To process white wine grapes the vintner always tries to harvest, whenever possible, at cool temperatures. This makes it possible to keep the mash longer for maceration periods without taking a microbiologically high risk of, for example, the formation of volatile acids.
Basically, one can differentiate the following possibilities: The berries can be destemmed as in red wine which means that the berries are separated from the stems. The grapes themselves, if in very healthy condition, can either be gently crushed or filled without additional treatment directly into the press. This is called whole cluster pressing. The winemaker’s decision is based mainly on the health of the grapes, whether the stems are still green or already lignified, whether a maceration period is required and whether particular attention must be paid to the preservation of the acidity.
To fill the press either a conveyor belt or a forklift is used to empty the harvest box. Depending on the maceration time, the press is then turned around and the juice runs by itself into the must vat. Thereafter, the actual pressing is started. For this purpose, a membrane is inflated with compressed air in the interior of the press which pushes the berries against a strainer. The less pressure is applied the gentler the grape juice can be obtained. It is also possible to separate the individual parts of the juice. We differentiate between free-run juice and juice from a pressing stage.
Due to the friction of the berry skins and seeds, some of the tannin gets into the must during pressing, therefore the juice from pressing can be treated separately. After the final pressing, the press is emptied and the residues are processed as compost.
The must is racked from the press into the tank and the sediments can settle on the bottom overnight. The next day, the clear must is racked into the fermentation tank and fermentation begins.