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.
Novel AWRI isolates of Oenococcus oeni showing potential in industry trials
After screening a large cohort of genomically sequenced AWRI isolates of O. oeni strains for tolerance to a range of stresses typically encountered during malolactic fermentation (MLF), seven robust strains were chosen for further analysis at laboratory scale. These strains proved to be efficient at performing MLF and from a comparative genomics perspective represented a broad range of genotypes. Trials were conducted in red, white and sparkling base wines. Only one of the seven strains was problematic in that it produced a red wine with slight reduced character; this strain was eliminated from further trials. Two of the strains that performed well at laboratory scale in all wines and produced fault-free wine were selected for trialling at winery scale with industry partners. Data from these trials is being processed but preliminary feedback from winemakers is promising. At least one of the strains will be used in much larger scale fermentations next vintage, in part because of positive sensory attributes that it imparted.