Term (also called pressing) both for the process of pressing the grapes and for the mechanical equipment necessary for it. Presses have been used since early antiquity, as evidenced by finds of several thousand year old artefacts in many ancient wine-growing areas. Among others, the Roman writer Cato the Elder (234-149 B.C.) reports about this in his works. Pressing is a crucial step in the winemaking process. As a rule, only healthy and physiologically ripe grapes should be used for processing, which is achieved by appropriate preparatory work such as selective grape harvesting. Depending on the type of wine, a decision must be made as to whether destemming (destemming, vine pruning) should be carried out before pressing, i.e. whether the grape skeleton should be removed. During pressing, the grape must is separated from the grapes by mechanical pressure. Depending on the type of wine, it is separated from the solid components and then processed further, especially in white vinification, where pressing is usually the first step. In red vinification, this is only done after the classic maceration.
When the combs are pressed along with the grapes, they release tannins (tannins) and pigments (colourings), which can be desirable for grapes with a strong fruit flavour or is common in red wine making, for example, with the maceration carbonique technique. The grapes should be processed as gently as possible by minimising mechanical influence in order to keep the undesirable turbidity (smallest suspended matter from berry skins and fruit flesh) and tannin content in the must as low as possible during white vinification. Modern cellar technology therefore tries to use the natural force of gravity instead of pumping to move the grapes and must. Each pumping process increases the trub content by up to 1%. In this respect, pneumatic tank presses are the most gentle.
By using pneumatic presses and frequent whole grape pressing, undamaged grapes are processed because the gentle pressing process does not crush the combs and there is no danger of too much tannin in the must. Depending on the variant, the grapes (with or without combs) are then crushed or ground, thus breaking up the berries and making it easier for the juice to escape. The desired intensity can be variably adjusted. An ancient form of crushing is to crush the grapes with bare feet in a container. This is still common today, especially in southern countries, for example in the production of port wine. The result of destemming and crushing is called mash. In red wine making, mash fermentation now starts without pressing, in white wine making, pressing is now used. For an optimal course of fermentation an appropriate must treatment must be carried out.
The mechanical device required for pressing is called a press or wine press. A distinction is made between conventional vertical presses and horizontal presses, which are common in newer systems. One of the oldest forms is the Torggel (Torkel), which was in use until the Middle Ages. For many centuries the very similar tree presses were used, which today can only be admired as exhibits in many old cellars. Over a long beam called a tree, a massive plate is pressed down on the grapes or mash in a basket. The must runs off through the slits of vertically arranged wooden slats fixed by hoops. There are different variants in detail, the principle method of operation is as follows:
With the so-called Basket presses the pressure on the plate is achieved either manually or mechanically with a rotating spindle. The disadvantage is the relatively small filling quantity, but above all the strong oxidation and the big problems or effort to keep it clean. The advantage, however, is the relatively low because very slow, gentle pressing pressure. In the Champagne region, special basket presses are therefore traditionally still obligatory in some houses for the production of the best Champagne qualities.
Today, horizontal presses are mostly used (especially in larger companies). With the screw press, mash is constantly being filled in at one end, the juice flows through sieve walls and the pressed pomace emerges at the other end. In large wineries, this is mainly used for bulk wines, because it achieves a high must yield of up to 85% corresponding to lower quality. Other conventional types are spindle, screw or toggle presses. In these presses, a movable plate in the basket is pressed against a fixed end plate or two movable plates move towards each other. These systems, which operate on the hydraulic principle, are the most frequently used presses today.
In the pneumatic tube press, a long press tube located inside a container is inflated, thereby pressing the mash against the walls. Since there is a much larger pressing surface, the berries are treated more gently and less tannins (tannins) get into the must. These presses combine the advantages of the tree press (low pressure) with low oxidation and germ-free conditions. They can also be fed with variable quantities. A further development is the pneumatic tank press. These can also be filled with inert gas (protective gas) to keep the oxygen away. There are also variants with a perforated outer jacket, which are particularly suitable for white wine.
Whole grape pressing is a pressing method in the production of white wine and sparkling base wine. It was only with the spread of pneumatic presses or tank presses that it became widely used worldwide. In this process the intact whole grapes are pressed without prior destemming or crushing. One mashing stage is eliminated. Traditionally this is used in the production of champagne, as in this case the blue grapes must not give off any colour and tannins to the must. The must obtained in this way produces a delicately aromatic, delicately fruity wine typical of the grape variety with a slightly higher acidity. However, the must yield is up to 10% less.
Due to the large pressing surface and the low pressure that is thus made possible, no parts of the bellows (berry skin) get into the must, which contains aromatic and flavour substances, even in the case of white grapes. It must therefore be accepted that the total extract is reduced, which can lead to wines with a weak expression. In order to prevent this, sometimes only a part of the grapes is processed in this way. The process requires years of experience. It is mandatory for the production of champagne and crémant.
In general, 1,000 kilograms of grapes yield about 750 to 800 litres of grape must, depending on the grape variety, grape ripeness, vintage and pressing technique. Depending on the desired end product, pressing can be carried out in several passes, with the must quality steadily decreasing. In between, the press cake is loosened (failed). In conventional mash pressing, the must is divided into three fractions. In the graphic it is clearly shown which parts of the berries or which of the relevant constituents of the grapes are affected (see 11.a First pressing, 10.a Second pressing, 12.a Third pressing):
Even before pressing, the grape's own weight causes the flow of the must (filter must). It makes up about 30 to 50% of the total volume, consists mainly of sugar, must acids and some extractives, but is low in tannins. Pressed must obtained at low to medium pressure accounts for about 40 to 60%. It is richer in extracts and contains many tannins and minerals. Preliminary and press must complement each other and are processed together to produce a strong, tasty wine.
The result of the last pressing processes, which must already be carried out at relatively high pressure, is called must failure. The quantity is now only 5 to 10%. This must has a multiple of oxidizable cloudy substances, tannins and oxidases. The latter are responsible for the browning, which is why sulphurization must take place. If it is added to the main must, a gelatine treatment is necessary. In most cases, however, it is processed separately and yields a wine rich in tannins of inferior quality or it is distilled. Only the best pressing results(cuvée and waist) are used in the production of champagne.
A complete list of the numerous vinification measures and cellar techniques, as well as the various types of wine, sparkling wine and distillate regulated by wine law, can be found under the keyword vinification. Comprehensive information on wine law can be found under the keyword wine law.
Animated tree press: By Vignes - own work, CC0, Link
Gasoline pump: By Bauer Karl - own plant, CC BY-SA 3.0, Link
Tree press Salem: From CrazyD - even photogr. , CC BY-SA 3.0, Link
Basket press: Caravan