Innovations in the use of bentonite in enology: interactions with grape and wine proteins, colloids, polyphenols and aroma compounds.

Abstract

The use of bentonite in oenology rounds around the limpidity and the stability that determine consumer acceptability. As a matter of fact, the haze formation in wine reduces its commercial value and makes it unacceptable for sale. Stabilization treatments are, therefore, essential to ensure a long-time limpidity and to forecast the formation of deposits in the bottle. Bentonite that is normally used in oenology for clarifying-fining purpose, shows a natural clay-based mineral structure allowing it to swell and to jelly in water and hence in must and wine. The exchangeable cations in its lamellar structures strongly influence some properties, like, for instance, the specific surface, the exchange capacity, as well as the adsorption behaviour. The interactions with haze forming proteins, other colloids, as well as aroma compounds and polyphenols would have been to discover as the modulation of wine colloids by an adjuvant severely affects the wine sensory profile. Body Oenologists do not really know on which parameters they have to focus for the choice of the bentonite targeted at gaining both the desired degree of limpidity and stability coupled with the avoiding of undesirable side effects. In this field, the authors have carried out many scientific and technical activities that led to detect: -The proteins targeted by the bentonite; -The endogenous allergenic wine compounds that are removed by bentonite; -The effect of protein origin, content, and pH toward wine colloidal (heat) stability; -The bentonite optimization for red wine fining; -The bentonite side effects on polyphenols and colour; -The interactions with the free- and glycosylated-varietal aroma in musts and wines; -The removal of fermentative aroma according to the wine aging, colloids and protein content; -The adsorption mechanism and modelling of wine aroma compounds onto bentonite. Conclusion The role of bentonite added to settling juices and/or to fining wine was not fully clear. This work collects several studies from authors focusing on the impact of several commercial bentonite samples, used for both juice clarification and wine fining, on the colloids, proteins, polyphenols and aroma compounds of white and red wines. Some parameters of practical value, such as the heat-stability of colloids, the concentration of total and haze-forming proteins, the content of the most relevant varietal and fermentative aroma were assessed to track bentonite effects and to achieve findings that are immediately applicable in the field of oenology.