In winemaking, 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 stressed mechanically as little as possible in order to avoid unwanted oxygen contact and loss of aroma. The composition of the must (ingredients) determines the necessary steps of the treatment. Care must be taken that no undesirable microorganisms such as Acetobacter (acetic acid bacteria) get into the must. Sulphurisation of the mash/grapes is obligatory.
The must itself should only be sulphurised if it has been left to stand for a long time or if the grapes are rotten. Aeration promotes the formation of yeasts and thus fermentation. However, this is only recommended in the case of over-sulphurised must, badly rotten grapes or white pressed dark grapes. A relatively new process is must oxidation with deliberate massive oxygenation. Must clarification, on the other hand, is obligatory in order to remove unwanted substances and thus prevent fermentation faults and the resulting rapid ageing of the wine. See also under grape must.