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The Yeasties, The Yeasties – The WILD Beasties in my Beer!


(Picture from
(Picture from

In my post “The Yeasties, The Yeasties – The Beasties in my Beer!,” I discussed the definition and meaning of the terms “Ale” and “Lager” and the yeast that give them their names.  These two yeast species, Sacchromyces cerevisiae and Sacchromyces pastorianus, are the worlds most commonly used yeast species in modern brewing.  But they aren’t the only creatures associated with brewing.  Wild yeast and bacteria have forever been linked to the world of beer. But the question remains, what are the “wild” yeasts?

In modern breweries, they’re infections.  They can get into the equipment forcing a brewery to shut down and completely sanitize every nook and cranny with extreme prejudice.  Modern brewing’s key trait is consistency of recipe.  Brewers wants their beers to taste the same all the time.  A Sierra Nevada Pale Ale will taste the same batch to batch, year to year because the brewery wants to have a loyal following of customers who know what they’re buying.  With variance in ingredients and the potential for yeast drift (your yeast “evolving” and changing its characteristics), it’s sometimes a struggle to keep the beer tasting consistent over time.  A brewery that navigates these turbulant waters and manages to create consistent and good tasting beer will see its customer base grow.  Besides modern sanitation process, the most important piece of consistent beer puzzle is the use and management of a house yeast strain.

Brewers spend endless amounts of time devoted to maintaining the purity and health of their yeast.  It’s often a joke in the brewing community that in reality, brewers are nothing more than slaves to a single-cell fungus.  During the 19th Century, one of the biggest innovations, besides better malting processes, was the “discovery” of and isolation of brewing yeasts.  This meant separating our two previously mentioned friends, S. cerevisiae and S. pastorianius, from the “wild” yeast species. Some of the wild species include: S. diastaticus; wild or “Natural” beer, wine or bread S. cerevisiae and S. Bayanus; Candida and Pichia yeasts, and Brettanomyces.  In nature, yeast abounds.  It’s floating on the air, living on the skins of fruit, or growing in wood vessels and the beams.  Yeast is literally EVERYWHERE.  And it doesn’t live on its own.  Many varieties of yeast species exist together in an environment.

But yeast aren’t the only microorganisms that can become involved in the brewing process.  Bacteria, to a lesser extent, can be either beneficial or a spoiling agents.  Fortunately for humanity, no known pathogenic bacteria have ever been associated with beer.  The very nature of beer protects it from most bacteria.  Beer is acidic, alcoholic, and has a low oxygen content; all of which inhibits bacterial growth.  Of course, there are exceptions.  Acetic acid bacteria, lactic acid bacteria, Pediococcus, Obesumbacterium, Zymomonas, and Pectinatus can all be involved in brewing, negatively or positively.

Modern brewing involves keeping the ambient yeast and bacteria out of the brewery and brewing process.  But this wasn’t always so.  It’s only been the case for the last 150 years.  Modern sanitation, coupled with microbiology, has changed the face of brewing forever, and in most cases, for the better.  Batches of beer are rarely thrown out because of contamination.  Sour beers, once the unintentional norm, became a thing of the past.  But somehow, some sour beers managed to survive the modernization and industrialization of beer.  These beers belong loosely to the category of “sours” or “wild beers.”

Sour Beers

For a long time, Belgium’s lambics, oud bruins, Flemish reds and Germany’s Berliner weise managed to not go extinct.  Despite losing their popularity in their home markets, a few intrepid brewers/breweries kept the tradition alive until such a time that these wonderful products could be rediscovered.  Fortunately, thanks largely to folks like the late Michael Jackson, these beers found a new audience with Americans who were beginning to yearn for beers other than the bland, mass-produced macro beers they had been forced to buy for years because of a lack of real market diversity.  With the reawakening of the American desire for good beer, came the importation of these fantastic beers from overseas.  The new money coming into the breweries allowed them to thrive.  This also allowed them an opportunity to reintroduce their beers to their home markets and remind the locals of what amazing gems they had in their own backyards.  Today, the sour beers of Belgium are strong and growing stronger, both abroad and at home.  Unfortunately, this same revitalization hasn’t happened in Germany with Berliner Weises.  Most of the experimentation with this style is coming from intrepid American brewers.

The Actual Bugs – Yeast

Brettanomyces is a another genus of yeast.  The two most common species used in brewing are B. bruxelensis and B. anomalus.  In reality, these are the two used despite the different names brewers often give them.  Brett, as it’s commonly refered, can be a dangerous but fun bug to play with.  In the presence of residual sugar and oxygen, it can create acetic acid which can sour the beer.  This is usually seen in primary fermentation or in secondary non-bottle fermentation.  Lauren Salazar of New Belgium, at their Sour Symposium, stated that Brett is so tough and hungry that they ferment their beer dry before it goes into the wood foedres for conditioning.  She said that if it gets hungry, it’ll just eat the sugars out of the oak staves.  In their case, this allows them to control the action of the Brett so it doesn’t go crazy on them.

