I retired from Niagara College exactly one year ago today, and other than two short posts last winter, there has been radio silence on this channel ever since. There were some compelling reasons: The first three months of 2017 were spent fixing up our house so we could sell it. The next three months were spent selling the house, packing up our stuff and moving out to Vancouver Island on the West Coast of Canada. Since then, we have been unpacking and getting used to our new surroundings.
Well, the vacation’s over, it’s time to do some writing!
First up, I’d like to address the subject of “wild yeast”, specifically the yeast known as Brettanomyces (pronounced bret-TAN-oh-MY-sees, and often shortened to “Brett”, much to the eternal chagrin of brewers actually named Brett).
I was recently at a beer tasting at a local liquor store where we were served a beer fermented with Brett. The store employee leading the tasting assured us that Brettanomyces was a wild yeast existing in the air that brewers used to spontaneously ferment their beer in order to make it sour. There were so many errors in that single statement that I decided I needed to spend some time clearing up a few misconceptions about Brett.
Firs, let’s talk about ordinary domestic brewers’ yeast: The role of yeast in fermentation was actually a big mystery until relatively recently. As late as the 1830s, respected scientists insisted that yeast was an inorganic substance that was somehow spontaneously created during fermentation — in other words, fermentation created yeast. It wasn’t until the 1860s that Louis Pasteur studied the issue and irrefutably established that yeast was a single-celled critter that ate sugar and produced CO2 and alcohol as a result.
Eight years later, Emile Christian Hansen, the head of Carlsberg’s laboratories, successfully isolated the two main types of domestic brewers yeast.
The first one, which could ferment at room temperatures, he named Saccharomyces cerevisiae (“sugar-eating fungus of beer”). This is the “top-fermenting” ale yeast that has been making beer for humanity for thousands of years.
He was also able to isolate a different strain of yeast from his own Carlsberg lager, a “bottom-fermenting” strain that could ferment at much lower temperatures. This yeast strain, which produced lagers, had actually been donated to Carlsberg by Spaten Brewery of Munich forty years previously, and had already been named Saccharomyces pastorianus (“sugar-eating fungus of Pasteur”) in 1870 by German scientist Max Reess. However, Hansen insisted that his Carlsberg yeast was a new strain, which he emphasized by calling it Saccharomyces Carlbergensis. Hansen’s name persisted for almost a century until genetic testing proved that S. pastorianus and S. Carlbergensis were in fact the same yeast. Since Reess had named the yeast first, “pastorianus” had precedence and replaced “Carlsbergensis” as the name we use today for bottom fermenting lager yeasts.
Both S. cerevisiae and S. pastorianus are very domesticated. After centuries of eating only very simple sugars, that’s pretty much all they can digest: single molecules of glucose, or maltose (a pairing of two glucose molecules), or maltotriose (a short strong of three molecules of glucose). Once all these simple sugars have been digested, any sugars more complex than this are left in the beer, giving it body and some sweetness.
Hansen declared these two strains of domesticated yeasts to be the only “true” brewers’ yeasts. Every other type of yeast found in beer was an undesirable accident that Hansen branded “wild yeast”.
In 1904, another Carlsberg scientist, Hjelte Claussen, isolated a strain of “wild yeast” that was spoiling British beers, and named it Brettanomyces (“British fungus”). Claussen noted several characteristics about this strain: it produced acetic acid (vinegar) and other “off flavours”; and it was able to digest very large and complex sugar molecules. As a matter of fact, it was able to live inside the cells of wood, digesting the large sugar molecules found there. This meant that once Brett had infested a wooden vessel at the cellular level, there was no practical way to disinfect the wood — the vessel had to be thrown out, lest the infection spread throughout the brewery. For this reason, 20th-century brewers regarded Brettanomyces the same way that doctors regarded measles: a communicable disease that was difficult to eradicate.
However, Brett has likely been in our beer just as long as S. cerevisiae and S. pastorianus. In the late 18th and early 19th centuries, when British brewers aged their porter in giant vats for up to a year, it was undoubtedly Brett that helped to give aged porter a complex, viniferous character (likely similar to Rodenbach’s red Flanders ale).
In the 20th century, these flavours fell out of style in Europe and North America, and were seen as highly undesirable.
But more recently, with the rise of the craft beer revolution and the search for new flavours, our attitudes about Brettanomyces have begun to change. It is true that Brett produces some acetic acid, but not terribly efficiently. If a craft brewer wants to produce a sour-tasting beer, he or she would be better off using either lactobacillus, the lactic-acid producing bacterium responsible for spoiled milk, or pediococcus, a bacterium that produces acetic acid in far greater quantities than Brett. Brewers using Brett are mainly interested in the other flavours produced: phenolic, funky, musty, spicy, barnyard, horse blanket and cloves are just a few of the flavour compounds that Brett can produce. As Nate Ferguson, co-founder of Escarpment Labs, told me, “I wouldn’t use Brett primarily for souring a beer, I would use pediococcus or lactobacillus. But those bacteria also produce diacetyl [gives beer a buttered popcorn taste], which Brett can clean up. So for a sour beer, I would use Brett for diacetyl clean-up. But that’s really using Brett as a janitor. I would primarily use Brett for the wide range of flavours it is capable of producing.”
Brett‘s insatiable appetite for complex molecules can also have another effect on beer. Since Brett will convert ALL the sugar molecules in the wort into alcohol and CO2 — even those “non-fermentable” sugars left behind by traditional brewers’ yeast — Brett will produce a stronger, drier beer with a thinner mouthfeel. As Nate pointed out to me, “Brett dries out the beer, which helps to emphasize sourness.”
This search for new beer flavours has led to something of a “yeast revolution”. Far from being considered “wild”, hundreds of strains of Brett with various flavour profiles have been isolated by yeast labs, and can be ordered by a brewer and pitched into beer in exactly the same way as S. cerevisiae and S. pastorianus.
Brett can be used in one of two ways:
- Once standard fermentation has ended using a traditional yeast, Brett can then be added to start a seconday fermentation, where it will go to work on the residual sugars left behind by traditoional yeasts.
- More rarely, Brett is used in the primary fermentation — this is called an “all-Brett beer”.
For brewers that use Brett, opinion varies as to which method produces a more “Brett-y” beer.
One thing is clear, though: even in the age of stainless steel vessels, if the brewer does not practice the strictest protocols in isolating vessels, valves pipes and hoses used in making a Brett beer and then sanitizing and testing for residual yeast, Brett still has the ability to survive and cross-contaminate. This recently happened at one BC brewery — Brett had been used in a seasonal one-off, a hose was not sanitized properly, and a batch of one of their regular beers was subsequently contaminated with Brett.
So, in conclusion:
- Brettanomyces isn’t a wild yeast that spontaneously ferments beer by falling into it from the air — it is pitched into a beer exactly the same way as traditional yeasts. It was given the label “wild” by an uptight Danish scientist.
- Although Brett can have a slight souring effect on beer due to the acetic acid it produces, brewers are much more excited by the other flavours that it produces, and its ability to dry out a beer by reducing residual sweetness.
- However, unless a brewer wants all his or her beers to taste like Brett, extreme care has to be used in cleaning and sanitation.
Student of Beer 