Characterization of suspended solids in thermo-treated red musts

Abstract

Aims: Thermo-treatment of grapes, followed by pressing and fermentation in liquid phase, is a growing practice in red winemaking to obtain light and fruity wines. Must clarification before fermentation, a key step to get the expected wine profile, is hardly controlled and strongly varies between different musts. To better understand this variability and its potential impact on quality, suspended solids in several red musts were characterized and the performances of different clarification techniques compared. Methods and results: Results show a large variability in turbidity and total wet suspended solids between different raw and clarified musts, and a lack of correlation between these values. Clarification is always higher for vacuum filtration than for disk-stack or decanter centrifugation, with strong differences between musts for a given process. Despite a large size distribution, most of suspended particles are micronic and sub-micronic. TEM observations and analyses indicate that they are mostly membrane and organelle fragments along with (macro)molecular aggregates formed during juice extraction. Their overall composition differs from that found in white musts. Conclusion: Particle heterogeneity and size distribution account for the difficulties encountered in red must clarification. Results also raise the question of the relationship between must turbidity and content in compounds likely to affect wine quality. Significance and impact of the study: This study constitutes a first characterization of suspended solids in thermo-treated red musts. It provides elements to (i) reason their clarification and (ii) identify the technological and qualitative impact of must suspended solids.

Keywords

• thermo-treated red musts
• clarification
• suspended solids
• composition
• size distribution