A couple of yeast walk into a bar…

A couple of weeks ago, the “offbeat news” feeds lit up with the discovery of a Japanese striped beakfish off the Washington state coast. What was surprising about this find was that the fish was in a bait box on a Japanese fishing boat believed to have drifted to its current position following the March 2011 tsunami in Japan.

A picture of the Japanese Striped Beakfish, Oplegnathus fasciatus.

This little guy laughs in the face of tsunamis. Creative Commons image, attributed to user E-190, retrieved via Wikimedia Commons.

The fish has, it seems, generated a lot of publicity for the Oregon aquarium now housing it. But it puts me in mind of another, even more unbelievable journey.

Our story starts around six hundred years ago with some Bavarian brewers of beer. Now, beer has been around since approximately a week longer than there have been humans, or at least humans who farmed barley1. By the 15th century, in Europe2, you could even say they’d gotten pretty good at it. Many of the styles of beer that we’re familiar with today were being produced3, and while yeast wasn’t well-understood by brewers until much later, they knew that adding the dregs of a good beer to newly-cooked wort would make the result similar, and these carefully-tended “starters” became the closely-guarded trade secrets of commercial and monastic breweries.

16th century engraving, by J. Amman, depicting a brewery.

The good old days, where nobody minded if you stuck your hand in the beer.
Public domain image retrieved via Wikimedia Commons.

All that beer had one thing in common: it all used strains of yeast that preferred to ferment sugars under warmer conditions. These so-called “top-fermenting” or “ale” yeasts, nearly always strains of Saccharomyces cerevisiae4, had a tendency to result in a cloudy beer, and to leave behind often-unwelcome5 flavors in the beer through the production of esters if the temperature was too high or not stable enough during fermentation. They also didn’t keep very long, developing a funky, “skunked” taste soon after they were brewed, as undesirable bacteria and yeasts moved in to metabolize sugars and proteins that S. cerevisiae left behind.

The stability problem was helped by the addition of hops, perfected sometime in the 13th century. The mildly antibiotic properties of hops help to keep bacteria and non-brewing yeasts from getting a foothold in the fermenting beer, while allowing the brewing yeast, usually introduced as a well-established colony via a starter, to ferment the wort without competition6. Despite this innovation, however, even hopped beers had a tendency to deteriorate over time, and many people didn’t care for the flavor they imparted to the beer.

Something changed in the late 15th century, though. Those Bavarian brewers I spoke of earlier started making a new type of beer. Brewed in caves, deep cellars, or even under blocks of ice, lager, as the new beer was called, could be fermented at much lower temperatures than previous beers7. Brewing at lower temperatures meant that other organisms were too sluggish to reproduce in the wort to levels that resulted in off-flavors, and caused grain proteins as well as the yeast itself to fall to the bottom of the beer more quickly and completely, resulting in a clearer, more stable brew, with a cleaner taste. These lagers actually benefited from prolonged storage, as long as the temperature was kept low, becoming clearer and cleaner with time, and they were often stored for six months or more8.

A picture of Paulaner dunkel, a dark lager beer.

Today lagers are the most-often drunk beers in the world.
Public domain image retrieved via Wikimedia Commons.

It wasn’t until the 19th century that the fermenting action of yeast would become understood, and the various strains of it used in brewing classified. In 1883, a chemist working for Carlsberg brewery isolated the strain of yeast responsible for lager. He called it Saccharomyces carlsbergensis, but today it is more commonly known as S. pastorianus.

Saccharomyces cerevisiae under a microscope.

Ben Franklin supposedly said beer is proof that God loves us. Does that mean yeast are God?
Public domain image retrieved via Wikimedia Commons.

What happened in the 15th century to cause S. pastorianus to be discovered and rise so quickly to prominence in brewing? For many years, it was believed that S. pastorianus was a hybrid of S. cerevisiae and another strain of yeast (or sometimes two or more). Saccharomyces bayanus, Saccharomyces monacensis, and Saccharomyces uvarum, all used in wine and cidermaking, have each been proposed at one time or another as “second parents” to S. pastorianus, but with the advent of genetic sequencing in the 20th century, it became clear that none of those strains were a perfect fit. Each strain left too many stretches in the S. pastorianus genome that couldn’t be traced to either proposed “parent”, leading some researchers to postulate that another, heretofore undiscovered, strain of Saccharomyces must have been responsible, and others to suggest that the new strain must have undergone a large number of mutations before finding its home in some lucky brewer’s fresh wort.

That is, until 2011, when an international group of researchers announced that they had identified a likely candidate for the mysterious “second strain” of S. pastorinanus‘ parentage – in South America. The group isolated and sequenced Saccharomyces eubayanus, a strain of yeast that likes to live on beech trees in Patagonia (and one that’s yet to be found in the wild in Europe despite extensive searching), and found that it possesses genes that represent 99.5% of those found in S. pastorianus and not in S. cerevisiae, making it a compelling candidate for S. pastorianus‘ ancestry.

But how did S. eubayanus find its way into the breweries of Europe from Patagonia? Likely the same way our friend the striped beakfish got to the waters off of Washington: on a boat. One theory is that fruit flies, attracted to barrels of beer or fruit juice on the earliest European vessels to cross the Atlantic to the Americas, brought the yeast with them, stuck to their feet. From there, S. eubayanus somehow found its way into a brewery (maybe through the reuse of barrels or on a person who visited the brewery soon after getting off the ship) and from there into beer, where it got up close and personal with S. cerevisiae, giving rise to a child strain that was perfectly suited for lagering: able to grow and reproduce in much colder temperatures and to thrive on the mix of sugars and nutrients found in beer wort. Now that’s a hell of a journey.

1.A week being about how long it will take to ferment barley and water into something you could call beer, if you were really hard up or had no tastebuds. <<back
2.And quite probably other places, but I’m not familiar enough with the history of beer outside of Europe to say for sure. <<back
3.Some of them by breweries that still exist, and produce beer, even now; the oldest continuously-operating brewery in the world will celebrate its thousandth birthday in 2040. <<back
4.”Saccharomyces” means “sugar mold”. Try not to think about that the next time you’re enjoying an adult beverage. You’re welcome. <<back
5.But not always: the distinctive “banana and clove” flavor of Hefeweizens is a result of esters produced by the yeast used, for example. <<back
6.This was the reason for the creation of the IPA, or India Pale Ale style: it was highly-hopped so as to help it survive long shipping times from England to India during the colonial period. <<back
7.Today beers fermented at higher temperatures are typically called ales, although the term has meant several different things over the centuries. <<back
8.Modern ales usually undergo a period of conditioning as well, but this became possible due to the 19th-century advent of pasteurization and germ-aware sanitation techniques that prevent the beer from becoming infected with undesirable organisms. <<back

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