How long does port keep after opening?

The Instituto dos Vinhos do Douro e do Porto gives a guideline period per style, from 1 to 2 days for vintage to 3 to 4 weeks for tawny.

The institute also gives 8 to 10 days for ruby and ruby reserve, 8 to 10 days for modern white port and 15 to 20 days for traditional white port. The IVDP itself notes that these are guidelines and that the storage place counts.

Count those periods from the moment you open the bottle, not from the purchase.

Tawny ages for years in wooden casks and has already seen a lot of oxygen there; vintage ages in the bottle.

The IVDP describes tawny with an indication of age as port that ages in oak casks, and colheita as a port that stays in cask for at least seven years. Vintage is bottled two to three years after the harvest and then develops for 10 to 50 years in the bottle.

An opened bottle of tawny therefore changes less quickly than a vintage, which only comes into contact with air when it is opened.

Keeping it cool and dark extends the life of an opened bottle of port.

The IVDP points out that the periods given are guidelines and that it matters where the bottle is kept. A fridge is a practical place for white port and for tawny. Do take red port out for a while before you pour, though, because the serving temperature the institute gives is higher.

In any case, put the cork or cap straight back on.

According to the IVDP, vintage port continues to develop for 10 to 50 years in the bottle after bottling.

For that style, keeping it is therefore worthwhile: store the bottle cool, dark and undisturbed. According to the institute, crusted port must spend at least three years in the bottle before it is sold, and late bottled vintage ages four to six years in wood.

It is different for the wood-aged styles: they have already done their ageing in the cask.

According to the IVDP, port is between 19 and 22 per cent alcohol by volume.

That is because fermentation is stopped with grape spirit. The institute specifies one part grape spirit to four parts must; the sugar that has not yet fermented stays in the wine.

That higher alcohol content makes port more stable than ordinary wine, but it does not keep indefinitely once opened. The IVDP's guideline periods still apply.