Unrefined oil is perishable. That is not a flaw in it — it is the direct consequence of leaving in the things refining takes out. Vitamin E, the natural antioxidants, the aroma compounds, the fine sediment: all of that is food, and food has a clock on it.
The good news is that the clock runs at a speed you control. Four things decide how long a bottle of cold pressed oil stays good, and three of them are settled by where you put it.
What "rancid" actually means
Rancidity is oxidation. Oxygen reacts with the fatty acids in the oil and breaks them into smaller compounds — aldehydes and ketones, mostly — and those are what you smell and taste. It is the same chemistry that turns an old packet of groundnuts bitter, or makes a tin of ghee smell like crayons.
Oxidation is always happening. Light, heat and contact with air all speed it up; refrigeration and a sealed dark container slow it down. Unrefined oil starts with more natural antioxidants than refined oil does, which buys it some time, but it also holds onto trace moisture and seed particles, which can work the other way. On balance, treat an unrefined bottle as fresh produce rather than a pantry staple that lives forever.
The four things that spoil oil
- Light. Sunlight and even strong kitchen light drive oxidation. A clear bottle on a windowsill is the worst case.
- Heat. Every rise in temperature speeds the reaction up. The shelf directly above the stove is a warm shelf.
- Air. A half-empty bottle is half full of oxygen. Headspace matters more than people expect.
- Water. A wet spoon or a damp bottle neck introduces moisture, which drives a separate spoilage route and encourages mould at the cap.
Where the bottle should actually live
A cool, dark, closed cupboard, away from the cooking range. Not on the counter beside the hob, not on top of the fridge (the compressor puts out heat), not on a window ledge.
Keep the cap on tight between uses, and pour rather than dip. If you use a ladle or spoon, make sure it is dry. Wipe the neck of the bottle occasionally — the film that collects there is the first bit to oxidise and it will make the whole bottle smell older than it is.
Refrigeration is optional for cooking oils and genuinely useful for oils you use slowly. Sesame oil that you only reach for at tempering time will last noticeably longer in the fridge door. It may cloud or thicken in the cold; that is physical, not spoilage, and it clears at room temperature.
The 15 litre tin problem
Buying a 15 L tin saves money per litre, and it is the right call for a large household or a small kitchen business. But a tin that is opened and closed twice a day for four months is a tin that is being aerated twice a day for four months.
The fix is simple: decant. Keep a 500 ml or 1 L bottle in the kitchen as your working bottle, and keep the tin sealed somewhere cool and dark — a store room floor, a low cupboard, anywhere away from the kitchen's heat. Refill the small bottle as needed. The tin then gets opened once a week instead of fourteen times, and the oil at the bottom of it is as good as the oil at the top was.
Sediment and solidifying are not spoilage
Two things worry people that should not.
A layer of fine sediment at the bottom is normal in oil that has been settled and simply filtered rather than industrially polished. It is seed matter. You can pour around it or stir it in; either is fine.
Coconut oil turns solid and white below roughly 24°C. In Bengaluru in December it will set in the bottle; in Mangaluru it rarely will. Stand the bottle in warm water for a few minutes and it melts clear again, with nothing lost. Repeated melting and setting does no harm.
How to tell if oil has actually turned
Smell is the reliable test. Fresh cold pressed oil smells strongly of its seed — groundnut smells like groundnut, niger smells green and grassy. Oil that has gone rancid smells flat, waxy, or faintly of old paint and putty.
Taste confirms it. A rancid oil is bitter at the back of the throat in a way that fresh oil is not. A sticky, varnish-like film around the cap is another sign: that is polymerised oil, and it means the bottle has been sitting open and warm.
If oil has turned, do not cook with it. It tastes bad, and it carries that taste into everything you fry in it.
How long does a bottle keep?
Unopened and stored cool and dark, our oils hold their character comfortably. Once opened, use within three to six months. That is the number we print, and it is not conservatism for its own sake — it is what small-batch, unbleached, undeodorised oil honestly does. Read how we press and filter it if you want to know why.
Buy the size you will finish in that window. A household of three cooking daily will get through 5 L of groundnut oil in about that time; two people who mostly use it for tadka should be buying 500 ml or 1 L, not a tin. Sizes for every oil are on the full range page.
Frequently asked questions
Can I store cold pressed oil in the fridge?
Yes, and it helps for oils you use slowly. Clouding or thickening in the cold is normal and reverses at room temperature.
Is the sediment at the bottom a sign of adulteration?
No — it is the opposite. Settled seed matter is what unfiltered-to-death, unbleached oil looks like. If you want to check purity properly, there are five home tests here.
Should I keep oil in a steel container or a plastic bottle?
Food-grade steel and dark glass are both good, because they keep light out. If you decant, a steel can or an opaque bottle beats a clear one.
My 15 L tin will take me eight months to finish. Is that a problem?
It is longer than we would recommend for one opened container. Keep the tin sealed and cool, decant into a small working bottle, and consider whether two 5 L cans bought a few months apart would suit you better.