[Robert]

This just appeared in my feed.
https://www.nature.com/articles/d41586-019-00088-y
A bit above my pay grade,  but the TL;DR for us appears to be, all of you who are worried about storing yeast, chillax.  The yeasties were way ahead of you planning for it.

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[ynotbrusum]

I wondered how some yeast strains looked so good after a pretty long time in storage.  But given a choice, I will still use the freshest yeast I can!

[Robert]

Sound practice.  And this is really, I guess, just an explanation of the mechanism of behavior we already observed.  Also it underscores the need to store yeast in its own beer and not rinse, I think.  It shows how yeast are adapted to expect a repeated cycle of feeding on the same nutrient medium, even if they don't know what the interval will be.   Disruption of that cycle by introducing them into an unanticipated environment is something they can't sustain,  I gather.  Once they think they're at the start of the cycle, they're committed, and have no plan B.

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[Lazy Ant Brewing]

Sound practice.  And this is really, I guess, just an explanation of the mechanism of behavior we already observed.  Also it underscores the need to store yeast in its own beer and not rinse, I think.  It shows how yeast are adapted to expect a repeated cycle of feeding on the same nutrient medium, even if they don't know what the interval will be.   Disruption of that cycle by introducing them into an unanticipated environment is something they can't sustain,  I gather.  Once they think they're at the start of the cycle, they're committed, and have no plan B.

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In discussing this an important distinction needs to be made between the domesticated strains of yeast we use in brewing and wild-type strains.

Robert makes the point that "yeast are adapted to a repeated cycle of feeding on the same nutrient even if they don't know what that interval will be."

That is due to  brewers' rigorous artificial selection of those strains that offer the best results under a regimen of  "a repeated cycle of feeding on the same nutrient even if they don't know what that interval will be."

Wild yeast don't get that luxury.  They must be able to survive under unstable conditions. 

It's an axiom of evolution, that portions of the genetic code that are unused, frequently become degraded over time.  And DNA begets RNA during translation into proteins and enzymes. With organisms like yeast that can reproduce exponentially under ideal conditions, that impairment may happen more quickly as compared to organisms like mammals that have slower reproduction.

Brewers have selected strains that do very well under the conditions we impose on them, but are genetic "weaklings" in combating the varied conditions that wild yeast face.

Compared to the total cost of brewing including both the other ingredients and my time, my choice is to always buy new yeast.

[Robert]

Good you bring up cost and, implicitly,  risk.  Breweries make it cost effective to reuse yeast by employing microbiologists to manage the risk.   This would not be cost effective for me.  FWIW after countless years and countless generations of reusing yeast without problems, no doubt partly by luck as well as due to this adaptation of the yeast, I'm increasingly using dry yeast, fresh each time, effectively outsourcing all laboratory work including storage and propagation to better equipped facilities. It's just so cheap  and easy.  But if repitching is for some reason desirable,  this information is encouraging with respect to the ability of yeast to endure storage, so long as we store it under the correct conditions.

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[Lazy Ant Brewing]

I didn't mention in my post that I'm a home brewer.  I do appreciate the advice of all the guys and gals that brew for a living and accumulate experiences and knowledge at a faster rate than most of us.

[Robert]

I'm just a homebrewer too.  But I did a lot of yeast wrangling over the years, in part because I found it interesting and rewarding.  Sometimes it's worth it, but lately I just need to pick my battles.  I think a lot of small and midsize breweries face the same thing.   Dry yeast or ready-to-pitch liquid outsources some of the work, but they still need someone trained in microbiology and lab work to monitor conditions in the brewery.   And the economics scale very differently for them, I suppose.

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[Lazy Ant Brewing]

I like a clean, neutral yeast so I use US05 and buy a new packet for each beer. 

I mostly brew American brown ales, porters and stouts and prefer low to medium hop rates.  I have liked the occasional saison I've tasted and have brewed one with disappointing results due to an error I made in the recipe.