WHAT: a yeast that divides by fission (division in half, rather than budding like most yeast, hence “Schizo”), ferments sugars (hence “saccharomyces” or “sugar-loving”), and was first identified in African millet beer (hence “pombe” meaning “beer” in Swahili.)
Relevance to wine: S. pombe has traditionally been grouped among the spoilage organisms by the wine industry. Unlike its friendly, helpful cousin Saccharomyces cerivisiae (the major player in wine fermentation and bread making), S. pombe tends to throw off a lot of icky-tasting or -smelling byproducts as it turns sugar into alcohol. Sulfur is not a desirable aroma in wine!
S. pombe has one truly nifty feature; however, that is earning it a useful place in winemaking. It can ferment malic acid into alcohol. Malic acid is one of the three major acids in grape juice that carries over into wine (along with tartaric acid and citric acid.) Its fresh, fruity acidity is a boon in fresh, fruity wines, but too much and you’ll find yourself puckering.
The usual savior of malic acid overload is malolactic fermentation – conversion of malic acid into lactic acid by lactic acid bacteria after alcoholic fermentation yeasts have worked their magic. Great for rich, buttery wines — lots of unctuous flavors come along with the malic-to-lactic conversion — but not so great if you were going for a fresh and fruity style in the first place.
Could S. pombe help? What about the sulfur aromas and other issues?
A fair bit of research has investigated ways of using S. pombe in wine: to permit the inclusion of rotten grapes in Sherry and the potential of using genetic engineering to create a Schizoid-Schizosaccharomyces that keeps the good and does away with the bad, for example.
Lallemand, a major yeast company, has recently released ProMalic® “for naturally lowering juice acidity,” based on S. pombe. The yeast is submerged in the wine in something like a big yeast tea-bag, allowed to steep until your pH is up (and your malic acid down) to where you want it, and then pulled out before the yeast gets carried away with making other less-desirable stuff.
Some super-enthusiastic yeast folk from the Forsberg lab at the University of Southern California say that they have tried fermenting beer with their pombe with results that suggest skunk cabbage more than the local brewpub. With a respectful nod to classic eastern African beverages, however, they note that their attempts involved neither millet nor traditional methods. Anyone tasted any African millet beer?
Some home-brewers out there are apparently giving it a try: http://www.homebrewtalk.com/f12/pombe-brew-138520/
For the truly curious yeast fiends out there, see the Forsberg lab Pombe pages at http://www-bcf.usc.edu/~forsburg/main.html#what for a truly excellent discussion of pombe in all its glory.
Erika Szymanski is a PhD student in microbial enology at Washington State University and an independent contributor to this blog. She is in no way affiliated with the sponsoring company. This blog was originally posted on her blog: The Wine-o-scope.