed, nut or grain. Most comes from Spain, Italy, France, Greece and North Africa, with a little from California. As with wine, its color and taste change with the kind of tree, how ripe the olives are, the soil, the climate and the maker. Color runs from deep green to nearly clear, set by ripeness at pressing and by how far the oil is refined, but color tells you nothing about taste. Choose by the dish: some foods want a strong oil, others a mild one. A good olive oil is thicker than a refined vegetable oil without feeling greasy.

The label grades show how acidic the oil is (less is better) and how it was made:

Olive oil grades.

Flavored oils

Flavored oils, also called infused oils, carry basil or other herbs, garlic, citrus or spice. Serve them as a dip for bread, cook with them, or use them to accent a marinade, dressing or sauce. They are usually based on olive oil, for its taste, or on canola. The best commercial ones are made by drawing the aromatic oils out of the flavoring, blending them into a good oil, and spinning out any bits in a centrifuge. That gives a stronger taste than steeping the flavoring in the oil. Store a flavored oil as you would any good oil.

For potentially hazardous foods and the danger zone, see chapter 2: Potentially hazardous foods

Storing oils and fats

Fat that spoils goes rancid: air, light or heat change it, and it smells and tastes bad. Some fats turn faster than others, but every fat keeps better refrigerated and shielded from moisture, light and air. That is why some oil comes in green or yellow glass, which blocks the light that harms it.

• An oil that turns thick and cloudy in the refrigerator has come to no harm. It clears again at room temperature.
• Keep stored fats covered, or they take on the smells around them.
• Store a flavored oil the same way as any good oil.

For straining used frying oil and the off taste it develops, see chapter 8: Deep-fryer safety