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Beer's last secret is found in a 500-year-old microbe

For lager lovers worldwide, it is possibly the best micro-organism in the world.

But the identity of the yeast that made cold refreshing beer possible has been a mystery for centuries.

Now scientists believe they have unmasked the microbe -- a stowaway that sailed to Europe from the New World 500 years ago.

The yeast ended up in the caves and monasteries where beer was brewed in Bavaria for the first time in the 15th Century.

There, it crossed with a distant relative, a yeast used for millennia to make bread and ferment wine and ale. The rest was history.

The yeast conferred characteristics that for the first time meant that beer could ferment in the cold.

"People have been hunting for this thing for decades," said Professor Chris Hittinger, from the University of Wisconsin-Madison in the US. "And now we've found it. It is clearly the missing species."