Brettanomyces - The definitively short backstory of horse-blankets and modern brewing

"British Fungus" or "British Yeast". That's what brettanomyces means in Greek, translated literally.

For a huge portion of history, and for most styles of traditionally brewed beer, brettanomyces (or "brett", for short) was an unwanted, nasty, and wild yeast that infected your beer, ruined your wine, and rotted your fruit (brett naturally lives happily on the skins of most fruits). Today, brett is a popular yeast used by breweries all around the world. In fact, there are a number of U.S craft breweries that are now solely dedicated to brett-based fermentation. When I say solely dedicated, that means they choose not to use any strains of traditional Saccharomyces brewer's yeast, either ale or lager yeasts, during the fermentation process. It's a bold move, both because of the amount of time it takes to properly ferment a beer using only brett, and also because of its infamous unpredictability. Marginal differences in fermentation temperature, light exposure, and other incremental environmental factors can have a huge effect on a beer that's being fermented with just brett. 


Let's back it up a bit. We've established that brett is a wild yeast. You'll see the term "wild ale" and "wild yeast" tossed around a bit when reading about your favorite breweries. If something is deemed "wild", it just means that the liquid was deliberately exposed to bacteria/yeast that aren't normally (or haven't traditionally been) used in the brewing process. This could be as simple as letting the beer naturally ferment in the open (remember...yeast are everywhere. Literally. You have millions of them on you right now), or this could mean that a brewer pitched ("pitching" means "adding" in brewing terminology) a specific strain of wild bacteria or yeast into the wort themselves. Whatever the cause of the fermentation was, it's a "wild" fermentation for this reason. 

Brettanomyces (this is pronounced "Bret-tann-oh-my-sees", for the record) is a wild yeast. Not a bacteria, a yeast. There are quite a few commonly used strains of Brettanomyces yeast that impart extremely unique flavors and aromas to beer.  A "strain" of yeast is simply one of the many different kinds available. Brettanomyces (which is the genus) is the umbrella category for many different strains in that family of fungus, including:

  • Brettanomyces Bruxellensis (Aka "Brett B")- Generally responsible for the most famous brett flavors and aromas, like horse-blanket, rotting cheese, wet dog, an all manner of crazy, funky stuff.
  • Brettanomyces Claussenii (Also knows as "Brett C")- Fruiter, brighter flavors, with a hint of funk. Less intense. It's like smelling an old basement full of really fresh peaches.
  • Brettanomyces Drei - Big aroma, tingly nose, less funk.
  • Brettanomyces Lambicus - This can be a ton of flavors, given the right conditions. Usually strong and musty, funky, bright, pick.
  • The list goes on...

Most breweries do not make a beer that's fermented with 100% brett. If they're going to use brett in their beer, it's usually a small portion of the total yeast used (usually less than 25% of the total yeast pitched, on average). Because brett is now in common use at some of your favorite local craft breweries, companies that specialize in yeast cultures for brewing have made them available for purchase. They're still considered to be a "wild" yeast, but we've taken some of the unpredictability out of them by honing in on specific strains. 

Finally, I've often heard the misconception that brett is the primary souring agent used to make sour beer styles. Historically, brett has been used in conjunction with a souring bacteria called Lactobacillus ("Lacto" for short) in a few of your favorite sour beer styles. Brett can eventually produce a mild sour flavor in beer, mostly due to its esters, but it's not the primary souring agent. Lacto does almost all of the heavy lifting the through the creation of lactic acid in your beer, which is extremely sour. Yes, that's the same lactic acid that makes your milk go bad and smell terrible. Pretty fun eh?

So that our friend Brettanomyces. Happy Monday.

- Chris