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More on yeasts gone wild!

October 31, 2009 |  1:39 am
Our article Wednesday on "natural wines" stirred up some interesting responses. While some wine lovers like the idea of wines fermented by "wild yeast," several readers pointed out that if commercial yeast has ever been used in a winery, some of those yeast cells remain and will ferment subsequent wines made there, whether newly harvested grapes are inoculated with commercial yeast or not.

Nobody knows how long yeast can linger in a building, or on winemaking equipment, but it is believed to be able to survive for years until it gets more freshly picked grapes to ferment. As an experiment, Italian wine researcher Alessandro Martini once ordered a winery steam-cleaned and all yeast killed after using a particular strain of commercial yeast. The following year, though he did not add any yeast to freshly harvested grapes, the commercial strain from the previous year returned to do the job.

Of course, it's possible for a new winery to be built with no commercial yeast ever used in it. In that case, microbiologist Lisa Van de Water, director of Vinotec Napa, says the first wine fermented is unlikely to be good, unless the winery is fortunate enough to have Saccharomyces yeast take over right away, probably hitching a ride in on previously used equipment.

"By the second fermentation, probably Saccharomyces will take over," Van de Water said. "But it isn't the wonderful yeasts from the fields of lavender. It's just the yeast that is able to kill a lot of the other ones by alcohol. It will struggle up and become dominant."

Here's a quick yeast primer: Saccharomyces is the good yeast that ferments wine; many strains of it exist, and the mixing of different strains is often responsible for greater complexity. It persists more in wineries and used barrels than in vineyards.

Kloeckera apiculata is the main yeast found on wine grapes in vineyards. In small amounts, it can add banana or hay notes to wine. But Van de Water says that if Saccharomyces does not out-compete Kloeckera, the latter will produce wine she described as "a banana wearing nail polish in a field of rotten hay."

Other yeasts that can affect the taste of fermenting grapes include the wonderfully named Schizosaccharomyces (just in time for Halloween, it's psychotic yeast!), which can make wine smell like rotten eggs, and the controversial Brettanomyces, which the great majority of wine researchers call spoilage but some winemakers defend in small amounts as adding complexity. We're not going to get into that one today.

The main point Van de Water wanted to make is about the word "natural." She says that whether a specific strain of yeast is chosen by the winery or the winemaker allows random chance and multiple strains, ultimately Saccharomyces -- and quite likely commercial strains of it -- will do the work.

"I can't stand people who talk about natural yeast, because it's all natural," Van de Water said.

But a word is just a word. Van de Water talked about French scientist Denis Dubourdieu finding 23 different strains of Saccharomyces in one wine. That's exactly the kind of outcome that will lead to complexity -- whether you call it "natural" or not.

-- W. Blake Gray

Photo of Saccharomyces yeasts from DiWineTaste.com