Evaluation of ageing dynamics in the northeastern Italy white wines: studies approaches and winemaking strategies

In the world of winemaking, the concept of shelf life takes on a dynamic meaning as it relates to the intrinsic and unstoppable evolving capacities of the chemical system specific to each wine. Manifestations of product transformations are also influenced by the closing system and by the physical demands of the commercial and environmental supply chain to which the product is subjected. Bottled wine evolves and its ability to preserve and change its pleasant qualities over time determines its value and commercial success. In the global market, renewed health requirements relating to a reduction in alcohol content and chemical preservatives, new logistical needs and a strategic vision to increase the production values, require bottled wine to have a longer shelf life and to be able to withstand greater physical stress in relation to transportation and storage. The semiotic extension of the concept of homeostasis, i.e. the natural tendency to achieve relative internal stability, sought after by winemakers is in contrast with the congenital oxidative chemical dynamism that each wine possesses due to its compositional characteristics and external actions. The progressive sensory transformation that takes place from the time of bottling does not generate a trend of normal stability followed by a linear hedonistic decay proportional to oxidation, but rather produces a curve of evolution with an initial positive trend varying in duration from a few months to many years, before reaching a stage of settlement, also of a variable duration, before declining to a state of extreme evolution attributable to the irreversible oxidisation of the medium. This research involves the study of the management of the oxidative processes, or better, of the holistic consideration of all those substances and conditions that interfere and interact with the redox concatenations of complex mineral and organic systems in hydro-alcoholic solution. A research project was designed as a consequence of the demands of the current world market where the growth of white wine is particularly significant in the world of sparkling wines and considering the strategic importance of the production environment studied in the wine sector of the entire northeast of Italy, specifically the three regions of Veneto, Friuli Venezia Giulia and Trentino Alto Adige, strongly characterised by the production of white wines. This project aims at increasing the knowledge of the evolutionary dynamics of these wines. Extensive experience in managing the production and preservation of white wines of the territory with respect to the time variable will allow addressing and developing with greater safety the world market in the coming years by following the national strategic development objectives of the wine industry proposed by MIPAAF. Producing wines able to evolve positively over time allows increasing the credibility, reputation and ultimately the value of the product, as well as the work needed for its production and the territories of origin. An analysis of the processes characterising the ageing process of white wines, market trends and legal standards has led to the development of three sections: the first is dedicated to describing successful case histories, the second aims at investigating the evolutionary processes of sparkling wines in bottles and the third is dedicated to the technological restructuring of the wine-making processes and outlook for future areas of research. The study on representative samples of white wines evolved in North-eastern Italy has shown that there is a possibility to investigate the evolutionary conditions through the SIMCA modelling of voltammetry phenomena correlated to the technological variables applied in wine making. The redox state plays a key role in the ageing of white wines and depends on a multitude of compositional and environmental factors such as the closing system. The redox potential is a parameter useful for studying winemaking applications and innovative applications in predictive oenological strategies, and the voltammetry method has proven to be a useful analytical tool. All the wines studied have shown behaviour in line with the time variable. The multivariate analysis has produced correlations with the extraction techniques, with the type of vinification and ageing, as well as the sulphur and ascorbic acid content and type of closing system. The latter being a very important field, which however was not examined in this study. The use of fermentation in bottles as a process to preserve the wine can substantially reduce the use of chemical additives, such as sulphur. The extensive presence of secondary esters of fermentation characterise the aromatic profile of sparkling wine re-fermented in the bottle and stored on yeast lees. Autolysis of yeast occurs during the ageing of wine fermented in-bottle. This factor leads to a number of chemical and sensory effects. It was noted that a higher amount of lees present in the bottle corresponds to a greater supply of polysaccharides in the medium and that a greater presence of lees in the bottle does not correspond to a higher presence of thiol groups. Second fermentation in the bottle can promote the often spontaneous malolactic fermentation that could produce biogenic amines in quantities above the threshold. This field was only partially addressed and did not produce significant results. The indigenous yeasts have characterised, due to the apple descriptor, the sparkling wines with statistically significant differences in the territory of Conegliano Valdobbiadene DOCG. The protocol proposed has therefore opened an interesting path of development for the organoleptic characterisation of the territory of Prosecco Superiore DOCG. Further investigations on the reducing capacity of the faces obtained by indigenous starters must be implemented in order to better understand the microbiological results on the evolutionary dynamics of white wines. Observation of the evolutionary dynamics of thiol compounds interfering on the redox state in the white wines analysed and observed leads to the conclusion that there are technological differences between the various ageing processes. The use of barrels influences the decrease of the –SH groups in the medium term of ageing, most likely due to the oxygen that leaks from the bunghole. In fact, these containers show better performances of resuspension of the lees than stainless steel tanks, probably due to a geometry more suited to the batonnage process. Further investigations such as tests of maceration-fermentation in closed barrels of white grapes, full vinification with fermentation on the skins and development of a new grape ripening index based on the absolute chemical reactivity of grapes during harvest could be interesting areas of research, which have in part already begun.