I have long been interested in native yeasts as an aspect of terroir. It is common knowledge that varieties of yeast impart unique flavors and aromas to fermented beverages; the type of yeast doing the “work” of fermentation can be just as important to the finished beverage as the grape varietal. Winemakers can, and often do, choose to inoculate with cultivated yeasts, which are more predictable and typically “stronger” than ambient, native yeast strains which exist in the vineyard and in the cellar. In this case, the cultivated yeasts overpower and kill the native varieties in a coup of sorts. However, some choose a different approach, often referred to as natural, non-interventionist, or even, traditional.
Yeast is a fungus that reproduces both sexually and asexually. It is prolific, and grows extremely quickly. These little fungi are everywhere in our environment, tucked into every imaginable nook and cranny, indoors and out, even floating in the air.
Non-inoculated wines are fermented using only the strains of yeast that exist as part of the vineyard's native fauna. They have a distinctly different profile than their “cleaner” counterparts, and many argue that they are the truest expressions of terroir.
This story of airborne yeast is one that I've been told over and over again in conversations about native yeast fermentation (also called “wild” fermentation, or even vin sauvage). As that story goes, yeast floating in the air and blowing in the breeze simply attaches to the skins of the fruit. Recently, however, I learned that the reality is not quite that simple.
The airborne yeast story is only half true. Strains of yeast such as Kloeckera, Candida, and others are, in fact, airborne. However, you wouldn't want any of these yeasts to do the important job of fermenting your juice. They would die when alcohol levels reach 3-5%, leaving the job far from done! The only “wild” yeast capable of taking the task to its fully-formed conclusion is Saccheromyces cerevisiae, which is much too heavy to catch a ride on a summer breeze. In order to move around, Saccheromyces cerevisiae requires a more substantial vector: bugs.
Everyone knows that bees and other flying insects are necessary for pollination, but few are aware that we also have them to thank for spreading around the all-important Saccheromyces cerevisiae. Even more importantly, one species of wasp may be responsible for the continued overall existence of Saccheromyces cerevisiae. Until recently, scientists didn't even know where this yeast goes in the winter, or how it survives year-round. In 2012 scientists discovered that Vespa crabro, known as the European hornet, carries Saccheromyces cerevisiae in its gut, and even passes it along to its young when it reproduces. These stinging pests, cursed and swatted by humans everywhere, are spreading the magic every time they dig into their choice food source, sweet fruit.
These scientific discoveries are important reminders of the interconnectedness, beauty, and fragility of the natural world. Our tendency is to try to keep what we want (food and wine), while eradicating what we don't. However, the revelation that the vile wasp has all the while been doing us such a huge favor is something to consider, maybe over a glass or two of “wild” wine.