Yeast with Fortitude
Anyone who has enjoyed wine for more than the past five or six years has likely noticed a steady increase in wine’s alcohol content. Alcohol content in today’s red wines can reach 15.5 percent and higher, up from 12-14 percent not that many years ago. Alcohol in white wines has also increased significantly. New world wines are generally highest in alcohol, though French wines have also been increasing.
Commentators on the subject point to various factors—including the influence of wine critic Robert Parker’s preference for “fruit bombs” and global warming—for the increase. Whoever, or whatever, is to blame (or to be credited, depending on your perspective), the fact of the matter is that alcohol content is higher because the grapes contain more sugar at picking.
Ethanol, the alcohol in wine, is produced by yeast, various strains of Saccharomyces cerevisiae, as a byproduct of digestion. The more sugar yeast has to eat, the more alcohol it produces.
Sugars are higher primarily because grape growers are delaying picking the grapes. “One of the biggest changes, I think, is that winemakers let grapes sit in the vineyard for far longer than they used to,” says Washington State University wine researcher Charles Edwards.
“On the positive side,” he says, “you get much better flavors.”
But getting there requires more of the yeast and subjects it to harsher conditions, among them a higher pH and nutrient imbalance. The alcohol level presents no problem to the yeast. Hardy strains can endure up to 18 percent alcohol. Rather, the working conditions on the way to the alcohol present the problem. Wine must provide yeast with a rich—and potentially hostile—ecosystem in which to work, and the yeast can use any advantage it can get.
Edwards started working with Lallemand, the world’s major yeast producer, several years ago to give S. cerevisiae the boost it needs in today’s winemaking conditions.
The result was not a new yeast (Edwards is emphatic that this is NOT a genetically modified yeast). Rather, it benefits from a modified production process. The result is what Lallemand calls YSEO, short for “Yeast Security Optimization.”
Commercial yeast is grown under obsessively clean conditions in order to make sure unwanted organisms don’t contaminate the culture. Fed molasses, the yeast multiply to a desired population, then are separated from the nutrients and dried for packaging and distribution. Various tweaks in the process—well-protected secrets—resulted in YSEO.
Edwards’s role has been primarily in the evaluation of the product, both in the laboratory and, on a grander scale, with a state winery. One of the batches they tested was worth three-quarters of a million dollars. It made him a “little nervous,” says Edwards.
But the results were great: Faster fermentation, leaving less time for things to go wrong. Significantly less production of sulfur compounds, such as hydrogen sulfide, which can result when yeast are stressed. H2S can result in very unattractive odors and flavors. It is much to be avoided.
A major emphasis of Edwards’s general research is “stuck” fermentation, a situation that the YSEO yeasts seem adept at avoiding.
About 10 percent of Lallemand’s wine yeast strains are now being produced with YSEO, says Gordon Specht, North American area manager who worked with Edwards on the project. Every package of YSEO yeast includes a line noting WSU’s part in the work.
For an animated explanation of YSEO:
To read a paper on the process by Edwards, Specht, and others:
This entry was posted on Monday, January 26th, 2009 at 4:12 pm and is filed under Biological sciences. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.