E-liquid is more robust than people expect, but it is not indefinite. Left in the wrong place it darkens, the flavour dulls and the nicotine slowly loses its edge. None of that is dangerous, it is simply a waste of a bottle you paid for. A few small habits will keep everything you own tasting as it should.

What actually spoils e-liquid

Three things do the damage, and all three are easy to avoid.

• Light. Ultraviolet light breaks down both nicotine and flavour compounds. This is the main reason bottles are made of dark plastic or coloured glass in the first place.
• Heat. Warmth speeds up every chemical reaction in the bottle, including the ones you do not want. A liquid left somewhere hot ages far quicker than one kept cool.
• Air. Oxygen slowly oxidises nicotine, which is what turns a pale liquid amber or brown over time. A cap left loose lets this happen much faster.

Darkening on its own is not a sign the liquid has gone off. A perfectly good bottle will deepen in colour over months. It is a change in smell or a noticeably flat, muted taste that tells you it is past its best.

Step 1: Pick the right spot

A drawer, a cupboard or a box that stays cool and dark is ideal. Room temperature is fine. What you are avoiding is a windowsill, the top of a radiator, the dashboard or parcel shelf of a car, and anywhere that gets direct sun for part of the day.

Cars are the worst offender by a distance. A closed car in summer gets far hotter than most people realise, and a bottle left in one for an afternoon will have aged more than it would in months in a cupboard. Cold is much gentler on e-liquid than heat, though very cold liquid thickens and needs to warm up before it wicks properly, which our piece on winter, weather and heat goes into.

Step 2: Keep the caps tight and the bottles upright

Screw caps down properly every time. It limits how much air gets in and it stops leaks, which matters more than it sounds when a bottle is sharing a bag with your keys.

Store bottles standing up. Lying on their side puts constant pressure on the seal, and over weeks that is how you find a sticky patch at the bottom of a drawer. Upright also makes it obvious at a glance how much is left.

Step 3: Buy at a pace that suits you

Unopened e-liquid generally keeps well for around two years from manufacture, and most bottles carry a best before date. Once opened, aim to finish it within a couple of months for the best flavour, though it will remain perfectly usable well beyond that.

The practical advice is to stock up on the flavours you know you get through and buy single bottles of anything you are trying for the first time. A cupboard of half-finished experiments is how most people end up with liquid past its best.

Step 4: Treat nicotine shots and shortfills with extra care

Nicotine shots are nicotine in a more concentrated form, so keep them well out of reach of children and pets, and store them separately from your everyday bottles so they do not get picked up by mistake.

Once you have mixed a shortfill, it behaves like any other nicotine liquid and follows the same rules. Give it a shake before each fill if it has been sitting for a while.

Step 5: Keep them somewhere sensible when you travel

Bottles that live in a bag get warm, get knocked about and get left in places you would not choose. A little planning avoids most of it.

Carry the bottle you are actually using and leave the rest at home. Stand it upright in a side pocket rather than loose at the bottom of a bag where it will be sat on. If you are flying, e-liquid goes in your hand luggage in the clear liquids bag, and cabin pressure changes mean a partly full bottle can weep, so wrap it in a freezer bag before you pack it.

Hotel rooms are usually fine. What is not fine is leaving a bottle on a sunny balcony table or in a hire car for the day, which brings you straight back to heat and light.

Step 6: Label anything you have decanted

If you keep a small bottle topped up from a bigger one, or you have mixed a shortfill, write the strength and the date on it. Unlabelled bottles are how people end up vaping something far stronger or weaker than they meant to, and how a nicotine-free liquid gets confused with a 20mg one.

A strip of masking tape and a biro is enough. Note the flavour, the nicotine strength and the date you mixed or decanted it. Your future self will be grateful, and so will anyone else in the house.

How to tell a bottle has gone off

Trust your nose first. Open the cap and smell it. Fresh e-liquid smells like the flavour on the label. A bottle past its best smells faintly chemical, or of nothing much at all.

After that, look at it. Deep browning well beyond where it started, or anything separated or cloudy that a shake will not resolve, is a reasonable point to stop. And if it simply tastes flat compared with a fresh bottle of the same thing, that is answer enough. There is no benefit to persevering with a liquid you are not enjoying.

The short version

• Cool, dark and dry, so a drawer or cupboard rather than a windowsill.
• Never leave bottles in a car.
• Caps tight, bottles upright.
• Nicotine shots stored separately and well out of reach.
• Travel with one bottle, upright, bagged if you are flying.
• Label anything decanted or mixed with flavour, strength and date.
• Open bottles are best within a couple of months, unopened keep for around two years.
• If it smells or tastes wrong, replace it.

Look after them and your bottles will taste on the last fill much as they did on the first. Our e-liquid collection and 10ml range cover the everyday flavours, and we are rated 4.8 out of 5 by over 4,800 UK customers, so if you are not sure whether a bottle is still good, bring it in and an adviser will take a look.