Red wine astringency: evolution of tribological parameters during different harvest dates

Abstract

Astringency is a specific oral sensation dominated by dryness and puckering feeling and is one of the leading quality factors for red wines, as well as some fruit products. Based on this sensory parameter, are made relevant decisions in wine production including the moment of grape harvest (phenolic ripeness), the time and intensity of maceration, the time and type of aging process, and the target market of wines. Notably, the selection of the optimal grape astringency during ripeness is one of the most crucial decisions in winemaking. However, grape astringency is an attribute challenging to evaluate and standardize by tasters since the grapes are heterogeneous and generate along their ripeness different sensory descriptors, such as the typical drying astringency found in immature grapes. Here we used a tribological system to determinate the red wine astringency produced on different harvest dates. Mixtures of whole human saliva and red wines as Cabernet Sauvignon and Carménère, with similar tannin content but different sub-quality (rough and soft/velvety, respectively), were evaluated by their lubrication behavior. Red wines produced significant changes in the saliva friction coefficient during the harvest dates, with an opposite evolution between the Cabernet Sauvignon and Carménère. Also, microstructure observation revealed differences between conformation and surface of the tan-ninprotein aggregates of both red wines, suggesting a correlation between them and the astringency sensory perception. Results from this work demonstrate that tribology techniques can be a useful tool for both to evaluate astringency on red wines and to help us to understand the phenomenon of sub-qualities.