What is the alcoholic fermentation of wine?

In the alcoholic fermentation of wine, yeasts are the main protagonists

The alcoholic fermentation of wine is a fundamental biochemical process in the production of this age-old wine

Life is a constant transformation. People change over time. Spaces acquire new uses. Technology evolves. Customs adapt to new times… Wine is a perfect example of this idea. From the time the grapes are harvested until we taste a bottle of wine, it undergoes a constant transformation.

One of the key moments in the eternal mutation of this process is undoubtedly the alcoholic fermentation of wine, which takes place after the grapes have been harvested, macerated, and racked. That is when the must is already clean and ready to be fermented.

What is the alcoholic fermentation of wine? A biochemical process by which yeasts convert the glucose and fructose molecules present in the grape must into ethanol and carbon dioxide, essential to protect the wine from the effects of oxidation.

In addition, heat is also produced during this process, because the alcoholic fermentation of wine is also an exothermic process. So one of the key issues is to control the temperature so that it is optimal throughout the alcoholic fermentation of wine and its elevation cannot cause it to stop.

We will now unravel the keys to the alcoholic fermentation of wine to understand a fascinating process that determines the characteristics of winemaking.

Yeasts, the stars of the show

When we think of yeasts, it is impossible for our heads not to be filled with beautiful pieces of bread and delicious biscuits. However, these single-celled microorganisms of the fungi family are essential for making other products of our daily lives, such as beer and, of course, wine.

Given what we have just described, we can see the importance of yeasts during alcoholic fermentation, one of the most important moments in the winemaking process.

It is not that they are relevant, but rather that they are indispensable since they are in charge of fermenting the must.

Most yeasts used in the alcoholic fermentation of wine come from the saccharomyces family, such as the most common, saccharomyces cerevisiae.

Now that we have defined the role that yeasts play as protagonists in the alcoholic fermentation process of wine, it is time to answer a question that you have probably already asked yourself: where do yeasts come from?

Yeasts are present in the vineyards and can be found on the grape skins. However, commercial yeasts, i.e. yeasts cultivated in laboratories, can also be used in the winemaking process.

Each winemaking team must decide whether to use only natural yeasts or, on the other hand, select other yeast strains, depending on the wines it intends to make.

Moreover, technology and science have advanced so much in recent decades that wineries themselves can make a selection of yeasts from their vineyards to decide which yeasts to use in each of the winemaking processes they create.

The alcoholic fermentation of the wine is a critical process for these products

Key factors in wine alcoholic fermentation

Does alcoholic fermentation consist only of letting the yeasts do their job? Of course, it is not. It is a delicate and crucial process that must be continuously and exhaustively monitored to achieve the desired results.

To achieve this, it is essential to take into account and manage all the factors that affect the alcoholic fermentation of wine:


This factor directly affects yeast activity. The usual temperature of the alcoholic fermentation process is different in white and red wines. White wines ferment at temperatures below 20º, for example, while Albariño wines ferment between 15 and 18º. Red wines ferment at higher temperatures, approaching 30º.

It should also be borne in mind that the higher the temperature, the faster the yeasts will act. However, it should be borne in mind that too high temperatures can cause the fermentation process to stop (from 34º). In addition, as mentioned above, this biochemical process generates heat, which, if the temperature of the fermentation process is not controlled, will increase. This is why wineries have systems to control the temperature and maintain it at an optimum level throughout the alcoholic fermentation of wine.


If controlling the temperature is crucial, the other factor that is continuously monitored throughout the process is the density of the winemaking process. Why? Thanks to this measure, it is possible to know how much sugar is still in the must.

As time passes and the yeasts do their work, the sugar will decrease and the alcohol level will increase.


How long does the alcoholic fermentation of wine take? Each winery and each winemaking process is different, but the period for what is known as tumultuous fermentation is generally between 15 and 20 days. The adjective tumultuous refers to the fact that the wine is boiling over as a result of the biochemical process carried out by the yeasts.

If the alcoholic fermentation of wine lasts longer, the yeasts will be allowed to act more and, therefore, they will consume more sugar.


Both in the alcoholic fermentation of wine and in its subsequent aging, the tanks used play an essential role.

The most common containers used in wineries around the world are stainless steel tanks. However, containers made of other materials such as wood or concrete are also used.

