Winemakers to blame for rising alcohols in California

Different viticulture techniques and later picking times – rather than climate change – have caused alcohol levels in Californian wines to rise, according to Christopher Howell, winemaker and general manager at Cain vineyard and winery.

Speaking at the Napa Valley Climate Seminar at Vinexpo in Bordeaux yesterday and referring to data collected since 1991 in Napa and Sonoma, Howell (left) said: “Temperatures have changed but nothing like as dramatically as the [grape] sugars… just over a period of two decades we have seen a huge increase in sugars and our claim is that most of this is due to fashion and winemaker choice.”

The overriding influence on the surge in sugar levels – and hence eventual abv – Howell ascribed to harvest times. “We are picking later than we used to, even if we have more warmth,” he stated.

He also explained that altered approaches to viticulture in the Napa Valley had affected alcohol levels, such as the use of different rootstocks, increasing the planting density and changing the trellising techniques. “Historically Napa looked like a big jungle, what was known as the Californian sprawl – visualise a teenager on the sofa – and so the fruit was buried in the leaves and it didn’t ripen properly,” he said.

Today however, more efficient training techniques such as the vertical trellis with shoot-positioning system (VSP) which, when combined with closely spaced vines, are producing grapes with a higher sugar content than 15 to 20 years ago.

As for climate change in the region, he pointed out that records over the last 15 years showed a slight average temperature increase but more dramatic changes when it came to nightime and morning temperatures.

“What we are finding in Napa is that the afternoon temperatures are going up but not as fast as the morning cold temperatures… it is the low temperature that is rising,” he explained.

He added: “Afternoon temperatures are not rising as much and this seems to be especially true as you go up the valley, and high up, summertime temperatures have not gone up at all.”

However, Cain stressed: “Reporting this is politically sensitive and we don’t want to be seen as climate change deniers.”

Turning the discussion towards future changes to mitigate the influence of rising nightime and morning temperatures, he said: “If we pick earlier you can get in trouble, you just get vegetables with lower alcohol, so we [Napa Valley] will always be picking at higher sugar levels than Bordeaux.”

He identified his concern surrounding the changing climate, saying: “Colder nights preserve the acidity but with warmer nights the acidity is metabolised in the grape berry and so warmer nights means there is less acidity – and so I would expect the pH to go up and the acidity to drop.”

Nevertheless, he suggested two possible solutions. “We want to train our fruit a little higher so it doesn’t get as much warmth from ground and we want to have a little bit more leaf area to provide some shade [for the grapes] – I think the best condition is dappled sunlight.”

Concluding, Howell turned his attention to the demands of the market and commented on the influence of consumer taste. “I don’t think the US market has reacted against the taste of the wines and in fact they like them.”

“If you look at harvest times from 1985 to 2005 in almost every case we are waiting longer to pick our grapes. We may not need to wait as long and we have been waiting dramatically longer, especially if we remember how our vineyard has changed.”

Then, he asked rhetorically: “But can I train them [the US consumer] to drink wines with lower alcohol, higher acidity, and perhaps a herbaceous note?”

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Patrick Schmitt, 22.06.2011