The harvest season is over. The grapes are already in the cellar, de-stemmed and placed in deposits. It’s the beginning of the fermentation step. What kind of fermentations can be carried out? How do the yeasts act? This is the transformation of grape juice into wine.

Another year has gone by and the beautiful harvest time it’s over. The staff is ready to begin developing the new wine. The grapes come into the winery and head to the stemmer / crusher machine, which will leave the grapes without the scratch or stalk, by this we mean without the plant structure of the cluster. For the production of red wine, the must obtained passes to macerate in to the tank along with the grape skins achieving the extraction of color and aromas. The pigments in charge of the color of the wines are called polyphenols, found it mainly in the skin and seed of the grapes and going through the wine by maceration. These chemicals are antioxidants and give the wine beneficial properties for health, such as reducing the risk of cardiovascular disease, among others. In the case of white wines, the grapes are pressed right away, the skin won’t be present during fermentation.

We have already isolated the must. The second step will be to transfer the must to the tank where the alcoholic fermentation will begin by fermentation yeasts. The work of these yeasts are to consume the sugars of the must to produce ethanol and CO2, i.e. transforms sugar into alcohol.

Fermentation can be spontaneous or inoculated. What is the difference? In spontaneous fermentation yeasts are called “indigenous”. They are naturally present in the grape skins and are typical of the terroir. A wide variety of yeasts are involved, which will sequentially grow and develop throughout the process. This stage is unpredictable and sometimes delays or stops in fermentation may occur. However, it has a feature that makes it special: you can get wines with increased sensory complexity (the reflect of high microbial diversity) and identity that reflect their geographical area, the soil and climate of the vintage.


Furthermore, the inoculated fermentation is applied in the wineries by 80 or 90 percent of cases. In this case, man decide the most appropriate yeast strain to achieve specific sensory results with a better aromatic extraction or higher organoleptic complexity. These yeasts have been specially selected for their excellent adaptation to the environment and offer a wide range of possibilities available to the winemaker. With this inoculated yeast we want to ensure that fermentation will be completed in a reasonable time, imposing itself on natural microbiota ensuring the absence of unexpected sensory deviations. For example, certain strains of yeast (“the killer” type) ensures a quick and full implementation, useful in difficult conditions such as high temperatures or in presence of large populations of indigenous yeasts.

There are two main reasons why wineries often opt for the development of inoculated fermentations. As the process is controlled and will be complete, without delay or stuck fermentations, it’s easier to maintain health and safety in the course of fermentation. The final wines will be homogeneous, reducing the chances and, therefore, the possibility of suffering problems.

Nowadays, platforms like WineSeq can already see what indigenous yeasts are present in grapes and which of them can provide a better quality in the wine organoleptic properties, maintaining the identity that gives the terroir. Thanks to this tool, the winery receives advice about plots with greater microbiological potential or those which can lead fermentative risks, by this; you can reduce the risks involved in making a spontaneous fermentation.

After the alcoholic fermentation stage, there is a subsequent fermentation where microorganisms act again, the malolactic, where lactic acid bacteria are responsible for lowering the acidity of the wine.

As you have seen, bacteria and yeasts are behind all the fermentative process and have a very important role conferring the aroma and taste of wine. Do you already know your “MicroWineMakers”?