How to Tell If Olive Oil Has Gone Off
How to tell if olive oil is rancid or defective: what rancid, fusty, musty and winey smell like, what causes them, and when to bin the bottle for good.
Smell it. Rancid olive oil smells like crayon, putty, stale nuts or old paint, and it tastes flat and greasy with no fresh olive character. If you get that, the oil has oxidised and it is past use. Other faults smell sweaty, mouldy or vinegary. Any of these means the oil has a defect. When the smell is clearly off, bin the bottle.
The quick test
You do not need a lab. Pour a little into a glass, warm it in your hand, and smell it the way a taster would. Fresh extra virgin smells green and lively: grass, tomato leaf, green apple, pepper. A spoiled oil smells dull, waxy or stale, with none of that freshness. Our tasting guide covers the full method, but for spotting a fault the nose does most of the work.
Trust your nose over the date on the bottle. A best-before date assumes good storage. An oil kept in heat and light can turn well before that date, and the fault will not show until you smell or taste it.
The common defects
A trained sensory panel checks every oil for defects, and any defect at real strength drops it below extra virgin under the Australian standard AS 5264. Four faults come up most often.
Rancid
The big one. Rancid is oxidation, the same process that turns any fat stale. It smells of crayon, putty, stale nuts, old walnuts or drying paint. The taste is flat and slightly greasy, with the fresh olive character gone. This is the defect you are most likely to meet, because it develops on the shelf and at home over time.
Fusty
A sweaty, muddy, slightly sour smell. It comes from olives left piled in heaps too long before pressing, where they start to ferment. You meet fusty in cheap, carelessly made oils rather than in a bottle that has aged at home.
Musty
Damp and mouldy, like a wet cardboard box or a neglected cellar. Caused by mould and yeast growing on olives that were stored damp before pressing. Once you have smelled it, it is hard to miss.
Winey
Sharp and vinegary, sometimes with a nail-polish edge. It comes from fermentation in the fruit or the oil. In small amounts it reads as sour; stronger, it is unmistakably like vinegar.
Fusty, musty and winey are mostly production faults, baked in before you ever bought the bottle. Rancidity is the one that develops in your kitchen. Our tasting guide shows how a panel scores these, and the grades pillar explains how they push an oil down the ladder.
What causes oil to go off
Four things turn olive oil, and three of them are in your control.
- Age. Olive oil is a fresh product, not a fine wine. It is at its best young and fades over months. Buy on harvest date, not just best-before, and use it within a year of opening.
- Light. Light drives oxidation. Clear bottles on a bright shelf are the enemy. Choose dark glass or tins and keep the bottle in a cupboard.
- Heat. Storing oil next to the stove or oven cooks it slowly. Keep it somewhere cool.
- Poor fruit or handling. Bruised, mouldy or long-stored olives, and sloppy pressing, bake defects in before the oil is bottled. This is where fusty, musty and winey come from.
Store your oil cool and dark, keep the cap on, and buy sizes you will finish in a couple of months once opened.
Is rancid olive oil dangerous
Rancid oil will not usually make you sick from one taste. The real problem is that it tastes bad and it has lost most of the antioxidants that give olive oil its health benefits. Oxidised oil works against you rather than for you. There is no good reason to cook with it.
When to bin the bottle
Bin it when:
- It smells of crayon, putty, stale nuts or paint.
- It smells sweaty, mouldy or vinegary.
- It has been open for well over a year.
- It has sat in heat or bright light for months.
- It simply smells of nothing and tastes flat, with no fresh olive character.
A flat, tired oil is not the same as a genuinely light oil, which is mild by design. But a fresh extra virgin should always smell alive. If yours does not, replace it. Use our label guide and the extra virgin vs virgin breakdown to pick a better bottle next time, and check the harvest date so you start fresh.
The bottom line
Rancid oil smells of crayon and stale nuts and tastes flat. Fusty, musty and winey are the other faults to know. Age, light and heat are the causes you control, so store oil cool and dark and buy it fresh. When the smell is clearly off, do not cook with it. Bin it and open something new.