Wine Terroir by Microbe
UC Davis researcher linking DNA analysis with wine origins
Dr. David Mills is raising the possibility. The professor with the Department of Viticulture & Enology at the University of California, Davis, presented an early peek at research regarding the possible differences in the microbiota of wines from four of California’s wine regions during UC Davis’ annual Recent Advances in Viticulture and Enology (RAVE) conference on March 14.
Mills said there appear to be distinct differences in the microbiota found in wines from different regions as well regional differences in the same varietal wine. Even wines from different locations in Napa County exhibited marked differences in which microbial organisms were present.
Mills said rapid advances in the technology used with PCR (or polymerase chain reaction) analysis make it possible to quickly identify hundreds of specific DNA from a sample. “The technology is completely changing,” he said. “It really gives you a picture of the whole diversity.…It’s a huge amount of information you can generate.” (Editor’s note: See the Inquiring Winemaker column from July 2011 for more information about PCR analysis.)
For his study, Mills collected 240 must samples from wineries in Napa and Sonoma counties, northern San Joaquin County near Lodi, Calif., and the Central Coast.
The results showed differences in the microbiota for each region, and Mills said differences appeared between Napa Valley regions such as St. Helena and Oakville. “I would say in this case the microbes are a reflection of the terroir,” he said.
Mills said there is quite a bit more research to be done, but the early results offer an interesting possibility that wine could be further identified not just by where it’s from but what microbes inhabit it. Speculating on the future, Mills also wondered if the microbiota information could be used to predict wine quality by offering an insight into vineyard health.
Mills credited the work his graduate student Nicholas Bokulich did on the project. Bokulich also presented a poster describing his work studying the microbe populations on winery equipment and surfaces before, during and after harvest.
Bokulich used some of the same DNA analysis methods to identify the microorganisms at the same place throughout the teaching winery at UC Davis. He said results indicate that, as one may expect, fermentation yeasts dominated during harvest. Equipment often used with fermenting must and juice also appeared to serve as microbial “reservoirs” that contributed to fermentation. Other microorganisms not related to fermentation comprised the majority of the populations before and after harvest, and these appeared to be able to resist “colonization” by the fermentation microbiota.
Researchers presented on projects with posters or gave short presentations to the audience of about 150 people who attended the daylong event.
Another poster project was that of Byron Elmendorf, who is studying the aging of wine with micro-oxygenation and staves to compare with barrels. He said while the use of micro-ox and barrel alternatives is now widespread in the industry, there is still a lack of published research about how it compares to barrels and what it is actually doing to the wine.
He said after aging for six months, the wine was bottle and analyzed. Early results from studying the wine found that both methods helped enhance the perception of “smoothness,” but the alternatives and micro-ox had less of a positive effect than barrels. The wines will also receive phloroglucinolysis and LC-MS analysis to find any other differences.
Jess Jackson winery to open soon
Dr. David Block, the V&E department head, had a few general updates about the program. He noted that plant systems biologist Dr. Dario Kantu joined the department at the start of October. “We’re very happy to have him here,” Block said.
The school also received the funding for an extension specialist in viticulture position at its Oakville research center. “We think it’s an absolutely critical position for us,” Block said. He added that Dr. Andy Walker also will be working out of the Oakville center in a move to “revitalize” it into a magnate of research and best practices for viticulture.
Work also is finishing on the Jess S. Jackson sustainable winery building that is expected to be complete in just a few weeks and was built with a gift of $3 million from the late Jackson, Block said. Chik Brenneman, the school’s winemaker, presented a poster about the winery, which is set to be the first winery in the world to be completely self-sufficient and LEED-Platinum certified. Brenneman said the winery will feature a solar-powered icemaker for the winery’s cooling needs, have a hydrogen fuel cell, reverse osmosis membranes for treating collected rainwater for reuse as process water and designed only to see a maximum interior temperature of just under 80°F even after five days of an interior California summer heat storm. “The only mechanical feature in this building is the ability to cool at night,” Brenneman said.
“There will be nothing like it anywhere else in the world,” Block said.