Life's A Party: How Yeast Works to Create Wine

Wine --  all alcohol -- is not possible without yeast.  For a long time, the process of fermentation was a mystery, and the origins of the word yeast reflects this; it means ‘to boil’ or ‘to be troubled,’ referring to the appearance of a liquid undergoing fermentation.  It is now known that yeasts, hundreds of different strains of them, exist everywhere.  Over the past 100 million years, these single-celled fungi have evolved, using enzymes to breakdown organic compounds, such as sugar, and surviving off of the resulting energy.  

In vineyards, yeasts are found clinging in large concentrations to the waxy skins of grapes, patiently waiting for the wealth of sugar that lies within to be exposed.  During wine production, when the grapes are harvested and put together in a tank, the skins break and the frenzy begins.  The yeast’s metabolism of the sugars, in addition to releasing small amounts of energy, results in the formation of alcohol and carbon dioxide.  With so much sugar at their disposal, yeasts reproduce extremely rapidly.  The tank, now full of newly-formed, chemically reacting organisms, also produces a lot of heat as well, further propelling the yeasts’ metabolism.

Not all strains of yeast that existed on the grape skin can keep up with the true star of winemaking, Saccharomyces cerevisiae, and most die when alcohol concentrations reach 5%.  With the floor clear, Saccharomyces takes advantage, continuing to thrive until either all of the sugar in the grape juice is consumed or when alcohol rises to around 15%.  At this point, the fermentation tank becomes the scene of a small-scale apocalypse.  The yeast perish, en masse, and settle to the bottom of the tank, where they are known, in winemaking parlance, as lees.  But the spores live on, in the rafters of the winery, on the blades of the tractors, in soil of the vineyards, waiting for their opportunity to feast next year.

Notwithstanding their seeming simplicity, yeasts, specifically Saccharomyces, has become something of an unlikely scientific superstar.  It was one of the first organisms to have its entire genetic code sequenced, and has more recently been selected for interplanetary travel.  Geneticists even believe that Saccharomyces may someday unlock the secret to aging itself, dramatically extending the human lifespan.

This is quite heady territory for a microscopic fungus that exists, simply floating in the air, quietly looking for sugar to metabolize.  But yeast have something else to teach, regardless of their eventual scientific contributions.  The way that Saccharomyces produces wine, by heedlessly consuming sugar until it brings about its own oblivion, is hardwired.  Humans are under no such mandate.  Delighting in the result of Saccharomyces troubled existence can offer a reflection on the importance of our choice not to follow the same path.