EVALUATION OF THE EFFICACY OF POWER ULTRASOUNDS ON THE PREFERMENTATIVE EXTRACTION IN WHITE GRAPES

The application of power ultrasounds (US) is a recent hotspot in applied enology and their utilisation has been successfully proposed for many winemaking practises: during skin contact fermentation or ageing steps in red winemaking, in the sanitation of vessels, and increasing the yield in filtration and polysaccharide extraction from yeast lees. However, their use in white winemaking as an extraction-aiding technology during prefermentative operations is still scarcely explored. Diversely to red winemaking, a prefermentative skin contact maceration foresees a lesser contact time due to the high risk of microbial spoilage, thus limiting potential extraction from skins of wine beneficial compounds. The present work was aimed to study the application on grapes of US at lab scale for the evaluation of their potentiality as an aiding technology for the prefermentative extraction. For this, grape samples were firstly characterised by their mechanical features (thickness, compression and force) and treated for 3’ and 5’ with US (frequency: 20 kHz, wave amplitude: 153 μm). Grapes were then pressed at standardized conditions and sampled for analysis. The evaluation of the efficacy of the treatment was performed on conductivity, hydroxicinamatetartaric acids, total polyphenols or catechins, used as indicators of skin extraction. Results determined by both treatments were differentiated from the untreated control, showing the effectiveness of the US treatment. Further research is however needed in order set up properly the treatment at industrial conditions, also based on the characteristics of grapes