How do I recognize rancid olive oil? What causes olive oil to become rancid? Is rancid olive oil bad for me? How do I avoid it? An expert's tips help us separate fact from fiction!
What is rancidity?
Generally speaking, rancidity is caused by the oxidation of oils and fats. The reaction of fats and oils with atmospheric oxygen causes unpleasant flavors and odors to develop. Although hydrolysis is a player, in bottled olive oil the major path to rancidity is through oxidation—or at least that is how the process begins. Unsaturated fats—the (healthy) type most common in olive oil—are more prone to oxidation and therefore contributing to rancidity than saturated fats, so we need to pay attention to our olive oil.
How do I recognize rancid oil?
First off, let’s bust a myth: olive oil rancidity does not taste bitter! If anything, it’s the opposite (see “polyphenol content” below). It’s a safe bet that most people have tasted a rancid nut, but they may not have identified rancidity as the problem: “Ick. Bad nut!” may have been it. There are a few helpful references for recognizing rancidity: crayons, wax, linseed oil/traditional varnish (not polyurethane), window putty and old peanut butter or nuts.
The Freshness Continuum
Olive oil oxidation is a process. A good way to think of it is as a journey on a path that starts with just-made, perfectly fresh extra virgin olive oil at harvest. As the oil ages, it changes. The first changes are an overall mellowing and softening of the flavors. As the oil gets closer to its Best Before date, it can be considerably milder than it was when it was newly made.
Eventually, the oil will start to show characteristics that olive oil tasters refer to as “tired.” A tired oil will give a flat impression, lacking vibrant fruity flavors and having little or no bitter and peppery tastes. Tasters may also comment on the mouthfeel of a tired oil: oiliness can linger in the mouth, unlike a fresh oil that has an exceptionally clean mouthfeel. This tired character will eventually cross the line into rancidity, where it will develop odors associated with advanced oxidation (primarily from aldehydes and ketones).
How can I prevent rancidity? HALT the damage!
An easy acronym for the enemies of olive oil is H-A-L-T: Heat, Air, Light, Time.
· Heat: The best place to keep olive oil is in a pantry or cupboard in a cool part of the house. The target is cellar temperature, 59–63 ºF (the closer you are to that range, the better, but you don’t have to go crazy, just seek coolness). Refrigeration will cause your olive oil to develop solid lumps that need to reach room temp to disappear, and also condensation can cause moisture to collect in the bottle (not good), so it’s not recommended.
· Air: Oxygen = bad. Once a bottle is opened, the clock ticks faster. Bag-in-box is a great solution for larger volumes because the bag collapses and eliminates the airspace. If you buy a large tin, gently pour it (pour slowly down the side to minimize bubbles!) into clean dry smaller bottles filled right to the top.
· Light: Light, especially UV, is very damaging for olive oil. Buy olive oils in dark or coated glass, tins or bag-in-box. Store it in the dark. If you do get a clear bottle, an easy hack is to wrap it in aluminum foil to keep out light.
· Time: Olive oil is best when it’s fresh, and all olive oil will become rancid eventually. So use it up!
How Long Does Olive Oil Last?
The shelf life of an olive oil is affected by many things, some of which you can control (see above), some not so much. Figure that an unopened, well-made, properly stored extra virgin olive oil will be good for at least two years from harvest, and possibly more. Once you open a bottle, try to use it within 6-8 weeks. If you are using your olive oil at a fast pace, a bottle next to the stove is okay because you will finish it up in a couple of weeks. But if you expect to keep an oil for more than a few weeks, keep it somewhere cool and it will stay fresher longer.
There are other things that affect the shelf life of an olive oil as well—these are already there in a particular bottle of olive oil.
· Polyphenol content: Extra virgin olive oils contain all the naturally-occuring polyphenols and other so-called “minor”compounds; some of these are antioxidants and serve as natural protection from oxidation. This is why milder tasting oils tend to have a shorter shelf life—these peppery and bitter tasting polyphenols are naturally lower in riper fruit. Pour these delicate oils generously while they are at their fresh best!
· High quality: Better quality olive oil—made from perfect olives and expertly milled—lasts longer. Poor quality fruit and a lot of oxygen or heat exposure in milling will yield a less resilient olive oil.
· Proper storage and packaging: A producer who uses nitrogen or argon gas in tanks and bottles, and chooses stainless steel instead of plastic for totes and barrels, is protecting the oil before it even gets to the shelf.
· Good handling in retail spaces: Supermarkets vary a lot in the attention they give to the olive oil section. Notice things that indicate carelessness like the newest stock in the front instead of the back, and dusty bottles on the shelf. In specialty stores where you are paying top dollar for your extra virgin olive oil, you should expect the olive oil section to be away from windows and not under bright fluorescent lights; dark glass helps, but it’s not light proof. Turnover can be slower in these settings, so pay attention.
· Buy from the farmer-producer: Consider buying direct from the person who grows the olives and makes the oil—they have the biggest investment in keeping the product in optimum condition. And knowing the farmers is a big plus for many people.
How do I avoid rancid olive oil in the market?
· Choose olive oils that are in light protective packaging.
· Check the Harvest or Best Before dates. Don’t be afraid of buying an olive oil from the previous harvest; well-made oils will retain their quality. But...
· Taste it when you get home. Try a little bit in a spoon and if you get the impression of old walnuts, crayons or other rancidity signs, take it back to the store for a refund.
Is rancid olive oil unhealthy?
Although there is no research that proves that consuming rancid olive oil will make you sick, it is safe to say that it probably won’t be as good for you as a fresh olive oil. This is because those minor components that function as antioxidants get used up protecting the oil from oxidation, so you may miss out on health benefits from them. And frankly, rancid olive oil just tastes yucky. Pitch it and get yourself a fresh tasty bottle!