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Good olive oil is a fresh product, closer to a squeezed fruit juice than a long-life pantry staple. That peppery, grassy, slightly bitter character you paid for begins to fade the moment the bottle is opened, and it fades faster still in the wrong corner of a British kitchen. The good news is that protecting it takes very little effort: keep it away from heat, light and air, seal it well after every use, and decant only what you need for the week ahead.

Why Olive Oil Loses Its Flavour

Three things quietly dismantle a good oil: light, warmth and oxygen. Sunlight and bright kitchen lighting break down the chlorophyll and antioxidants that give extra virgin olive oil its colour and its lively, peppery finish. Heat speeds up every chemical reaction, so a bottle sitting beside the hob or above the kettle ages at several times the speed of one kept in a cool cupboard. Oxygen gets in every time you open the bottle and starts the slow slide towards rancidity.

Ideal conditions are dull and steady: somewhere dark, between about 14°C and 18°C, away from the oven, radiator, extractor fan and windowsill. If your kitchen has no such spot, a cupboard in a cooler hallway or utility room is fine. Chilling oil in the fridge is not a disaster — it will turn cloudy and may solidify, then return to normal at room temperature — but it is really only worth doing for long-term storage of a large quantity.

Signs that an oil is tiring include:

• a flat, greasy or waxy smell, often described as crayon-like
• a bitterness that feels harsh rather than fresh and peppery
• a dull, brownish-grey colour instead of green or gold
• a finish that lingers unpleasantly rather than fading cleanly

Pick the Right Bottle and the Right Spot

Dark glass is the classic choice for a bottle you use often. Ceramic and stainless steel are excellent for larger quantities, because they block light completely. Clear glass and clear plastic are the two containers to avoid: clear glass lets light straight through, and thin plastic can pick up and pass on flavours over time. A pretty clear bottle on an open shelf looks lovely in photographs, but it is the worst possible home for a delicate oil.

Keep bottles upright rather than on their side. Upright, the oil touches less of the cap and closure, which are usually the weakest point for air ingress. And resist the tempting olive oil rack mounted beside the cooker: it is convenient, but it combines three of the four worst enemies at once — light, heat and a bottle that is opened constantly.

Seal It Properly, Every Single Time

Air is the enemy you have most control over. Screw the cap down firmly after each pour, and never leave a bottle open while you cook, even for a minute or two. Pourer spouts and self-closing nozzles are handy, but many of them let a slow trickle of air in and out continuously, so if you use one, choose a design with a close-fitting stopper and keep the bottle in a cupboard rather than on the worktop.

Wipe the neck and the threads of the bottle with a clean cloth now and then. Dried oil around the rim forms a sticky, gummy ring that stops the cap sealing tightly and gives off a stale smell the next time you pour. If you decant into a bottle with a cork or stopper, replace it as soon as you have finished, and check the fit — a loose stopper is barely better than no lid at all.

Decant Only What You Need

The most practical habit in any kitchen is a two-bottle system. Keep a small dark glass bottle of around 250ml for everyday pouring, and store the main container sealed in a dark cupboard. Refill the small bottle as needed, so the large one is opened rarely and spends most of its life closed. A 250ml bottle used for dressings, roasting and finishing should last a fortnight or so in a busy household.

Two rules matter here. First, never top up a part-used bottle with fresh oil — mixing old and new simply ages the fresh oil sooner. Second, wash and dry your decanter thoroughly between refills, because a film of old oil at the bottom will flavour everything you put in afterwards. A small funnel and a strip of masking tape with the opening date written on it will keep you honest.

Bulk Buys and Longer-Term Storage

Tins are a sensible way to buy larger quantities: they block light completely and often cost less per litre. Once opened, however, a tin is awkward to reseal and hard to pour from neatly. Decant the contents into smaller dark glass jars filled almost to the top, since it is the headspace that holds the oxygen doing the damage. Shop by harvest date rather than best-before date, and buy only as much as you will use within roughly six to twelve months.

Keep your store away from anything strongly scented as well. Olive oil absorbs aromas readily, so a cupboard shared with spices, vanilla, coffee or cleaning products is not the place for it.

Herbs from the Garden: Flavoured Oils Done Safely

If you grow rosemary, thyme, bay, oregano or chillies on a windowsill or in a pot by the back door, you already have the ingredients for beautiful flavoured oils — with one important caution. Fresh herbs and, above all, fresh garlic can carry bacteria that thrive in an oxygen-free oil environment, so an oil infused with raw garlic and left at room temperature is a genuine food safety risk.

The safer approach is to use dried herbs, which infuse slowly and store far better, or to warm the oil gently with fresh herbs and use it within a few days from the fridge. A quick alternative is to blitz fresh herbs into oil and use the mixture straight away, spooned over tomatoes, grilled vegetables or bread. Whichever route you take, keep the finished oil sealed, dark and cool — the same rules that protect the oil itself will protect your flavouring.