Sourdough Plating #3 and DCambic Update

This is the third and final attempt at plating out the whole sourdough starter. I did a few things differently:

  • I fed the three sourdough starters and let them ferment for 12 hours before starting. Last time two of the starters were right out of the fridge.
  • I put even less of each culture in the sterile water to dilute it
  • I used bromocresol green + potato dextrose plates, plus one potato lactose plate

The rye starter’s plate grew mold in a few days. It totally took over before I had a chance to see anything else growing. The other two starter’s plates plus the lactose plate (on which I plated the wheat starter) were totally fine. I let them grow out for 16 days.

Clockwise from top left: brown rice flour starter, wheat flour starter, wheat starter on potato lactose plate

The colonies look translucent and shiny from certain lighting angles, but they are off-white, smooth and round and actually matte. I did not see any flat colonies like last time. The weirdest surprise is the almost identical growth on the lactose plate. I am going to assume that this is due to whatever sugar was in the potato and not the lactose. My goal in doing so was to see if I could get the bacteria to grow on there and was not expecting the yeast to grow at all. You can see very tiny colonies on each of the plates between the large yeast colonies and smaller yeast colonies. They are transparent and shiny. I believe these are the lactic bacteria.

I think I may not have used enough bromocresol green, or the plates were old enough that it had already started to fade. I was expecting green colonies here, too, but they were white. On my first (recent) attempt I did see green colonies but the plates were also darker back then. The colonies looked quite similar between the two starters. This is a change from the first time I did this (earlier in the year) but could be because I am using a different medium.

I picked out a yeast colony from each and plated it on YEPM medium (recipe from jaapie’s site; the ingredients are not cheap or easy to find for hobbyists like me). In the past, the yeast I isolated from the wheat starter didn’t appear to ferment maltose whereas the rice starter’s did. We’ll see if these grow on it (from what I can tell, yeasts generally but not always can grow on something they can ferment and vice-versa).

On another note, I finally resumed the DCambic project from April. I had isolated a yeast from it back then but it appeared to not do much besides make lots of strong fruit esters. Notably, it didn’t seem to produce any alcohol. This time I instead went for growing it in liquid first instead of plating directly from the sample. I now seem to have two different types of yeast in liquid, judging from the two colors of sediment I see. A darker sediment formed first. I then started shaking to aerate the culture on a regular basis for a few days and then added this to more sterile wort, which I similarly shake on a regular basis. I am now seeing a lighter color sediment forming as well. I also see lots of evidence of fermentation, though I did not see any krausen at any point. I shook up the culture yesterday and streaked a sample on a PDA plate. I’m hopeful that this time I can get the yeast that produces the distinct Bretty aroma I can smell from the culture.

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4 thoughts on “Sourdough Plating #3 and DCambic Update

  1. eurekabrewing

    Hi there,
    your plates look very nice. Concerning the green yeast colonies and bromocresol green. I would not be surprised if there are yeast strains able to metabolise the dye and therefore growing as white colonies rather than green ones. I am not sure if Dmitri (BKyeast) reported about such a case already. And good luck with your DCambic project.
    Cheers, Sam

    Reply
    1. DC Yeast Lab Post author

      Thanks!

      I should try plating a regular commercial brewing yeast on there, since those are definitely not supposed to metabolize the dye. I was thinking that the yeasts might be S. cerevisiae, especially since they appear to be growing on YPEM, but who knows, maybe they are something totally different that can also grown on maltose. The yeast most commonly associated with sourdough neither grows on it nor ferments it.

      Reply
  2. Pingback: Baking with SD Isolate | DC Yeast Lab

  3. Pingback: DCY02 & DCY03: DCambic Isolates | DC Yeast Lab

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