The three things that degrade olive oil
Light is the most damaging factor. Ultraviolet and visible light accelerate the oxidation of polyphenols, chlorophyll and fatty acids in olive oil. This is why quality producers use dark glass — and why olive oil in clear bottles on brightly lit supermarket shelves is at a disadvantage regardless of initial quality.
Heat degrades polyphenols and aromatic compounds. Storing olive oil next to the cooker or hob — where it is convenient — exposes it to repeated cycles of warmth that cumulatively reduce its quality. A dark cupboard or pantry, ideally below 18°C, is significantly better.
Air triggers oxidation. Once opened, every introduction of air starts the clock. Seal the bottle tightly after each use. Do not decant into a wide-mouthed container or leave the cap off during cooking.
Ideal storage conditions
Temperature: 14–18°C is optimal. A cool kitchen cupboard works. A wine cellar or unheated pantry is ideal. Avoid anywhere that cycles between warm and cool.
Light: Complete darkness or opaque packaging. Dark green or amber glass provides partial protection; an opaque tin or black glass provides full protection. If your oil is in clear glass, keep it in a cupboard or wrap it.
Container: Sealed tightly after each use. Do not use wide-bottomed decanters or cruets that maximise air contact. If you buy in a large format, consider decanting a smaller portion into a dark bottle for daily use and sealing the main container.
After opening: Use within 4–6 weeks for best quality in terms of flavour and polyphenol content. The oil will remain safe to eat for longer — it will not cause illness — but the organoleptic and nutritional qualities decline noticeably after 6–8 weeks once opened and exposed to air.
Should you refrigerate olive oil?
Refrigeration is not recommended for everyday use. At refrigerator temperatures (4–7°C), olive oil will solidify and become cloudy — a normal physical response to cold that does not harm the oil, but makes it difficult to pour and use.
More practically, the repeated warming and cooling as you take the bottle in and out of the fridge creates condensation inside the bottle and temperature cycling, both of which can accelerate degradation.
The exception: if you have a large bottle that you will not finish within 3–4 months, refrigeration can slow polyphenol degradation and extend flavour life. Let it return to room temperature before use — it will liquify without any lasting effect on quality.
How long does extra virgin olive oil last?
Unopened: Up to 18–24 months from pressing, if stored correctly in the dark and cool. After this, the oil is still safe but polyphenol content and flavour will have significantly declined.
After opening: 4–6 weeks for peak quality; 3–4 months before it becomes noticeably stale.
The more important date is the harvest date. A bottle with an 18-month shelf life but a harvest date 14 months ago has 4 months of freshness remaining — and the oil has already been declining for over a year. Knowing the harvest date tells you far more than the best-before.
Castruriali ships current-harvest oil — 2024/2025 pressing — so every bottle you receive is as close to the source as is practical for UK delivery.
How to tell if olive oil has gone bad
Smell: Rancid olive oil smells of crayons, putty, old nuts or stale fat. Fresh extra virgin olive oil smells of grass, green apple, artichoke or ripe fruit depending on variety. If the smell has lost its character and replaced it with something stale or fatty, the oil has oxidised.
Taste: Rancidity is detectable on the palate as a flat, stale or waxy flavour. You will also notice the absence of pepper and bitterness — both degrade as polyphenols oxidise. An oil with no pepper and a dull, fatty taste is past its best.
Appearance: Cloudiness at room temperature can be normal if the oil was unfiltered or recently cold — it will clear at room temperature. Actual degradation does not cause cloudiness; the appearance remains relatively stable as oils oxidise. Do not use appearance as a quality indicator — use smell and taste.