3 zones for grape berry juice
Juice from a grape berry comes from three different zones. The composition of the juice is different in each zone. Working from the inside of the berry out towards the skin, the three zones are: central, intermediate and peripheral.
Crushing a berry (breaking open the skin) releases the free run juice. This is the sweetest juice, with the most nutrients and the least amount of harsh phenolics (tannins.) This juice comes from the intermediate zone …
When a grape berry is first pressed (where physical pressure is placed on it to extract juice) the first press juice also comes from the intermediate zone, in the middle of the berry, where most of the pulp/juice/water is located.
The pips/seeds are located in the central zone,in the center of the berry. When grapes are crushed (just broken open, not pressed) the crusher has to be set just right so that it doesn’t squeeze too hard and break open the pips. Pips have very aggressive tannins and that are typically considered to be undesirable in the winemaking process.
The peripheral zone is the area that sits just underneath the skin. There is very little juice in this area, but this is where many of the aromatics are located. You can not strip the skin away from this pulp without breaking open the skin cells. Breaking open the skin cells will also introduce undesirable, harsh tannins into the wine. A ‘cold soak’ is an effective way to get at these aromatics without breaking open the skin cells. The grapes are typically crushed (just split open) so the skin can come into contact with the free run juice from the intermediate zone. The mixture (called the ‘must’) is held for a short time at a cold temperature to prevent fermentation from starting. This maceration period on the skins allows for the aromatics to be leached out of the peripheral zone without releasing the harsh phenolics (tannins) from the skins.