Cheers to 500 years of different beers, thanks to brewer's yeast


Without the humble microbe, we wouldn't have our vast array of beer, wine or bread. Geneticists traced brewer's yeast strains to their last common ancestor – and uncovered a surprise or two along the way.  Belinda Smith reports.


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Crisp lager, smoky Hefeweizen or a rich, oaty stout? Whatever your beer preference, you probably have brewers from the 1500s to thank for it, a new study shows.

Chances are our beer range wouldn’t exist today without their unconscious efforts selectively picking the tastiest, booziest or fastest-growing strains of the yeast Saccharomyces cerevisiae – the microbe responsible for much of the taste and all of the alcohol in your pint glass.

And now, a team in the US and Belgium (where else?) traced the genomes and fermentation characteristics of more than 150 types of S. cerevisiae and found different strains consume specific sugars, tolerate brewery conditions and produce a huge spectrum of flavours.

The work, published in Cell, allowed the team to create new, hybrid strains that fermented beer well but smelled completely different.

"We're drinking the best beers now because ancient brewers were smart enough to start breeding yeast before they knew what they were doing,” says Kevin Verstrepen, a yeast geneticist at the University of Leuven and senior author of the study.

“It was really an art."

S. cerevisiae is the most widely used brewers yeast today thanks to, in part, its tolerance of booze. Even after other yeast species have succumbed to the alcoholic environment, S. cerevisiae will happily keep churning out carbon dioxide and ethanol.

What about taste? Yeast also produces molecules which comprise a huge part of beer's flavour.

But when it comes to brewing different types of beer, “it’s easy to forget about microbes”, says Ben Schulz, a microbiologist from the University of Queensland in Australia, and who was not involved with the study.

The basic ingredients of beer are simple: water, starch from grain which is converted to sugars, yeast to feed on those sugars and ferment the mix, and hops for flavour.

While craft breweries tend to tinker with hops and grains to create different taste profiles, Schulz says, “the flavours yeasts generate are complex”.

Indeed, as species evolve in the wild – or die out – so too do yeasts in the brewery, with different strains producing new taste and fermentation characteristics. If the brewer liked those qualities, he or she kept some of the yeasty sediment aside to use in future batches.

But with hundreds of different S. cerevisiae strains today, when did their last common ancestor live? And how do they differ?

Verstrepen, Brigida Gallone, Jan Steensels and colleagues set out to find out.

They analysed the genome of 157 S. cerevisiae strains used today in beer, wine, sake, spirits and bread, and found they shared a common ancestor in the 1500s – around a century before microbes were formally discovered – before different strains emerged and blossomed as brewers favoured them.

A few strains, such as one that produces spicy flavours found in German Hefeweizens, were genetically quite distinct. But generally, strains could be grouped according to their industrial purpose – such as beer or wine or bread.

Within those categories the team saw genomes clustered geographically – with those from the US similar to the UK, but very different to German and Belgian strains (which were quite similar to each other).

A number of interesting genetic patterns also arose. Wild yeast can reproduce sexually when they’re under stress, but beer yeasts have lost that ability – they’re only able to clone themselves, probably because they no longer find themselves in situations where they’re short of sugary food.

And brewers’ yeasts are able to break down maltotriose – a sugar made of three glucose molecules, which is plentiful in beer brewing but rarely found in nature, Schulz says.

wine yeasts, which could breed with feral yeasts, kept some of their wildness.

Of course, this means most strains of S. cerevisiae are forever confined to the brewery – they simply lack the genes to make it in the wild.

Does the same apply to wine? Interestingly, although wine yeasts share origins with their beer brethren, they’re much less domesticated.

This could be because while beer yeasts were generally kept in the brewery, wine was fermented with yeast found on grape skins “and on the feet of the people stomping them”, Schulz laughs.

So wine yeasts, which could breed with feral yeasts, kept some of their wildness.

“In that sense, beer yeasts are like dogs, completely ‘tamed’ and adapted to their relation with humans, whereas wine yeasts resemble the wilder character of cats," Gallone and Steensles say.

After analysing S. cerevisiae strains, it’s no surprise the Belgian team will soon add a brewery to the lab.

"It's a short jump from working with yeast to trying to make better beer yeast," Verstrepen says.

  1. http://www.cell.com/cell/fulltext/S0092-8674(16)31071-6
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