In reality, Brett doesn’t provide huge amounts of sourness.  Other agents, which I’ll discuss shortly, provide that function.  In most cases, Brett is used in bottle conditioning where it only provides an additional small level of tartness (due to the much lower oxygen levels involved).  What it really exceeds at is adding some funky and delicious flavors, which include: barnyard, horse blanket, floral, earthy, tropical fruit and more.  Usually when describing what Brett does, you’re required to say “but in a good way.”  Barnyard?  Yup, tasty.  Brett is involved, in some way, in all Belgian sours.  Its presence is stronger in the Lambic style beers than in the Flemish reds and browns.  In some “heritage” style Berliner weises, you can see some Brett as well.

Cantillon Brewery’s open air coolship is used to stimulate spontaneous fermentation. (Picture by

There is one other way in which Brett is used: spontaneous fermentation.  This method involves allowing the wort to come in contact with the ambient air.  In the Lembeek region of Belgium, the country side is filled with orchards which are alive with “wild yeast.”  The yeast settles into the wort and begins to ferment.  This, in fact, is the most ancient and primal way that beer was produced.  In addition, the breweries themselves are covered in what is literally the “house strain” of wild yeast (which includes Brett, wild Sacchromyces, and various bacteria).  The rafters, the equipment, the brewing spoons are all impregnated with it.

If you want to see Brett in action, I recommend these beers: Russian River Sanctification (100% Brett in both primary and bottle conditioning), Orval (bottle conditioned with Brett),  Green Flash Rayon Vert (Green Flash’s homage to Orval), and Boon Geuze (spontaneously fermented).

The Actual Bugs – Bacteria

Rodenbach’s Foedres are the home to all these microorganisms and are responsible for helping the brewer to control their activity.

Lactobacillus is one of the most common bacterium associated with brewing.  In standard beers, it’s a spoiling agent but in sour beers, it’s magic.  Lactobacillus, like yeast, eats sugars but instead of alcohol, produces lactic acid and CO2.  This is one of the common bugs used in Yogurt.  Berliner Weise is the style most famous for its lactic acid bacteria.  Traditional styles are often brewed with a ratio of 80/20 standard yeast to lactobacillus.  This bacterium also makes appearances in Flemish Reds and Browns and to a lesser extent, Lambics.  If you’d like to try some Lactic acid beers, I suggest: Full Sail Berliner Weiss (while it’s available), Bayerischer Bahnhof Brettanomyces Lambic Berliner Style Weise (Lacto with Brett), Rodenbach and Rodenbach Grand Cru, and New Belgium La Folie.

Pediococcus is the other common lactic acid bacteria seen in brewing, both negatively and positively.  This bacteria is most commonly associated with pickled products.  In addition to creating acid, Pediococcusimparts additional flavor and complexity to sour beers.  Recommended beers include: Rodenbach, Boon Geuze, and New Belgium La Folie.

Acetobacter, Gluconobacter, and Gluconacetobacterare common Acetic Acid Bacteria that are used in vinegar production.  These are probably the least used and most dangerous of the souring agents that are associated with brewing.  They eat sugar, alcohol and other carbon compounds and turn them into various organic acids.  If there is enough oxygen, they will run rampant and turn as much sugar/alcohol as possible into acid and ruin the beer.  These bacteria are most commonly seen in Flemish Reds and Browns, and to a much lesser extent, lambics.  Fortunately, aging in large oak vats keeps the oxygen levels very low so that these bacteria don’t go wild.  The oak allows a small bit of oxygen to pass through to edges of the conditioning beer.  The majority of the other microorganisms are functioning on an anaerobic mode (without oxygen).  Again, seek out Rodenbach and New Belgium La Folie as examples of acetobacteria.

Final Words

I hope this helps beer loves and sour beer lovers understand what’s going on in their beer.  Understanding these microorganisms is key to both producing fabulous sour beer and also to keeping your standard beers free from these contaminants.  Sour beers were once the norm for beer consumers, not by intention but because of the reality of production.  Today, they are considered (by many) the pinnacle of the brewer’s art.  The art of managing (you can’t really “control” them) their growth, blending the various flavors and the bravery it takes to introduce these bugs into a brewery have set many brewers apart in the new world.  Today’s American sour scene is flourishing.  The brewers are taking the old world traditions of Belgium (and to a lesser extent, Germany) and running with them.  With one foot in the New World and one foot in the Old World, American sours are becoming some of the most highly sought after beers among beer lovers, while the sour beers coming out of Belgium are increasing in variety and frequency, much to the delight of American sour fans.  The 21st century is indeed a bright one for both traditional European sours and American new sours, and one I’m excited to see and taste.

(For more information, check out “The Oxford Companion to Beer” edited by Garret Oliver, Oxford University Press ©2012. It’s a wonderful encyclopedia of beer knowledge that I used extensively in this post.)

Here is an excellent piece on the use of Brettanomyces in British historical brewing.  You can find it on the Zythophile blog.

30 thoughts on “The Yeasties, The Yeasties – The WILD Beasties in my Beer!

  1. Great stuff! You have left me parched. Good thing I have a Festina Peche in the fridge to quench my thirst. Heh.


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