High pressure homogenization of fermentation lees: acceleration of yeast autolysis and evolution of white wine during sur-lies ageing

Abstract

AIM: High pressure technologies represent a promising alternative to thermal treatments for improving quality and safety of liquid foods. High Hydrostatic Pressure (HHP), High Pressure Homogenization (HPH) and Ultra-High Pressure Homogenization (UHPH) are gaining increasing interest in wine industry, for their ability to inactivate microorganisms [1-3], improve the extraction of color and phenolic compounds from grapes [4,5] and to induce yeast autolysis [6] potentially accelerating wine ageing on lees (AOL). This work aims at evaluating the possibility of accelerating AOL of white wines by HPH processing of fermentation lees, considering the effects of the treatment on microbial populations, wine composition, sensory and aroma profile, as well as the potential impact on wine filterability.

METHODS: Lees were collected at the end of alcoholic fermentation (fresh lees) and after six months of ageing (aged lees) and processed by HPH at 60 and 150 MPa (1 and 2 passes). The effects on microbial populations and the release of polysaccharides were evaluated in comparison with untreated samples and β-glucanase addition. The modifications induced on yeast cells were also investigated by Transmission Electronic Microscopy. Treated lees were added (5 % v/v) to a white wine and samples were analyzed after one and six months of AOL, concerning polysaccharide content, microbial composition, basic chemical parameters, aroma and sensory profile. Finally, to assess the impact of HPH on wine filterability, the Particle Size Distribution of colloidal particles and a filtration test were determined at the end of ageing period.

RESULTS: HPH favored the release of polysaccharides from lees, with a higher efficiency if lees are treated immediately after alcoholic fermentation (fresh lees), revealing to be averagely more efficient than β-glucanase enzymes. HPH also determined a significant reduction of viable yeasts and lactic bacteria in treated lees, potentially allowing to reduce the use of sulfur dioxide during AOL; the effects on microorganisms were dependent on the pressure applied and the number of passes. High pressure treatments provoked a complete disruption of yeast cells, forming cell debris with a greater particle size with respect to what detected in untreated samples or in the lees treated with enzymes. This determined the formation of a persistent haze in lees samples. The effect of this particles on wine filterability was negligible if the pressure applied during lees treatment was low, but filtration became more difficult as operating pressure and number of passes increased.

CONCLUSIONS

High pressure techniques represent an interesting perspective for the application investigated in the present study. The possibility of their exploitation at winery scale requires the identification of suitable operating conditions and the evaluation of the economic aspects connected with their scale-up at industrial level.