Good olive oil is not cheap, and it is not meant to sit at the back of a cupboard for years. In a Mediterranean kitchen, oil is used daily, poured with a generous hand over tomatoes, beans, bread and grilled fish. That constant turnover is part of what keeps it tasting sweet and peppery. In a UK home, where we might buy a litre and use it more slowly, storage matters even more. Heat, light and air are the three culprits that turn a vibrant, grassy oil into something dull, waxy and eventually rancid. The good news is that a few simple habits will keep your oil, and your olives, in fine fettle.

Why olive oil goes stale

Olive oil is a fresh fruit juice, more or less. It contains natural antioxidants, but they are not indestructible. When oil is exposed to heat, light or oxygen, a process called oxidation begins. Fatty acids break down, and the delicate aromas that make a good oil so appealing disappear. What is left is a flat, sometimes slightly crayon-like flavour. Rancidity is the end point, and it is not just a matter of taste. Rancid oil contains free radicals and can upset digestion. The speed of decline depends on the oil itself. A robust, peppery oil with high polyphenols lasts longer than a delicate, filtered oil. But no oil is immune. The three enemies work together. A warm, bright kitchen is the worst place for a bottle of oil, even if it is only there for a few weeks.

The right spot: cool, dark and steady

The ideal storage temperature for olive oil is between 14°C and 18°C. That is cooler than most British kitchens in summer, but warmer than a fridge. A dedicated cupboard away from the oven, hob, dishwasher and kettle is perfect. If you have a larder or a north-facing pantry, even better. Avoid the shelf above the radiator, the windowsill and the top of the fridge. Those spots fluctuate in temperature, and every warm spell accelerates ageing. Light is just as damaging as heat. Ultraviolet light breaks down the oil's chlorophyll and antioxidants. Dark glass or a tin is essential. If you decant oil into a pretty clear bottle for the table, use a small one and refill it often. Never leave a clear bottle on a sunny worktop. A dark cupboard, a tin or an opaque bottle: that is the simple formula.

Choosing containers and decanting wisely

Olive oil often comes in dark glass, tins or plastic. Tins are excellent for long-term storage because they block light completely. Dark glass is good for everyday use, provided you keep it closed. Plastic is acceptable for short periods, but it is slightly porous and can absorb flavours. If you buy a large tin, decant a week's worth into a smaller bottle and keep the rest sealed in the tin. That reduces the amount of air sitting above the oil. Oxygen is the third enemy, so the less headspace, the better. A smaller bottle that you refill from the tin is ideal. Always close the cap tightly after pouring. Do not leave the bottle open while you cook. And do not store oil next to strong-smelling foods like garlic, onions or spices, because oil can pick up their aromas over time.

Everyday habits for UK kitchens (and olives too)

Use your oil. That sounds obvious, but the best storage is a well-used bottle. Aim to finish an opened bottle within two to three months. If you buy in bulk, keep the bulk tin in a cool cupboard and decant as needed. Write the opening date on the bottle or tin with a marker, so you are not guessing. For frying, a good everyday olive oil is fine, but for drizzling, keep a separate, better bottle for finishing. Olives need similar care. Buy them in brine or oil, and once opened, keep them submerged in their liquid in a sealed container in the fridge. They will last for weeks, but they do not improve with age. If you buy dry-cured olives, store them in a cool cupboard with a little oil to cover. A bowl of olives left on a sunny counter will dry out and lose their fruity tang. Treat them as you would the oil itself: cool, dark and sealed.

Spotting the signs and using it up

No matter how careful you are, oil will eventually turn. Learn to trust your senses. Fresh olive oil smells grassy, fruity, sometimes peppery or slightly bitter. If it smells like crayons, putty, stale nuts or old cardboard, it is past its best. Taste a drop: a rancid oil leaves a greasy, unpleasant coating on the tongue. If it is only slightly tired, use it for cooking rather than raw dressings. Heat will mask some of the flatness, but do not use truly rancid oil. It will taint your food. The best-before date on the bottle is a guide, not a guarantee. A well-stored oil can last a few months beyond it, especially if unopened and kept in a tin. An opened bottle in a warm kitchen may decline much sooner. Buy smaller quantities more often, and enjoy the bright, peppery flavour that makes Mediterranean cooking so rewarding.