Alternatives to Bentonite

This major goal of this project is to reduce bentonite use by better clarification of the conditions under which its use will be successful and to explore the feasibility of development of alternatives to bentonite. Bentonite functions in wine protein removal via simple ionic and absorptive interactions. Bentonite has a net negative charge at wine pH while most of the wine proteins are positively charged (have picked up protons) under the acidic conditions of wine. This simple charge interaction is not very specific and bentonite is known to strip wine of other components as well. An alternative method to achieve wine stability would be to utilize the specificity of an enzymatic system for protein destruction. In earlier grant years we identified proteases that are catalytically active in wine and that are capable of degrading wine proteins. However, while haze formation was reduced somewhat, haze was still formed in these wines. Our more recent goal was to determine why haze was still appearing in these wines to determine if a more effective protease could be identified. Using MALDI-TOF mass spectrometry we have determined that peptides and low molecular weight protein materials can also be main contributors to haze. Thus, protease treatment will likely not be fully effective in reducing the haze-forming potential of a wine. We have further characterized the proteins most associated with haze also using MALDI-TOF mass spectrometry in order to determine if an alternate strategy might be developed based upon the unique chemical properties of the unstable proteins. Our preliminary work with Sauvignon blanc indicates that the unstable proteins are proteins that have become “glucosylated”, that is, that have interacted and formed a covalent bond with juice glucose (or fructose). While this is an important finding towards understanding the kinetics of haze formation, we will not be able to take advantage of this property in the design of resins to remove wine protein as many key flavor components are also glucosylated and would likely be stripped by the new matrix. In addition, frequently the haze that forms in wine is not proteinaceous in nature so that bentonite is completely ineffective. Winemakers currently do not have any readily utilizable methodology to determine if their haze problem is caused by protein components that will respond to bentonite, is caused by proteins not interacting with bentonite or is not proteinaceous in nature at all. We have developed an amido black assay that can easily be used in a winery situation that will allow winemakers to determine the nature of the haze of their wines and to predict the effectiveness of bentonite.