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.
The use of wine yeasts that produce wine with less alcohol than those currently available to winemakers is one of the strategies we are exploring. Therefore, we are trying to generate novel strains of wine yeast which metabolise sugar in such a way that substantially less ethanol is produced while maintaining high wine quality. We are applying both, non-genetically modified (non-GM) and genetically modified (GM) approaches; the latter approach is being used for research purposes to inform us better about what might be possible.
Although the Australian wine industry does not use genetically modified organisms (GMOs), we use this technology since it will (i) enable the identification of targets for non-GM approaches to wine yeast strain development, (ii) show how far we can push the low-ethanol phenotype in wine yeast without compromising quality, and (iii) deliver the best ‘low-ethanol’ strains in readiness for adoption by winemakers if/when the industry and consumers are accepting of GMOs.
We are also researching other strategies to lower alcohol concentration in wine described in an AWRI Fact Sheet we have developed. Indeed, we have established a multi-disciplinary approach to assess the impact of harvesting time and grape maturity on tannin development, alcohol content, wine flavour, sensory profile and consumer preference.
We have generated a genetically modified (GM) wine yeast, AWRI2532, which was able to decrease ethanol concentration by 3.5%(v/v), i.e. from 15.7% v/v to 12.2% v/v, when fermenting Chardonnay and Cabernet Sauvignon musts.
We developed an AWRI Fact Sheet with recommendations and opportunities for grapegrowers and winemakers on a range of approaches that may be used to adjust alcohol concentration.
What this means for grapegrowers and winemakers
The GM prototype leads the way for us to develop non-GM wine yeasts with similar performance. Winemakers will know the effects on wine flavour and aroma from lowering alcohol in wine by using low-alcohol yeast.
Growers and winemakers can evaluate the recommendations described in the AWRI Fact Sheet in order to produce wines with lower concentrations of alcohol.
Project leader: Dr Paul Chambers
Project team members:
Varela, C., Kutyna, D., Stanley, G.A., Henschke, P., Chambers, P. 2010. Yeast provides a lower alcohol pathway. Aust. N.Z. Grapegrower Winemaker 561: 80-83 (click here to order).
Varela, C., Chambers, P.J., Coulter, A., Dry, P.R., Francis, I.L., Gawel, R., Muhlack, R., Henschke, P.A., Stockley, C.S., Herderich M.J. & Pretorius, I.S. 2010. Controlling the highs and the lows of alcohol in wine. Aust. N.Z. Wine Ind. J. (2010) 25(4): 14-19 (click here to order).
Coulter, A., Stockley, C., Varela, C., Francis, I.L., Chambers, P.J., Henschke, P.A., Dry, P., Gawel, R., Muhlack, R. Reducing alcohol levels in wine. 2010. AWRI Technical Review 186: 11-15.
Chambers, P., Borneman, A., Schmidt, S., Hack, J., Varela, C., Mercurio, M., Curtin, C., Cozzolino, D., Ugliano, M., Herderich M. & Pretorius, I.S. 2009. The dawn of a new paradigm for wine yeast strain development. Aust. N.Z. Wine Ind. J. 24(3): 16-18 (click here to order).
Varela, C., Kutyna, D., Henschke, P., Chambers, P., Herderich, M., Pretorius, I.S. 2008. Taking control of alcohol. Aust. N.Z. Wine Ind. J. 23(6): 41-43 (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. (click here to order).
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., Varela, C., Henschke, P. 2006. Persuading wine yeast to make less alcohol. AWRI Technical Review 161: 8-10.
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).
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: 208215 (click here to order).