Winemaking treatment – Yeast choice

Choice of yeast strain is a key decision for winemakers, with different strains known to perform differently and produce different aroma and flavour compounds. More than 200 yeast strains are commercially available for use in winemaking (Schmidt et al. 2017). Winemakers also have the option to allow natural microflora (yeast) to conduct their fermentations. Either way there are choices for winemakers to make.

Traditionally, strains of Saccharomyces cerevisiae have been used for fermenting grape juice, but recent developments in yeast breeding research have seen a range of new hybrid yeast strains become available. An example of one of these hybrids is AWRI2526, which was used as one of the winemaking treatments in the 2019 Chardonnay treatment trial. This strain is available commercially from AB Biotek and was developed to add flavour and aroma complexity to wines.

Practical and logistical considerations when choosing a yeast strain

Nitrogen requirements
Nitrogen is a critical grape nutrient for yeast growth and fermentation activity and affects the rate and completion of fermentation, as well as wine aroma and style. It is therefore important to know the nitrogen or YAN concentration in must prior to fermentation, as there is a direct relationship between YAN levels, yeast cell growth and fermentation rate (Bell and Henschke 2005). Understanding the nitrogen demand of the chosen yeast is also important as yeast vary in their nitrogen requirements, meaning you can have low-, medium- or high-nitrogen demand yeast. If sufficient nitrogen is not available for the yeast’s requirements, this can lead to sluggish or stuck fermentations and in turn to off-flavours and winemaking faults. Further information on how to prevent and or manage a slow or stuck fermentation can be found on the wine fermentation page on the AWRI website.

YAN analysis provides information on the nitrogen status of grapes, musts and juices: specifically, the amount of nitrogen available for yeast to use during fermentation. Recommended nitrogen levels for successful fermentations can be found on the YAN page on the AWRI website and a calculator for making diammonium phosphate (DAP) additions to increase YAN levels is included on the winemaking calculators page.

Rehydrating yeast
The effective rehydration of active dry wine yeast (ADWY) is paramount in obtaining a healthy and viable yeast inoculum for a successful fermentation. Details on how to rehydrate ADWY are provided on the ADWY rehydration page.

Uninoculated fermentations

Uninoculated ferments rely on natural microflora present on the grapes or in the winery to begin fermentation without intervention. Work by Varela et al. (2017) reports that the microflora in the early stages of an uninoculated fermentation are dominated by non-Saccharomyces yeasts, whereas the majority of the alcoholic fermentation is conducted by Saccharomyces yeast.

One of the main risks associated with uninoculated fermentation is the possibility of high levels of acetic acid or ethyl acetate forming early in the ferment. These volatile compounds can be produced by Hansenula and Kloeckera spp., which may dominate ferments early when there is no SO2 present. Kloeckera can also significantly deplete nitrogen and thiamine and it is therefore recommended to supplement uninoculated fermentations with nitrogen and vitamins. It is not advisable to perform this technique in years where there is significant disease pressure.

An AWRI research project Bioprospecting Australian microbial genetic diversity is investigating and isolating the microbes present in Australian uninoculated ferments.

The AWRI Wine Microorganism Culture Collection

The AWRI Wine Microorganism Culture Collection (AWMCC) is a world-class repository of diverse, wine-relevant strains of yeast and bacteria that can be readily accessed by Australian wine producers and researchers.

Experimental yeast strains developed through AWRI research are available for use in production trials. Examples include hybrid Saccharomyces strains, non-Saccharomyces strains and strains with interesting features (e.g. low H2S production, high fruity ester production, low temperature fermentation).

A number yeast and bacteria strains isolated or developed by the AWRI for winemaking have been commercialised by yeast and bacteria manufacturers. These strains are listed on the available microbial strains page on the AWRI website.

Additional resources and references

AWRI fact sheet – Sequencing natural ferments

Bellon, J.R., Schmid, F., Capone, D.L., Dunn, B.L., Chambers, P.J. 2013. Introducing a new breed of wine yeast: Interspecific hybridisation between a commercial Saccharomyces cerevisiae wine yeast and Saccharomyces mikatae. Plos One. 8(4): 1-14.

Bellon, J.R., Yang, F., Day, M.P., Inglis, D.L., Chambers, P.J. 2015. Designing and creating Saccharomyces interspecific hybrids for improved, industry relevant, phenotypes. Appl. Microbiol. Biotechnol. 99: 8597-8609.

Chambers, P.J., Borneman, A.R., Varela, C., Cordente, A.G., Bellon, J.R., Tran, T.M.T., Henschke, P.A., Curtin, C.D. 2015. Ongoing domestication of wine yeast: past, present and future. Aust. J. Grape Wine Res. 21: 642-650.

Information pack – Winemaking with non-conventional yeast

Schmidt, S., Borneman, A., Kolouchova, R., McCarthy, J., Bellon, J., Herderich, M., Johnson, D. 2017. Spoilt for choice: picking the right yeast in a vibrant market. Wine Vitic. J. 32(5): 35, 37-38.

Varela, C., Borneman, A.R. 2017. Yeasts found in wineries and vineyards. Yeast 34(3): 111-128.