Lager can be traced back to fungus growing in Irish forest

By Mark Waghorn via SWNS

Ireland might be famous for its stouts such as Guinness but scientists have discovered the yeast first used in lager originated in their forests.

The yeast used to brew cold beer is known by the scientific name Saccharomyces pastorianus.

Its ancestor has remained a mystery - until now. Students at University College Dublin found it in a wooded area of their campus.

Lead author Professor Geraldine Butler said: "This discovery is a fantastic example of research-led teaching."

Lager was invented in Bavaria 600 years ago. Historically, all beers were fermented with one particular strain of yeast – with a few variations.

Saccharomyces Cerevisiae has been used in beer for thousands of years. It ferments warm and relatively quickly - creating what we refer to as ale.

Close 'cousin' Saccharomyces Pastorianus works at a much slower rate at cooler temperatures in caves and cellars. It dates back to the middle ages.

During that period, beer could only be brewed in the cooler months of the year, typically September through May.

The old train of thought was that Cerevisiae gradually evolved into Pastorianus over the centuries as it adapted to this environment.

In any event, sometime in 1500s, German brewers had a new yeast to work with that was ideally suited to cool fermentation and aging.

But where this new yeast really came from has been debated for centuries. The study in FEMS Yeast Research sheds fresh light on the mystery.

Butler said: "Our undergraduates have found more than a hundred yeast species in Irish soil samples over the past five years.

"We're delighted to stumble across S. eubayanus on our own doorstep."

Although the records show that the first use of S. pastorianus was in breweries in southern Germany, the S. eubayanus parent was never found in Europe.

Instead, researchers have discovered the yeast in South America, North America, China, Tibet, and New Zealand.

This curiosity caused some researchers to wonder whether S. eubayanus had, in fact, ever been in Europe, and, if not, where the lager yeast S. pastorianus had come from.

Brewing is one of the oldest human industries. Scientists have uncovered evidence of fermented beverages from China from at least 7,000 years ago, and from Israel from up to 13,000 years ago.

Modern brewing developed in Europe, where, until the Middle Ages, most beer brewing was associated with a yeast called Saccharomyces cerevisiae.

This is the same species of yeast that is still used today to make ale-style beer, wine, and bread.

Most beer made nowadays, however, is lager beer, not ale, and there is considerable interest in understanding the historical shift from ale to lager in Europe.

Lager brewing, which first appeared in the 13th century in Bavaria, uses a different species of yeast, Saccharomyces pastorianus. S. pastorianus is a hybrid of two parents, only one of which is S. cerevisiae.

The identity of the second parent was a mystery until 2011, when Saccharomyces eubayanus was discovered in the Patagonian Andes in South America.

Like S. pastorianus, S. eubayanus is cold-tolerant and scientists believe that the lager-style of cold brewing selected for the formation of the S. pastorianus hybrid yeast from an ale strain of S. cerevisiae and a wild S. eubayanus isolate.

Butler added: "We're hoping to find a commercial partner to brew with it so we can find out what it tastes like."