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WSU Scientist Identifies Unknown Spoilage Bacterium in Wine

PULLMAN, Wash. — A previously unknown spoilage bacterium that can stall or stop alcoholic fermentation in wines made without sulfites has been identified by a Washington State University food scientist.

Charles Edwards, associate professor of food science, isolated and identified the novel bacterium — Lactobacillus kunkeei — from a commercial wine undergoing a sluggish fermentation.

Edwards does not know how significant his finding is to the wine industry because stalled fermentation can be caused by a variety of factors, including insufficient nutrients.

“I have heard about wines in California, Washington, and as far away as New Zealand that show symptoms related to what this bacteria could potentially cause,” Edwards said.

“Winemakers would tell stories of fermentation proceeding normally. Then, in the span of two or three days, an unknown bacterium would begin to grow and the fermentation would slow.  At the time we started our research, a cause and effect relationship between the growth of these bacteria and the slowing of fermentation had been suggested but not proven.”

Edwards asked wineries to send him samples of wines that they suspected of having the spoilage bacteria.  He received eight samples from commercial winemakers in Washington, California and Idaho.

While he did not focus solely on the problem caused by Lactobacillus, he hypothesized that he might find the culprit in that genus based on descriptions of the microorganism given him by winemakers.

Lactobacillus is a genus made up of rod shaped bacteria that produce lactic acid as a product of metabolism.  “They are one of the few groups of organisms that can grow in wine and grape juice,” Edwards said. “Both of those environments are very inhospitable to most microorganisms.”

Through the efforts of Y. C. Huang and K. M. Haag, two of his graduate students, Edwards had demonstrated that one of the organisms isolated from the commercial wines inhibited yeast.  Last year Edwards received confirmation from an expert in the United Kingdom that the bacterium was novel.

“Our laboratory group was really excited about this discovery,” Edwards said.

The next step in Edwards’ research is to find how the bacterium inhibits yeast and Edwards is working on that.  “If we can figure out how yeast are inhibited, we can figure out ways to remove the inhibition once the winery has the problem.”

Where does the bacteria come from?

“There’s a thought that the spoilage bacterium may originally come from specific vineyards, but at this point, there isn’t any evidence,” Edwards said.  Not all wineries that have refrained from using sulfites have the problem.

Sulfites have been used since ancient times to control spoilage bacteria and are in use today by many wineries.  Some wineries have attempted to reduce their use because some consumers have an adverse reaction to them.

The new species of bacteria has been cataloged by the American Type Culture Collection at Bethesda, Md., and now has been included on a validation list published in the International Journal of Systematic Bacteriology.

Edwards has named the new bacteria Lactobacillus kunkeei in honor of Ralph Kunkee, a biochemist and former professor of enology at the University of California, Davis.  (Note to editors:  See sidebar from the University of California, Davis.)

“Ralph has been a good friend and a mentor,” Edwards said.  “He performed some pioneering work in bacterial fermentation back in the 60’s and continued well into the 90’s until his retirement.  I felt it was important to honor his contributions to wine microbiology.”

Edwards’ research has been funded by the Washington Wine Advisory Board and the Northwest Center for Small Fruit Research.

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