Vinification is the process through which must is transformed into wine. It is a very simple biochemical process from which are obtained all the different types of wine: red wines, white wines, sweet wines, etc… Vinification represents a key point in the production of wine, just like grape harvesting. It requires skills, precision and at the same time a propensity for experimentation. There is not just one kind of wine making process, but different processes according to the result to be obtained. The basic phases and techniques for the production of wine are as simple as they are complex at the same time.
Vinification: what it is
Therefore we said vinification is a biochemical process through which must, previously obtained by crushing grapes, is transformed into wine. The main characteristic of must is to be rich in sugars, in particular glucose and fructose. These sugars are transformed, in a very natural way, thanks to the action of yeasts. Yeasts are substances present in nature and belonging to the genus of saccharomyces, that is a particular species of fungus.
The skin of grape is capable of keeping some of these yeasts which have the time to transform sugar into alcohol. A natural process which is called alcoholic fermentation.
The importance of yeasts
Up to this point it is clear the fundamental importance of yeasts in the wine making process. Yeasts used are the ones belonging to the Saccharomyces cerevisiae species, artificially selected, the same ones used for beer as well. To be exact, yeasts are microorganisms with a spherical, oval or elliptical shape, infinitely small (5-30 μm long and 1-5 μm wide).
Yeasts populate grape skins, especially ripe grapes. In unripe grapes, ripening and harvesting allow sugars to reach the surface, thus feeding the yeasts which grow in population. In nature there are also natural yeasts, that is indigenous, belonging to families different from the selected ones.
On immature bunches we mainly find:
On ripe bunches, however, we find apiculate yeasts with oxidative metabolism:
At the beginning of the winemaking process, yeasts take advantage of oxygen in the air to transform sugars into CO2 and H2O. In this way they produce the right amount of energy which allows them to proliferate. The real fermentation process starts only after yeasts, due to lack of oxygen, pass from an aerobic metabolism to an anaerobic one.
The processes through which sugars are transformed, is called glycolysis, which takes place inside yeast cells. In the end we obtain
- ATP – adenosine triphosphate, high energy molecule
- Pyruvic acid – starting molecule for subsequent reactions
Under anaerobic conditions, yeasts transform pyruvic acid into carbon dioxide and ethyl alcohol, concluding the process of alcoholic fermentation.
Vinification: types, characteristics and differences
According to the different type of wine to be obtained, there are different vinification techniques:
- White vinification – draining is the phase in which the crushed grapes are separated from skins and seeds. It is done just after pressing and it is used to prevent tannins and other coloring substances from being transferred to the final product.
- Vinification in red – is the technique used for wines such as Amarone della Valpolicella and Recioto della Valpolicella. Crushed grapes are left to macerate together with skins and seeds. Tannins and coloring substances are therefore transferred into the wine, thus producing red wine.
- Rosé Vinification – is similar to the one of red wines, however the time of contact of must with skins changes. As a consequence the quantity of tannins and coloring substances transferred to the wine varies.
- Carbonic maceration – is used for the production of young wines. Grapes are pressed in the mass followed by anaerobic fermentation. The two phases allow the extraction of a higher quantity of coloring and aromatic substances.
The production of wine has many important phases which influence the final result: from viticulture, that is the set of agronomical techniques used to cultivate vines, to the selection of vines, that is the varieties of vines, every step is of fundamental importance. Not less important are the different wine making techniques which allow the production of a product, rather than another one, also influencing its quality.