I have been wanting to post this for a while but research, parenthood, and preparing for the yeast class this coming Wednesday, has been keeping me busy. Two posts back I mentioned that I was able to isolate some wild yeast from the dregs of a bottle of Cantillon Blabåer (2010 vintage).
To recap, I diluted the dregs to get single colonies plated on regular MYPG agar but I saw no growth. I then plated straight dregs form the bottle and also saw no growth for two weeks. I found this to be strange since an earlier experiment with Lou Pepe dregs at least grew coliform bacteria. I then decided to inoculate a very small amount of Blabåer sediment into 10 mls of sterilized wort and after four days in a shaking incubator I saw growth.
I plated what grew onto three different selective agar:
- WLN media – allows for the growth of anything
- WLD media – contains cycloheximide which blocks S. cerevisiae growth, but not Dekkera/Brett
- MYPG + Bromocresol green - S. cerevisiae will not metabolize the dye and colonies will look green.
Check out the Wild Yeast Project main page to see the preparation and controls for the above mentioned growth mediums.
Here are my results:
MYPG + Bromocresol Green
A couple of important things to note. First, the wild yeast that grew did not obey the selective media similar to Brett B and Brett L. Specifically, this yeast grew less under cycloheximide selection and did not metabolize the dye. They looked like S. cerevisie. Secondly, the colonies are almost uniform. This suggests that one yeast strain dominated the wort culture. There is an exception to this however, as one (yes one!) yeast cell grew into a colony that looked different from the others:
Next, I picked two colonies, one normal one and the different colony, and looked at the cells using an 100x immersion oil objective. For simplicity, I named the flower-like colony CB1 and the other colony CB2.
These two strains definitely look like wild yeast, especially CB-2. The long cells are reminiscent of Brett L. It is interesting to note that the CB-1 does not have the same cellular morphology (elongated cells) as CB-2 and suggests these are two independent strains. Only PCR to look at genetic markers will identify these strains as different and wild. Another curiosity is why I got no bacteria in this culture but the opposite in my Lou Pepe experiment. Whatever strain(s) this wild yeast is, it outcompeted all other wild yeast and bacteria. Also, the wild yeast isolated behaved just like S. cerevisie. The yeast were largely inhibited by cycloheximide and did not metabolize the Bromocresol green dye. Chad Yakobson of the Brettanomyces project and Crooked Stave has mentioned that non-commercial wild yeast might behave completely different since hardly anything is known about them. For now I’ll consider this a success in isolating wild yeast and brewing a batch of homebrew with this yeast is in my future!
The next step in characterizing these strains are some forced fermentation tests.