Not so fast, say three researchers of the University of California, Davis, and a collaborator with the Liquor Control Board of Ontario, Canada.
|Hang time vs. climate change|
In a 25-page paper for the latest issues of the Journal of Wine Economics, they conclude that higher sugars and consequently higher alcohol levels in the resulting wine are due less to climate change than the modern practice of letting grapes hang on the vine longer than in the past.
The paper - "Too Much of a Good Thing? Causes and Consequences of Increases in Sugar Content of California Wine Grapes" - is long on complicated mathematical formulas and precise detail but short on forthright conclusions and provocative interpretation. It's a study that begs for a sequel, and the authors indicate that more research is in order.
One solid conclusion they draw is that sugar content of wine grapes at harvest and alcohol levels in the finished wines have expanded hand in hand. Between 1980 and 2008, the sugar content of California wine grapes at harvest rose from an average 21.4 Brix to an average 23.3 Brix, a nine percent increase. In looking for a trend concerning alcohol content of wine, they turned to the Liquor Control Board of Ontario, Canada, which tests every wine it imports to the province. The board examines several characteristics of each wine, including alcohol level. In comparing alcohol figures from 1990 and 2000, the researchers found that the average alcohol percentage rose by .3 percent, with white wines showing a larger increase (.38 percent) than red wines (.25 percent). "This increase in alcohol percentage is consistent with an increase in the sugar content of the grapes used to make that wine of .55 degrees Brix, on average," the paper states.
The researchers also conclude firmly that the rise in sugar content and alcohol level can't be attributed to climate change. "Our data do not show a substantial rise in temperature between 1990 and 2007, as measured by the heat index," they state. "Our results imply that warming average temperatures in the growing season did not contribute substantially or significantly to the increase in sugar content of California's wine grapes during the almost 20-year period 1990-2008," the paper iterates later on.
If not global warming, what accounts for the increases in sugar and alcohol? Here, the paper speculates more than concludes. Cultural changes in viticulture could explain the increase, they suggest, noting that over the past two decades new kinds of rootstock and clones have been introduced to California. Denser vineyard plantings and new trellising systems also could be a factor. They don't say it, but the implication is that new vineyard practices help grapes more efficiently generate sugars. The fruit possibly accumulates plenty of sugar before it reaches ideal phenolic maturity, thus prompting winemakers to let it hang longer on the vine before picking than has been the custom.
"Still others claim that higher sugar at harvest is simply a style choice, with no underlying physiological reason to be found in the vineyard," write the authors. In other words, growers and vintners could be responding to a market that they see as preferring wines with ripe flavors and lower tannin, "attributes associated with grapes that are picked at higher degrees Brix."
In an email exchange, James Lapsley of the Department of Viticulture & Enology at the University of California, Davis, one of the four authors, says, "We are saying that sugar levels at harvest have gone up much faster than have temperatures, and thus the major point driving this must be a management decision." That decision could be motivated by one or more of several factors, from an aesthetic goal for the wine to the price for the fruit.
Beyond debunking the link between global warming and higher alcohol in wine, the paper scatters a few intriguing factoids among its findings, to wit:
- "In 1985, only 19 percent of California table wine carried a varietal label, but within 15 years, by 2000, varietally labeled wine accounted for 71 percent of all California table wine by volume." Who would have guessed that the change has been that quick and that reaching? Time for a backlash, perhaps, which could help explain the current rise in blended wines bearing proprietary names.
- Thirty years ago, more than half of California's wine-grape acreage was in the southern San Joaquin Valley. By 2008, however, the region was responsible for just a bit more than a third. During that span, total wine-grape acreage in California rose 59 percent, but in the San Joaquin Valley it grew by just 8.5 percent.
- By percentage, no wine-grape region in California has grown more impressively over the past three decades than the Sacramento/San Joaquin River Delta, where acreage expanded from 17,355 acres in 1981 to 49,558 acres in 2008, a jump of 185 percent. Other fast-growing regions are the North Coast counties, up 128 percent from 55,474 acres in 1981 to 87,726 acres in 2008, and the Central Coast, where the acreage has doubled, from 41,015 acres in 1981 to 82,600 acres in 2008.
- In 2008, incidentally, the North Coast accounted for a little less than 10 percent of all grapes crushed in California, but the value of that fruit commanded more than 38 percent of total revenues for the state's crop. The Central Coast grew 9.4 percent of the tons crushed and accounted for 18.8 percent of revenues, while the Delta delivered 17.1 percent of all grapes crushed and drew 13.5 percent of the revenue. The southern San Joaquin Valley, meanwhile, accounted for 61 percent of the harvest but not quite 27 percent of the revenue. This helps explain why a bottle of cabernet sauvignon with a "California" appellation costs, say, $7, while a cabernet sauvignon with a "Dry Creek Valley" appellation will command $40 or so.
- In comparing the percentage of alcohol on wine labels with the actual alcohol content of the wine, as measured by the Liquor Control Board of Ontario, the researchers found "some remarkable discrepancies." "On average across 7,920 observations of California wines, the actual alcohol percentage (13.35 percent by volume) exceeded the declared alcohol percentage (12.63 percent by volume) by .72 percent by volume," states the paper. The researchers didn't further explore this difference, but they did speculate on its cause: "It seems unlikely that wineries are making consistent errors of this magnitude in measuring the true alcohol content of the wine. One possibility is that wine producers may be attempting to avoid tax, given that tax rates vary with alcohol percentage; another is that there may be marketing advantages from having label claims of alcohol percentages that are consistent with consumers' expectations for given types of wine; a third is that they simply cannot be bothered getting it right."