In the cellar or winery everything is ready for the grapes which are being picked. Things have to be done quickly; fermentation could begin even before the grapes have been crushed. And this is also the reason why the most careful vinegrowers collect grapes as carefully as possible in small containers.
Once the grapes have been harvested they are destemmed (separated from the stems) and crushed (in practice they are squashed).
For red wines the crushing and stemming are carried out together. There are machines which first separate out the stalks and then break the grapes without spoiling the skin and without crushing the seeds. This ensures that the tannins contained in the woody stalks get into the wine as little as possible (they give a strong herbaceous taste with a bitter undertone) and avoids crushing the seeds which would cause too much tannin to come out as well as an oily substance which would have a bad effect on the wine.
For white wines (obtained both from white grapes and from dark-skinned grapes) pneumatic presses are normally used. These can crush the grapes gently to obtain clean enough must with refined, delicate, fruity perfumes and very few tannins. The grapes may be in whole bunches or first separated from the stalks. The must then has to be separated from the skins and other solid parts of the bunch immediately after crushing. Before fermentation is started the must is usually clarified.
RosÈ wines, on the other hand, are left in contact with the skins for a very short period (24-36 hours) and then separated and clarified as for white wines.