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Comparison of two grapes shrivels techniques: mechanical ventilation and dehumidification Piernicola Masella, Lorenzo Guerrini, Fabio Baldi, Paolo Spugnoli, and Alessandro Parenti. GESAAF – Università degli Studi di Firenze, 50144 Firenze, Piazzale delle Cascine 16. Correspondence: [email protected] Introduction Off-vine grape dehydration is a technique used to produce several sweet wine such as Vinsanto from Toscana, Trentino or Veneto, Recioto di Soave, Passito di Gambellara or della Valpolicella, Torcolato, Cinque Terre Sciacchetrà, Vins de Paille of Jura, Strohwein of Austria, and Ribeiro Toasted. During the dehydration grapes undergo to many changes in chemical profile, due to water losses and to changes in berries metabolism. As a result, berries becoming more dark; sugar concentration rises, and the acidic profile changes. The dehydration process could be carried out naturally, or in chambers under controlled conditions. Particularly, higher temperature, lower humidity, and faster flow rate accelerate the process. Especially higher ventilation can improve water losses from berries owing to the removal of the high humidity boundary layer. Moreover, direct removal of water around the grapes by dehumidification can accelerate the raising process. In these ways risk related to slow drying rate (i.e. insect attack, or fungi producing toxin attack) are reduced. Materials and Methods Trials were carried out for 100 days on grapes (cv Corvina) in two dedicated rooms.During the tests the evolution of grapes quality was monitored with the analysis of four parameters: berries weight, berries sugar content, malic acid concentration, and total titratable acidity. Ventilation system In ventilation system air flows on grapes to facilitate the dehydration. In this system fans forced air circulation from outside into the room, removing the humidity, and avoiding the development of stagnant air microclimate near the grapes. 0 20 40 60 80 100 120 0 20 40 60 80 100 120 Grapes weight losses V D days w e i g h t l o s s e s ( % ) Results and discussion During test ventilation provides faster weight losses than ventilation: However, berries final sugar content is 322 g/kg in ventilation, and 338 g/kg -1 in dehumidification. Hence, the grater weight loss in the latter system do not concurs with an effective berries enrichment in term of sugar. Total acidity remains quite constant with ventilation, and increase from 6.5 g kg -1 to 8.8 g kg -1 with dehumidification. On the other hand, the malic acid concentration remain constant in dehumidification, and decrease from 2.9 g kg -1 to 1.5 g kg -1 with ventilation. Conclusions Dehumidification systems could be used to reduce the raising time, and consequently the risk related to molds and insects. On the other hand, it could modify the acidic profile of the must. Dehumidification system Dehumidification system is the evolution of the ventilation system. The system uses the outside air as main raising agent, Furthermore, when is not possible to open windows for high external humidity the dehumidifier is activated until a pre-set internal humidity value is reached. The fans work during all day, while the outside windows are automatically opened when the outside relative humidity is less than the inside relative humidity. When this condition became false, and the outdoor humidity became higher the windows were automatically closed. 0 20 40 60 80 100 120 0 1 2 3 4 5 6 7 8 9 10 Acidity trends TA V TA D MA V MA D days c o n c e n t r a t i o n ( g / k g )
