Good Oils Gone Bad: Recognizing Olive Oil Defects

Nov. 15, 2010
By Alexandra Kicenik Devarenne

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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.

Olive oil 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.


Olive oil is best con­sumed within a year of har­vest.

Most oils, if unopened and stored in a cool dark place, will still be good for up to two years, but they steadily lose the fresh fruiti­ness that you want in olive oil. Greener har­vest, robust olive oils will keep better than del­i­cate ripe ones because of the higher con­tent of com­pounds called polyphe­nols in greener oils. You can rec­og­nize the pres­ence of these polyphe­nols because they con­tribute pep­per­i­ness and bit­ter­ness to the flavor of an oil. If an oil is del­i­cate and soft, made from ripe olives, then you will want to use it quickly, within six months or a year at the most.

The second most common defect of olive oil is called “fusty.”

Fustiness is caused by fer­men­ta­tion in the absence of oxygen; this occurs within the olives before they are milled. This is why it is so impor­tant for olives to be processed into oil within as short a time as pos­si­ble after har­vest. Olives left to sit in bags or piles for even a few days will pro­duce fusty olive oil.

And what does fusty smell and taste like? Unfortunately, the answer for a lot of people is “olive oil.” For many people, both in the US and abroad, fusty fla­vors in olive oil are the norm. When I was train­ing for an olive oil taste panel, I remem­ber vividly the day I poured my usual sup­pos­edly extra virgin olive oil into a warm skil­let and was enveloped by the smell of fusti­ness. I threw out that bottle and never looked back.

Now I know that good olive oilsmells like fresh green or ripe olives, and that the smell I always asso­ci­ated with olive oil was in fact the smell of fer­mented olives. It’s dif­fi­cult to come up with a single descrip­tor for the fusty smell, but here are some things that might help: sweaty socks, swampy veg­e­ta­tion, or too-wet com­post heap. A good way to taste an exam­ple of the fusty defect involves table olives. Look through a batch of Kalamata-style olives and see if you can find any that are not purple or maroon-black and firm, but instead are brown and mushy. Eat one. THAT is the flavor of fusty.

Rancid and fusty are by far the most common defects of olive oil. Occasionally you may run into a winey-vine­gary defect. That is caused by fer­men­ta­tion with oxygen, and can be rem­i­nis­cent of vine­gar or nail polish. Another defect that crops up once in a while is musty. Caused by moldy olives, it tastes of dusty, musty old clothes, or the base­ment floor.


How does a shop­per put their knowl­edge of this cham­ber of hor­rors to use?

Start with fresh­ness. Look for dates on olive oil bot­tles. Try local pro­duc­ers if you are lucky enough to live in an area where olive oil is made. Learn as much as you can about the grower.

Whenever pos­si­ble, taste before you buy. And if you open a bottle and find that it’s rancid, return it. An eth­i­cal pro­ducer will do every­thing they can to get a qual­ity prod­uct to you, but they lose con­trol once the bottle is out there in the dis­tri­b­u­tion chain. Buy from people you trust.

By paying more atten­tion to the fla­vors of olive oil, and exper­i­ment­ing in your kitchen and at the table, you will dis­cover the amaz­ing diver­sity of this won­der­ful food. Let knowl­edge and expe­ri­ence embolden you; damn the croc­o­diles — full speed ahead!