Microbial enhancement of wine quality and complexity

Abstract

This report details the outputs from a substantial 4 year research project, including publications and other communications, and highlights areas for further research. Where the findings of this work have been published we have used extracts from such publications to provide the bulk of the material reported herein.
This project has sought to provide a better understanding of the potential influence of the microbial component of winemaking on the process and the resulting wine. We have succeeded in more fully defining the actual or potential contribution of LAB and in particular their enzymatic activities to wine composition. A survey of 40 LAB strains for over 10 enzymatic activities revealed many to be represented. Several such enzymes were minimally inhibited by low pH, temperature and high ethanol and sugar contents, unlike some existing preparations, such as those of fungal origin. These findings go some way to allowing for a more informed application of LAB to winemaking and/or the preparation of enzyme extracts from these organisms for use by the industry.
Use of sophisticated techniques such as adaptive evolution, recombinant DNA technology and classical yeast genetics has allowed several improved yeast strains to be produced and genes important to fermentation reliability and wine composition to be identified. Of particular interest have been strains bearing modifications to GID7, NGR1 and PUT4. These strains are either better able to complete fermentation under nitrogen-limited conditions, produce an altered metabolite profile or show enhanced tolerance to stress conditions. Many tens of further strains have been identified through non-recombinant methods. Great interest has been generated in those arising from adaptive evolution as these show superior fermentative capabilities and reduced ethanol yield.
Many of the future directions detailed herein have been incorporated into a new project: UA 05/01, Better wine from novel and better informed use of microbiology.

Summary

The technique of adaptive evolution has been used for the first time to produce new yeasts in a non recombinant way. These evolved strains were better able to complete a model fermentation and/or yield a fermentation in altered media.