Researcher: Dr. Debra Rossouw (South African Grape and Wine Research Institute, Stellenbosch University)
Aim and industry relevance
Protein haze in white wines is a serious global problem, and is avoided in most wineries through standard procedures, primarily the application of bentonite. Estimates of the global financial costs of bentonite-fining vary depending on parameters being considered but exceed 1 billion US$/year. Besides direct and indirect costs, bentonite fining also has other significant disadvantages, including concerns regarding its impact on cellar worker health during application, non-sustainable waste disposal, and possible unwanted impacts on the organoleptic quality of the final product. Based on their published and unpublished work, the researchers propose to evaluate a new strategy based on the use of specifically selected yeast strains with significantly increased cell wall chitin. Such yeasts have been shown to significantly reduce haze formation (Ndlovu et al. 2018). Yeast strains will be evaluated as fermentation strains and as processed derivatives (yeast hulls / cell wall extracts), acting as more natural, biological alternatives to bentonite treatment. Since yeasts are an essential part of the process of winemaking and are already employed as starter cultures or in processed form (nutrients, mannoproteins), such optimised strains would present an elegant option potentially reducing costs and increasing sustainability. The project proposes to evaluate 20 selected yeast strains in small scale real grape juice fermentations for their chitinase-binding and haze protective cell wall properties, either as fermenting yeast or when used as treatment (yeast cell walls). From these initial experiments, researchers will select a maximum of 10 yeast strains (five as fermenting yeasts and five as treatment yeasts) to be assessed at semi-industrial scale (50l or 100l fermentations).
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