Wines & Vines

TECHNOLOGY Enologist Interview Andrew Waterhouse UC Davis professor discusses oxygen issues related to closures By Laurie Daniel A ndrew L. Waterhouse has a long background in chemistry, with a bachelor's degree from the University of Notre Dame and a doctorate from the University of California, Berkeley. But his exploration of wine chemistry began when he joined the Department of Enology and Viticulture faculty at the University of California, Davis, in 1991, and he's gone on to become internationally recognized in the field. Waterhouse has published a number of articles related to his research of phenolic compounds, how they relate to the taste of wine and their possible health effects for wine consumers. As part of his research into the effects of oxidation on wine chemistry and quality, he is conducting experiments to determine the oxygen-transfer rates for various types of wine closures. In addition to being a professor of enology at Davis, Waterhouse is an honorary professor at the University of Auckland in New Zealand, an associate editor of the American Journal of Enology and Viticulture and is on the editorial board for the Journal of the Science of Food and Agriculture. Wines & Vines: How did you become in- terested in researching the oxygen-transfer rates for various types of closures? Andrew Waterhouse: Some years ago I was consulting on a wine company quality problem that appeared to be inconsistent pinking. In those discussions, the internal insurance program manager told me that she had no way to anticipate problems. She said, "Someone just calls and says this or that wine is bad, and I have to cover the losses." She had no means to find out if a particular wine or type of wine is more or less fragile, or liable to losses. I thought that was a particularly problematic way to run a business and have a long-term goal of providing wine companies with some means to evaluate shelf life. We are interested in wine oxidation chemistry, and oxidation is key to aging. 44 W in e s & V i ne s AU G U ST 20 13 Since the OTR controls the amount of oxygen available to the wine, that variable is most important to the aging process. W&V: Please describe the research you're conducting that involves bottles of Sauvignon Blanc and the results you've seen so far. Waterhouse: To test closure consistency, we bottled a Sauvignon Blanc wine in March 2012 with natural and synthetic corks and screwcaps. Cade in Napa Valley provided the wine. We are analyzing the color of every bottle by looking through them using a spectrophotometer to precisely measure it. Colleagues in Australia have shown that color darkening is related to wine oxidation, and we plan to sort out the bottles with the largest and smallest oxidation for each closure. Those will be opened and tested for chemical changes as well as sensory differences. We would like to know if wine consumers can taste the difference between closures of a specific type in order to assess closure consistency. Theoretically, plastic can give or take TCA N atural cork takes a lot of the blame for cork taint, prompting me to ask Andrew L. Waterhouse whether it is possible for a screwcap to transfer trichloroanisole (TCA) to a bottle of wine. "This is theoretically possible for any plastic material that comes in contact with wine," he said, "but this is also true for natural cork, as both materials bind to TCA and can release it later." However, he added, "The converse is also true: The closure—screwcap lining, synthetic or natural cork—could absorb TCA out of a wine contaminated in production." In theory, that means that the TCA level could be lessened in the wine, he said, although he wasn't aware of any direct study assessing such an occurrence. L.D.

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