From frying chicken and roasting vegetables to salad dressings and hummus, oil is an essential ingredient in any kitchen. However, there are numerous types of oils, all with different chemical and nutritional properties.
So which one should you choose for a recipe? And why do we even need oil in cooking and baking? This guide will help you get to know oils better and feel more confident buying and cooking with them.
While most of the cooking oils we buy today are made from using modern technology to extract the oil from seeds, vegetables or nuts, some oils have been around for thousands of years.
Traditionally, oils were obtained by by crushing nuts, vegetables or seeds into a paste and then either pressing it through a sieve to drain out the oil. Some oils, like peanuts and sunflower seeds, were traditionally boiled after being mashed into a paste so that the oil could be skimmed off the top.
However, with the 20th century came new technology, and we can now obtain oil from even more plant sources. While the basics of making oil remain the same: mechanically crush the nuts or seeds and press, what happens next can greatly affect the chemical and nutritional properties of the oil.
When oils are bottled after pressing, without any further processing, they’re labeled as “cold-pressed raw” or “virgin” and retain their natural minerals and compounds. However, they often don’t do well with heat and can go rancid quickly.
Most vegetable oils that we consume have been processed further by bleaching, filtering and/or exposing them to high-temperature heating to create refined oils that longer shelf-lives and higher smoke points (we’ll get to that below). However this process can also strip the oil of its flavor and beneficial nutrients.
Role in cooking/baking
Oil has numerous roles in cooking and baking, all of which can largely fall under two categories: flavor and texture. While in no means an exhaustive list, here are some of the reasons why oil is used in baking and cooking.
Let’s start with baking:
- Provides moisture (think moist cupcakes or fudgy brownies)
- Adds richness for a smoother, more indulgent mouthfeel
- Affects texture by slowing down gluten development. When oil and flour come into contact, oil coats the flour and acts as a barrier between the gluten proteins and the water. As a result, you end up with a more tender baked good (always a good thing, unless you’re making a chewy bread loaf or pizza dough).
- Plays a role in enabling the browning process
- Helps to move heat through the baked good
For cooking, many of the same roles apply, plus a few more:
- Affects the actual flavor of food as oils can absorb and preserve flavors, which is why you often see infused oils. Plus, the fats in oil also coat your tongue, allowing flavors to linger longer, so you get the full tasting experience.
- Allows for heat transfer during cooking. For example, when you stir-fry food, you usually start with oil. Not only does the oil keep the food from sticking to the bottom of the pan, but it also helps to transfer heat to the surface of foods without overcooking the insides. Think about deep-fat frying: you end up with juicy chicken on the inside but a crispy crust on the outside.
- Contributes a creaminess to dishes such as hummus and pesto.
- Needed for emulsions, like salad dressings, mayo, gravies, and cheese sauces.
Of course, for nutrition, oil also plays an important role in the absorption of fat-soluble nutrients, including vitamins A, D, E and K.
Putting coconut oil aside, vegetable oils are a rich source of polyunsaturated fatty acids in the diet, with some also being good sources of monounsaturated fatty acids, such as olive oil.
Omega-6 Content of Oils
If you aren’t familiar, polyunsaturated fatty acids include two essential fatty acids: omega-3’s and omega-6’s. While we need both in our diets (thus the word “essential), there’s a concern that Western diets that many of us consume are too high in omega-6’s and too low in omega-3’s.
Both omega-3’s and 6’s play important functions in the body, however their primary roles have to do with inflammation. Omega-6 fatty acids are thought to promote inflammation, which despite sounding negative, is important for wound healing and fighting off infections.
On the other hand, omega-3’s are anti-inflammatory and thought to help protect us from chronic disease.
For optimal health, our bodies need a balance of these fats. While the optimal ratio is still unknown, many hypothesis that it’s anywhere from 2:1 to 1:4 (omega-6 to omega-3).
To put this into perspective, it’s estimated that the average ratio of Americans is 16:1 – that’s a pretty big difference, and this off-balanced intake is concerning as the high levels of omega-6’s may be causing chronic inflammation and increasing our risk of diseases such as diabetes and heart disease.
While there’s a great chart over on HealthLine comparing the fat content of common fats and oils, oils highest in omega-6’s include: sunflower, corn, soybean, peanut, and cottonseed. In general, it’s best to limit these oils in your diet.
What about Coconut Oil?
While we’ll delve into coconut oil in it’s own post, coconut oil differs from the rest as it’s mostly saturated fat, with just a little bit of monounsaturated and omega-6 fatty acids.
How to select
There are two main factors to consider when choosing an oil to cook with:
- Smoke Point
Let’s start with flavor. As we discussed above, oils play a big role in the final flavor of a dish. Some like canola oil have barely any flavor to them, making it a good option for sweeter recipes, especially baked goods and pancakes, where you don’t want it to taste savory.
On the other hand, oils like olive and sesame have very distinct flavors that contribute to the final dish.
Why Smoke Point of Oils is Important
Smoke point is the temperature at which an oil (or any fat) starts to break down, releasing smoke as well as free radicals that can be potentially carcinogenic if inhaled. Another compound that’s released is acrolein, which will give your food an unpleasant burnt flavor and smell.
So, for health as well as flavor, you want to pick an oil that can hold up to the heat that you’ll be using when cooking.
Refined oils generally have the highest smoke points between 400-510oF, while unrefined oils typically have smoke points closer to 325-400oF. As a result, for high heat cooking, especially deep fat frying, you want to go with a refined oil and save the unrefined for lower heat sauteing, baking, and drizzling.
Some example smoke points:
- Safflower oil: 510oF
- Naturally refined avocado oil: 520oF
- Coconut oil (refined): 450oF
- Canola oil: 400oF
- Virgin avocado oil: 375-400oF
- Unrefined sesame oil: 350-410oF
- Coconut oil (extra-virgin): 350-385oF
- Extra-Virgin olive oil: 325-375oF
- Flaxseed oil: 225oF
- Butter: 200-250oF
For smoke points of more oils, check out Serious Eat’s chart here.
How to store
Most oils do best stored at room temperature, in a cool dry place and out of direct sunlight. This is key as sunlight can cause the oil to go rancid faster). Also, make sure the lids are screwed on tight to avoid oxidation, which, again, will result in your oil spoiling. While different oils last longer than others, unrefined oils last anywhere from 3-6 months after they’re opened and refined oils can keep as long as one to two years.
Corn, sunflower, sesame, walnut, and flaxseed oils all do best stored in the fridge. Sesame, flaxseed, and walnut oils will last about 6 months.
This Month’s Featured Oils
While there are numerous oils to get familiar with, this month we’ll focus on four oils that you’re likely to come across when cooking healthier recipes:
- Canola oil
- Olive oil
- Avocado oil
- Coconut oil