In the ever-fluid list of criteria to determine whether a wine is “natural” or not, the idea of natural, native fermentation always seems to bubble at or near the top of the charts. The fundamental principle behind native fermentation is that the wine maker does not inoculate the crushed grape juice with a commercial strain of lab-developed yeast but rather lets the native yeast that exist in the air and on the grape skins do the fermentation naturally. In this way, the theory goes, not only are you capturing the terroir of the fruit and the soil, but also the micro-organisms the populate the area in and around the vineyard.
It’s all a very romantic thought and perhaps it bears out in practice in isolated winery sites that have been producing wine in this way for centuries, but from a practical standpoint true 100% natural fermentation from native yeast is quite difficult to achieve.
There are dozens of strains of yeast that can produce fermentation and there are always several different strains fighting for dominance in the same batch of wine. Different strains of yeast produce different aromas and flavors in wine but, eventually, the hardiest strain wins out and is responsible for most of a wine’s fermentation and whatever esthers and phenols accompany that fermentation. Laboratory yeast are used in wine making because they are typically very efficient, ethanol-tolerant, and neutral in terms of flavor additive. These are hardy, durable yeast and given that after fermentation yeast can’t exactly be rounded up and exterminated, they end up colonizing corners of the winery and wine making equipment. When it comes time to make wine again, those commercial yeast have become part of the winery’s biosphere and, in all likelihood, will be the dominant yeast in many subsequent fermentations, because that’s what they were cultured to be.
Relatedly, in warmer wine regions, like much of California, many natural yeasts can’t survive in highly ethanolic environments, which means that without inoculation with ethanol-tolerant commercial yeast, the fermentation will become “stuck,” leaving behind residual sugar and opening the window for the possibility of later re-fermentation in the bottle leading to spoilage.
This was all explained to me by a wine maker colleague the other day and, while it’s not something I’d ever thought about before, it makes perfect sense. Wine isn’t made in pharmaceutical clean rooms, it’s made in barns and warehouses and garages. We do our best to keep the equipment clean, but it’s far from a sterile operation. This wine maker also made the point that, if you truly want to make a natural wine that is expressive of the fruit from which it’s produced–a product of the vineyard–do you really want the flavors and aromas of yeast to predominate at the expense of the grapes?
That’s an open question and I definitely see both sides of the argument, but for me fruit is essential above all else. I don’t particularly want brettanomyces in my wine for the exact same reason I don’t typically want a mega-dose of new oak barrel aging: it makes the wine about something other than the fruit and land it comes from.