Better quality wine and lower production costs from new processing technologies for protein-haze removal
Abstract
Fining to remove what is known as protein haze or heat instability is an essential winemaking process to ensure white wine is well presented to consumers. This project investigated the performance of bentonite, a commonly used fining agent, and found efficiencies can arise through the way this agent is prepared and by in-line dosing rather than batch additions to wine.
Summary
The way bentonite works is through a cation exchange where there is adsorption of wine proteins and settling of the bentonite particles, thus removing potential for haze. Research interests have been set around improving bentonite performance by various means including roughening the surface of particles to include the contact area where proteins can be attached, increasing the area by fusing particles, heat treatments and formulations other than sodium bentonite (e.g. calcium bentonite). In the study the available formulations and new treatments of bentonite were examined in the laboratory and at the winery scale. In addition, an in-line dosing system was designed and installed for assessment in a commercial situation.
Results of most interest to winemakers were the adsorption capacities and settling rates of commercial bentonites, determination of optimal conditions for bentonite slurry preparation and identification of slurry age, wine pH and potassium concentration as the most important factors affecting protein adsorption during bentonite fining. The project found that modification of commercial bentonites by heat treatment had the potential to improve fining by reducing the volume of lees and achieving more rapid settling (some heat-treated bentonites reduced the volume of lees three-fold). Other information arising from the project that should influence decisions includes a high rating for in-line dosing of bentonite with centrifugal clarification in place of batch additions, and an indication that more attention should be given to the performance rather than initial cost of fining products (particularly the amount of wine lost in the process of fining) as studies showed a large variation in effectiveness. Other outcomes have been development, for research applications, of a new method for purification of gram quantities of heat unstable proteins from juice and a means of quantifying protein content in wine and identifying those proteins responsible for haze formation.