UBC Okanagan researchers Sierra Rayne and Nigel Eggers sampled wine as part of their research - photo by Bud Mortenson

UBC Reports | Vol. 52 | No. 10 | Oct. 5, 2006

Researchers Sniff Out Causes of Wine Aroma Defects

Is there wine on the table this Thanksgiving? Winemakers agonize over their vintages, patiently tending them along the path to perfection. Now they are enlisting the help of science to bolster their craft.

By Bud Mortenson

Chemistry researchers at UBC Okanagan -- in the heart of B.C.’s wine country -- have embarked on North America’s first large-scale examination of how contaminants such as unwanted yeasts and forest fire smoke can affect the aroma of wines.

Each year about 98 per cent of British Columbia’s 17,000 tonnes of wine grapes are grown in the sunny, vineyard-rich Okanagan Valley. With more than 60 wineries taking advantage of such abundance, the region is an ideal place to study issues that affect grape and wine production.

“Certainly the 2003 season with the Okanagan Mountain Park fire provided ample opportunity for additional ‘seasoning’ of the grapes,” says Nigel Eggers, Associate Professor of Chemistry with the Irving K. Barber School of Arts and Sciences. “Forest fires are known to produce phenols and guaiacols from the burning of lignins in trees, and these chemicals can impart a smokey, burnt smell to nearby fruit.”

Eggers and post-doctoral research fellow Sierra Rayne have synthesized versions of the compounds known to occur in smoke. Along with some innovative lab and field-based ‘burning’ experiments on fir, pine, and other native Okanagan trees and grasses, they are using new instruments to better understand the sources, distribution, and levels of these smoke-related compounds in local grapes and wines.

Eggers has received nearly $200,000 in funding from the British Columbia Wine Institute, the Investment Agriculture Foundation of British Columbia, and the Western Diversification Program to conduct extensive field sampling at small, medium, and large wineries and vineyards in the Okanagan.

“These grants have allowed us to stay busy working with viticulturalists, winemakers, and research scientists at Agriculture Canada’s Pacific Agri-Food Research Centre in Summerland, B.C., sampling from wine cellars and vineyards up and down the Okanagan,” says Eggers.

A major part of their research is exploring the impact of Brettanomyces (Brett) -- an undesirable yeast that can produce aroma defects in wines. Brett often exists in wine barrels, but can also find its way into wine from the raw grapes. Rayne notes that by causing aroma defects in wine, the yeast has become a bane to winemakers in many parts of the world.

“We’re collecting nearly 100 samples a month from individual oak barrels at 10 wineries and analyzing them for 4-ethylphenol and 4-ethylguaiacol, the two compounds with horsey, leathery and smokey, barnyard-like odours the Brett yeast is known to produce in high concentrations,” Rayne explains.

While collecting samples, Eggers and Rayne are also monitoring parameters such as dissolved oxygen, temperature, humidity, and sulfur dioxide (a preservative to prevent unwanted bacterial and yeast growth during barrel aging and in the bottle) -- in the hopes of better understanding the underlying production factors that can allow Brettanomyces growth in one barrel, while another barrel right next door can go untouched.

This work is the first comprehensive North American survey for Brett defects in wines, and will indicate whether the rigorous hygiene practiced in Okanagan wineries is holding off infection from this yeast. Rayne notes that experience in other winemaking regions has shown that once Brett takes hold, it is very difficult to control or get rid of.

“This is research that may help improve grape and wine production not only in the Okanagan but around the world,” Eggers says. The research will continue for two years and cover progress of the 2005 and 2006 vintages, as well as the analysis of 2003 and 2004 vintages that have already spent years in a barrel.

“Together, the two projects are helping to establish a world-class wine chemistry research centre at UBC Okanagan,” says Eggers. “By working closely with industry and government, we are striving to maintain and improve the quality of our local wines.”