In vinification, the short phase between harvesting, pressing and fermentation plays an eminently important role. The period should be as short as possible and the grapes should be moved or strained as little as possible mechanically to avoid undesirable contact with oxygen and loss of aroma. The composition of the must (ingredients) determines the necessary treatment steps. Care must be taken to ensure that no undesirable microorganisms such as Acetobacter (acetic acid bacteria) enter the must. Sulphurization of the mash/grapes is obligatory.
The must itself should only be sulphurised if left standing for a longer period of time or if the grapes are rotten. Aeration promotes the formation of yeasts and thus fermentation. However, this is only recommended for over-sulphurised must, heavily rotten grapes or for white pressing of dark grapes. A relatively new process is must oxidation with a deliberately massive supply of oxygen. A degumming (must clarification), on the other hand, is obligatory in order to remove undesirable substances and thus prevent fermentation errors and the resulting too rapid ageing of the wine. See also under grape must.