Why very hot weather is bad news for wine


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.

The sun brings another danger as grapes, like humans, can suffer from sunburn. It is thought that burnt grapes can also affect the fruit characters of a wine and so they are generally discarded, at least by the better winemakers.

Excessive heat and drought especially in late summer at peak ripening time is catastrophic as they effectively shut down the grape, causing photosynthesis and therefore ripening to stop. The temperature at which this is believed to happen is 'only' about 32° Celsius so not excessive for some wine-producing countries in the height of summer. Bitter flavours can develop in grapes suffering from heat stress, grapes are likely to be smaller and therefore yields lower and the vine's leaves which normally provide shade can drop off.

However it is the fall in acidity that is arguably the biggest issue for wine produced in a heat wave vintage. As sugar rises acidity in the grapes falls - see my blog on acidity in wine. Even in years with a more usual weather pattern wine producers constantly measure acidity levels to make sure they do not fall too much. In excessive temperatures the need to monitor acidity is crucial as a drop is much more likely and more acute. Grapes that are low in acidity will produce wines that are heavy, jammy, lacking in freshness and flat in taste or 'flabby' in wine terminology. To make sure that wines are fresh, fruity perfumed and elegant, it is imperative to harvest before acidity has fallen too much.

It is all a fine balancing act for wine producers especially as it is believed that grapes are affected more than any other fruit by differences in climate.


Wine characteristics resulting from excessive heat

The wines that are produced during very hot weather risk being high in alcohol, flat, bitter, jammy and unbalanced, so not too many positive features. In addition they are unlikely to be long-lived.

To add insult to injury - or perhaps with the characteristics mentioned above it is a blessing - there is likely to be less wine produced. In many areas affected by Lucifer the 2017 harvest is expected to be down substantially especially in those areas affected earlier in the year by spring frosts and / or a long period of drought. Spain for example has reported that in some regions yields are down by as much as 50%.

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

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.


© Wines With Attitude Limited, www.wineswithattitude.co.uk

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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.

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