Generating wine yeasts that produce reduced levels of ethanol
Background
A growing proportion of Australian wines now have a higher alcohol concentration than was the case a decade or more ago. While such wines, which are typically full-bodied, rich, with ripe-fruit flavour, have undoubtedly contributed to the success of the Australian wine sector, their relatively high alcohol content can compromise their desirability, particularly in overseas markets. The ‘big wine’ style described above is essentially the product of relatively dry climatic conditions, which facilitate lengthy maturation of grapes. These conditions, however, lead to grapes with high sugar levels, and this, in turn, leads to wines with high levels of alcohol. High alcohol content can be problematic because it potentially compromises wine flavour, increases export costs in countries where taxes are levied according to ethanol content, and raises health concerns associated with excessive alcohol consumption. Therefore, the wine sector is pursuing strategies to lower the ethanol content of wine without compromising quality or increasing input costs.
Progress
One strategy we are exploring utilises gene technologies for proof-of-concept to obtain genetically modified (GM) yeasts that divert some of their sugar metabolism away from ethanol production. One of the GM approaches we are using involves over-expression of the yeast’s genes, which lead to increased glycerol production at the expense of ethanol. The resultant GM yeasts will not be made commercially available to winemakers (no genetically modified organisms are used in the production of Australian wines) but they will provide us with information to enable the development of improved strategies for generating suitable wine yeasts using traditional, non-GM approaches.
A more difficult approach is to develop ‘low-alcohol yeasts’ using traditional breeding and selection techniques. Yeasts obtained by such means can be adopted immediately by the wine sector; ‘traditional’ methods are not controversial and are routinely used in food and beverage sectors. Selection strategies require a selective pressure that favours enrichment of the desired characteristic within the population, and are performed over many generations. Although this sounds simple, finding a selective pressure that favours low ethanol production, while not disrupting important winemaking properties, is not straightforward. Nonetheless, data from recent experiments have shown that yeast cultures can be generated that deliver a range of low-ethanol phenotypes. Although the decrease in ethanol levels is still small, we are confident that the selection is going in the right direction, and will further improve on what has been achieved so far. This work is being done in collaboration with Associate/Professor Grant Stanley (Victoria University).
Highlights
- A genetically modified (GM) wine yeast, producing less alcohol than its parent strain, has been generated for research purposes
Project leader: Dr Paul Chambers
Project team members:
Publications:
649 de Barros Lopes, M., Rehman, A.-U., Gockowiak, H., Heinrich, A.J., Langridge, P., Henschke, P.A. 2000. Fermentation properties of a wine yeast overexpressing the Saccharomyces cerevisiae glycerol 3-phosphate dehydrogenase gene (GPD2). Aust. J. Grape Wine Res. 6: 208–215 (click here to order).
864 Eglinton, J.M., Heinrich, A.J., Pollnitz, A.P., Langridge, P., Henschke, P.A., de Barros Lopes, M.A. 2002. Decreasing acetic acid accumulation by a glycerol overproducing strain of Saccharomyces cerevisiae by deleting the ALD6 aldehyde dehydrogenase gene. Yeast 19(4): 295-301 (click here to order).
Chambers, P., Varela, C., Henschke, P. 2006. Persuading wine yeast to make less alcohol. AWRI Technical Review 161: 8-10.
994 Bartowsky, E., Bellon, J., Borneman, A., Chambers, P., Cordente, A., Costello, P., Curtin, C., Forgan, A., Henschke, P., Kutyna, D., MaCarthy, J., Macintyre, O., Schmidt, S., Tran, T., Swiegers, H., Ugliano, M., Varela, C., Willmott, R., Pretorius, I.S. 2007. Not All Wine Yeasts Are Equal. Microbiology Australia 28: 55-58 (click here to order).
Chambers, P., Bellon, J., Schmidt, S., Varela, C., Pretorius, I.S. 2007. Non-GM approaches to isolating and generating novel yeasts for industrial applications. In Diversity and Potential Biotechnological Applications of Yeasts. Eds: G. Kunze and T. Satyanarayana.