In addition to the material from which the vessel is made, it is important that it also has a temperature control system, such as a cooling jackets.

These factors and their permanent control by enology teams show that the millenary art of winemaking has adapted to the passing of time and has been enriched by technological and scientific advances. Today, professionals can design wines with a level of precision and complexity that would astound the master winemakers of the past.

Alcoholic fermentation of wine occurs when yeast transforms the sugar in the grapes into ethanol

What happens after the alcoholic fermentation of wine?

The alcoholic fermentation of wine ends when the yeasts die. Some experts consider that, as a general rule, the process ends when, by measuring the density, it can be observed that less than 10 grams of sugar remain per liter. However, this depends on the type of wine to be obtained. Semi-dry wines and, above all, sweet wines have more grams of sugar per liter than dry wines.

How is alcoholic fermentation interrupted? There are several ways. Fermentation can come to an end naturally because the yeasts run out of nutrients and there is only a residual amount of sugar left in the wine. But it can also be brought to an end by removing the yeasts or by carrying out chemical processes such as fortification.

As we said before, once the alcoholic fermentation of wine is finished, the yeasts die and end up at the bottom of the tank, becoming what is known as lees.

From this moment on, the professionals in charge of winemaking must choose between two alternatives:

  1. Racking. Traditionally, winery professionals proceeded to separate the wine from the lees.
  2. Aging on the lees. Today, however, many wines, such as Pazo Baión’s albariños, are not racked at the end of the wine’s alcoholic fermentation but are aged on the lees. For this purpose, the technique of batonage or periodic stirring of the lees is used. The batonage influences aspects such as the smoothness of the wines and their aromas.

Alcoholic fermentation of wine and secondary aromas

Precisely, the aromatic composition is one of the most important elements of any wine. The notes that can be detected when tasting this type of elaboration are fundamental in providing the wine with complexity, confirming it as an extraordinary beverage.

In general terms, we can establish that there are three main groups of aromas in wine:

  • The primary ones, are associated with the grape and in which its variety and the terroir of the vines play a key role.
  • Secondary aromas originate during fermentation.
  • The tertiary or bouquet, is a product of the aging process of the wine.

Thus, the alcoholic fermentation of the wine plays a crucial role in its aromatic composition, because during this process the work of the yeasts and the temperature generate aromas of the bakery family. Hence, in some wines, notes of bread, sponge cake, or brioche can be found, as in the case of Vides de Fontán.

The alcoholic fermentation of Vides de Fontán is carried out in two different types of vessels

Single-estate wines made with «single-estate» yeasts

How is the alcoholic fermentation of wine in our winery? In terms of temperature, it is kept controlled between 15 and 17º. As regards the containers, we use small capacity tanks (50 and 100 hectoliters) made of stainless steel (with a small exception) and with refrigeration samias. But the most relevant, as it could not be otherwise, are the yeasts we use. Why? In this fermentation process, only native yeasts are used, that is to say, yeasts that come from the Pazo Baión vineyards.

These yeasts are deposited on the skins of the grapes from our vineyards and accompany them from the vineyard to the tanks where alcoholic fermentation takes place.

Working with indigenous yeasts is fundamental to achieving the typicity and uniqueness of the three elaborations that are carried out in the Pazo Baión winery: the only single-estate albariños. That is wines made exclusively from grapes harvested in the property’s vineyards.

Beyond the use of native yeasts, we can highlight other differential factors in the process of alcoholic fermentation of wine that allows us to produce not only a Rías Baixas that contains the essence of the albariño grape as Pazo Baión but also two wines as surprising as Vides de Fontán and Gran a Gran:

  • To make Vides de Fontán, the must is divided. One part of the must is fermented in French oak vats and the other in stainless steel.
  • In the case of Gran a Gran, the alcoholic fermentation of the wine stops when the wine has 18 grams of sugar. For this purpose, cold and sulfur dioxide are used to maintain this percentage of sugar and thus achieve a semi-dry Albariño.

In short, the alcoholic fermentation of wine is a fascinating biochemical process that is decisive when it comes to making unique, complex, and aromatic wines. When fermenting the must, the work carried out by the yeasts is as important as the techniques of the winemaking teams who spend two weeks controlling even the smallest detail of this incredible process.



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