Part II - What is mixed culture fermentation?


The foundation of our beer is our mixed culture. For those who aren’t familiar with the term, think of it like a rustic sourdough starter compared to store bought yeast. It’s what we use to ferment all of our beers. In the starter there’s many different types of yeast working in harmony. Compare this to your store bought yeast which is a single laboratory isolated strain.  With a sourdough starter there’s an added complexity, beyond what your grains are contributing. Every sourdough starter is a little different by location and even evolves over time.


Many businesses have a proprietary component - a unique software, patent or some intellectual property that distinguishes themselves from their competition and essentially holds all of their value. A brewery is a cross between the service sector and manufacturing and like many things in the service sector, there’s not a significant proprietary component. Most beers can be cloned and repeated by learning the recipe, propagating up the same single strain yeast and making small tweaks to your environment (water, temperature, etc) to match the original creations. Although the cloned beer won’t be exactly the same, it’ll be very close. Mixed culture fermentation on the other hand, is much harder to duplicate. That’s because the culture is alive, ever changing and unique to that brewery. The culture permeates the physical space. If you were to take our culture and try to replicate our beer, it would be different from the beginning and more and more different over time. Not worse, could even be better, but certainly different. Creating beers specific to a place has been intriguing to me as home brewer and is a guiding philosophy as we start Fair Isle.

A pellicle from our mixed culture fermenting our beer. 

A pellicle from our mixed culture fermenting our beer. 

To further illustrate, let me give you a bit of background on current industry processes:


It’s common practice in the industry to purchase a significant volume of a single strain of yeast from one of the few US yeast propagators (Such as Wyeast Laboratories and White Labs). You’d then pitch (add the yeast) into a batch of wort (unfermented beer). The yeast multiplies, consumes sugars, creates more yeast, alcohol and CO2 and wort becomes beer! For the next batch, you’d collect a portion of yeast from the initial batch and pitch this new generation of yeast on a new batch of wort. Over several batches and generations the yeast mutates and evolves and this changes things like flavor notes and attenuation.  Because yeast evolves every time it multiplies and changes the beer slightly, after roughly seven generations it’s standard industry practice to dump the yeast and purchase a new fresh volume of yeast.

There is some variation to the above across the industry. Many large breweries have an in-house yeast lab where they bank and propagate their own proprietary yeasts, some re-pitch after one generation and others after ten.  The main point is that for the most part, standard practice is to try to eliminate as many variables as possible so that the same exact beer can be made over and over again.  Our approach is to embrace these variables.  


Now let me be clear, there’s nothing wrong with the industry approach described above, many of our favorite beers are brewed this way. We’ve just chosen to take a different approach; to embrace the evolution and changing nature of our culture rather than oppose it with an iron fist.


- Andrew Pogue | Co-Founder of Fair Isle Brewing