13 Nov Colour extraction in winemaking: soft and smart.
Polyphenols, tannins (or more accurately known as flavonoids or proanthocyanidins) and anthocyanins, which are responsible for most of the features regarding the quality of red wines, as well as aromatic compounds, can be found in grape skins.
That is why in the vinification of red grapes maceration and extraction, a process in which the substances contained in the skins are extracted and pass into solution in juices and wine, is a crucial process to produce quality wines. Starting with quality grapes of course, the key is to extract what we are interested in as part of the maceration process and then to maintain it, stabilise it, and to make it evolve into the desired features as it both matures and ages.
While anthocyanins are found in a solution inside the vacuole of the cells of the skin and then simply pass into the juice via a phenomenon known as diffusion, from the early stages of maceration, proanthocyanidins are bound more firmly into the structures of the cell, and require the presence of an extraction agent (alcohol), while at least a small section of the cell wall must also disintegrate.
Tannins (flavonoid proanthocyanidins) are also present in grape seeds from where they are extracted however, only later when the protective layers of the cuticle are dissolved by alcohol action. These tannins are often characterised by herbaceous taste and smell and a strong astringency, and only cases where the maturation of seeds is particularly good can their extraction be an advantage when it comes to the final quality of the wines.
Extraction techniques are in some cases very old, and have been technologically reviewed recently (such as punch down or submerged cap fermentation), others are recent or highly advanced, while some others, developed in relatively recent years, however, were soon abandoned (who cannot fail to remember horizontal rotary fermenters, like “concrete mixers”?). In order to give wines their quality features and to extract only the useful substances (and not those which are responsible for vegetable like features or tastes described as “dry”), we will list some of the maceration techniques and devices which allow the application to respond to some of the principles:
adapting it to the characteristics of quality and the ripeness of the grapes;
avoiding tearing of the tissues of the skin which increases the extraction substances with green and veggy characters, and which increases problems of excessive lees which absorb colour;
facilitating the processes of diffusion from inside to outside the berry, revitalising it by mixing the juice when in contact with the skins;
allowing a uniform and homogenous liquid-solid contact;
wetting the cap in a homogeneous way, washing away the substances extracted from the entire volume, thus avoiding the formation of preferential paths of the liquid element, and a different distribution of the interior temperature.
not overlooking any microbiological aspects. The juice is a breeding ground for all micro-organisms, bacteria, yeasts and mould: the moving parts must be easy to clean and no dirty surfaces should remain in contact with the air between any one leaching operation and another.
Follature (Punch down)
Punching down is the technique which allows the cap to be wetted and toppled by pushing it down with a body of a different shape, a disc or a crate, either manually or mechanically or automatically.
A good punching down process must have a slow and gradual movement for lowering and wetting the cap without bumping and causing damage to the skins; it must move throughout the cap so that the leaching process takes place in a uniform manner; finally, it must be constructed in such a way as to spill out easily the cap, and to remain clean between punching down operations.
This extraction technique has spread since the advent of electricity in the cellars. It consists of drawing the liquid from the bottom of the tank and using it to spray the top cake which is made from solid parts.
The liquid is removed by a pump, and the volume of liquid being pumped over therefore depends on the time it is pumped, and on the capacity of the pump: pumps with low flow and frequent pumping (possibly using automated systems) causes soft leaching, and prevents the liquid jet from colliding violently with the skins. The adjustment of the pump and of the spraying times are not sufficient to ensure a good leaching process, which is also dependent on the shape of the tank, on the position of the sprayer, and its characteristics. The spreaders are the tools used to distribute the juice on the marc cap. They can be just a simple splitter jet (such as the so-called Chinese cap), or a rotary driven by the pressure of the jet itself or finally an engine based device with separate nozzles.
The rotors (those driven by pressure) distribute the must often very heterogeneously. The must is projected in the peripheral part of the tank where it causes an over extraction of marcs that are close to the wall.
The intelligent spreader developed by Parsec is equipped with two independent engines. Six customizable programs allow the device to work on tanks with six different geometries.
Spraying is made homogeneous by several innovative solutions:
the parabolic speed of the nozzle accelerates on the vertical when the surface to be wet is small and slows down in a horizontal position when on the contrary the surface of the marc is more important;
the modulation of the flow changes with the angle of the nozzle, limiting the spray when it is in vertical position and perpendicular to the cap, to avoid triturate the marc and increasing it when instead the nozzle back in a horizontal position.
Other innovations allow to optimize the use of the spreader , such as changing all corners of a program by changing the parameter of the filling level , or even during a delestage, automatically following the ascent of the marc during filling of the tank.
In a test carried out in France in 2009 in the Medoc region of Merlot, a spray system with traditional rotor was compared to the Intelligent Spreader of Parsec. The results showed a greater ability of the second system when it comes to extracting colour throughout the maceration phase. A sensory analysis conducted after the racking phase had shown that the intelligent spraying system was able to produce wines with less veggy and astringency characters which were characterised by greater softness and an overall quality in terms of taste.