Best practices during pressing
Traditionally, the maximum pressure for a horizontal press is 2 bars. The presses are then separated according to various criteria detailed in the following section (link). Generally, extraction is considered to be quite high over 1.6 bars on a pneumatic press. For a vertical press, the pressure values are different. The maximum pressure is around 5 bars, although some vertical presses can potentially reach 14 bars.
To obtain a good-quality pressing, it is necessary to:
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Have a steady flow of wine
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Avoid crushing the grapes during filling and during the pressing itself. This is achieved by minimizing the number of rotations of the marc. For this reason, chain presses are not recommended.
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Avoid rapid pressure build-up, as this does not favour a steady flow rate and increases the risk of extracting bitter and vegetal compounds.
Pressing times are longer during the early stages because there is more juice flowing out. On the other hand, at high pressures, there is very little juice and in order to maintain a constant flow rate, the time required at a given pressure level is considerably shorter.
New pressing systems now make it possible to have a customized programme for each pressing. The press itself is equipped with a sensor measuring the flow. As long as the flow is constant, the pressure is maintained. If it decreases, the pressure increases.
There is thus a pressing programme for each vat. Its only limit is the final pressing time, which remains variable. Working on a just-in-time basis can sometimes be complex.