Merced County Cooperative Extension
Merced County Cooperative Extension
Merced County Cooperative Extension
University of California
Merced County Cooperative Extension

Posts Tagged: wine quality

Increasing temperatures led to better-tasting wine grapes, but for how long?

A worker installs a shade film in Napa, California, to protect cabernet sauvignon grapes from overexposure to the sun. Photo by Kaan Kurtural, UC Davis

Study shows sugar, color content should be watched

Warming temperatures over the past 60 years have led to increased wine quality, but a new study looking at sugar and color content in grapes indicates the industry may be facing trouble if trends continue, according to collaborative research out of the University of California, Davis, and University of Bordeaux.

“Quality has increased steadily up to now,” said lead author Kaan Kurtural, a professor of viticulture and enology and an extension specialist at UC Davis. “We just don't know the tipping point.”

Kurtural's research, published in the journal OENO One, focuses on two renowned wine regions — Napa Valley and Bordeaux, France.

Cabernet sauvignon grapes. Photo by Jack Kelly Clark

Researchers looked at ripening, grape quality and temperature data over six decades in both regions and then confirmed the findings with a five-year trial in Napa. They also consulted wine ratings in publications like Wine Spectator to gauge consumer demand.

One key finding: As temperatures exceeded what was considered the optimal level for quality, the grapes produced better wines.

“Previous research had few field data, but a record of assumptions,” said Kurtural.

Other quality factors at play

Temperature is a factor, but the paper suggests that sugar and color content should not be discounted. The authors also identified a biomarker that affects taste, color and other factors that can be the bellwether for climate change in red-skinned wine grapes.    

“Temperature is always there,” he said. “Temperature is not your bellwether.”

Higher temperatures can harm grape composition, including color, taste and aroma. Researchers examined pigment and sugar content of five California vintages of cabernet sauvignon, finding that as the grapes got sweeter the skin and color deteriorated.

The degradation of these quality-related compounds and the observed plateaus of wine quality ratings suggests there can be too much of a good thing.

Researchers have long theorized that increasing temperatures from climate change would lead to shifts in wine-growing regions, opening up some new areas for vineyards and making others unsustainable.

That shift could be a boon to some economies and devastating to others, something the industry should watch.

“Since the 1980s, grapes got riper and they were able to make better flavor and color compounds,” Kurtural said. “Are we going to lose this or adapt more?”

Gregory A. Gambetta with the University of Bordeaux is a corresponding author on the paper.

For more information:

Posted on Monday, October 4, 2021 at 1:30 PM
  • Author: Emily C. Dooley
Focus Area Tags: Agriculture

Farewell corks? Screw caps may outshine corks in wine quality

While many of us cherish the mystique of popping a wine cork, screw caps are becoming more commonplace in the wine industry. Half a century ago, screw caps were associated with cheap rotgut wine, but now they have replaced corks in many premium wines and at many of the world’s best wineries.

Wine bottles are sealed primarily in three ways — natural corks, synthetic corks or screw caps. All have their advantages and disadvantages, and most certainly their proponents and opponents. While synthetic corks never gained much of a foothold in the wine industry, screw caps are being studied more frequently for their efficacy and quality.

While screw caps were originally thought to be airtight, resulting in the unpleasant aroma of hydrogen sulfide inside some sealed wine bottles, screw caps have been developed with different levels of permeability. Most aluminum Stelvin caps are lined with a polyvinylidene chloride–tin foil combination (Saran-Tin), or a polyvinylidene chloride–polyethylene mix (Saranex); each yielding different permeabilities, and chemical and taste profiles in the wine.

Research is weighing the value of screw caps on wine quality and consumers’ ability to taste differences in wine bottled with a cork or a screw cap.

Professor Andrew Waterhouse, UC Davis wine chemist
A new UC Davis study spearheaded by wine chemist Andrew Waterhouse, professor in the Department of Viticulture and Enology, is examining Sauvignon Blanc wine quality during aging, and consumers’ ability to taste differences such as oxidation in wine capped with natural cork, synthetic cork or screw caps. The UC Davis research team includes John Boone, a radiologist, and David Fyhrie, a biomedical engineer — both professors in the UC Davis School of Medicine — who will work with Waterhouse to analyze the corks, the wine color and oxidation of the wine.

The study, which will be completed next year, is not touted to give a definitive answer to the best type of wine closure, but it will, according to Waterhouse, give winemakers reliable information on which to judge the type of closure that works best on their wines. (Watch Waterhouse explain the study in a video.)

An earlier study at Oregon State University, and reported in ScienceNews, said that consumers could not discern a difference in Pinot Noir and Chardonnay wines capped with natural corks or screw caps.

Perhaps what merits future study is the type of linings in screw caps. As screw caps continue to gain a foothold in the wine industry, it’s reasonable to assume that additional research on cap linings will produce additional options for winemakers, resulting in high-quality wines with greater longevity.

Based on research studies and wine experts’ judgments, here are some advantages and disadvantages of different types of wine closures:

Natural Corks:

  • Traditionalists claim that "real" corks allow healthy gas exchange for flavorful wine
  • Some claim that good sources of natural cork are dwindling
  • Not all natural corks are alike, resulting in variable cork properties
  • Higher chance of “corked” wines and trichloranisole (TCA) taint

Synthetic Corks:

  • Considered expensive and unpopular with consumers
  • Many synthetic corks let too much air into the wine bottle
  • They’re often difficult to remove from the bottle, and to re-cork the bottle

Screw Caps:

  • Less chance that wines will be “corked,” and probably fewer tainted wines
  • Some say that air-tight screw caps are “suffocating” to wines

 

Read more:

  1. Corks and screw caps? Can wine consumers taste the variation? UC Davis study
  2. Wine corks are going: the screwcaps are winning. HubPages
  3. Cap or cork, it’s the wine that matters most. ScienceNews
  4. Great wines under cork and screw cap. Forbes
  5. Corks vs. screwcaps. Total Wine & More
  6. Chateau Margaux corks a problem with a screw cap. The Wall Street Journal
  7. 7. Cork vs. screw cap: what’s all the fuss about? Imbibe Liquid Culture
Posted on Tuesday, October 23, 2012 at 9:16 AM
Tags: Andrew Waterhouse (2), corks (1), David Fyhrie (1), John Boone (1), screw caps (1), UC Davis (46), wine (13), wine quality (2)

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