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Busting Vineyard Myths

Researchers find some practices may be based on folklore

by Paul Franson
Busting Vineyard Myths
Reno, Nev. -- One of the most interesting sessions at the recent American Society for Enology and Viticulture conference might have been titled, "Busting Wine Myths." The first speaker, Michael Anderson from UC Davis, stated its focus well: "I'm frustrated by viticultural practices based on folklore instead of research." In his talk, and in those by the other speakers, Anderson punctured some widely held beliefs of both growers and wine writers.

Myth? Dropping fruit concentrates the rest

In the first address, "Effect of Crop Load Adjustment on Fruit Ripening, Uniformity and Sensory Characteristics," Anderson investigated the common practice of removing grape clusters "to concentrate the rest."

He noted that it's commonly believed that a vine can only ripen so much fruit, and that berries that don't quickly color at veraison never catch up to ripen with the rest. His research found otherwise. "No matter how much fruit is removed, there is no significant difference in Brix at harvest," he said. And that goes even for the pea-size fruit. "If we removed 40% of the fruit at veraison, the situation actually got a little worse. The fruit that would have been dropped had the same Brix as the rest."

His team anticipated Brix differences early on, but by harvest at 25° Brix, if not before, there were no significant differences by treatment. This may explain why previous studies did show differences when they were harvested at lower Brix. That the Brix values come together by harvest may be an interesting effect of increased "hang time".

He admitted that the grapes left might not taste exactly the same. "The fruit has sensory differences, but we don't know if that affects the wine. Is it worth the lost fruit?" he asked. Unfortunately, the data presented were only for one year, and the project has not been resumed. Anderson is seeking funding to continue the studies.

Myth? Vertical positioning improves quality

David Sorokowsky of RH Phillips Wine Company in Esparto, Calif., was curious if the expensive Smart Dyson training system gave better quality of Syrah than traditional California sprawl. He reported his results in the "Impact of Training System on Berry Composition and Wine Quality of Syrah."

He noted that grapes raised on Smart Dyson trellising are fully exposed to the sun as basal leaves senesce, and in the hot climate of Dunnigan Hills, that means they bake in the sun. They also cost 7 cents per vine every time a worker has to place canes under the wires.

He decided to try both traditional sprawl and a modified "half sprawl" version, where the canes were pushed only to the sunny side of the vines.

He found that the grapes raised with the southern sprawl, which saved $113 in labor per acre per season, had slightly higher anthocyanins and Brix, but had little difference in pH or hue overall. In 2005, tasters preferred the structure and fruit from the southern sprawl, which provided dapple light, whereas the full sprawl created wines with harsher astringency yet not as many tannins The southern sprawl also produced less herbal grapes.

Myth? Deficit irrigation improves quality

It's well known that early deficit irrigation improves wine quality by restricting vegetation and maintaining small berries, but many growers continue to restrict water through harvest. This results in lower yield due to dehydration, but many winemakers think it improves quality. Martin Mendez-Costabel of UC Davis questioned that, as part of his graduate thesis, and reported on his findings in "Effects of Irrigation Levels."

His conclusion: "Irrigation late in the season affects yield, but has little impact on fruit or wine composition."

"Grapes mature from green flavors to red fruit to blue and black fruit, and growers hope that if they leave the grapes on the vine, the green flavors go away. But the longer you leave them on the vine, the more yield loss there is." He says the peak weight occurs at 22° to 23° Brix, then the grapes lose about 20% of their weight at 28° to 29° Brix, depending on factors like cultivar, irrigation management, weather and other variables.

He said he wanted to develop an irrigation strategy that minimizes yield loss without having a detrimental effect on wine quality. The questions were:
  1. Does water keep vines active longer?
  2. Can you reduce yield loss without affecting quality?
He discovered that you should stress the vines before they reach 20° to 22° Brix, depending on the variety (18° to 20° for Syrah, for example), then ramp up water after that. "Deficit irrigated vines become senescent rapidly, but if you keep irrigating them, you maintain leaf area and keep them green, so they continue photosynthesis. This pumps more sugar as well as water into the berries"

He noted no significant difference in chemical properties, but said that methoxypyrazine, which account for much of the "green" flavors, peaks before veraison, and doesn't increase with watering late during ripening.

His strategy: Stress early to control canopy and create optimum berry size, then water after about 20° Brix. "This reduces yield loss and doesn't decrease quality.

Note that these are only brief summaries, and the studies may have involved limitations. Contact the authors for more information.
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