Q: How long does a wine keep once opened?
A: Once you expose wine to air, it accelerates the natural process of ageing. This benefits some young, tannic red wines, which is why we decant them, or swirl them around in our glasses.
But most wines begin to deteriorate within a few hours of opening, so we need to protect any leftovers from oxygen. The majority of wine comes in 75cl bottles and a lot of the time we cannot finish them at one sitting; this is why bag-in-box can be such a useful (and green) alternative.
You can slow down the process of oxygenation by chilling your wine — red and white. If you keep an empty half-bottle and cork handy, you can pour your leftovers into this, reseal it and keep it in the fridge for up to a week. Lighter wines, including whites and rosés, deteriorate faster, tannic reds and fortified wines survive the longest.
There are various gadgets that suck air out of a bottle, or wine preserver canisters containing argon or nitrogen gas that you spray into the bottle, replacing the oxygen. I am lucky enough to have a Coravin, an ingenious device that allows you to extract a glass of wine through the cork using a very thin needle, without opening the bottle, and replaces it with Argon gas. This means you can help yourself to as much or as little wine and keep the remainder indefinitely.
The downsides are that it doesn’t work on screw-caps (although there is an alternative that does), or on plastic corks. The biggest drawback, however, is the price — expect to pay more than €100 for the pivot, which works for four weeks, or in excess of €200 for the original device, that keeps wine for months, or even years.
Most of the time I put any unfinished wine in the fridge overnight and drink it the following evening with a minor loss of flavour. This includes sparkling wine, where I use a special stopper to prevent the fizz escaping.