Madeira breaks all the rules. It’s the only wine that’s deliberately oxidised during production; it’s the only wine that improves with heat; and, even if left opened, it’s the only wine that gets better and better with age almost without limit. And its discovery was accidental.
The Portuguese island of Madeira, lying in the Atlantic 480 miles south-west of Lisbon, was a vital re-stocking port on the trade routes to East and West. Their wines were fortified with brandy to preserve them during the long sea voyages but it was discovered that the heat of the ship’s hold dramatically improved these wines, produced from highly acidic indigenous grapes, making them richer, more complex, and capable of ageing almost indefinitely. The wine was found to be even better on the return journey.
Later eighteenth-century winemakers replicated the same process on land by leaving the barrels out in the searing summer sun. This method, the Canteiro process, is still used today. After fortification with grape spirit, the casks are left in lodges where the temperature can reach more than 30C, with 90 per cent humidity, during which around 4-5 per cent is lost by evaporation.