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New Study Could Prove Effectiveness of Screw Caps

UC Davis and PlumpJack Group team up to test quality and ageability of screw cap closures on wine

Augustus Weed
Posted: June 28, 2012

The University of California at Davis is conducting a new study that could help end the debate on whether screw cap closures are as effective as natural corks when it comes to aging wine. The university is working with the PlumpJack Group, a wine and hospitality company, cofounded by billionaire philanthropist Gordon Getty and California Lt. Gov. Gavin Newsom, to assess the quality and aging potential of different closures. The goal is to provide direction for the industry so vintners can make informed decisions about what to use on their bottles.

The two-year study will analyze wines under three different types of closures—screw caps, synthetic corks and natural corks. The test group, which consists of 200 bottles of Cade Sauvignon Blanc 2011, will be monitored every few months using a spectrometer to detect changes in color. The wines will also be chemically analyzed using oxygen sensors placed inside the bottles. The sensors allow the university to measure how a wine is aging without opening it. The wines that show differences will be opened at the end of the study and tasted to determine if the quality has been compromised.

The study will determine the range of differences in each closure group, specifically, how much oxygen has been allowed into the bottles. When oxygen interacts with a wine it causes it to oxidize, changing its color and taste. Corks and screw caps limit the amount of air a wine is exposed to, preventing it from aging prematurely. "It's really a variability study," said Dr. Andrew Waterhouse, professor of viticulture and enology at UC Davis. "We want to see how different they can be between themselves."

This is not the first scientific study to be conducted on screw caps (see sidebar) but it does employ new technology. PlumpJack used a CT scanner to measure the permeability of the natural and synthetic corks to eliminate potential flaws. "For this study we chose the best corks, the least permeable corks, so that we have a very even playing field for all three closures," said John Conover, general manager at PlumpJack and Cade wineries in Napa.

PlumpJack became interested in comparing screw caps to corks after the company's founders questioned why it was OK for even a small percentage of its wine to be damaged because of the closure. According to Conover they were frustrated with the percentage of wines affected by TCA (2, 4, 6-trichloroanisole). "We work so hard to grow the grapes and make the wine, and then to have it ruined because of the closure for us was unacceptable," he said.

TCA is at the center of the debate on alternative closures. Proponents of screw caps point to its ability to eliminate the potential for "corky" wines. But opponents consider the closure to be inferior to traditional corks for aging.

The company, which owns two wineries in Napa as well as two hotels, a wine shop and several restaurants, has been conducting in-house studies on the aging potential of screw caps for years. Starting with the 1997 vintage it has been bottling half of its PlumpJack Reserve Cabernet Sauvignons under screw cap. But it decided to approach UC Davis because it wanted an independent body to assess the closures.

It remains to be seen whether the study will support the case for screw caps; the results will not be published until 2013. And many vintners are still finding it hard to market screw caps to consumers. But Conover said a younger generation of wine drinkers is willing to embrace alternative closures. "For us as a company we have received very little resistance from our customers with screw caps," he said.

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