Shortening the ageing on lees process in wines by using ultrasound and microwave treatments both combined with stirring and abrasion techniques

Over recent years, ageing on lees has acquired a great distinction in winemaking as an interesting technique for improving wine quality. The aim of the present work was to evaluate the effectiveness of two novel processing techniques, ultrasounds and microwaves (both combined with stirring and abrasion treatments), in order to accelerate the autolytic process in wine yeast. Furthermore, the effects of ultrasonic treatment on the organoleptic properties of a red wine aged on lees were also studied. The content of polysaccharides (HPLC-RI), anthocyanins (HPLC-PDAD/ESI-MS), volatile compounds (GC-FID), colour parameters (spectrophotometry) and sensory analysis was periodically evaluated. Results showed that ultrasound treatment is a reliable technique for shortening the ageing on lees process by strongly increasing the concentration of polysaccharides released into the wine after only 2 weeks of treatment and without adversely affecting the sensory quality of the wine. Furthermore, the addition of glass beads stood out as a good abrasive agent increasing the polysaccharides release up to 10 times the control when coupled with ultrasound treatment. Nevertheless, both stirring and microwave treatments were less effective, possibly due to the short period of application used. The impact of the alcoholic degree on the yeast autolysis was also evaluated, and, moreover, it was confirmed that moderate heating promotes a higher release of polysaccharides into the wine.