California Vineyard Uses High-Tech Chemistry to Choose Optimum Picking Time for Grapes

A Modesto winemaker is using the latest 21st century analytical chemistry technology to supplement the time-honored practice of tasting a mouthful of grapes to determine when the fruit is ready for picking.

The winery has turned to spectroscopy and chromatography to evaluate aroma, color, taste and mouthfeel of grapes, according to Michael Cleary, senior manager of grape and wine chemistry at E & J Gallo Winery, who described the firm's Grape Assessment Program at the 232nd national meeting of the American Chemical Society, the world's largest scientific society. Annual California wine production is currently a $16.5 billion industry.

Chromatography is a laboratory process for chemically separating mixtures into their component parts. Using this process, grapes can be analyzed for their molecular makeup. Molecules indicative of aroma, taste and feel to the palate can be identified and the grapes then harvested when these molecules are at their highest concentrations, Cleary explains.

The purpose of using analytical chemistry testing, he says, is to complement historical time-consuming -- though still useful -- evaluation methods like chewing the grapes to best determine when to pick them. "It takes good grapes to make good wine and we're trying to improve our predictions of when to harvest," he says. The pharmaceutical, petroleum, food and beverage industries, and others also use technologies like chromatography to assess their products, he adds.

Cleary's presentation is one of four papers in a Chemistry of Wine symposium, to be held Sunday afternoon, Sept. 10, and sponsored by the ACS Younger Chemists Committee. The other papers deal with wine flavor chemistry, an overview of the chemistry of winemaking and the world of the winemaking consultant.