Beer Science: What Puts the Funk in Brett?

If you haven't read part one of this two-part write-up, I kindly direct you for background information here. Now that some background details are out of the way, let me share with you some of my research and knowledge on Brettanomyces (pronounced "brett-TAN-oh-MY-cees", and referred to by the shortened name "Brett" here and elsewhere).  Brettanomyces is a yeast species, also known as "wild yeast".  Brettanomyces has long been known by brewers and wine-makers alike for the ability to produce interesting and complex flavor profiles.  In fact, some wine makers abhor the word "Brett" because for many wineries Brettanomyces is known as a spoilage yeast.  This yeast has been known to ruin batches of wine and beer.  So what's different about Brettanomyces from traditional yeast?

The flavors produced by Brettanomyces yeast are extremely deviant from a normal beer flavor.  Beer brewed with Brettanomyces can be overwhelmingly fruity, funky, and many other colorful words.  Specifically, the beer will taste very acidic- almost wine or champagne-like in character.  Despite the havoc Brettanomyces can cause on winery (and brewery) premises, wine-lovers tend to enjoy these flavors when present in beer because they are reminded of familiar wine tastes.  Beer-lovers enjoy these flavors because, when managed correctly, these flavors can be strikingly different and delightful from traditional Saccharomyces yeast beer flavors.  For a recent review of a Brett beer I tasted, click here.

What Do Brett Yeast Look Like?
So let's take a peek with a microscope at what Brettanomyces cells actually look like compared to "normal" Saccharomyces brewing yeast.  I searched for images that would show you the relative shape of the two species. 

 

 "Typical" Saccharomyces yeast cells.

  

Brettanomyces yeast cells.

Notice how different the cell morphology is between a Saccharomyces cell (top figure) and a Brettanomyces cell (bottom figure).  Although these are both yeast species, they are quite different in their morphology and certainly in their metabolism.  Brettanomyces yeast grow slower than Saccharomyces yeast.

Why Do Brett Yeast Taste So Funky?
As previously mentioned, Brettanomyces yeast can produce very unusual flavors.  But why?  Well, as all fermenting yeast, Brett yeast use sugars for energy and convert these sugars into alcohol and other products of metabolism.  The key phrase here is other products of metabolism.  In addition to alcohol, different yeast (strains and species) will produce different chemicals using different pathways.  These different chemicals result in a different tasting beer.  Brettanomyces and Saccharomyces species not only look different under the microscope, but they also produce different chemicals.

What Chemicals are Different?
The predominant chemicals that are produced by Brettanomyces species are known as phenols.  From my research, two particular phenols are noted as being responsible for the flavor profiles caused by Brettanomyces yeast:

4-ethylphenol (abbreviated 4-EP) : Tastes identified as: band-aids, barnyard, horse stable, antiseptic.

4-ethylguaiacol (abbreviated 4-EG): Tastes identified as: bacon, spice, cloves, smoky.

Interestingly, the ratio of 4-EP to 4-EG was determined to be important in flavor perception.  Beers that possess the same concentration of 4-EP, but different concentrations of 4-EG, may be perceived to taste different.  A summary of  Brettanomyces fermentation is shown below.

Brewers may also choose to add Brettanomyces yeast at a certain time point after Saccharomyces yeast has been added.  This can create even more complex flavor profiles, and presumably can help manage the funkiness of the Brettanomyces special flavors.

Where Can I Find a "Brett" Beer?
Beer containing Brettanomyces can be predominantly found in such styles as traditional Belgian ales, lambics, gueuze, saison, and farmhouse ales.  You can find Brettanomyces beers in stock at Consumer's Beverage locations as well as regularly on tap at Blue Monk and Moor Pat.



Here is a list of references that I used to help generate my report.
A great NYTimes article about Crooked Stave Artisan beer brewer Chad Yakobson.
A very mezmerizing video of vibrating French Saccharomyces yeast cells (WTF?).
A book on American Sour beers available for purchase.
A technical report on 4-EP and 4-EG from ETS Laboratories.
http://www.brettanomycesproject.com/
Huffington Post write-up on sours.