This is the third in a series of answer posts to reader-submitted questions. Some of these posts may be incorporated into the revised edition of the Learn to Cook book. If I’ve left out any information, or if anything is unclear, please tell me in the comments section so that I can amend this post. Thank you for your help!
“You could talk about which oils are appropriate for different temperatures and methods, and what happens when an oil scorches.”
“Frying! How to get the temp right, the mess, what to do with the leftover oil, etc.”
Again, these are excellent questions and I was just thinking a couple weeks back that no where in the first edition of the Learn to Cook book did I discuss types of cooking oils. For shame! Let’s remedy that oversight right now.
This article will cover cooking oils extracted from seeds, nuts, vegetables, and fruits. Check out this article for information on cooking with butter, including ghee and clarified butter.
I’ll begin with some oil terminology. The next 800 words or so may be a little boring because I may have gone into WAY too much detail. Is that even possible???? Scroll down to get to the culinary applications of oil, beginning with smoke point.
Fat or Oil?
These terms are somewhat interchangeable because chemically they are almost the same thing. Oils and fats are both made up of fat molecules (more on that later) but the term “oil” refers to a type of fat that is liquid at room temperature (like olive oil) and “fat” refers to a type of fat that is solid at room temperature (like lard, shortening, or butter).
Oil may be extracted from foods either chemically or mechanically (which includes centrifuge and expeller pressing). As you probably can imagine, chemical solvents are the most efficient for getting ALL of the oil out of the product. Centrifuge is next, then pressing (either expeller-pressed or cold-pressed). Large-scale operations probably use a combination of all three methods. Small-batch and “health conscious” brands will typically use (and label the product as such) expeller or cold-pressing; cold-pressed is the preferred method for extra-virgin olive oils and specialty oils such as walnut and flax seed. Specifying the method of extraction is not required by law, but companies producing oil through expeller or cold-pressing will be sure to tell you on the label!
Chemical extraction is usually done with hexane. In addition to extracting oil from grains and seeds, hexane is also used to extract protein from soy. It is derived from crude oil refinement. The process is something like this: chop up seeds, mix with hexane, hexane draws out and combines with the oil, hexane/oil mixture is separated from the solids, hexane is removed by vaporization, oil is left behind. It sounds pretty intense, and potentially hazardous, though it’s been going on since the 1930s. Soy and corn oils are commonly extracted this way.
Centrifuges and centrifugal force are probably something you recall from physics or chemistry class. The product is mashed into a pulp and the oil is separated from the water and solids using high-speed rotating decanters. Because oil is less dense than the water and vegetable solids, most of it is easily isolated from the pulp.
Expeller pressing and cold-pressing are the most gentle methods. In both, the base product is crushed between stone or steel plates literally squeezing the oil out. Some heat is created from friction and the harder the nut or seed, the more heat. Heat can degrade some flavors and nutrition in oils. Cold-pressed oils are expeller-pressed oils that are kept below 120 degrees Fahrenheit during pressing. Many oils with delicate flavors (extra-virgin olive, nut, coconut, and avocado oils) are produced by cold-pressing to ensure their flavors and aromas remain intact.
Refined vs Unrefined
After the oil is extracted it may be refined. Refining removes all lecithins, waxes, scents, pigments … everything that’s not straight-up oil. Oils may be chemically refined through the addition of sodium hydroxide, sodium carbonate, activated carbon and lots of other tricks. Refined oils are more shelf-stable (they resist rancidity better than unrefined oils) and more stable at higher temperatures making them suitable for frying and high-heat cooking. They are also fairly neutral in flavor and color. Examples of commonly refined oils are soybean, peanut, corn, safflower, and canola.
Unrefined oils are bottled directly after mechanical extraction (by default, oils that are chemically extracted will also be refined) and may have a cloudy appearance or a sediment layer in the bottle; this is completely normal. They will also have more prominent flavors. Unrefined oils are best used raw in salad dressings or in low to moderate-heat cooking such as baking. They are also more prone to rancidity so if you don’t use them often, you ought to keep them in the refrigerator to prolong freshness.
Again, labeling oils with the method of refining is not required by law, but if an oil is unrefined or “naturally refined” (meaning only filtered) it will often specify that on the label.
Saturated and Unsaturated Fats
Time for some SCIENCE. Fat molecules (aka lipids or triglycerides) consist of 3 fatty acid chains (“fatty acids” for short) connected by a glycerol “backbone”. Different fats are distinguished by their fatty acid components. Different fatty acids are composed of between 4 and 28 carbon atoms linked together. The number of double-bonded carbon atoms in each fatty acid chain determines whether it is a saturated or unsaturated fat. All oils contain some percentage of both saturated and unsaturated fats.
Saturated fats have no double-bonded carbon atoms in their fatty acid chains. Instead, their carbon atoms are bonded to hydrogen atoms. They are fully “saturated” with hydrogen atoms. Saturated fats are solid at room temperature and are heat-stable. Some foods that have a high percentage of naturally occurring saturated fat are coconut oil, palm oil, cocoa butter, lard, butter, suet, cheese, uh… pretty much any animal product. Some foods have a high percentage of unnaturally occurring saturated fat (see the next section on hydrogenated oils).
