Fermentation: FROM GRAPE JUICE TO WINE

After harvesting, we get the must through crushing or mashing processes. The biochemical transformation process in which all the sugars, or most of them, are converted into alcohol and carbon dioxide is known as alcoholic fermentation.

The primary aromas are hidden in the grapes and it is the fermentation that frees them in the wine produced.

At the end of fermentation we will have two types of aromas:

- aromatic compounds first bound to sugars and then released

- the aromas produced by the metabolism of yeast, an actor in the fermentation process

 

What is yeast and how does it behave?

The yeast is the protagonist, it can be selected and added to the mass or we can use the spontaneous population already present on the outer surface of the grapes making the so-called "spontaneous fermentation" from indigenous yeasts .

At the beginning of the fermentation process the yeasts in the tank use the oxygen present in the must to breathe and produce energy, transforming the sugars into water and carbon dioxide.

Then it will find itself in a reductive environment, therefore in the absence of oxygen.

The second option, but not the preferred one, is to transform sugars into a by-product, or alcohol, in addition to producing carbon dioxide in this case as well.

This chemical reaction also gives rise to other compounds or "by-products", which play a very important role in the overall aromatic and gustatory profile of the wine; the most relevant are acetaldehyde, acetic acid, ethyl acetate, glycerol and other alcoholic molecules.

Glycerol occurs in the initial phase and is a very important concentration that will accompany alcohol in the softness of a wine.

The importance of alcoholic fermentation

The alcoholic fermentation was strongly misunderstood for a very long time but identifies the process that allows the winemaker to transfer from the grapes and enrich the future wine through metabolic pathways, which can evolve complex and maturing, or deteriorate over time for a fermentation that has not given the right merit to the harvested grapes.

2 Comments

  1. Molto utile , però vorrei capire questo passaggio
    The second option, but not the preferred one, is to transform sugars into a by-product, or alcohol, in addition to producing carbon dioxide in this case as well.
    Credevo che la formazione di alcol fosse lo scopo della fermentazione alcolica…

    • Ciao Natalia,
      Ti ringrazio del commento.
      La via preferenziale dei lieviti è la respirazione quindi utilizzare l’ossigeno del mosto per produrre attraverso la respirazione acqua e anidride carbonica, oltre ovviamente ad altri composti secondari biochimicamente prodotti.
      Terminato l’ossigeno il lievito si ritrova in ambiente riduttivo con sola anidride carbonica.
      Ecco che si innesca la fase fermentativa dove gli zuccheri vengono trasformati in alcool, prodotto si scarto per la cellula del lievito.
      Quindi ti dico che è il nostro scopo far produrre alcool al lievito attraverso la fermentazione, ma non lo scopo preferenziale della cellula del microrganismo.

      Spero di aver chiarito.
      Saluti
      A presto
      Christian

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