We use oils a lot in cooking, so it’s worth understanding a bit about them to guide how to use them.
Oils are a type of fat. Edible fats are one form of energy storage, but they also contain essential fatty acids used by a number of different organs and cells in our bodies as well as other nutrients such as vitamin A, and cholesterol necessary for making vitamin D and bile acid. Needless to say, they are an essential component of our diet – even if some are “healthier” than others.
Oils are fats that are liquid at room temperature. All chemicals can be solid, liquid or gas depending upon their temperature. Because oils are liquid at room temperature, they are very handy to work with in cooking. Contrast that with most animal fats – like the kind you cut off when preparing meat to cook – that are solid at room temperature. Sometimes, though, we actually want our fat to be solid at room temperature, such as butter or margarine. Margarine is usually vegetable oil that has been chemically changed – “hydrogenated” – to make it a soft solid when it’s sitting on the dining room table; unfortunately the hydrogenating process makes it far less healthy to eat than the underlying oil it’s made from.
We use oils in three different ways in cooking:
- As a cooking medium;
- As an ingredient;
- As a finishing touch on a dish.
Oil is handy for cooking because liquids tend to be very good thermal conductors: they can move heat from a pan to a piece of food. And as a liquid they can move around and fill in gaps to ensure more even cooking for something with an irregular texture or shape. What makes oil particularly useful is that the temperature range where it remains a liquid goes from below room temperature up through at least the mid-300-degrees. Compare that to water, which is also liquid at room temperature but boils off at 212 degrees; it’s disappeared long before you reach the temperate range where food browns. That’s why cooking oils are used for both sauteing and deep-frying.
But beware: oils have different temperature ranges, and the differences matter to us a lot as cooks. The high end of the liquid range for an oil is called its “smoke point”: when an oil reaches its smoke point, some of the liquid evaporates, but other chemical reactions occur as well that turn parts of the oils into a range of nasty chemicals that smell bad, taste worse, and can ruin your food. It’s very important that when you work with oils you take care to keep them below their smoke point.
Oils also have different flavors. Several have almost no taste at all, and are referred to as “neutral”; using them generally won’t change the flavor of your food. Depending on their source, though, others may have a variety of different flavors, including olive oil, sesame oil, peanut oil, oils from various strong-flavored nuts, and avocado oil. So when choosing a cooking oil, we want to select it based upon both its smoke point and its flavor.
Here’s a handy guide to a number of popular, easy-to-obtain cooking oils.
You’ll quickly notice that extra-virgin olive oil, which is widely celebrated for its healthy properties, is not a good cooking oil: it has a strong flavor, but more importantly it has a low smoke point: 320 degrees, below the 350-degree point where the Maillard reaction will cause food to brown.
Several good choices exist for cooking oil, though, including canola, corn, sunflower and safflower oil. All have neutral flavors and much higher smoke points. There are others that have high smoke points but aren’t neutral flavored; it’s fine to use them, but know that they may affect how your food tastes (which may be a good thing, and in fact may be associated with particular regional cuisines). Also, some of the specialty oils, including avocado, are more expensive and may not be a cost-effective choice as a cooking oil.
Cooking oils can also be used as ingredient oils – both neutral and flavored ones. Ingredient oils are used widely in baking (as are butter and margarine, of course), to give baked goods softer, moister, more luxurious textures since the oil won’t boil off like water or milk. Oils are also often used with roasting to keep the outside from drying out. The trick with incorporating oils into recipes is balancing out the texture and the flavor; for that reason you should be careful when substituting oils in a recipe.
Flavored oils such as olive, truffle and sesame oil are often drizzled over a dish just before serving, to add a complementary flavor without cooking the oil – even cooking a flavored oil to a temperature well below is smoke point can alter or diminish its flavor. This is why in Italian restaurants you often see bread served with a small bowl of olive oil and balsamic vinegar, and why olive and other flavored oils are used in salad dressings. Finishing oils are all about the flavor.
Freshness is a real concern for oil that you are storing in your home. Oil that is kept at room temperature and/or exposed to sunlight or air will begin to break down and turn “rancid,” with an off-putting aroma and flavor. Ideally oil should be stored in air-tight containers in a cool, dark place; even then, it has a limited shelf-life. Make sure to check your oil before using it, especially if it has been sitting on the shelf for a while. Many people keep a pour-bottle of cooking oil next to their stove, which is not a particularly good practice unless you get through it fast enough so that it’s used up before it goes rancid.
The bottom line
There is no single oil that will cover all of your cooking needs. You should have a minimum of two oils in your house:
- a neutral one with a high smoke point that you can use as both a cooking oil and an ingredient oil, such as canola, corn or safflower;
- a flavored one, such as olive oil, that can be both an ingredient oil and a finishing oil.
Over time you may buy other oils that work particularly well for specific dishes or tasks, but these two will cover more of your needs. I keep a jug of peanut oil for the rare instances where I deep fry something, and a bottle of sesame oil for use in both marinades and finishes of Asian dishes.