Alternatives to Bentonite

Bentonite is the most effective, all-purpose reliable agent for the removal of wine proteins and haze-forming potential. However, bentonite is non-specific, having a tendency to over-fine wine removing complexity and can result in a significant loss of wine volume as bentonite lees. Bentonite lees also represent a significant amount of solid waste of high biological and chemical oxygen demand, the treatment and disposal of which may become increasingly costly. Alternative methods to achieving wine stability not suffering from these drawbacks is highly desirable. Therefore, we are exploring the feasibility of use of yeast acid proteases to degrade wine proteins preventing haze formation. We are also determining in finer detail the composition of hazes to determine the wine components involved in the formation of haze. Toward these ends, in this grant period a plasmid over-expressing Protease A of Saccharomyces was constructed which will be utilized in lees contact experiments to determine if the increase of protease activity is correlated with decreased susceptibility to haze. In addition, we have completed the third year of a comparison of bentonite treatment of juice to bentonite treatment of determine if less bentonite is necessary with a juice treatment. We have found that indeed bentonite treatment of some juices is more efficient than treatment of the resulting wines, but this is very juice specific. We have not been able to reproduce the haze-protecting effect reported for yeast polysaccharide or mannoprotein material of yeast cell walls. However, we have not yet truly duplicated the original observation by purifying the polysaccharide material from wine yeast lees. Finally, chemical analysis of heat and ethanol induced hazes revealed that these hazes are distinct. Ethanol hazes contain a much greater level of polysaccharide material and less protein than heat hazes. There are striking varietal specific haze problems as well.