Skin and seeds might immediately be removed from the juice. Pressing will then occur. You can also separate solids from juice through the use of a centrifuge. Grapes on the vine are covered with yeast, mold and bacteria . The grape juice will have fermented.
Fermentation is carried out in stainless steel vessels.
Yeast also gives flavor to the wine. But the yeast that is on the grape skin when it is harvested may not have the desired flavor. Unfortunately, the sulfites which remain in the wine may cause a lot of discomfort to some wine drinkers. The most common wine yeast is Saccharomyces. But if there's too much heat, the yeast won't work.