Premature oxidation was first discovered in white wines that lost their fruit aromas more quickly than anticipated, developing instead heavier smells such as honey and beeswax, while their colour faded quickly to russet and brown.

Signs of ageing occur in all wines over time, but the accelerated version seen with premox is detrimental when it affects wines that are sold as having great ageing potential – hence the focus on white Burgundy initially, as the expectation for ageing is so high for those wines, so the corresponding disappointment was inevitably acute.

In red wines, the warning signs come with prune, fig and other dried fruit aromas – these are positively sought in specific types of wines such as Amarone or Port, but would be a likely indication in a young dry red that the wine will not age as it should. Some styles of dry reds – such as still Douro reds and some Languedoc wines – naturally have dried fruit aromas when young, and are made from grapes with high natural acidity and resistance to heat. But the danger comes with other grape varieties that are more susceptible to fluctuations in temperature.

The focus of the Bordeaux research so far has been Merlot, as that is the most widely planted variety in Bordeaux, and it suffers in very hot years, but any heat-sensitive grapes are at risk.

Written by Jane Anson