Characterization of Different Bentonites and Their Properties as a Protein-Fining Agent in Wine

Abstract

Bentonite is a natural clay that is used in different industries as a desiccant, ion-exchange material, or additive to remove impurities. For example, marketed as healing clay and as protein-fining agent in wine, bentonite is expected to adsorb specific compounds while having no negative effects on the quality of the product in which it is used. In this study, 34 commercially available bentonites for different applications were selected and analyzed for their elemental composition, extraction of heavy metals, swelling behavior, and protein removal rate under conditions relevant to wine. The results indicate that bentonites can have a very variable composition that does not correlate with the intended use. The extraction of heavy metals is not directly related to the raw material and depends on swelling behavior and surface area of the clay. Interestingly, there is a similar degree of variability in swelling behavior among wine bentonites as there is for healing clays. This correlates with the protein removal rate but also with the extraction of iron, a transition metal that is known for its catalytic activity for oxidation reactions. Even though the protein removal rate is much higher than for other clays, bentonites that are marketed for wine show an extraction behavior that can have a negative effect on the final product.