Strange Brews: Tapping Yeast Genetics for Uniquely Flavoured Beer
It’s small — microscopic, in fact — but it packs a punch. The creature is barred from entering certain laboratories in the United States to safeguard against contamination. It’s feared by the general public as an abomination of nature, an organism whose critics say it was created by the hands of a man playing god. The creature is the target of lobbyists and NGOs that would like nothing more than for it to be destroyed. But, is this creature — actually a man-made strain of yeast, a single-celled organism humans have been cultivating for at least 7,000 years — just misunderstood?
Without yeast, all beer would taste pretty much the same: cloyingly sweet liquid boiled from grain, also known as wort. It’s only when yeast ferments that the flavors (and, of course, alcohol) we know and love finally emerge.
Budweiser famously keeps its yeast under armed security!
Perhaps surprisingly, the genomes of the yeast that create drastically different beers are nearly identical. It wasn’t until recently that DNA sequencing became easy or cheap enough to justify studying beer yeast, meaning we could soon understand the genetic basis of, say, a lager versus an
ale.And now, Belgian researchers at the Center for Microbiology at VIB, investigating the genetics of yeast to produce floral aromas by using genetic analysis and targeted gene splicing.
Beer may be as old as civilization itself, but modern molecular biology could teach craft brewers some new tricks.
The genetic technique, from experts at VIB, could make the flavor-refining process cheaper, quicker and easier than breeding strains of yeast naturally.
Flavor compound production is influenced by many different genes, and researchers already knew about some of the genes responsible for phenyl ethyl acetate. But those genes were difficult to manipulate without causing other, undesirable changes, said Johan Thevelein, a cell biologist at the VIB-KU Leuven Center in Belgium and senior author of the paper.
In the course of their study, scientists Johan Thevelein and Maria R. Foulquié-Moreno led their team in screening a vast library of yeast strains to find one that naturally produces extra phenyl ethyl acetate, and bred that strain with a more standard type of yeast. Then, they compared the genetics of strong-smelling yeast offspring with that of weaker-smelling offspring. This allowed them to identify two new genes never before implicated in phenylethyl acetate production.
They found that alleles or ‘versions’ of two genes, TOR1 and FAS2, were responsible for the highest production of phenyl ethyl acetate.
The team used CRISPR/Cas9 editing – a cut and paste technique – to swap those alleles into other yeast strains and discovered that it boosted phenylethyl acetate production.
TOR1 was found to contain mutations that reduced honey-rose scents below normal levels, so brewers are unlikely to be interested in it, said Thevelein. But the other gene, FAS2, contained two small mutations that boost phenylethyl acetate production.
When the researchers stitched the FAS2 gene with these mutations into a standard yeast strain using the gene editing technology CRISPR-Cas9, they were able to increase that strain’s production of honey-rose scent by about 30 percent.
CRISPR/Cas9 offers a more efficient way to precisely engineer desirable traits in yeasts without affecting other traits, Thevelein says. In recent years, microbiologists have connected specific genes to an array of flavors, including nerolidol (a woody scent), ethyl acetate (a sweet smell, as in nail polish), and sulfur flavors.
In their work at VIB, Thevelein and Foulquié-Moreno have also identified genes responsible for banana- and butter-like flavors.
CRISPR/Cas9 can add desirable genes and swap out the undesirables, usually without the time, expense, and unwelcome side effects of cross-breeding strains. “With CRISPR, we never leave a scar,” says Foulquié-Moreno. Because the engineered yeast strains have alleles that have been swapped from other yeasts, they should be indistinguishable from strains produced by breeding or by mutagenesis and selection, she says.
The particular rose-scented yeast is still going through the breeding process to develop a non-CRISPR strain, Foulquié-Moreno said. (The use of gene splicing for beer production is in the process of being patented for the VIB lab, and brewers can reach out to buy rights to use them.)
Yeast are now routinely being modified in labs, and it’s not hard to imagine someone creating a beer super yeast using genetic tools in the future: Want a beer with higher alcohol content and more cherry notes? Just add this gene. Or that gene.
That said, genetic modification is arguably at odds with the ethos of craft beer. And sour beers, which can be fermented with the natural microflora of a brewery rather than a pure culture, may in part be a romantic reaction against the carefully regimented science of brewing.
Science can push the boundaries of beer, but boozy trends (aka what you want to be caught drinking at a party) is ultimately subject to the whims of popularity.
