Mastering malolactic fermentation

New technology and genomic discoveries are helping to further unlock the complex and occasionally troublesome process of malolactic fermentation.

The Australian Wine Research Institute’s Senior Research Microbiologist Eveline Bartowsky has been studying malolactic fermentation (MLF) at the AWRI since 1994, and throughout this 20-year period she has helped to unravel much of the mystery and science of MLF.

‘The four fundamentals to a good MLF still stand; getting the right pH, temperature, SO₂and ethanol, are all critical. We also now know that having compatible yeast and bacterial strains are important too’, Dr Bartowsky said.

‘But more recently, we’ve come to understand a lot more about how aroma and flavour compounds are formed, their enzymes and pathways – which translates into being able to use specific winemaking techniques to modulate wine styles.’

The importance of removing malic acid to stabilise wine is well-known, but the potential for bacterial metabolism to influence aroma and flavour of the wine is increasingly being appreciated.

For example, a recent research project on co-inoculation of MLF and alcohol fermentation (AF) has shown potential cost and time savings, while also helping to lift fruity aromas and flavours in red wine.

‘We’ve found a shorter vinification (AF and MLF) can, in some styles and varieties, bring out more of the varietal characters of the fruit’, she said.

‘Our work in this area is about delivering greater insight into the role of MLF but ultimately it’s also providing winemakers with more options to use the outcome of MLF to help influence the sensory profiles of their wine too.’

Eveline said the next big stage of this research lies in the combination of sensory science and aroma compound composition with the new work in genomics.

In particular, the work being undertaken on mapping strains of Oenococcus oeni – the main lactic acid bacteria that conducts MLF.

‘We know that O. oeni has a critical effect on flavour, aroma and mouth-feel but we also now know how important strain variation is’, she said.

‘We have mapped the whole genome sequences of 12 strains already, and this has shown us that the scale and scope of the genetic variations is much greater than we originally expected.

‘The more we learn about these strains the more we hope to be able to identify how the strains perform, their ability to modulate wine chemical composition and ultimately potential phenotypic characteristics they might give to the wine.

‘This is where the sensory science becomes so critical – as it gives us the information we need for sensory thresholds and physical expressions that are desired by consumers and winemakers.’

The future, Dr Bartowsky said, is providing winemakers with the options of selecting specific strains of O. oeni to meet or enhance the desired characteristics of wine.

For more information contact Dr Liz Waters, GWRDC Program Manager,

Image: AWRI’s Peter Costello and Randell Taylor undertaking a ‘bench tasting’ where MLF trial wines are checked for faults and treatment differences before going onto sensory descriptive analysis.

MLF sensory_GWRDC