Nature has always intrigued me. As a youngster, the ferocity of weather dazzled me, from experiencing the magnificence of a thunderstorm to the unbound energy of hurricanes and tornados. But I never became a meteorologist.
In adult life, I have become captivated by the processes involved in winemaking and am continually amazed at the natural process of the transformation of pressed grape juice into an alcoholic beverage. But I’m not an oenologist.
The transubstantiation of fruit into a complex elixir is a marvel of nature. The combination of events and interactions of varied elements that must interact in perfect harmony – every time they interact – is a feat that boggles my mind. Last week I reported on a newly developed synthetic form of yeast that may alleviate certain allergic reactions to wine. A reader queried me on the role yeast plays in wine production.
As with all things scientific, a logical structure and chemical interaction can explain this marvel. But the process of taking an agricultural product like grapes and converting it to wine, that has numerous variations, to me is more alchemy than laboratory. Wine is a living, breathing organism, changing as it progresses through its life cycle, influenced by its changing chemical composition both in the winery and in the bottle.
Early in the life cycle of wine, an amazing transformation occurs. In its most elementary formation, wine is a byproduct of grape juice, yeast, bacteria and oxygen. Crushed grapes carry on their skins various forms of yeast. These yeasts transform the natural sugars in the juice into alcohol and carbon dioxide.
After fermentation, the small amounts of bacteria remaining from the dead yeast cells create a secondary (malolactic) fermentation that results in a softer, less acidic wine. All through the fermentation, aging and bottle life processes, oxygen is ever-present and interacts with the components in wine to assist in refining and aging (or spoiling) wine over a period of time.
Let’s take a closer look at the role of yeast in winemaking. Given my lack of scientific skills, I researched several sources for an understanding of this phenomenon. Here is my best effort at distilling and presenting an analysis, from the perspective of a right-brain dominant mind.
Numerous strains of yeast develop in vineyards. Each one affects fermentation in a slightly different way, hence influencing varying characteristics of wines. These yeast strains are a critical component in the concept of terroir.
While many winemakers trigger the fermentation process with the “wild” yeasts carried by the harvested grapes, a number seek out natural strains that have been cultivated elsewhere and packaged to meet specific characteristics sought by a winemaker. Grape must be inoculated with the purchased yeast and these organisms carry out their transformative role.
Each yeast cell secretes more than 20 enzymes, which in turn create over 30 chemical reactions that initiate and perpetuate fermentation. The winemaker’s influence is in selecting the proper strain of yeast and then nurturing it throughout its reproductive and dying cycles.
Yeast cells are quite productive. One drop of fermenting juice can contain five million yeast cells that are capable of doubling their number every two hours under perfect conditions.
Complete fermentation can take up to 14 days, creating a frenzy of activity. It is not unusual to witness a froth of carbon dioxide bubbles on the surface of the fermenting barrel or tank as the density of yeast cells climbs into the hundreds of millions per ounce of juice. Once the yeast cells deplete all of the oxygen and nutrients in the juice, most die off and fermentation is complete (unless the winemaker chooses to retain the remaining bacteria, triggering the secondary – malolactic – fermentation process).
The marvels of science are diligently at work in the seemingly simple process of fermentation. The art of winemaking will always be dependent on a microscopic organism with a penchant for reproduction. I’ll drink to that. At this, I’ve become expert.
Nick Antonaccio is a 40-year Pleasantville resident. For over 25 years he has conducted wine tastings and lectures. Nick is a member of the Wine Media Guild of wine writers. He also offers personalized wine tastings and wine travel services. Nick’s credo: continuous experimenting results in instinctive behavior. You can reach him at firstname.lastname@example.org or on Twitter @sharingwine.