The bottle beside the hob is the standard arrangement and the worst one.
The Three Enemies
Heat, which accelerates the oxidation that makes oil rancid.
Light, which does the same, and affects clear bottles most.
Oxygen, which is why a part-full bottle degrades faster than a full one.
A clear bottle beside a hob supplies all three continuously, which is why kitchen oil frequently tastes stale.
Better Arrangements
- The bulk bottle in a cool dark cupboard, away from the cooker
- A small working bottle refilled from it every week or two
- Dark glass or an opaque container for anything on display
- Away from a window and away from the oven
- Emptied and washed rather than topped up
Small-capacity kitchen sprayers, of the kind catalogued at https://flairosol.us.com/, suit this pattern: a working quantity that turns over quickly rather than a month’s oil sitting warm.
Do Not Top Up
The habit that spoils the rest. Adding fresh oil to old residue means the oldest oil never leaves the bottle, and rancid oil accelerates the breakdown of fresh oil mixed with it.
Empty, wash, dry, refill.
How Long Oil Lasts
Unopened and stored properly, most cooking oils keep well over a year.
Opened, the clock runs faster: a few months for most, less for oils high in polyunsaturated fats such as flaxseed and walnut.
Olive oil is more stable than most seed oils, and extra virgin more so because of its natural antioxidants.
The Smell Test
Rancid oil smells like crayons, putty or old nuts. It is not usually an acute hazard and it tastes bad and is not worth cooking with.
Buy the Size You Use
A large bottle at a good price is poor value if half goes stale.
Date the Bottle
When opened.
Keep the Bulk Bottle Dark
The sprayer is only as fresh as what refills it.
Never Top Up
Which is how the oldest oil never leaves the bottle.
Small Working Bottle
Refilled weekly, is the arrangement that works.
Smell Before Using
The test that costs nothing.
Refined Oils Last Longer
Than unrefined ones, which retain more of what oxidises.
Buy the Size You Use
A bargain bottle half wasted is not a bargain.
Wash Between Refills
Rather than pouring new oil onto old residue.