Oxygen has a complicated relationship with wine. Sometimes it’s a friend, as in our . Controlled, it can be advantageous at certain stages of winemaking. But if you open a bottle and leave some wine undrunk, oxygen in the air becomes an enemy – in a matter of minutes (for an old, mature wine) or days (for a young, fruity wine).
In a series of chemical reactions with components of the wine, it ‘oxidises’ the wine. The colour turns towards orange and brown, and the wine begins to taste flatter, less fruity, losing varietal aromas and taking on dull, baked-apple, nutty flavours.
It may taste more tannic (bitter and astringent) because fruitiness no longer distracts from the bitterness. At some point it turns vinegary.
Several devices claim to protect opened wine from oxygen in the air. Each of the seven devices tested by our experts aimed to work on one of four principles:
We tasted after three, seven and 14 days. Had we left the bottles untouched for 14 days, it could be that some of the devices might have preserved the wines for longer.
After completing the original two-week test of still wine preservers, our experts Charles Metcalfe and Kathryn McWhirter kept the two most successful samples for a further six weeks in a cool, dark place before testing them again.
Only logged-in Which? members can view the wine preservers test results below. If you're not yet a member, you'll see an alphabetically ordered list of the wine preservers we tested. now to get instant access to our test scores and Best Buy recommendation below.
All prices correct as of October 2020.
Replacement capsules: £16 for a pack of two
Replacement screw caps: £30 for a pack of six
Replacement needles: £63.95 for a pack of three
The Coravin works by replacing wine drawn from the bottle with inert gas. It fits onto an unopened bottle of cork-sealed wine. (We did not test the screw cap version).
With gentle hand pressure, a thin, hollow but sturdy needle passes down through the cork and into the wine. As you tip the bottle over the glass and press a switch, wine pours out of a spout, driven by pressurised (inert) argon gas, which then remains to fill the bottle space.
When you remove the device, the hole in the cork closes up. There are caps to use with screw top wines.
A capsule of gas lasts for roughly four bottles and a needle needs replacing when the non-stick coating wears off. There are more expensive Coravin models and accessories available.
The makers of Coravin claim that if it’s used correctly, oxygen never touches the wine in the bottle. The wine continues, therefore, to evolve in the same way as if the bottle had remained untouched. The wine will stay protected for weeks, months and even years. Screw top wines will keep for up to three months.
A sturdy stopper that its maker claims ‘preserves freshness and flavour of unfinished wines’. Press the large button on top to create a vacuum.
This smart-looking stopper has a silicone seal that expands to fit the bottle when you press down on the flat top. The manufacturer claims the seal makes a perfect fit to preserve the flavour and prevent leaks and drips.
A light, aluminium canister filled with a mix of inert gases nitrogen, carbon dioxide and argon. A recommended one-second squirt plus three short ones are delivered via a straw held against the inner side of the bottle. The inert gas, heavier than air, should form a barrier over the wine to protect it from oxygen.
The manufacturer claims it protects the freshness and flavour of wine for days, weeks, months and years. It will not strip out aromatic components of the wine (unlike vacuum pumps, says the manufacturer). A canister is good for approximately 120 uses.
A silicone stopper with a built-in active carbon filter. The manufacturer claims the filter ‘stops the oxidation process and preserves all the organoleptic properties of the wine’ (ie its taste) for up to 10 days.
‘Oxygen is no more associated to the wine and is neither producing acetic acid nor damaging the wine. Unpleasant smell and vinegar taste wine are thus avoided.’
The device is said to remain active for up to five years and 1,000 bottles.
‘Totally efficient with 99 per cent of wines,’ says the leaflet.
An airtight bottle stopper. Combines a pourer and a valve attachable to a vacuum pump to extract the air from the bottle after pouring. Manufacturer claims it slows down the oxidation process.
Replacement cartridges: £14.99 for a pack of two
Sleek, futuristic. Into the bottom of the stopper screws a cartridge (of an undisclosed food-grade material) that ‘rapidly absorbs oxygen’.
The stopper is topped with a ‘halo’ of battery-operated light, green or red showing either that it’s working or that a new cartridge is needed.
When not in a wine bottle, the cartridge must be urgently inserted into a special sealed holder, otherwise the oxygen in the room quickly exhausts the cartridge.
The makers of the Zos Halo Wine Preserver claim it ‘eliminates 100% of the oxygen that spoils your wine (…) in less than 30 minutes (…) saves the wine for up to 60 days (…) Every glass will taste as fresh as if the wine has just been opened. Easy to use and works on all types of wine. (…) Each cartridge lasts up to 15 bottles.’
Can also be used on sparkling wine.
How fast an opened wine oxidises depends on lots of things, grape variety, oak, acidity, age.
Broadly, big, firm red wine is somewhat protected from oxidation by its tannin and might therefore keep better than light red or white wine.
However, many young whites and rosés are bottled with an almost imperceptible touch of carbon dioxide dissolved in them, to add freshness, and this helps protect them from oxidation.
You are also more likely to keep white or rosé wine in the fridge, and like other things, wines at cooler temperatures spoil more slowly.
Past experience with vacuuming wine preservers has taught our experts these are not ideal for fresh, young white and rosé wines.
That’s because, as mentioned previously, they’re bottled deliberately infused with a tiny refreshing and protective prickle of carbon dioxide.
If you try pumping a white wine, you may see the bubbles being pulled out of solution.
When setting up the test, one bottle was simply re-sealed with its cork. After three days our experts found this bottle ‘flatter’ and ‘less fruity’ but not oxidised. They gave it 6/10.
By the seventh day, it was down to 3/10 and showed some oxidation.
By day 14 it had ‘almost no fruit’ and was ‘oxidised, acetic, not nice, cooking wine.’
At each opening session, our experts also opened a new, fresh bottle for comparison with the test samples.
Our experts were:
Charles Metcalfe, wine taster and co-chair of the International Wine Challenge (IWC)
Kathryn McWhirter, wine taster, author and translator