Unsaturated fats include polyunsaturated and monounsaturated fats. As I’m sure you’ve guessed: polyunsaturated fats have multiple double-bonded carbon per fat molecule and monounsaturated fats have only one double-bonded carbon per molecule. Monounsaturated fats are more stable at high temperatures than polyunsaturated, making them a better choice for frying. Unsaturated fats are found in high amounts in vegetables, nuts and seeds, and the polyunsaturated fat Omega-3 is found in fish.
Hydrogenated and Partially-hydrogenated Oils
Hydrogenated and partially-hydrogenated oils are unsaturated oils that have been transformed into saturated oils. Basically, unsaturated oils are heated under pressure to an incredibly high temperature and then hydrogen gas is added which intercepts the fatty acid chains’ carbon bonds (all, “May I have this dance?”) thereby saturating the previously unsaturated oil. Cottonseed oil was historically used. Hydrogenated oils (just like naturally saturated oils) are solid or semi-solid at room temperature, very shelf-stable, and have a much higher smoke point than untreated oils. Vegetable shortening such as Crisco and most margarines are made from hydrogenated or partially hydrogenated oils. The stability and longevity of these treated oils are what makes them desirable for use in those delicious mini powdered donuts and other junk food.
The process of hydrogenation also creates trans fats which have had much coverage in the news lately as major culprits of heart disease. In the face of this news, manufacturers have begun to replace all or part of the hydrogenated oil with naturally saturated fats like palm oil and coconut oil. Modern Crisco is made with soybean and palm oil.
With relish, dear reader. I hope you found all that useful, or at least figured out how to skip ahead to this part. I’m really going to talk about culinary uses for oils now.
The smoke point of an oil is the temperature at which an oil begins to smoke, although it’s more useful to think of it as a range than a specific temperature. Understanding an oil’s smoke point is the best way to determine its safest and most delicious applications. Before an oil reaches its smoke point, some molecules have already begun to break down into their fatty acid and glycerol parts; once the oil begins to smoke, much of the nutritive qualities and flavor are destroyed and free radicals have begun to form. This is why it’s very important to use oils with a high smoke point for high-heat frying like stir frying and deep-frying. The more refined an oil is, the higher its smoke point; the less refined, the lower the smoke point (think about how quickly butter burns with all of its protein and sugar “impurities”). The smoke point of any oil will decrease after its been used so be careful when reusing oil (as you might in a deep-fryer) and limit it to no more than once or twice.
Here is a general guide to safe temperature ranges and best uses of oils. Because the smoke point can vary even from brand to brand depending on the cultivar it was extracted from and how it was processed and refined, it’s a good idea to check the label. It will usually offer the recommended (safe) uses, if not exact temperatures. The asterisks (*) indicate my personal preferences for health, tastiness, and affordability (not necessarily in that order).
Raw in Salads, Uncooked sauces & Garnishes: Oils with smoke points under 300 F/150 C. This is the time to use cold-pressed, unrefined and unfiltered oils to their best advantage. Unrefined almond, avocado, flax, hazelnut, sesame, walnut, and extra-virgin olive oil are all good to use uncooked. Heat destroys many of the subtle flavors in seed and nut oils so use them uncooked and appreciate the nuances they add to recipes.
While refined almond, sesame, and avocado oils are safe to use at high temperatures, their flavors are better appreciated if added at the end of cooking. Some oils which are safe to use at high temperatures also make a good base oil for salad dressings and vinaigrettes because of their mild flavor: canola, corn, safflower, sunflower. Here is a good, basic salad dressing recipe to start with, and a vinaigrette pasta salad to try.
- Extra-virgin olive*
- Flax seed*
Baking, Cakes & Cookies: Oils with smoke points between 300-375 F/ 150-190 C. Of course butter is popular, but lard is also great for baking. Vegetable oils appropriate for baking include almond, canola, olive, safflower, and sunflower. Extra-virgin olive oil also works well in baked goods, but its flavor might overwhelm some recipes. Virgin coconut oil makes great lightly-coconut flavored pie crust and pastry. Margarine and shortening are of course options, too.
- Coconut (virgin or refined)*
- Olive (virgin or extra-virgin)*
Medium-heat Sauteeing & Sweating: Oils with smoke points between 300-400 F/ 150-204 C. In addition to the oils suitable for baking, I’ll add ghee (clarified butter), grapeseed oil, virgin olive oil, peanut oil. Practice sauteing these crab cakes or some fajita chicken.
- Bacon fat*
- Canola (refined)
- Ghee (clarified butter)*
- Refined coconut*
- Refined sesame*
- Virgin Olive*
High-heat Stirfrying & Deep frying: Oils with smoke points above 400 F/ 204 C. Almost any refined oil will work for frying, but the most common are canola, corn, grapeseed, peanut, safflower, extra-light olive oil, and “vegetable oil” which is a marketing term for a blend of oils (or sometimes just soybean oil) designed to have a mild flavor and high smoke point. Avocado oil has a remarkably high smoke point, but its expense might make it unfeasible to use for deep frying. High-oleic oils come from plants that have been bred to be extra-high in monounsaturated fats, making them good choices for high-heat frying. You can find canola, safflower, and sunflower oils in the high-oleic form. Deep-frying is one time I use vegetable shortening; because it reverts back to a solid when cool, it is easy to dispose of in the trash.
