Cry of the Vine : Professor Involved in Wine Study ‘Hears’ Grapevines’ Plea for Water

Prof. Mark Matthews sat in the University of California experimental greenhouse wearing a headset, listening to the stressful cry of a thirsty grapevine.

The vine was emitting a series of clicking sounds at a higher frequency than humans can hear. The headset was attached to audio emissions equipment that amplified the noises coming from the plant.

“It’s a signal from the vine. The plant in effect is crying for help, telling us it needs water,” said Matthews, 35, plant physiologist and professor of viticulture and enology at UC Davis.

Matthews quickly noted that he was not being anthropomorphic--attributing human feelings to non-human beings, plants or objects.

“Obviously, grapevines don’t have a brain,” he said. “The vines are not crying out with pain. But a physiological phenomenon occurs when grapevines dry down, causing the vines to emit high frequency sounds.”

He has discovered the cry of the grape leaf and grapevine in a study on how the plant adapts to water stress. As a vine runs out of water, he said, air bubbles appear and expand in vessels that conduct the water throughout the plant.

“The clicking noises apparently are tiny explosions within the plant’s vessels resulting from the formation and expanding of air bubbles from the roots up through the leaves,” Matthews said.

And, more important for California’s wine industry, he believes, is that a certain amount of water stress in the vine may improve the quality of wine.

Report to Experts

Last month, Matthews and his wife, Rie Ishii Matthews, a researcher in the UC Davis food sciences department, appeared before the annual meeting of the American Society of Enology and Viticulture to give a scientific paper on the possibility of improving wine quality through water stress techniques.

Matthews deliberately withheld water from several vines in the university’s vineyard and provided adequate water to similar vines in the same test plot.

“We used grapes from both sets of vines to make separate batches of Cabernet Franc wine. Then we had 20 persons make sensory analysis based on appearance, aroma and flavor of the two wines,” Matthews said.

“The results in all three categories were that the wine from the water-stressed vines looked, smelled and tasted better than the wine made from the vines receiving normal irrigation.”

Matthews has attached sensors to water-stressed grapevines. Electrical signals are sent to the audio emissions equipment from the sensors and recorded for study.

Growers Cooperating

Growers have financed his research for the last four years to the tune of $20,000 a year. Several growers cooperating in the study in Napa Valley have experimental water-stress plots. Others in the Santa Rosa, Calif., area have set up experimental plots in their vineyards.

Phil Freese, 43, director of viticulture research for Robert Mondavi Winery in Oakville, Calif., said that “water relations in the vineyard is probably one of the least understood factors in the production of premium wines.

“We don’t want the vines to have too much or too little water. Mark Matthews is showing that some water stress enhances quality.

“He is on the track of something that may prove to be extremely beneficial to the wine industry. . . . (But) it is a long-term study, something that cannot be accomplished overnight.”

Studies are being conducted to determine how much water stress is beneficial to the plants. “We know there is a trade-off. Less water means less yield but the quality appears to be notably better,” Matthews said.

Regulate Irrigation

If his findings produce better quality wine, Matthews envisions sensors attached to individual vines throughout a vineyard sending electrical signals to computers that would automatically regulate irrigation systems.

An Australian researcher first discovered 20 years ago that dried plants made audible high frequency noises when he stuck a phonograph needle into a castor plant.

But it was Matthews who heard it through the grapevine.