Comparison of two grapes shrivels techniques: mechanical ventilation and dehumidification

The raisin wines are produced with grapes that have been dried to concentrate their juice. The dehydration could be natural, when the grapes are picked up and stocked for a certain time, or induced, controlling the environment of the room where the berries are placed after the harvest. The water losses from grapes could be accelerated with ventilation, when an air flux is forced on berries, or with dehumidification, the removal of moisture from the room. The manner adopted to accelerate the grapes shrivel process could affect some berries chemical parameters, and consequently the produced wine. Hence, a comparison between these techniques has been done. Trials were carried out using grapes, cultivar Corvina. For one hundred days four parameters were monitored: berries weight, sugar content, total acidity, and malic acid concentration. Dehumidification halves the grapes weight in 100 days, improving the water losses of about 20% than the ventilation. As a consequence, the sugar concentration raise up faster in the dehumidification thesis. In fact, at the end of the tests, ventilated berries shows 322 g/kg of sugars, while dehidratated ones 338 g/kg. The two treatments give different trends of total acidity and malic acid concentration. In fact, ventilation does not affect the total acidity, while dehumidification increases it from 6.5 g/kg to 8.8 g/kg. The malic acid concentration is not affected by dehumidification, while its concentration decrease with ventilation from 2.9 g/kg to 1.5 g/kg. Hence, the shrivel technique affects the four considered parameters, giving different berries in terms of weight, sugar, acidity and malic acid content.