Tests have found that many olive oils claiming to be extra virgin are, in fact, not. And consumers are getting ripped off, shelling out big bucks for what they think is pure olive oil only to end up with a product containing soybean and other cheaper oils. With so much olive oil fraud happening, there's a chance you've been spending a little extra money to make sure you're getting the real deal.

Extra virgin olive oil is frequently more expensive than the non-extra virgin variety, and very good quality EVOO can get pricey. However, quality EVOO can also go rancid more quickly than other oils.

What does rancid mean?

Foods that have fats or oils in them can go rancid, or stale. Foods that have gone rancid have a "rank smell or taste usually due to chemical change or decomposition," according to Vocabulary.com.

EVOO comes from the first press of olives. When the olives are pressed, the oil is extracted naturally, using no heat or chemicals. It's basically olive juice, and to be labeled extra virgin, it must have no defects. Once this high quality oil spoils, not only will it taste and smell bad, its health benefits will be diminished also. The antioxidant polyphenols in the oil, the same compounds that make red wine healthy, will have disappeared, the Daily Meal reports.

How to detect a rancid oil

smelling-olive-oil If you're not sure if your extra virgin olive oil is still good, a big sniff is the first step in finding out. (Photo: lithian/Shutterstock)

I bought my first really good, expensive EVOO at a wine expo about a decade ago. I spent $25 on a small metal container of oil from Italy. I brought it home, used it once, put it in the cupboard above my stove, and forgot about it. Eventually, it got shoved to the back of the cabinet, and it wasn't until about five years later that I rediscovered the container way out of sight in the high cabinet.

When I opened it, there was no doubt the oil had gone rancid. The smell was enough to convince me to toss the entire container. What a waste.

Rancidity is not always that obvious, and it can happen long before the oil is five years old. The Daily Meal suggests the following steps to test for rancidity using both your sense of smell and taste.

  1. Pour a small amount of olive oil into a cup so you can get a good sniff.
  2. If the oil has an unpleasant sweetness, "like fermenting fruit or fruit that's just gone completely bad," it's rancid. The sweetness is also described as being reminiscent of the smell of Elmer's Glue.
  3. Do a taste test, also, because many EVOOs have a naturally sweet smell that an inexperienced person could easily mistake as rancidity.
  4. Before tasting, warm the cup in your hands to bring it to room temperature.
  5. 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."

If your EVOO, or any other oil, has gone rancid, there is no saving it.

How to keeping EVOO from going rancid

The good news is there are ways to prevent extra virgin olive oil, and other oils, from going rancid, or at least slow down the process.

  • Look at the harvest date on the bottle when you buy it. Get the newest bottle available because the shelf life of EVOO is about two years after harvest, even if you store it properly.
  • Light is an enemy of olive oil, so oils packaged in dark glass or metal tins should last longer than oils packaged in clear glass.
  • If you're buying oil in clear glass, chose a bottle from the back of the store shelf where it's darker.
  • Once you have the oil home, store it in a cool, dry, dark place.
  • Do not store your oil above the stove (as I did with my first good olive oil purchase) because the heat and steam from the stove will make it spoil more quickly. Oil does not like humidity.
  • If you purchase a large container of oil, transfer a small amount of it into a dark bottle (a clean dark wine bottle fitted with a pouring spout would work) to use as needed. Store the larger container in a dark, cool place and keep the smaller bottle at arms reach, but still away from light and heat. This will keep the oil in the large container from going rancid more quickly because it will be away from too much oxygen (another enemy of olive oil) and frequent fluctuations in light and temperature.

Robin Shreeves ( @rshreeves ) focuses on food from a family perspective from her home base in New Jersey.