Yeast Technology Eliminates H2S

Dr. Linda Bisson.Davis, Calif. -- Geneticist Dr. Linda Bisson, a
viticulture/enology professor at the University of California, Davis, has
developed a yeast technology to prevent the formation of hydrogen sulfide (H2S)
during fermentation. Hydrogen sulfide is an especially noxious gas, and one of
the most common sensory defects detected in wine. The human nose detects
infinitesimal quantities of its rotten-egg scent, and it can react with other
wine materials to form off-odors and off-flavors that can be difficult and
costly to remove.

During roughly a decade of research, supported in large part by funds from the
American Vineyard Foundation (AVF), Bisson and her team first identified a
particular genetic trait that can be crossed into any strain of yeast to
minimize H2S during winemaking. Once identified, it was sequenced, "So we knew
what the specific genetic change was and could follow it in crosses," Bisson
told Wines & Vines. Only then was it ready to be used in breeding strategies,
she explained. The scientists performed their research using classic, non-GMO
breeding techniques.

"A typical breeding strategy of crossing it into the desired parent, then
back-crossing that strain against its parent, will take about three months,
unless the parental strain has difficulty sporulating," Bisson said. "It can be
self-cloned into a strain in about week."

So far, the researchers have incorporated this useful trait into the popular
UCD522 (Montrachet) yeast "and some strains that are not commercial strains
yet," Bisson said. "The big demand from the industry was for Montrachet, as it
reportedly gives great flavors sur lie, but gives too much H2S during the
primary fermentation. Any commercial strain can become a non-producer (of H2S),"
when the newly identified trait is incorporated.

Bission acknowledged that because H2S is volatile, it does dissipate if a wine
is allowed to breathe. "When it is no longer detectable, the wines have breathed
enough," she said. "The problem nowadays is that many consumers do not have the
patience to do this."

The new (and still unnamed) trait has been licensed to Functional Technologies
Corp., to be marketed under its Phyterra Yeast brand (phyterra.com).

"It can be transferred into any strain of Saccharomyces," she emphasized. "Since
it can go into any yeast strain," it will be advantageous for any winegrape
variety, whatever commercial yeast is preferred by the winemaker.

But, she cautioned, "If the source of the H2S is sulfur added in the vineyard
which simply gets reduced chemically during fermentation, there will likely
still be some sulfides present. This technology does not mean that sulfur
applications in the vineyard can be made close to harvest."

Since 1978, the AVF, a nonprofit organization supported by growers and vintners,
has funded nearly $20 million in wine- and grape-related research. Learn more at
avf.org