Maceration is one of the most delicate and important moments of the preparations of red wines and is a crucial point of the whole production process. Essentially, that period can be subdivided into three parts: pre-fermentation aqueous maceration (PMF), relatively short; maceration parallel to alcoholic fermentation, lasting for 2 to 7 days depending on the conditions; post fermentation maceration, typical of the wine to age, lasting from some days to some weeks. The control of maceration during the red winemaking is made depending on the quality of the raw material and of its ripening degree (1). The variables on which you can intervene are the so-called maceration factors. These factors can be subdivided into: endogenous factors, such us warmth, ethanol, carbon dioxide, and exogenous factors, i.e. sulphur dioxide, pectolytic enzymes, the operations of must-wine stirring. The last operations, maintaining the concentration gradient of wetting liquid, solid parts, and the liquid mass active, allow extracting most phenolic compounds (2, 3), in an optimal time depending on the type of wine produced. Besides the pumping-over, the most common operations include the wine-crushing, often preceded by the wetting of the cap to improve its submersion, as well as most recent technologies, such as deléstage (4).
Independently from the extractive technique used during maceration, the phenolic compounds fi rstly of the must and then of the wine are involved in a series of chemical reactions leading to the formation of different structures and to the stabilization of the colouring material (5) in the course of time. The reaction of combination between the phenolic compounds leading to the chromatic stabilization and to the modifi cation of the sensorial characteristics of the wine is caused by processes of slow and controlled oxidation starting already in the phase of maceration. In the recent years the role of oxygen in the winemaking process has been widely revised above all in relation to the first winemaking phases. The control of the intervention of the oxygen is not simple and requires a careful evaluation of its critical points, i.e. the phases where an exceeding quantity of it can cause rapid and violent oxidation with the consequent depreciation of the qualitative characteristics of the product.
The first scientific experiences have been led starting form the harvest of 1998 by the Institute of Oenology and Food Engineering of Università Cattolica del Sacro Cuore di Piacenza in cooperation with the company Gimar Tecno of Occimiano (Alessandria) and from the very beginning they have been oriented to the evaluation of the effects produced by aeration during maceration and to optimize its control. The researches developed till now enabled to: predispose and validate an aeration system of the must-wine during the maceration-fermentation (6, 7); define the methods of in-line measurement of oxygen, the quantity of oxygen diluted in the wine and the kinetics of gas consumption in the various moments of alcoholic fermentation (8, 9); identify the role played by oxygen on the fermentative activity of the yeasts and on the formation of some components of the aroma (10); evaluating the effect of the presence of oxygen in maceration on the composition of the colouring material of red wine before and after the refinement on the sensorial profile of the final product (10). Currently it is necessary to implement the pumping-over and aeration systems to optimize the operational condition according to the desired characteristics for the fi nal wine.
The experimental tests performed at Azienda Torraccia del Piantavigna in Ghemme belong to a project of research developed in cooperation by the winery, the Istitute of Enology and Food Engineering of Università Cattolica del Sacro Cuore di Piacenza and Gimar Tecno of Occimiano (Alessandria), a company manufacturing the “Selector system” winemaking vat with automatic pumping-over. The vats are equipped with both a device allowing to perform the pumping-over with or without the presence of air (oxycontrol) and with a system for the recirculation of a part of must, aerated or not, either under the cap (oxyplus) or inside it (oxyfl ow). Before the racking and the recirculation it is possible to perform the wetting of the cap through the intermittent opening of a valve closing the upper collection tank of the must-wine (multisteep) (picture 1). The innovation consists of the “oxyfl ow” device used for the fi rst time in winemaking to attain a targeted introduction of parts of must-wine, be it aerated or not, directly inside the cap of marc to facilitate a frequent and regular turnover of the liquid inside it (picture 2). Therefore, the aim of this system is promoting the passage into the solution of the noble compounds of the skins, facilitated by the good maintenance of the concentration gradient not only between marc and must-wine, yet also in the interstitial liquid present in the marc.