Wine Fermentation
It is in wine fermentation that the magic begins… and this is nothing new. Wine fermentation — or rather, the fermentation of the must or grape juice — is a process thousands of years old. In Europe there are records of traces of wine found in Georgia, in amphorae dating back 6,000 years BC. This means that grapes have been fermented for at least some 8,000 years.
The oldest known winery dates from 4,100 years BC and was found in the town of Areni, in Armenia, where wine is still made today. In fact, history has it that ever since obsidian was used for tools, Man has been fermenting wine. In other words, this process goes back to the Stone Age.
What Is Wine Fermentation?
So what is wine fermentation? Alcoholic fermentation is understood to be the biochemical process during which yeasts transform the sugars present in the must into alcohol. During this process there are further results beyond ethanol, namely the formation of carbon dioxide and other by-products that are essential in wine production, since they contribute considerably to the chemical and sensory composition of the final result.
How Does Wine Fermentation Happen?
Wine fermentation can be a spontaneous or an induced process. In the case of wine made by natural or spontaneous fermentation, little or nothing is added to the must, with the fermentation of the grapes carried out by the indigenous yeasts of the vineyard or of the cellar where the wine is made. In the more conventional way, fermentation is normally induced by the addition of selected yeasts that the winemaker has chosen and which are aimed at a specific result designed by whoever makes the wine.
The Wine Fermentation Process
The wine fermentation process consists of transforming the sugars present in the grapes into alcohol. Once picked, the grapes are transported to the cellar where the grape fermentation process begins. The winemaker has several options in the way they will produce and transform the grapes into wine, but essentially they have to crush the grapes to obtain the must, or grape juice, which at that moment is merely sugar and water, together with all the precursors that will determine the quality of the wine.
Once the must is obtained, alcoholic fermentation begins, in which the yeasts transform the sugars into ethanol. And so the fermentation process ends, which is simple. The complexity of producing a good wine begins in the vineyard. Once in the cellar, it is a matter of controlling every phase of the wine’s fermentation and following it closely so that there are no deviations during the process, whether it is a wine of natural fermentation or of fermentation with selected yeasts.
How to Stop Wine Fermentation?
Wine fermentation stops naturally.
When? At the point when the fermentable sugars in the must run out, or else when the fermentation conditions cease to be favourable to the yeasts.
There are, however, various ways of stopping wine fermentation, among them cooling the must to temperatures at which the yeasts are unable to ferment.
There are even wines, such as late-harvest wines, in which fermentation stops halfway, owing to the high concentration of sugars still to ferment.
In this case, together with the alcohol already produced, the sugars limit the life of the yeasts, which end up dying before the end of alcoholic fermentation, resulting in a sweet wine.
We will speak of these and other partially-fermented wines in a future article on the winemaker’s blog. Until then.
From the page to the glass
- Cascale T Tinto — Spontaneously fermented at 690 metres, 18 months in French oak. Organic.
- Cascale Petroleiro Palhete em Talha — White and red varieties together in clay talha, sealed for eight months.
- Portie Vinho do Porto Vintage — A single-harvest 2010, foot-trodden in the stone lagares of the Douro.
