Efficient and reliable malolactic fermentation and identification of wine relevant genetic markers in wine bacteria
Malolactic fermentation (MLF) is an important but sometimes unreliable stage in the winemaking process, with the potential to impact significantly on wine quality. In recent years research at the AWRI has improved MLF efficiency by developing co-inoculation strategies (yeast and bacteria inoculated together) that have been demonstrated to reduce overall fermentation time. However, achieving a reliable MLF still provides winemakers with challenges from time to time. One contributing factor is the lack of MLF starter strains specifically suited to Australian winemaking conditions, as commercially available strains have largely been selected and developed for overseas markets. In addition, while MLF is primarily used for wine deacidification, there is a significant but largely hidden pool of grape and wine aroma compounds in wines that can be released during MLF to influence wine style and enhance complexity. In previous research the AWRI has identified compounds and potential enzymatic pathways that enable some Oenococcus oeni strains to enhance berry aromas in red wine. More recently, the genomes of many O. oeni strains have been sequenced and this revealed extreme genetic diversity across the species. While a high level of genetic diversity provides a promising opportunity to identify MLF strains with unique properties, there is currently little information available regarding genomic markers for wine-relevant phenotypes.
Characterisation of MLF genomics and performance
Draft genome sequences of 169 wine bacteria have been assembled, comprising 158 O. oeni, 8 Lactobacillus spp., 2 Pediococcus spp. and 1 Gluconobacter oxydans. In addition, 66 O. oeni strains were screened for MLF robustness at low pH, high alcohol and low temperature in red and white wines. A spectrum of phenotypic traits has been observed. For example, several strains that show relatively high tolerance to low pH in white wine are less tolerant to the same stress in red wine, and strains exhibiting tolerance to alcohol in red wine do not necessarily show the same tolerance in white wine. Seven O. oeni strains that display the desirable stress tolerance phenotype while representing two distinctively different genotypes have been identified and are currently been trialled.
A potential application of this project is the identification of strains in the AWMCC that are of known provenance, have desirable traits and are genetically distinct from commercial strains. Winemakers interested in enhancing regional identity of their products could choose isolates from their region to conduct their MLFs.