In winemaking, the appearance of turbidity in white and wine is a serious visual defect, which lowers significantly its commercial value. A major cause of the formation of turbidity in wine is attributed to the presence of temperature-sensitive proteins. The proteins undergo slow conformational changes, leading to aggregation and flocculation phenomena. The process can be accelerated by exposure of wine to high temperatures during transportation or storage. In recent years heat-unstable proteins in white wine were identified as grape class IV chitinases, β-glucanases and a fraction of thaumatin-like proteins. Although proteins play a central role in the formation of turbidity, other components present in wine such as polyphenols, sulfate anion, polysaccharides as well as ionic strength and pH value play an important role in these phenomenon.
The lack of reliable tests assessing the risk of protein clouding during bottle storage is a recurring problem of winemakers. Currently used test assessing haze potential involves heating which often causes overdosing of fining agent. Despite the large progress in the white wine research and substantial development of the analytical methods applied the phenomenon of white wine haze formation remains unrevealed. The traditional treatment used to stabilize wine includes the addition of bentonite, which is certainly effective but due to its non-specific binding results in a considerable decrease in aroma compounds and therefore the quality of the wine. Thus, a strong need to establish a more selective and economically justified method of wine stabilization, which will preserve the aroma compounds in white and rosé wine, is undeniable.
This study aimed at the development of more reliable haze potential tests and more specific treatments for wine. To achieve this objective the knowledge the protein binding properties of different types of commercial bentonite have been analyzed, including the following: elemental analysis, surface charge density, swell index, external and internal specific surface area. The effect of quality of water used for hydration and wine pH on the swelling properties of bentonite have been also investigated. The proteins and polyphenols bound by different types of bentonite as well as the quality of the obtained wine (aroma compounds) have been identified using the above-mentioned methods and compared during three harvest periods. Finally, we have established the possibility of using bentonite alternatively on must with the development of a specific test to establish the dose of treatment.
Authors: Benoit Bach, Anne-Claire Silvestri, Jean-Christophe Perret, Marilyn Cléroux, Marie Blackford, Agnieszka Kosinska Cagnazzo, Marc Mathieu, Wilfried Andlauer
Changins, viticulture and enology, University of Applied Sciences and Arts Western Switzerland, Route de Duillier 50, 1260 Nyon, Switzerland
Institute of Life Technologies, University of Applied Sciences and Arts Western Switzerland Valais, Route du Rawyl 64, 1950 Sion, Switzerland
Keywords: wine, protein, haze, bentonite