- High-oleic canola, safflower, sunflower*
- Light olive oil*
- Vegetable oil
Which brings us to…
Deep Frying Guidelines
Deep frying differs from pan frying in the amount of oil used. In deep frying, the oil should be deep enough that the food is completely submerged in oil. It produces a crispy, brown exterior while keeping the interior of the food juicy. Deep frying is done with the oil temperature between 325-375 F (165-190 C). A frying thermometer is the best, most reliable way to maintain an even temperature which is important for ensuring a crisp, non-greasy product. When your oil temperature is too low, your fried foods will have a greasy finish. This is why it’s not a good idea to overload the oil — the temperature will drop as you add food and the more added at once, the more it drops and the longer it will take to come back up to temperature. The thermometer should not touch the bottom or sides of the pot or fryer for an accurate reading.
If you don’t have a thermometer you can still estimate the temperature of the oil using the “Bread Cube Method”. Drop a cube of bread into the oil and count how many seconds it takes to brown.
- 20 seconds: oil is between 385-395 F (196-201 C)
- 40 seconds: oil is between 375-385 F (190-196 C)
- 60 seconds: oil is between 360-375 F (182-190 C)
- 325 F (163 C) Oil blanching (the initial frying of potatoes in making French fries)
- 350 F (177 C) Battered fruits, vegetables, seafood (as in tempura)
- 360 F (182 C) Donuts, hushpuppies
- 365 F (185 C) Fried chicken, fritters
- 375 F (190 C) French fries (second frying) and potato chips (single-fry)
To reduce the mess associated with deep frying and frying, I recommend using a splatter screen, which will catch most of the popping oil while allowing steam to escape. Also make sure the that pot or fryer you are using isn’t filled up too high; leave at least 2 inches of space between the oil level and the lip of the frying vessel. This helps prevent boiling over, which is not only dangerous, but also a pain in the ass to clean up.
Flash Point and Oil Fires
Beyond the smoke point lies the flash point, the temperature at which an oil ignites spontaneously, around 600 degrees Fahrenheit. This is a very dangerous situation. To prevent this, use a thermometer when deep frying. If your oil does ignite, DO NOT put water on it. Water will splatter and cause a mini-explosion. Instead, smother the fire with a metal lid over the pot. If the fire is not contained, but has spread to other surfaces, smother it with baking soda or use a fire extinguisher.
As long as you’re switching out liquid oils with basically the same smoke point, your recipe should still work fine. It might not taste the same, but chemically you’re in the clear. When you start switching out oils for fats and vice-versa is when it gets a little messy. While all oils are 100% fat, some fats are not 100% fat. I know. It’s okay. Some fats (butter, shortening, and margarine specifically) have a certain percentage of water (or other things) in them, too. For instance, 100 grams of oil contains 100 grams of fat; 100 grams of butter might only contain 81 grams of fat (it varies so check the label). So when you try replacing the oil called for in a recipe with the same amount of butter, it’s not really an equal exchange. If you must, you can replace the butter called for in a recipe with a lesser amount of oil, but it requires some algebra to figure out the exact amount.
How to Store Oils
To maintain freshness and protect them from going rancid, store oils away from heat and light. Unrefined nut and seed oils are especially prone to going rancid so it’s best to store them in the refrigerator. Olive oil may turn solid in the refrigerator, but will liquify after several minutes at room temperature. This is the reason many salad dressing recipes will use both extra-virgin olive oil (for flavor) in combination with a refined oil (to keep it fluid).
Discarding Leftover Oil
To help your city’s water company, please do not dispose of oil down the drain (or the toilet)! Not only can it cause blocked pipes, oil is problematic to water treatment plants.
The best way to dispose of large amounts of oil (more than a spoonful) is through the solid waste department. If you’re dealing with shortening, lard, bacon fat, or other saturated fats, allow them to cool until they solidify, then scrape into the trash can. (Though, like many a grandma, I keep leftover bacon fat in a jar in the refrigerator to use for cooking.) Smaller amounts can even be wiped out with a paper towel or a napkin from Chipotle (of which I have hundreds) and tossed before washing the pan.
Liquid oils should be allowed to cool and then poured back into their bottles or any disposable container and thrown away. You can also double up some plastic grocery bags, pour the cooled oil in that, then tie it shut and put it in your regular trash. Some cities may offer vegetable oil recycling or you could contact a nearby restaurant that recycles their cooking oil and ask if you can add yours to their bucket. If you don’t do a whole helluva lot of frying, you might want to find a large gallon jug or pickle jar, keep it under your sink or in the garage and pour your used oil into that until it’s full, then drop off the whole lot at once.
I’m not sure if it’s exactly right or not, but if I’m dealing with the small (tablespoon) amounts of oil (not solid fat) left in a pan after sauteing and such, I don’t bother with any of the above and I just wash the damn thing.