One of my favorite cookbook authors recently posted an Instagram video about using extra virgin olive oil for cooking. He gave the green light to use it for deep frying. While he provided scientific evidence to support this idea, I’m going to explain why I don’t do this, as well as why I choose different oils for different purposes.
First, a little history. Olive trees are native to the eastern Mediterranean. Archeological evidence, as well as classical literature, suggests that their cultivation dates back to at least 6000 BCE. In Palestine and Syria, olive oil mills were cranking out olive oil used for daily cooking. This eventually caught on in Greece, where technological advances increased production. Greek colonization eventually brought olive farming to Sicily around 700 BCE and from there, it spread to France, Spain, Croatia, and Tunisia. We have to fast forward all the way to 1769 before the first olive trees were planted in California.
Olive oil is extracted from the pulp of the fruit. Its pulp contains up to 30% oil, along with an array of chemical compounds. These include pigments like chlorophyll and beta-carotene, which provide color. Esters, terpenes, and aldehydes contribute fruity, citrusy, and grassy aromas. The combination of these pigments and aromatic compounds contribute to the diversity we see amongst olive oils.
The olives are harvested a few weeks before they are fully ripe. From there, they head to the mill. Mechanical pressure is used to crush the olives. The pulp is then placed in a device called a malaxer, which churns the crushed olives into a paste. During malaxation, the oil and water in the paste begins to separate. After this, the paste is pumped into a centrifuge where the oil is is extracted. Before the oil is bottled, it is filtered in order to remove sediments and make the oil more shelf stable.
All of this seems pretty straightforward until you’re at the store staring at all of the options on the shelf. There’s extra-virgin, virgin, and pure (also referred to as regular or light olive oil), along with terms like “unrefined” and “cold pressed.” What does it all mean and how might this impact our cooking? In order to fully understand the differences between these products, we need to examine the chemical structure of oil.
An oil is a triglyceride. The “tri” refers to three fatty acids that are bonded to the “gly,” which is glycerol. When fatty acids are released from the glycerol they are referred to as free fatty acids.
The amount of free fatty acids in olive oil is influenced by the quality of the olives, environmental factors, and how the olives are processed. The higher the quality of the olive, the lower the percentage of free fatty acids. Yet even the best olives in the grove are at the mercy of Mother Nature. Damage caused by hail or pests allow both water and oxygen to enter the pulp, setting off chemical reactions that free the fatty acids from their glycerol molecules. Further harm can be caused by careless harvesting methods, using olives that have fallen to ground, or allowing the olives to sit for too long before being crushed. Once in the processing facility, crushing and grinding exposes the pulp to air, freeing up even more fatty acids. This is also why the temperature during maxalation is highly controlled as higher temperatures increase free fatty acids. For extra-virgin olive oil, the temperature cannot exceed 80.6 degrees F. This is why you often see the term “cold pressed” on a label.
Obviously, free fatty acids are not a good thing so this is one of the key considerations when labeling olive oils. Extra-virgin olive oil (EVOO) cannot contain any more than 0.8% free fatty acids. To achieve this, the best olives are used, they are harvested directly from the tree, and there is minimal exposure to heat and air during both processing, storage, and packaging. Virgin olive oil contains less than 2% free fatty acids. Pure olive oil is a blend of extra-virgin and refined olive oil. Refined olive oil has undergone additional processing, which exposes the it to higher temperatures. It’s made up of approximately 3% free fatty acids.
Free fatty acid percentage influences two things in cooking: stability of the oil and the smoke point. Stability refers to how likely an oil is going to oxidize. The more stable an oil, the less likely it is to oxidize. When oxidation occurs, this causes an oil to produce unpleasant aromas and flavors. An oil reaches its smoke point when it starts to decompose. One consequence is the breakdown of glycerol molecules which yields acrolein, a compound that stinks up the kitchen and makes food that tastes awful. Both stability and smoke point increase when the percentage of free fatty acids are lower.
With a measly 0.8 % free fatty acid percentage, EVOO is very stable. It has a respectable smoke point between 325 - 375 degrees Fahrenheit*. This would support the argument that cooking with it should be just fine. Not only that, EVOO is much more flavorful than other varieties and it has tremendous health benefits. So why am I opposed to using it for most of my cooking?
Let’s start with smoke point. To get a proper sear, the target pan temperature is 400 degrees F. In a quick internet search, I found reputable sources as high as 450 degrees F. This puts us well above the smoke point of extra-virgin olive oil. It’s also outside of the comfort zone of pure olive oil whose smoke point hovers just above 400 degrees F. For searing, I’m going to reach for grapeseed or avocado oil.
In culinary school, the deep fryer was always set to 350 degrees. This is also an appropriate temperature for sautéing. This falls within EVOOs range. However, unless one has a deep fryer or induction burner with temperature control, it’s very difficult to maintain a steady temperature. If the oil continues to heat up, disaster can ensue.
Aside from smoke point, remember those aromatic compounds that were mentioned earlier? Many of these compounds are quite volatile. Heating up the oil can potentially “cook off” the very compounds that made it taste unique in the first place. Why waste all of that flavor? This is why I like to drizzle cooked dishes with a high quality EVOO. Let those flavors shine after the dish leaves the stove.
My final argument comes down to cost. Olive oil prices are the highest that they have been in 26 years due to drought. The pure olive oil I use averages $20.00 a liter, while my go-to EVOOs comes in between $35.00 to $50.00 a liter. Compare this to canola oil which averages around $2.00 a liter. I use pure olive oil for all of my sautéing, but it’s simply too expensive for deep frying.
There are only two instances in which EVOO comes near the stove in my kitchen. The first is for some of my favorite cakes. Even though the oven temperature is 350 degrees F, the temperature of the cooked cake doesn’t exceed 200 degrees F. The flavor of the oil shines through. The second use is for making spice-infused oil. I’ll heat the oil until it reaches around 200 degrees F, add the spice, and immediately remove the pan from the burner (try this with Aleppo pepper… yum). Aside from that, EVOO finds its place in all sorts of other applications like dressings, dips, pestos, uncooked sauces, cold soups, and various condiments.
The bottom line is that how or why we use an ingredient isn’t always dictated by just one factor. While scientific evidence is helpful when making decisions, it’s important to look at the big picture. The source of the ingredient, how we intend to use it, what tools we have available, our comfort level in the kitchen, and our budget are all important considerations. My favorite food author was by no means wrong when he declared EVOO suitable for deep-frying, but he didn’t change my mind either.
*There is a lot of variability in smoke point charts across the internet. These inconsistencies are due, in part, to the methods used to determine smoke point. In addition, the chemical composition of the oils will vary across brands. For EVOO, I saw smoke point temperatures as high as 410 degrees F. An 85 degree difference between the lowest and highest smoke points is too much spread for me!