mnick12
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Alkali production by Brettanomyces Custersianus?
Hi everyone, I have an interesting observation that I would like to discuss.
First off I am a home brewer, and recently I have been streaking and slating various yeast strains so I can have them on hand at all times. Recently I
was lucky enough to get a culture of Brettanomyces Custersianus. Anyway I prepared some YEPD agar plates with the addition of bromothymol blue and
sodium carbonate (as a pH indicator). When solidified the plates were greenish-blue as expected. I streaked a sample of the Brett on two plates and
allowed them to grow. Growth was initially slow as brett prefers a lower pH. After about a week the plates were a dark orange yellow (from the brett
growth), and a single colony was used to inoculate a slant for long term storage.
I ended up discarding the plate I plucked the colony from, but for curiosity sake I kept the other. Anyway as the days progressed the orange plate
began turning blue again, and after some more time the plate is completely blue! I am highly confused as I had always assumed brett is an acidogenic
organism. More so I know other species are heterofermentive and will produce acetic acid in the presence of oxygen.
Anyone have any idea for the pH increase? It is really puzzling me!
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jwpa17
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Did the plate turn blue around the colonies, or all over? I don't recall whether yeast spread much while growing, so maybe that question doesn't make
sense. I'm thinking that the pH shift is due to chemical decomposition of the proteinaceous components of the yeast extract, like maybe
deaminidation. By chance do you have any plates prepared at the same time, but not inoculated?
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mnick12
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The growth was initially very slow, and the formed colonies were significantly less defined than regular sach colonies. However one day the plates got
a little to warm and condensation built up and fell on the colonies allowing for complete coverage of the plate. For a few days the plate was yellow
orange, then over the course of about 3 day the plate went from orange-->splotchy green-->solid blue. I couldn't tell if it was originating from
the colonies or not, but the entire plate ended up blue.
Now that you mention it breakdown of the yeast extract makes sense, but I am wondering if the brett had anything to do with it.
Also I did prepare three other plates, one with some another sach strain and the other with some mold I found growing on an orange. I had I control
too, but threw it out once I pulled all the colonies I wanted.
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jwpa17
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"I couldn't tell if it was originating from the colonies or not, but the entire plate ended up blue."
One way to find out...
Actually, a couple. The easiest (IMO, anyway) is to just prepare another plate, and keep it under the say conditions as before - including the warm
spell - for a similar period of time. Better of course would be to repeat the entire procedure and keep the control until you've gotten your answer.
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