3 Tips For Buying High-Quality Olive Oil (Beyond "Extra Virgin")

Olive oil is a common pantry item and probably one of your most reached-for ingredients—even more so if you're following a Mediterranean diet. Its heart-healthy benefits and high polyphenol content make it a great cooking oil to add to your rotation. But it's important to know that not all olive oils are created equal, so it's crucial to shop smart.

The truth of the matter is that just because something is labeled "extra-virgin" doesn't mean it still is when you actually get your hands on it. That's because factors like exposure to light and air, as well as the simple passage of time, allow the oil to oxidize. As it does, it loses the characteristics that qualify it as extra-virgin olive oil in the first place.

According to the USDA, to be called extra virgin, the olive oil must have both "excellent flavor and odor" and "a free fatty acid content, expressed as oleic acid, of not more than 0.8 grams per 100 grams." Essentially, it's not just about the taste—it's also about the chemical makeup of the oil.

In a 2010 study, researchers at the University of California–Davis assessed how much of the EVOO on shelves was truly extra virgin—and found that many imported varieties did not meet the standards for chemical makeup and sensory qualities (including flavor and aroma) that are set by the U.S. Department of Agriculture.

"When you buy a bottle labeled extra virgin, you are buying an olive oil that, at the moment of the pressing, has been declared extra virgin," explains Armando Manni, olive oil producer and founder of Manni Oil. "In that moment, it's fresh—two weeks later, it's oxidized. The polyphenols sacrifice themselves, one by one, in the bottle, to protect the fat cells from oxidation."

More recent studies have confirmed that factors such as oxygen, temperature, and light exposure can lead to the degradation of the oil. A 2018 study published in the Journal of Food Quality found that even in varieties with high antioxidant levels, like EVOO, olive oil is prone to oxidation due to external factors.

Before anything else, zero in on dark bottles. "You should never buy a bottle of extra-virgin olive oil in a transparent container," says Manni. "The oil will be exposed to UV rays and oxidize very quickly, losing its extra-virgin properties right away." Instead, research shows that storing oil in greenish glass2 effectively helps slow down the oxidation process.

If you've ever picked up a bottle of olive oil and noticed something granular circulating, there are two reasons you might want to put it back on the shelf. First of all, if you can see through the bottle, it's probably already not one you want. And the second reason relates to the sediment itself.