Which grapes stand up to heat?

The worry with a warming climate is not just that wine regions get hotter, but that we get used to what heat does to wine: riper, softer, more alcoholic, and eventually baked and jammy. In Do hot vintages really taste riper? I found that critics' language does shift in hot years. Here I ask the more practical question: which wines actually get worse, and which get better?

How I tested it

The same way as in Are vintage charts right?: each wine is compared only with the same producer, the same grape and the same critic in other vintages, so differences in who gets reviewed or what they charge drop out. Each vintage's growing season is then measured against that region's normal, from the ERA5-Land climate record. That covers 45,104 reviews from 4,944 producers in 43 regions, vintages 1997 to 2016. Scores are Wine Enthusiast points out of 100.

First, it depends where

The clearest result is not about grapes at all. In a cool region, a season warmer than usual makes better wine: the same producers score about +0.21 points higher for each extra degree. In a hot region, a warmer season does nothing for the wine at all, −0.01 points per degree. Past a normal season of about 18.8°C, extra warmth stops paying.

The shape is the story. In cool places, every step warmer helps, at least up to 1.5°C above normal; beyond that there are too few seasons to tell. In warm places, scores peak in a season just above normal, then slide: the hottest years come in at −0.11 points, and that is where the heat words appear most, in 15.1% of reviews against about 6% in normal years. Allowing for the general effect of warmth, each degree beyond +1°C costs warm regions about −0.31 points. That sounds small on a 100-point scale, but with the same reviews and the same method, a celebrated great vintage adds only about +0.33 (see Are vintage charts right?). One degree too hot undoes a great year.

Then, the grape

Grape and place are tangled together: Gamay is almost all Beaujolais, a cool region, and most Malbec is from hot Mendoza. So for each grape I first take out the effect of how warm its regions normally are, then ask how it responds to a warmer season in a region with a normal season of 17°C. Even then the grapes differ, more than chance would explain.

The grapes that welcome warmth are mostly late-ripening, thick-skinned reds. Cabernet Sauvignon is the clearest case, +0.20 points per degree on 3,434 reviews; Tempranillo (+0.36), Malbec (+0.32) and Merlot (+0.14) point the same way. Cabernet in particular can struggle to ripen fully in a cool year. Sauvignon Blanc, at +0.21, is the surprise among the whites. Gamay comes out top, but almost all of it is from Beaujolais, so that is really one region's result.

The grapes that get nothing from heat include some of the most prized. Riesling and Nebbiolo are flat, at −0.01 and −0.01, and Gewürztraminer (−0.25) and Sangiovese (−0.35) lean negative, Sangiovese mostly because of Brunello's poor 2003: without it, Sangiovese is close to flat. Riesling is telling: it grows in some of the coolest regions here, which elsewhere gain from a warm year, yet it does not. Its appeal is acidity and aroma, and heat takes both.

Pinot Noir and Chardonnay sit in between, +0.09 and +0.07: a warm year is no disaster, but no great gain either. Syrah, often called a heat-lover, gains nothing (+0.03): it ripens easily, so extra warmth adds little.

What the critics say

Scores are one thing; how the wine tastes is another. Across all 45,104 reviews, the share describing a wine as jammy, baked, raisined or hot rises by about +0.9 percentage points for every degree, from a base of 7.1%: the words turn up about 13% more often per degree, or about 25% more often in a season 2°C warmer than normal. Critics use them sparingly, because “baked” or “raisined” is close to calling a wine faulty, so even a small shift matters. For some grapes it rises much faster.

Nebbiolo stands out. Its scores do not move in hot years, but critics describe it very differently: heat words rise by +4.5 points per degree, the most of any grape. A hot Barolo still scores well; it just reads as a riper, warmer wine. Pinot Noir and Syrah shift the same way, more gently. At the other end, Malbec, Tempranillo and Zinfandel are described with heat words in about a quarter of reviews whatever the year: their usual style is already ripe, so a hot season changes little.

What it means if you are buying

• In a famously hot year, look to cool places. Burgundy, Champagne, Alsace or Willamette gain from the warmth; regions that are already hot gain nothing on average, and their hottest years cost them.
• Cabernet, Tempranillo and Malbec cope best with warm years, so a warm vintage is less of a risk for them.
• Be more careful with Riesling, Sangiovese and Gewürztraminer in hot years. They get nothing from heat, and their appeal, freshness and aroma, is what heat takes away.
• For Nebbiolo, expect a change of style, not of quality. A hot Barolo is riper and warmer, not worse on the critics' scale; whether you like that is up to you.
• As the climate warms, more regions will move past the point where warmth helps. That is why the cool places in hot regions are worth knowing now.

What it doesn't show

• Scores on release, from one publication. Wine Enthusiast reviews, mostly of young wine. Hot-year wines can show well young and age less gracefully, which this would not catch.
• The hottest seasons are few. Only a handful of region-vintages ran more than 1.5°C above normal, so the far end of the first chart is uncertain.
• Grape and place are not fully separable. Some grapes come from very few regions; Gamay is effectively Beaujolais and Nebbiolo effectively Piedmont. And producers adapt, picking earlier in hot years, which softens the effect in the glass.
• Region-wide climate. Each region's season is one average; a cool slope and a hot valley floor in the same region share the same number.

Conclusion

A warm year is not bad news everywhere. In cool regions it still makes better wine, and for late-ripening reds like Cabernet and Tempranillo it usually helps. But the benefit runs out: in regions that are already warm, extra heat adds nothing, and the hottest seasons cost points and bring the baked, jammy language with them. Tempranillo, Malbec, Sauvignon Blanc, Cabernet Sauvignon and Merlot handle warmth best; Riesling, Sangiovese and Gewürztraminer least. As more of the wine world crosses that line, the question to ask of a region is not just how good its best years are, but how warm its normal years already are.