This classic cooking oil remains one of the healthiest around, but even if you’ve been using it forever, you might still be making these slippery mistakes.
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You probably don’t lump olives in with other fall fruit (yep, they're a fruit!), but right now is prime harvest time for oil producers. They’re busy picking, pressing, and bottling the green gold in your pantry, with its rich stores of monounsaturated fat that have been linked to heart health and may help defend against age-related illnesses like dementia.

But not all EVOO is created equal. Before you buy your next bottle, hear what a certified oleologist has to say about misleading labels, what a harvest date is, and why you probably don’t know how non-rancid oil really tastes.

1. “Cold-Pressed” Oil...Isn’t

Back in pre-Industrial times, oil was made by literally pressing crushed olives, sometimes with giant stone wheels pulled by donkeys. But today, producers use a much more efficient centrifugal machine to separate oil, water, and solids. The modern technique has the added advantage of limiting the oil’s exposure to oxygen, the number one thing that can degrade it. Neither process uses heat, but the older terminology somehow stuck, so people still look for the words “cold pressed” on labels as a sign of quality, says Meagan Cole, a certified oleologist. Oil is not juice; no cold pressing needed.

2. It’s Got a Shelf Life

Oil doesn’t tend to be a food we think of as highly perishable, like milk. But it’s probably more fragile than you think. Light, heat, and oxygen can all chip away at its freshness, which is why good oil is sold in opaque bottles, not clear ones. But even under optimum storage conditions, oil will eventually go rancid. Most people aren’t even aware that producers print the harvest date on bottles, or what those numbers signify: namely, when the fruit was harvested and milled into oil. That date should be within the last year; otherwise the oil could already be rancid. “A sealed bottle of extra-virgin olive oil has a shelf life of 18 to 24 months,” says Cole. And an opened bottle should be used within a month or two.

3. You’ve Probably Been Using Rancid Oil Your Whole Life

You might assume rancid oil would be obvious, but odds are, you’re just used to the flavor. Good oil has a distinctive spicy burn that lets you know its polyphenols are still alive and well. (Among Italian producers, there’s even a saying that when tasting oil, one cough is good, two coughs is very good, and three coughs is excellent.) “A high-quality, extra-virgin grade olive oil should taste like fruit and fresh herbs,” says Cole. And its mouthfeel should be clean, not greasy. You don’t have to pay a lot for this kind of quality either; bottles can run between $15-$25.