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Old 01-15-2013, 04:19 AM   #11
dpark
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Originally Posted by thrstyunderwater View Post
Do you care to post anymore on this or can you point me to another source? I'd love to be freezing yeast but haven't ever found a source on how to properly use the glycerin.
Did you see this article?: Freezing Yeast.
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Old 01-15-2013, 06:21 AM   #12
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mutations in a yeast strain are only bad if they make your beer bad. genetic mutations can occur randomly by small changes to the DNA, but the whole population of cells can't suddenly mutate. but it's very true that the behavior of the population can change over only a few yeast generations. harvest just the last dusty bit of yeast to flocculate, and repitch that, you'll get a very different result than you expect from that strain. these behavioral changes are likely 'epigenetic', rather than due to DNA mutations; genes stay the same but get locked into certain on/off states, and it's these states that can confer certain properties, like willingness to flocculate, ability to consume maltotriose, whatever. but one random mutation in a population of hundreds of billions of cells cannot propagate rapidly through the population over the course of a few brews, with each brew hosting fewer than 10 yeast generations, even if you select for it. if you keep harvesting healthy clean yeast and your beer keeps being good, and the yeast behaves the way you want it to, keep using it. not that you shouldn't save a master stock if you can, and propagate new pitches from that whenever needed; it's a luxury but it's nice to have a few strains banked, and you will need to go back to the master stock eventually. remember it will take longer to get them up to a pitchable amount than a new smack pack, and you should work very cleanly at the early steps to avoid propagating contaminants.

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