Why very hot weather is bad news for wine
Looks positively glorious doesn't it? Beautiful clear skies, sunshine and heat, surely the perfect weather for wine grapes? But is it? Temperatures in Continental Europe in summer 2017 have been regularly above 40° Celsius; the continental climate is known for being extreme, with very hot summers, but this year it seems that it is hotter than ever. The heat wave, nicknamed Lucifer, is wreaking havoc on many crops including grapes destined for wine. You might think that wine grapes benefit from as much sunshine as possible but when is hot too hot for the grapes and what impact does hot weather have on the wine produced?
Effects of hot weather on grapes
In order to produce decent wine, grapes need sunshine and warmth to ripen (to varying degrees depending on the style of wine). As grapes ripen the level of sugar within them rises due to photosynthesis; the level of sugar at harvest is one crucial element in the sweetness but also in the quality of the resulting wine.
At the time of harvest if sugars are too high the wine will be high in alcohol, taste of cooked fruits, even taste jammy, and that can make the wine unbalanced. And as regular readers of my blog will know balance is crucial for good quality wine.
Wine characteristics resulting from excessive heat
The simple laws of supply and demand therefore suggest that wine prices could increase for 2017 vintage wines. This is not welcome news I know when we are already seeing wine prices increase mainly as a result of exchange rate movements post the Brexit referendum.
What winemakers can do to mitigate the effects of a heatwave
All is not lost. To combat the problems of too much sun, heat and drought there are things that can be done in the vineyard and in the winery such as
- providing a physical shade over the vines, using bush training for the vines or trimming leaves in such a way as to maximise shade for the grapes
- irrigating, though many areas are restricted from irrigation by the wine classification regulations or even by local government regulations
- crop thinning i.e. removal of the unhealthy fruit which helps the vine divert its resources to the remaining grapes producing more concentrated flavours although this process can speed up ripening further
- using organic and biodynamic principles as many believe these make vines more resistant to drought and excessive heat, though this is obviously not an instant remedy
- bringing forward the date of the harvest. This has already happened in some areas of Italy such as Sicily with the harvest in 2017 starting three weeks earlier than ever before
- harvesting as quickly as possible and at night to take advantage of cooler temperatures
- keeping the winery cool to prevent fermentation progressing too quickly
- adding acidity to the wine though the best producers who respect 'terroir' will not use this option or will only do this as a last resort and in some wine classifications it is not even permitted
It is also important to stress that mesoclimate is the key rather than the over-riding climate of the region - vineyards in excessively hot areas may see lower temperatures if they are higher up, on hillsides, north-facing, in windy areas or near large expanses of water. There's another reason to get to know more about individual wineries and their vineyards.
Is the 2017 vintage a write-off?
The bad news is that there is likely to be some poor quality 2017 wine affected by Lucifer - and we are likely to have to pay more for our wine. It's enough to drive you to pour a large glass of wine - chilled naturally...
The good news however is that not all 2017 wine will be a write-off. Stick to cool climate wines completely if you want to be sure; you can also look at wines from smaller but experienced wineries which will be doing what they can to avoid the problems caused by the hot weather - or trust in your wine merchant to seek out the best wines for you.
Lindsay Cornelissen DipWSET is passionate about good quality wine and set up her online wine business, Wines With Attitude, to share that passion with other wine lovers.
Sign up to our newsletter for our blogs, notification of new wines and of subscriber-only sales.