Last updated March 2, 2018 at 12:18 pm
Scientists in Belgium have found the genes in yeast responsible for producing this aroma during fermentation.
“In some wines, you can smell the rose flavour above all the others,” said lead researcher Johan Thevelein from the Vlaams Institute for Biotechnology. “But why certain yeast strains make more of this compound than other strains, there was no knowledge at all.”
Yeast plays a central role in creating the flavours of alcoholic drinks. During fermentation, it adds flavour and carbonation to beer, while in wine is alters the flavours from the grapes to create new tastes and aromas, while adding its own distinct character.
The researchers used high-throughput genomic analysis to study genes in a hybrid strain of Saccharomyces cerevisiae, or brewer’s yeast. They found four regions of DNA that contained multiple genes linked to higher production of phenylethyl acetate. Investigating further, they found that specific versions of two particular genes, TOR1 and FAS2, produced the highest amounts of the flavour compound.
Combined with previous work, this new finding links genes to specific flavours in wines and beers, which could allow us to more easily create yeast delivering a specific tasting drink. Traditionally, enhancing industrial yeast strains for desirable flavours has been a challenge. Cross-breeding certain strains has been used to select for certain genes and so create certain flavours, but the process is long and expensive. And after all that time and expense, the crossbreeding can cause other unwanted changes in the yeast.
“You have to do two things,” says Thevelein. “One is to improve the yeast trait that you want to improve. Second is to change nothing else in the yeast. In practice, the latter turns out to be much more difficult than the former.” A cross-bred yeast may work in the lab, but not in the brewery. “If the fermentation is bad, you have to throw away all the beer,” Thevelein says.
In the French region of Champagne, wine-making houses have their own unique strains of yeast, part of what makes wine from Pommery different to Thienot different to Pol Roger. Knowing the genetic basis for tastes and aromas would let winemakers, brewers, even bread makers tweak the flavours of their products, or even design their own flavour profiles from scratch and then create a yeast to produce it.
The ideal tool for tweaking the genes in yeast already exists – the genetic editing process known as CRISPR. The fast and precise genetic editing would let microbiologists quickly produce specific yeasts on demand, fulfilling requests such as changing levels of phenylethyl acetate, nerolidol (a woody scent), ethyl acetate (a sweet smell), and compounds causing banana- and butter-like flavours.
The proof will be in the drinking however, and for the ultimate test the researchers have teamed with a Belgian brewery to create several batches of beer using experimental strains of yeast. We’re just trying to work out how to get on the tasting panel.
The research was published in mBio