Good Oils Gone Bad: Recognizing Rancidity and Other Defects

By ALEXANDRA KICENIK DEVARENNE

The joy of olive oil lies in its many delightful aromas and flavors—from voluptuous ripe olive to bright green grassy notes and from a soft subtle finish to a zippy peppery kick—there is a world of sensory exploration awaiting the adventurer. But like any great explorer, you will be faced with risks—crocodiles in those placid waters. This is an introduction to the most common defects you will find in olive oil: what they are called, what causes them, and how to recognize their presence.

Any discussion of defects must start with rancidity.  The sad truth is that most people in the US, for example, are accustomed to the flavor of rancid olive oil. Olive oil is no longer an occasional presence in the kitchen so it is time to change that.

We need to start by recognizing one essential fact about olive oil: it is a perishable product. Olive oil tastes best when it is fresh. Think of olive oil on a freshness continuum that goes from just-made, harvest-fresh at one end, to completely rancid at the other. How long it takes an olive oil to go from one end of this freshness continuum to the other depends on many factors: storage temperature, exposure to air and light, and the amount of natural antioxidants in the olive oil in the first place. All olive oils, even the finest ones, will get rancid eventually. This is why you must never hoard olive oil: use it and enjoy it. Waiting for a special occasion to use your good olive oil? How about dinner!

Do you have a clear sense of what rancid oil smells and tastes like? A good image for many people is the smell of crayons. Another helpful item—something that almost everyone has tasted—is rancid nuts. Rancid is fat gone bad, something all of us have encountered at some time.  On a rancid scale of 0 to 10, almost everyone will notice a 9 or a 10. The trick is to develop the confidence to pick out rancidity when it is a 5, or a 3, or lower. The flavor of rancidity in olive oil is usually accompanied by a greasy mouthfeel; in fact, the greasiness often is noticeable first.

Go to your cupboard and pull out the olive oil. How old is it? Is there a “Best By” date? Generally that date is two years from the time that it was bottled.  Unfortunately, that doesn’t tell you when it was harvested and milled.  A harvest date is the most reliable indicator since it tells you when the olive oil was actually made. Sniff it. Taste it. Crayons? Putty? Old peanuts? Don’t feel bad about throwing out old olive oil, feel good about it! Don’t be surprised if the purge of your pantry includes not just old olive oil but things like old whole wheat flour (which gets rancid because of the oils in the wheat germ), crackers and cereals.

Comments:

Actually oil that is removed from its natural environment (from seed, nut and fruit) becomes rancid very quickly. Whether you are able to smell it or not. The high temperature processing can add to the damage. When you notice the rancidity a good proportion of the oil has already reacted with oxygen. A dog with much more sensitive smell would detect the rancidity long before you could. (In its natural environment the oil remains undamaged for much longer - but even then it is not immune to the ravages of oxygen which is all around us. (Rice is milled to remove the bran and germ from the grain because these contain oil. That oil can rapidly go off shortly after the rice is harvested. Before the rice has been harvested the oils are protected by the living plant.)

The most stable oils contain more saturated content these are not as susceptible to oxygen attack. It is the polyunsaturated oils that are at greatest risk. However, no oil or fat is purely saturated (sat), polyunsaturated (poly) or monounsaturated (mono). (Lard actually contains more mono fat than sat or poly. So technically it should be called a mono fat. It is the very same mono found in olive oil (oleic acid) - Shock horror).

Coconut fat contains more sat fat than anything else (short chain versions). That's right more than beef fat, lard, chicken fat etc. But it still contains a little poly and mono that can become rancid easily.