Californian heatwave: ‘Too soon to tell’ if yields affected

The Californian Wine Institute has said it is too soon to tell if last weekend’s heatwave across Napa will affect yields, but some winemakers are already claiming to have ‘dodged a bullet’.

Chardonnay grapes at Trefethen Vineyards in Napa

It comes after the San Francisco Chronicle reported that high temperatures across the Labor Day holiday weekend in Napa were shrivelling grapes before vineyards had had a chance to harvest them.

According to the US paper, temperatures at St Helena in the north of the region soared to more than 110 degree for three days in a row, with winey Crocker & Starr Wines estimating that some blocks had lost up to half of their crop as a result of water evaporating from the grape and shrivelling to raisins, while Hirsch Vineyards in Cazadero said yields could be down by 10% due to the excessive heat. It also expected to downgrade some of it wine for bulk, the San Francisco Chronicle reported.

However speaking to db today, Justin Knock MW, director of the Californian Wine Institute UK said it was too early to say what the effect of the unseasonably warm weather might have on yield expectations.

‘Too soon to tell’

“It’s going to be too early to say what the final impact on yields is going to be, as the impacts will be on a vineyard by vineyard basis,” he told db.

He pointed out that the harvest was still ongoing, with some vineyards already picked, making them unaffected. Those most badly affected were likely to be vineyards on the cusp of picking as grapes could overshoot quickly, leaving no opportunity for the vines to recover.

Knock argued that Pinot Noir and Chardonnay could be more affected than Cabernet, in part due to the focus of Napa’s Cabernet producers on quality and selection of the grapes, and Zinfandel, which can carry more richness.

“Ironically it could be the coolest sites most overtly affected – warmer sites may well have already harvested. Both the latter varieties are further away from harvest, particularly those in cooler sites, and have a little more time to recover,” he said.

Bryan Parker, winemaker at Federalist told db that although the vineyard was hit by temperatures of 113-114 degrees over the Labor Day weekend, overall the vines made it through the heat and the quality of the grapes was looking “excellent”.

“Because of the heat, we brought in one old vine dry farmed Zinfandel from Napa. We do see some raisining from this heat spike especially on Zinfandel but overall the vineyards made it through well. The quality looks excellent right now”, he told db.

He added that of the vineyards already picked, yields had been average or slightly lower, but Federalists was expecting Dry Creek to yield a “decent” crop of Merlot, Syrah and Cabernet Sauvignon, while the Mendocino Merlot, Cabernet Sauvignon, and Malbec were still several weeks away from picking.

Mitigated by winter rain

Furthermore, Knock pointed out that the heatwave of 1-2 September was likely to have been mitigated by rainfall early in the season, which had set up the soils well and helped to establish healthy canopies. This, he said, had led to expectation of a good sized crop, the first since 2014, and any comment on yield reduction should be set in that context.

“Excessive heat at the point of harvest is not ideal, but Californian wineries are as well placed as any to deal with these issues,” he added.

Jon Ruel of Trefethen Family Vinyards said the winery had been lucky to “dodge a bullet” at a sensitive time for the grapes, not only due to the winter rains that had broken last year’s drought but the significant 23% humidity which came along with the high temperatures at the start of September.

Picking Cabernet Franc at Trefethen Vineyards last week

”It was 108 degrees in the vineyard but there was significant humidity so it was not nearly as bad it could have been,” he said. He compared the temperatures favourably to 24 August 2010 when humidity sunk low as 10% (“desert conditions”) causing the vineyard to lose a significant portion of its Riesling in one day.

“We are quite excited about the quality of the 2017 vintage and we are expecting to get our target yields” he said.

He noted that the vineyard had also changed practises to better manage yields. This involved leaving more leaves on the vines to protect the grapes, modifying the trellis to manage the canopy and thinning the Merlot to one cluster to ensure hitting the yield.

“It is part of it being proactive, adapting, and irrigating and managing yields,” he said.

Matthew Crafton of Chateau Montelena in Calistoga said that while some sub-regions in warmed pockets of Napa might have been adversely affected, there has been little damage to the vines, with a low variation of around 10-15%.

He agreed it was necessary to take a more proactive approach and adapt to the conditions presented and embrace vintage variations that could produce interesting wines with dark fruit characteristics.

“If you adjust the winemaking and processes in the cellar then there are no major issues. But if you’re stuck in the mentality that the fruit has to be exactly the same as it is has been [every year], then yes, you will have problems, as it will be difficult to make that exact style of wine this year. 2017 will be more of a warm vintage like 2014, rather than a cooler 2009-style vintage,” he told db.