Originally Posted - Saturday, February 27, 2010
I attended the Rocky Mountain Microbrewing Symposium last week. This was my first time going to this yearly event and it was a good refresher of information I had learned at Siebel. What really piqued my interest was a presentation by Bob Sclafani on called 'Yeast and Civilization'. This presentation contained one piece of information about some Belgian yeast strains that was completely new to me.
Over time yeast strains have been classified and reclassified over and over again. In the case of lager yeast, it has been called Saccharomyces carlsbergensis, S. uvarum, S. cerevisiae var. carlsbergensis, and now apparently S. pastorianous. Over the past few years the genomes of some yeasts have been mapped and this has brought to light new information about the origins and hybridizations of yeasts strains, and yet more new classifications. What is especially striking is the origin of some Belgian yeast strains. What had always been thought to be just another variation S. cerevisiae is actually a hybrid of S. cerevisiae and a more ancient yeast S. kudriavzevii.
How could this hybridization happen? Although brewing yeast reproduces by meiosis or asexual reproduction under normal conditions, under stress can form spores and reproduce sexually. Think of it as a self defense mechanism. If the yeast is in danger of perishing due to a hostile environment, it sporulates in hopes of preserving it's genetic make-up. Since most fermentations in Belgium were mixed fermentations of various yeasts and some organisms that produced lactic and acetic acid, this may have been perfect environment for this hybridization to take place. How did S. Kudriavzevii get in there? It's possible that it could have been naturally in the environment. Another possible source is oak barrels, or more specifically oak bark where this species has been isolated.
This makes sense, normal variations of S. cerevisiae do not account for the unique properties of most Belgian yeast strain and this information helps shed light on why.