New yeast enhances floral aromas

Developing new non-genetically modified (non-GM) yeast tends to be a ‘large numbers’ game. Dr Toni Cordente and colleagues at the Australian Wine Research Institute (AWRI) started with approximately one billion separate cells in a quest to find one that could eventually help develop more pronounced floral and rose aromas in wine.

To date they are very much on track, with a commercial yeast supplier exploring the feasibility of propagating and drying commercial quantities of the yeast. The yeast will be tested by the AWRI and collaborating wineries during the coming vintage. If it all stacks up scientifically, logistically and financially, a finished product could be available for the 2018 vintage.

It’s part of a four-year project funded by Wine Australia, that seeks to develop a range of non-GM yeast strains that can enhance wine flavour, aroma or fermentation performance, avoid the generation of faults or help achieve optimal flocculation behaviour.

For Dr Cordente, who has spent much of his time in recent years finding ways to use yeast to prevent problems in wine, such as the distinctive rotten egg smell that too much hydrogen sulfide can cause, it’s a nice change to be working to create positive attributes.

‘One of our aims is to give winemakers new tools so that they can modulate wine the way they want,’ he said. ‘While floral aromas in wine are often derived from grapes, some products of yeast metabolism also contribute to floral/rose aroma. Many wine yeasts produce these compounds at levels below their aroma perception threshold, meaning that their contribution to wine style is minimal. Finding a yeast that can produce much higher levels of these characters could be very useful.’

The irony is that success was dependent on things appearing to go wrong; Dr Cordente wanted – in fact needed – some of the cells to mutate.

‘We selected one of the common neutral yeast strains we have in our collection that ferments well but is not very aromatic,’ he said. ‘We then put a billion identical cells into a solid media that included a toxic molecule, knowing that some of the cells would spontaneously mutate in an attempt to survive.’

‘We knew each of the survivors would have different characteristics and there was a chance some would include the ability to produce the aromas we were seeking.’

Each of the hundred survivors (that’s a ‘success’ rate of 1 in 10 million) was used to ferment a synthetic must that had all of the components of a natural grape must, and around a fifth of them produced enhanced floral aromas. One was chosen to ferment 20 litres of Chardonnay, which was then bottled.

‘We then undertook a formal sensory analysis and people picked the enhanced rose and floral aromas straight away’, Dr Cordente said.

Beyond this vintage’s trials of the rose yeast, there is also potential to see what can be achieved with the other survivors, which may have very different characteristics. There is no shortage of material with which to work.