Author Topic: Yeast Propagation Question  (Read 212 times)

Offline Lazy Ant Brewing

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Yeast Propagation Question
« on: April 09, 2021, 02:03:21 PM »
In the October 2020 issue of Brew Your Own, when trying to use yeast from sediment in the bottom of beer bottles, Ashton Lewis talked about streaking plates to isolate and select a single colony forming unit as an aid in getting the yeast strain you're seeking and leave unwanted microorganisms behind.

Let's say you've done  this and now have four petri dishes to select from.  If two look the same but differ in appearance from another pair which also resemble each other, how do you know which one to pick to ferment your next batch?
It's easier to read brewing books and get information from the forum than to sacrifice virgins to appease the brewing gods when bad beer happens!

Offline erockrph

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Re: Yeast Propagation Question
« Reply #1 on: April 09, 2021, 06:00:39 PM »
First and foremost, this presumes that the brewery uses a pure/single-strain culture, and that the bottling strain is the same strain as the fermentation strain. If any of those presumptions are incorrect, then you probably aren't going to get what you're looking for.

I haven't built starters from petri dishes too often, but I would look for an average-sized, light cream colored, waxy/shiny colony to load my loop from.

Personally, when I'm trying to build up a culture from bottle dregs, I make 100mL of starter wort from DME and add the dregs, plus about 100mL of the beer to the starter. This ends up with a half-strength starter mixed with a half-strength beer. The lower starter gravity is a bit easier on the yeast. The beer helps reduce the pH of the starter, and contains some alcohol and hop compounds. My thought is that this will mitigate the growth of any potential spoilage organisms while waiting for the yeast to wake up.

The beer will also bring over any yeast still in suspension, rather than only those that have flocced out. In the end this is kind of the opposite of selecting for a pure culture, since you're selecting both the most flocculant and least flocculant variants from a culture instead of one specific colony, but I've always felt like this has a better chance of replicating the performance of the original culture than selecting just from the dregs.
Eric B.

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Offline Lazy Ant Brewing

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Re: Yeast Propagation Question
« Reply #2 on: April 10, 2021, 01:11:51 PM »
Thanks, that sounds like good advice. 
It's easier to read brewing books and get information from the forum than to sacrifice virgins to appease the brewing gods when bad beer happens!