Tuesday, February 8, 2011

What Makes Napa Valley Cool

At the end of last week, the Napa Valley Vintners (NVV – the trade association responsible for promoting and protecting the Napa Valley appellation) released a climate study: Climate and Phenology in Napa Valley: A Compilation and Analysis of Historical Data.

Why this study in Napa? Back in 2006, a French researcher predicted that Napa Valley would soon become too warm to grow grapes for fine wine. We can imagine the concern (panic?) that this prediction caused in Napa. But many of the Napa growers didn’t believe the prediction. Their intuition was that Napa Valley wasn’t getting appreciably warmer.

NVV did what any trade association would do with such a damning prediction: it commissioned its own research. The researchers are done and the report is in. The key findings?
  • Napa Valley has gotten warmer, about 1 to 2 degrees Fahrenheit, over several decades.
  • Warming has occurred mainly in winter, spring, and summer, and more during nighttime than during daytime.
  • Napa Valley benefits from a great moderating effect on higher temperatures: the Humboldt Current from the Pacific Ocean. Warmer air from the interior of the Valley acts as a vacuum, pulling the cool air from the Humboldt Current into the Napa Valley; in fact, the study says that the warmer the interior Valley is, the further into the Valley the cooling air from the Pacific is drawn.  (Hmmm...global warming really does suck.)
  • The Humboldt Current is so effective at moderating higher temperatures that, “Globally, the years 1998, 2005, 2006 and now 2010 were the warmest years on record, but they were some of the coolest for the Napa Valley.”
  • There is little evidence that the growing season for grapevines has changed substantially.
But what I find interesting as well is that,
Analysis of comprehensive countywide crush reports from 1990 onward demonstrated that there is a strong trend of increasing Brix at harvest over time. [Brix is a measure of the amount of sugar in the grape. The higher the Brix, the more the sugar. Sugar converts to alcohol during fermentation. More sugar, higher alcohol.] The most dramatic increase was for Zinfandel, from close to 20 to above 26 over the 18-year record. Sauvignon Blanc has seen the least change, an increase of about 1 degree Brix. Cabernet has increased from about 23 to 26 degrees. There is also a trend across all varieties except Sauvignon Blanc for decreased yields over time, most dramatically for Zinfandel (from close to 6 to about 2.5 tons/acre) and Merlot. Chardonnay yields have declined only slightly, holding steady near 4 tons/acre. Sauvignon Blanc has the highest yields of all varieties studied, and has been increasing over time…
As a general pattern, Brix increases with later harvest dates. However, recent harvests (last 8 years) have been very high in Brix, and not anomalously late. Generally, the trend has been toward later harvest dates, though it varies by variety (Pinot earlier; Cab Franc, Cab Sauvignon and Merlot about 2-3 weeks later over 30+ year period). Recent Brix increase is believed to be due to stylistic and winemaking preferences, but needs further investigation [emphasis added].
I've read elsewhere that global warming is to blame for higher alcohol levels in wine.  As I understand this, these researchers say that higher alcohol levels in Napa Valley wines are not due to global warming. Rather, higher alcohol levels are due to what the winemakers are doing, deliberately, in the vineyard to get riper grapes.

Fully ripe grapes give winemakers the means to make high-alcohol, highly extracted, fruit bomb wines. For many years, that’s what got the high ratings. Oh, Parker!

Winemakers followed that fashion. The good news is that they can reverse it too...if that's what consumers want.

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  1. This is so interesting. I thought I heard somewhere that we, as consumers, were trending away from 'big' wines, but maybe I just read that in relation to those big Chardonnays.

  2. I've read the same thing, Holly, especially about Australia. If the pendulum is beginning to swing away from high alcohol fruit bombs, I'm just trying to push it a little more in that direction!