Is Your Olive Oil Rancid?

There are many things that keep Americans up at night — life, death, taxes, the job, the mortgage, the car payment, the marriage, the college fund, the retirement fund, the stock portfolio, and of course, whether the garage door is shut — but whether their olive oil has gone bad probably isn't one of them. But you should care about that. Here's why.

First of all, we should clarify that this discussion applies to extra-virgin olive oil, since refined olive oils, also marketed as "pure," "light," or "light-tasting," have a significantly extended shelf life. Extra-virgin olive oil actually has an official definition drafted by the International Olive Council, an intergovernmental organization that sets voluntary standards for olive oil classification and testing, among other things. Their definition states that an extra-virgin olive oil cannot have a free acidity of more than 0.8 percent by weight, must have fruitiness, and must be free from any faults. A fault is a major flaw that would legally prevent an olive oil from being labeled and sold as extra-virgin. There are five main technical faults, one of which is rancidity.

That extra-virgin olive oil will go rancid may not seem like news to anyone who's ever unwrapped an old block of butter, opened up a long-forgotten tub of lard, or unscrewed the cap on a bottle of vegetable oil that's been sitting around too long and experienced a major whiff of funk.

However, when it comes to extra-virgin olive oil, rancidity is a bit different. That's because extra-virgin olive oil has properties that separate it from other types of fat and cooking oil. The best way to explain this is with an analogy.

One can draw many parallels between extra-virgin olive oil and wine — the production since antiquity; the long and contentious histories involving fraud, conspiracy, and war; the historical use in religious rites; the prominent role in Mediterranean cuisine; the frequently lauded health benefits cited in study after study; the origin from fruit with specific varietals affected by climate and region; the general lack of understanding among the public; and the evaluation of their aromas and flavors by connoisseurs or snobs in fairly similar terms — that is to say, terms that lead to the public's confusion and diffidence. But one area where extra-virgin olive oil differs from wine is this: Unlike wine, it does not improve with age.

That's because extra-virgin olive oil derives many of its unique antioxidant and anti-inflammatory properties from a class of compounds known as polyphenols. Polyphenols are volatile, meaning that they break down over time as they are exposed to air, light, and heat. So as an extra-virgin olive oil sits on the shelf or in the pantry, its polyphenol count and, consequently, its health benefits, vaporize into thin air. Olive oil tasters frequently refer to this process as the "tiring" of olive oil — in contrast, for example, to the aging of wine, a desirable process.

Eventually, the count reaches zero, and the oil, at that point, is technically considered rancid and no longer has any antioxidant or anti-inflammatory properties. The oil can no longer be called extra-virgin.

That's useful if you have a lab in your kitchen. But in case you don't, there is another way to tell without any fancy lab equipment. All you need are two tools that won't cost you a dime and which people sometimes forget to use when figuring out when a food has gone bad.

We're talking about your nose and mouth, folks. That's right — with a little concentration, just about anyone can tell if extra-virgin olive oil has gone rancid. That's because the aroma and flavor will have changed significantly since bottling.

How so, exactly? A rancid extra-virgin olive oil will generally have a faintly sweet aroma, which one can describe as being similar to Elmer's glue. (If it is particularly strong, the oil has a different, more damning technical fault —it is considered "musty," "humid," or "earthy," classifications which, in an ideal world, would prevent an olive oil from reaching store shelves with an extra-virgin label in the first place.) This isn't a pleasant sweetness — it's sickly, like fermenting fruit or fruit that's just gone completely bad. The stronger the smell, the more rancid the oil is.

It's also worth noting that when doing the smell test, the oil should be poured out into a cup first. That's because olive oils are sold with plastic pourers that accumulate small amounts of oil. That oil is exposed to more air than the oil inside the bottle, so sniffing it straight from the opening wouldn't exactly be giving the oil a fair shake; the contents inside the bottle are often perfectly fine even if the stuff on the lip of the pourer is bad.

But smell isn't (and shouldn't) be the only test, at least for beginners. Novice sniffers may end up confusing a rancid oil with one that is perfectly fresh. That's because some oils will have a naturally ripe or sweet fruitiness on the nose, depending on a number of factors, including the varietal or blend of varietals, where it was grown, and what the soil and climate were like. But there is a difference between a ripe fruit aroma and a rancid one.

So, to confirm rancidity, it's important to also taste the oil. Warm the cup in your hand to get the oil to room temperature, slurp about a tablespoon of oil into your mouth without swallowing or exhaling, keep slurping, breathe out, and if it's completely tasteless, it's rancid.

This is due to the fact that one of the first flavor characteristics to go as an oil tires is fruitiness, says Simon Field, instructor for Savantes, a certification program for olive oil producers and retailers. Pepperiness and bitterness, the other two main flavor characteristics often (but not always) present in an extra-virgin olive oil, come from polyphenols and will also have faded completely.

At this point, you may be asking, "But why don't we just go by the expiration date?" While major manufacturers of supermarket extra-virgin olive oil will sometimes put a use-by date, it is, for all intents and purposes, an estimate. Your oil's mileage will vary, depending on the way the olive oil was processed, the way it was stored during transport and at the store, and the way you store it at home. For example, oils that have been sitting in shipping containers baking in the hot sun while waiting to be distributed to stores, or that have been sitting under harsh lighting on store shelves with little turnover, probably won't live up to their projected use-by dates. Sell-by dates are even less informative; how much time you have to use the product after the sell-by date isn't a hard-and-fast rule. The same goes for bottling dates. And smaller producers may not even put any sort of date at all.

So, it's probably best to go with your senses. The average life span of an extra-virgin olive oil isn't terribly long, at least when looking at supermarket extra-virgin olive oils, says Gabriel Estevez, Ph.D., chief operating officer of Sovena, a Portuguese food group formerly known as East Coast Olive Oil, the largest importer of olive oil and bottler of private labels for America. Supermarket extra-virgin olive oils are generally created from a blend of varietals, and manufacturers do their best to create a blend with maximum shelf life. However, the average life of such oils is about 18 months from crushing of the olives, says Estevez. And since it takes about six to 12 months to go from crushing to bottling, an olive oil that has reached supermarket shelves has at best six to 12 months of shelf life. And that doesn't account for shipping time and the store's rate of turnover, which can significantly impact the shelf life of an oil.

So the next time you are doing a little spring cleaning of the pantry, take a careful look at your extra-virgin olive oil. Because just like everything else, it's got a shelf life, too.

Click here to see What to Do with Old Olive Oil

Will Budiaman is the Recipe Editor at The Daily Meal. Follow him on Twitter @WillBudiaman.