During the pandemic I attended many webinars organized by my school, WSET/London. One of them caught my attention particularly, because it was about the important role that microbiology plays in wine fermentation. This seminar was presented by Ann Dummont, a Microbiologist from Lallemand Oenology. Her explanations not only satisfied the “wine nerd” in me but also helped me understand the winemaker’s intent behind each wine.
Take any wine that you like for example, do you truly believe its creation was a pure accident? Probably not.
The winemaker decided to create this style of wine, he/she gave this wine form and shape from the raw materials to the bottle. Every step was meticulously planned and prepared to create a specific result. And the use of specific yeasts and wine bacteria played a very important role not only affecting the quality and style of this wine but also its shelf life.
Every fermentation requires two key ingredients, ripe grapes (with enough sugar) and wine yeast, also known as saccharomyces cerevisiae. If the winemaker decides to also put the wines through malolactic fermentation, bacteria is also needed, specifically oenococcus oeni and lactobacillus plantarum. Their job is to soften malic acid into lactic acid, yielding a softer/ rounder wine, with less acidity.
There are two schools of thought regarding fermentation, those that follow and use spontaneous fermentation, with indigenous yeasts and those that use inoculated fermentation with lab created yeasts. Spontaneous fermentation is like a roll of the dice, or like leaving everything to chance, by simply allowing nature to take its course. Pro-spontaneous fermentation winemakers are proud of being so “natural”, of using indigenous yeasts found mostly in the wineries, brought by insects, in wine making material, grapes and skins. They are always defending the funky aromas and flavors of some of their wines, which according to them can only happen during a spontaneous fermentation. But, when you make wine commercially, is it smart to relinquish control over the whole fermentation process? I guess, much depends on your tolerance to risk. This is why most wineries take the second path, that allows less risk by using inoculated fermentation. Here not only you have control of the whole fermentation process, and therefore the resulting wine, but you also reduce the chances of deviating from your objective, which is to make a sound wine that has no faults.
Now, the microbiological population varies through the different stages of fermentation, as seen in the graph courtesy of Lallemand Oenology. At the beginning and inside the berry, we find mostly non-fermenting oxidative flora, when the fermentation takes place, the balance changes, the oxidative flora diminishes greatly, and the fermenting species, the saccharomyces cerevisiae prevail. The process will continue even during aging with further changes.
(graph used with permission of Lallemand Oenology (adapted from Renouf, 2016)
So, at the beginning of fermentation, non-saccharomyces cerevisiae will be present in higher numbers, but as the alcohol levels begin to increase, saccharomyces cerevisiae will take over. That is the path you want to take to a successful wine fermentation. If on the other hand non-saccharomyces cerevisiae are allowed to dominate, not only you will have problems in finishing the fermentation and getting a dry wine but they also can create faulty flavors that should be avoided.
Using inoculated/selected yeasts is not only important to control spoilage microorganisms, it also aids to express varietal and terroir typicity and to develop certain wine styles. There are about 300 commercially available lab yeasts, many created on demand, some of them are better for certain styles, say red or for white wine or sparkling. Using inoculated yeasts, can help to increase acidity and freshness for example, or help the development of certain aromatics compounds, reducing sulfites and volatile acidity.
Of course, those in favor of spontaneous fermentation may say, inoculated yeasts will never provide the same flavors in a wine, than natural yeasts. But I disagree, inoculated yeasts, though created in labs like Lallemand, were also taken from wineries, from their vineyards and plots, and put through a 3-10 years rigorous selection process, whose main objective was to create a certain specific wine style, in a way, they customize the final product, providing in the process, many of the wine aromatics we like so much. Cheers! Silvina
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