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ASEV Recognizes the 2020 Best Papers in Enology and Viticulture

Research on yeast inoculation at the top of tanks and a method to eliminate crown gall studies offer new information, and some hope for the future
by Linda Jones McKee
August 20, 2020

 

This year’s best papers selected by the American Society for Enology and Viticulture (ASEV) deal with topics that should rouse the interest of grape growers and/or winemakers no matter where they are located. The crown gall pathogen, Agrobacterium vitis, is a problem globally, and when a grower plants a vineyard, the threat of the vines developing a crown gall infection at some point in time is real. And many winemakers inoculate white juice with yeast from the top of the tanks, and then wonder why one tank ferments the juice more quickly or more cleanly than the next tank.

Until the Covid-19 pandemic shut down the 2020 joint national ASEV and ASEV-Eastern Section meeting in June, the recipients of the best paper awards presented their research to a live audience. Instead, two researchers conducted Zoom webinars on different days. Dr. Marc Fuchs, professor of plant pathology and plant-microbe biology at Cornell AgriTech School of Integrative Plant Science, presented the viticulture paper, “Elimination of the Crown Gall Pathogen, Agrobacterium vitis, from Systemically Infected Grapevines by Tissue Culture,” on July 30; and Dr. Dominik Durner of Dienstleistungszentrum Ländlicher Raum (DLR) Rheinpfalz, Germany, gave a talk on “Distribution of Yeast Cells, Temperature and Fermentation By-Products in White Wine Fermentations” on August 19.

The best viticulture paper: elimination of the crown gall pathogen

Crown gall is a serious bacterial disease caused by Agrobacterium vitis (A. vitis), and vinifera grapes are especially susceptible. Vineyard site selection for well-drained soils and good air circulation and cultural practices to reduce vine injuries that act as infection entry sites help to reduce the incidence of crown gall, but these practices do not cure the problem. Training of multiple trunks that allow for the removal of an injured or diseased trunk while leaving replacement trunks for crop production is another method of coping with the presence of crown gall. An additional problem is that there are no effective chemical controls to deal with crown gall. A more recent discovery that A. vitis can survive systemically in grapevine propagation material raised the question of whether it would be possible to produce vines that do not have the pathogen.

Other studies had utilized tissue culture approaches to eliminate viral and bacterial pathogens. Shoot tip cultures had been shown to be effective in eliminating A. vitis, but the detection method to evaluate its effectiveness was not that sensitive. The Cornell team developed a highly sensitive method of “magnetic capture hybridization in conjunction with real time PCR” (polymerase chain reaction). This MCH-qPCR method detects as few as 10 cells per sample.

The Cornell researchers achieved the elimination of A.vitis from severely infected Riesling vines “by culturing apical and axillary buds and meristems from shoot tips of greenhouse-grown plants, followed by micropropagation in tissue culture. Plants recovered had undetectable bacterial populations following repeated and extensive testing by MCH-qPCR, a very sensitive detection method, even after a dormancy period.”

It will probably take a few years before vines without the A. vitis pathogen will be available to plant in quantity. It’s a prospect all growers can anticipate with enthusiasm!

The best enology paper: the effects of tank top yeast inoculation without stirring

Many winemakers add yeast to the top of a fermentation tank full of white grape juice and then walk away without stirring that juice. What actually happens when yeast is added to the top of a tank of white grape juice and the winemaking team doesn’t stir it? How does this lack of stirring action affect the fermentation kinetics and the formation of acetaldehyde, acetic acid, and pyruvate?

The research team in Germany tested samples of Riesling grape juice in three sizes of tanks: tall and narrow experimental tanks with a 105 L capacity (230 cm high and only 21 cm wide), and two sizes of industrial-scale tanks, 2,500 and 7,000 L, to determine the distribution of temperature, yeast, and fermentation products in these different tanks.

Without stirring, specific gravity measurements showed that fermentation started earlier at the top of the tank than at lower levels, with specific gravity measurements between the top and bottom of the tanks differing by up to 8.6° C and 0.040 in specific gravity. The onset of fermentation at the bottom of the tank was delayed by up to seven days when the juice was not stirred. The inhomogeneities in the larger tanks lasted for four days. Even brief stirring after the yeast was introduced “provided uniform conditions during the early fermentation phase, except for temperature differences due to natural stratification.” It was also noted that tank sampling valves and temperature sensors did not reflect the entire tank during the early fermentation cycle when the yeast was not stirred into the juice.

Stirring shortened the length of fermentation and pyruvate concentration was lower, possibly because nutrient availability was increased throughout the tank. Low pyruvate concentrations decreased the SO2 demand and may reduce diacetyl formation.

The researchers concluded, “We suggest stirring the rehydrated yeast into the juice after inoculation from the top of the tank in order to ensure a uniform yeast distribution. This procedure prevents inhomogeneities and thus shortens the fermentation duration, reduces stress for years, and increases process control.”

Additional information about the best paper awards

The ASEV best paper awards committee reviews all manuscripts published during the previous year in the American Journal of Enology and Viticulture and selects one paper in viticulture and one in enology “that reflect the outstanding research and a substantial contribution to the field. This year’s best paper awards committee was chaired by Tom Collins, assistant professor of grape and wine chemistry research at the Washington State University Wine Science Center, Tri-Cities.

The best enology paper was written by Mira Schwinn, Dominik Durner, Antonio Delgado, and Ulrich Fischer, who are from the Dienstleistungszentrum Ländlicher Raum (DLR) Rheinpfalz, Institute for Viticulture and Oenology in Germany. It is available on the ASEV website, www.asev.org/post/2020-ajev-best-enology-paper-author-presentation.

The authors for the best viticulture paper were Luz Marcela Yepes, research associate; Tom Burr, Cherie Reid, and Marc Fuchs, all of whom are associated with Cornell AgriTech School of Integrative Plant Science. It is available on the ASEV website, www.asev.org/post/2020-ajev-best-viticulture-paper-author-presentation.

Future ASEV invasive pests symposium webinars

October 22: Lifecycle Modeling and the Impacts of Climate Change, by Gwen-Alyn Hoheisel (Washington State University, Prosser) at noon-1:00 p.m. (PDT).

November 12: Invasive Species Response: Lessons Learned from the European Grapevine Moth Collaboration Program, by Monica Cooper (University of California, Cooperative Extension, Napa County) at noon-1:00 p.m. (PDT).


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