Extraction equipment

The

extraction of polyphenolic compounds and aromas is an essential objective in red winemaking. This extraction is often difficult and always incomplete: only 30 to 60% of the berry's potential polyphenols are generally extracted. Depending on the quality of extraction, these elements can have a positive or negative impact on wine quality.

Manufacturers offer a wide range of equipment and processes to improve extraction. Comparisons between them have been the subject of numerous experiments, providing information on their respective performances. Each technique has its advantages and weaknesses. Results vary greatly depending on the grape variety and maturity of the harvest, as well as the conditions under which the equipment is used.|

The different extraction techniques

Pumping over

Pumping-over is currently the technique most commonly used to extract polyphenolic compounds from grapes during fermentation. This simple, inexpensive technique involves percolating the fermenting must through the marc cap. In order to carry out this operation as effectively as possible, the following rules should be observed: the entire surface of the cap should be watered evenly and completely, the shape of the tank should be the same height as its diameter, and the tank should be filled to a maximum of 80%. Pump overs can be carried out in different ways:

Pump over by spraying the marc

Pump over using a mobile pump remains the most frequently used method. The pumps are generally reciprocating piston pumps with high flow rates.

Conditions of use are often basic and sometimes unsuitable. It is 'accepted' that pumping a third or half of the must from the vat is a necessary and sufficient volume. This pumping-over method requires continuous monitoring.
The availability of pumps and staff very often determines the frequency of pump-overs.

To be effective, pumping-over requires the juice outlet to be unclogged. A large-diameter full-flow valve is required, as well as a filter. The classic filter is the faggot, which is often effective but not very hygienic. Various devices are available, such as wooden frames and grids, but their effectiveness and cleanability are not always guaranteed. The most rational solution is a large perforated grid, preferably placed vertically.

By spraying the entire surface of the marc, without creating preferential passages, the juice is renewed on contact with the solid parts and the extracted substances are diffused throughout the mass. This requires spraying devices adapted to different configurations (shape of tank, central or off-centre chimney, etc.).

Pump over using a tank-mounted pump. This system makes it possible to automate pumping, reducing the amount of monitoring required. This type of fixed installation is on the increase.

The duration and frequency of pump-overs can be programmed, making it possible to carry out sequenced pump-overs.

have shown that sequenced pump-overs extract more polyphenols than conventional pump-overs. The pumps are generally placed outside, on the tirage au clair. They are usually of the centrifugal type or, better still, with flexible vanes (impellers) or a helical rotor.
|The filtration grid must be correctly sized and positioned to prevent clogging and deformation by negative pressure. The pump used can also be of the submersible type, the benefits of which have yet to be demonstrated.|

Pump over pump fixed to tank

Pump overs by gas diffusion (stirring)

The gas diffusion pumping-over technique involves injecting gas(nitrogen or compressed air) under the cap of marc. A pipe fitted with diffusers is inserted either through the tap or through the cap via the upper hatch in the vat.
The injection of gas at pressures of 2 to 4 bars and flow rates of around 20 m³/h (N2), for a period of 2 to 3 minutes, causes the liquid to rise through the cap and break it up . This process, which has been shown to be effective, is much easier to use than classic pumping over.

Punching

Punching is a traditional technique, particularly in Burgundy. It consists of pushing the cap of marc into the juice, while crumbling it. Initially done by hand, pigeage can now be done mechanically. In general, pigeage improves extraction of polyphenols by around 20% compared to pumping over. However, the performance of this process varies greatly depending on the grapes being processed, and in particular the grape variety.

Turbine pump-overs use the pressure and flow provided by a turbine inside a stainless steel tube immersed in the vat to break up the marc skins

Specific tanks

Specific tanks incorporate one or more pieces of equipment designed primarily to optimise the extraction of phenolic compounds during (or after) alcoholic fermentation. The general principle is the temporary or continuous immersion of the marc cap and its regular destruction during maceration.
Various types of equipment are available: automatic fermentation vats, vats with immersed cap, delestage vats and special vinification vats.

Other post-fermentation techniques are used to extract polyphenolic compounds from the grapes: heat treatment of the harvest or flash détente. These very rigorous operations require very substantial infrastructures and quantities of thermal energy. Most of the time, they meet specific extraction needs that cannot be met by the maceration techniques described in the previous chapters.

It is important to note that some of these processes can radically alter the characteristics of the wines (structure, colour, etc.). As with all winemaking tools and products (temperature control, enzymes, tannins, etc.), the development of the musts and wines should be monitored very regularly (analyses, tastings, etc.) to ensure that the desired product is obtained. In all cases, it is essential to seek advice from an oenologist.

Experiment

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