There are many designs for wine presses but the object for all styles is the same ie. to extract juice from crushed grapes (the must) or sometimes whole uncrushed bunches.
The press exerts controlled pressure in order to free the juice from the grapes. The pressure must be controlled in order to avoid crushing the seeds and any remaining stalks which releases undesirable phenolics into the wine.
We have a simple manual basket press which is probably the most recognizable piece of wine equipment. It's basic design has not changed in nearly 10 centuries.
A basket press consists of a large slatted basket which is filled with the crushed grapes.
The basket consists of two halves which are locked together with pins
Pressure is applied through a plate that is forced down onto the fruit. In some cases, when grape volume is low, we need to add blocks on top of the plate to apply the necessary pressure.
The mechanism to lower the plate onto the grapes is a manually operated screw. A long handle inserted into a slot in the screw (on the right) enables more pressure to be exerted. More sophisticated and larger basket presses are hydraulic.
The juice flows through openings in the basket leaving the skins, seeds and stalks (the marc) behind.
For red wine considerable pressure is used to extract as much skin tannin (within reason) and colour as possible.
The marc can be virtually dry when pressing is finished. Many wineries separate free run and pressings to be blended later. We have never seen the need for that here and return the pressings immediately to the free run.
For white wine less pressure is used as we try to avoid skin tannins being introduced into the wine and concentrate on getting as much free run juice out of the must as possible. There requires constant tasting of the juice flowing from the press. The decision to stop is always subjective.
The picture above shows the difference in height of the marc remaining after pressing both Tempranillo and Semillon although the initial amount of must was approximately the same.
Luckily with our operation being non commercial we can err on the side of caution not having to worry about yield and economics, just quality.