Everything You Need to Know About Olive Oil

Olive oil, which is simply juice pressed from olives, has been an important part of Mediterranean cooking for thousands of years. The highest grade, called extra-virgin, is lively, bright, and full- bodied, with flavors ranging from peppery to buttery depending on the varieties of olives used and how ripe they were when harvested. In the Mediterranean, Spain is the leading producer of olive oil, followed by Italy and Greece. In the United States, California is the top producer (and in fact is the source of our winning supermarket extra-virgin olive oil).

Olive Oil is Healthy

We use extra-virgin olive oil (EVOO) as our main cooking oil as well as in raw applications. Olive oil supports one of the main pillars of the Mediterranean Diet Pyramid: to eat more healthy fats and fewer saturated fats. It is high in monounsaturated fatty acids, which are healthy fats, and also contains important minor components including antioxidants and other beneficial phytochemicals, plant-derived compounds thought to protect against disease. Studies have also shown that people who regularly include olive oil in their diets have lower rates of heart disease, lower blood pressure, and reduced rates of diabetes and some cancers.

The Fresher the Olive Oil, the Better

Olive oil tastes great when it’s fresh. But olives are highly perishable, and their complex flavor degrades quickly, which makes producing—and handling—a top-notch oil time-sensitive, labor-intensive, and expensive.

It’s OK to Cook with Extra-Virgin Olive Oil

Although conventional wisdom says that you shouldn’t cook with olive oil since its smoke point is low, we have found that this is not the case. With a smoke point of 410 degrees, extra-virgin olive oil is fine for most cooking applications, even frying. However, we don’t usually use olive oil for frying because it is not economical to use in large quantities.

Olive Oil is Versatile

Extra-virgin olive oil is of course a starring player in salad dressings, but we also use it as a condiment on vegetables, pastas, bean dishes, and grilled fish, and as a source of richness and body in soups and sauces. Since olive oil is a pricey purchase, we use what we term “supermarket” extra-virgin olive oil for everyday cooked applications and save the most flavorful “high-end” EVOO for drizzling.

How to Buy Olive Oil

Buying extra-virgin olive oil in American supermarkets can be a tricky business. The standards of the International Olive Council (IOC), the industry’s worldwide governing body, are not enforced in the U.S., and a widely reported 2010 study from the Olive Center at the University of California, Davis, revealed that 69 percent of tested supermarket olive oils sold as “extra-virgin” were actually lesser grades being passed off at premium prices.

Since then, the U.S. olive oil industry has taken steps to be more stringent. The state of California, where olive oil production has grown tenfold over the past decade, passed the California Department of Food and Agriculture olive oil standard in 2014. The most stringent standard in the country, it is mandatory for medium-and large-scale California olive oil production. In 2010, the U.S. Department of Agriculture (USDA) adopted chemical and sensory standards for olive oil grades similar to those established by the IOC. The USDA standard, however, is voluntary and rarely enforced, so choosing the right extra-virgin olive oil is a challenge, to say the least.

Finding the Best Olive Oil

To find the best “everyday” olive oil, we tasted 10 supermarket extra-virgin olive oils plain, with bread, over tomatoes and mozzarella, and in vinaigrette served on salad greens. We also sent each of the oils to an independent laboratory for chemical evaluation and to 10 trained olive oil tasters to get a second opinion on their flavor quality.

Our tasters were underwhelmed by the supermarket choices, but in the end, one oil stood out above the rest: California Olive Ranch Everyday Extra Virgin Olive Oil. We discovered that this largely boils down to the company’s control over every stage of the production process. The company uses a relatively new growing and harvesting process called super-high-density planting, in which the trees are planted together much more tightly than they would be in traditional groves.

As a result, the olives can be harvested by machines more efficiently than they would be if they were picked by hand. (Speed is of the essence, since olives begin to change flavor from the moment they are separated from the tree and must be pressed as quickly as possible to ensure that they retain the desired flavor profile.) Then, by bottling very close to the source, the company cuts out the risk that the oil will oxidize and spoil during transport to another facility.

And unlike some producers that sell their oil in clear glass or even plastic bottles, which expose the oil to more damaging light, our winning manufacturer uses dark-green glass bottles that help shield the oil. The upshot of all these factors: fresher and cheaper olive oil. While it costs more than mediocre oils from industrial bottlers, it’s far less expensive than our high-end extra-virgin favorite, Gaea Fresh.

When it comes to high-end olive oils, more expensive ones aren’t always better. Our winning high-end oil, Gaea Fresh, hails from Greece and, at half the price of some of the other oils in our tasting lineup, won’t break the bank. It won points with tasters for its bold yet nicely balanced flavor. We recommend using this oil in raw applications only.

Types of Olives Used to Make Olive Oil

There are over a thousand varieties of olives with a few dozen cultivated varieties that are commercially dominant. Some of the most commonly found varieties in the U.S. market are Arbequina and Picual from Spain, Koroneiki from Greece, and Coratina from Italy. Arbequina is noted for its ripe fruitiness, low bitterness, and pungency. Picual is very fruity with medium bitterness and pungency. Koroneiki is strongly fruity and herbaceous, with mild bitterness and pungency. Coratina is strongly green, herbaceous, bitter, and pungent.

Keeping Olive Oil Fresh

These three things can help you assess the quality of an extra-virgin olive oil before you buy it.

Harvest Date: A “best by” date might be 24 to 32 months after the oil was bottled, which in turn can be one to two years after it was pressed—so by the time that “best by” date rolls around, the oil could be about four years old. A harvest date is a more precise indication of freshness, since olive oil begins to degrade about 18 months after harvest. Look for the most recent date (certainly within the last 12 months), and note that in Europe and the United States, olives are harvested in the fall and winter, so most bottles list the previous year.

Dark Glass: Avoid clear glass; dark glass shields the oil from damaging light. Avoid clear plastic, too; it’s not a good barrier to light or air.

Oil Origin: Bottlers often print where their oil has been sourced from on the label; look for oil that has been sourced from a single country.

Storing Olive Oil

Never keep olive oil on your kitchen counter, since strong sunlight will oxidize the chlorophyll in the oil, producing stale, harsh flavors. Keeping your olive oil next to the stove is also a bad idea as heat accelerates spoilage. We recommend storing oil in a dark pantry or cupboard; do not store olive oil in the fridge, as it can become cloudy, thick, and viscous and can take a few hours to return to normal. You can keep unopened oil for about a year; but once opened, it lasts only about three months—so don’t buy in bulk. And if possible, check the harvest date to ensure the freshest bottle possible.

To check for freshness, pour a little oil in a small glass and sniff it. If it reminds you of crayons or stale walnuts, toss it.

This article originally appeared on America's Test Kitchen.