An investigation into the occurrence of Zygosaccharomyces spp. during winemaking. Improving detection, quality control and hygiene with grape concentrate producers
University of Stellenbosch. Faculty of AgriSciences. Institute for Wine Biotechnology
Du Toit, M
Microbiological problems of the spoilage yeast, Zygosaccharomyces spp., have become an industry concern following quality defects such as re-fermentations, swollen bags and turbidity in final products. It is believed that the phase-out of the use of natamycin in winemaking and the ineffectiveness of alternative preservatives such as DMDC (dimethyl dicarbonate) and potassium sorbate against these yeasts holds relevancy to the problems.
In addition, there is a concern regarding the effectiveness of sterile filtration on the microbial spores. Zygosaccharomyces spp. shows high tolerance towards the winemaking environment due to its high alcohol tolerance and high sulphur dioxide tolerance and for this reason off-dry wines (wines with higher residual sugar) and lower alcohol wines are more likely affected and increasing number of wineries are experiencing problems.
The outcome of the project is to improve the current quality control procedures for producers including accurate detection methods, identification of critical control points and improving hygiene practices. A standard protocol of these procedures, how to control and manage Zygosacchromyces spp., will be made available to industry.