Yeast Cake

[XXXBrewDude]

I've saved a couple yeast cakes in gallon jugs in y fridge for about 3 weeks now. Usually I will wash the yeast in a couple days and then store. Question; can I store the entire cake for several months before washing off the trub? I'm concerned maybe the mass from the trub may be harmful / to much pressure on the yeast cells and damage the walls. Any input is welcome


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[flars]

No problem with pressure causing damage to the yeast in that small of a container. It would be different if your jug was 20 feet tall and full.

 

[cjgenever]

Unrinsed yeast will die and mutate faster than rinsed. At three weeks plan on lower viability, but still usable. I'd make a starter with it to be safe.

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[fearwig]

Whatever it does, it won't "mutate" in the fridge, with no reproductive activity. Your yeast is fine this way for months, just scale up your pitch as needed. Use the repitch from slurry setting at mrmalty.com for an idea. I think it underestimates stored slurry viability but it's solid.

Washing slows metabolic activity a little better than storing with trub because it deprives the yeast of food. That's good, but it's not vital. If there is trub, loosen the cap in case residual activity leads to co2 buildup.

 

[cjgenever]

I don't think mutate needs to be in parenthesis there bud. I picked that up from brew strong. If jamil is wrong, so am I. I am speaking primarily of petite mutants. This is often caused by stressful situations for the yeast and can occur in just a single generation. They are smaller than other cells and have a respiratory deficiency. This it's my understanding. Perhaps I'm mistaken, I've been wrong before.

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[XXXBrewDude]

I just read a great overall on white labs web site with regards to harvesting, storing , repitching rates, etc. I feel I should not stop washing the yeast . They will store longer if washed and will also help more accurately estimate the amount of trub. They do suggest storing for no longer than 2 weeks but as a home brewer I'm sure we can push this . I don't intend on recycling 10 times anyway. 2 or 3 uses will be great.


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[fearwig]

OK, stressors in general can cause yeast to produce petite mutants more often when they finally get around to reproducing in your beer or starter. That's not the same as what runs through someone's head when they hear "your yeast will mutate if you do this". Keeping a sample under beer and not washing the trub out of it will maintain a little bit of metabolic activity (from trace food in the trub) and stress the yeast imperceptibly due to the alcohol. Any stress (including temp swings during fermentation) can "cause mutation" in that sense, but doing this is not going to leave you with a big batch of nothing but petite mutants.

Basically, it's probably not something that should concern a homebrewer at all, except to say "don't stress your yeast too much". As long as you aren't habitually overpitching you should be selecting for new healthy daughter cells in every batch.

People think every change in yeast character is due to a mutation and the word is exciting so it gets a lot of attention. A yeast culture isn't even genetically homogeneous, when people say "mutation" it's much more likely they're talking about a character change because the type of stress they're inducing selected for some yeast in the sample over others and changed the overall genetic makeup.

 

[fearwig]

But, the point is that you can store yeast just fine without washing and you will not have attenuation problems associated with petite mutation, and we know this because it is done all the time.

Doesn't mean you should stop, do it how you want. But if time spent washing yeast is time you could be spending making beer, well, don't let it hold you up!

 

[dinnerstick]

fear paramutation

 

[fearwig]

I don't think paramutation has anything to do with petite mutation... google doesn't think so either, but correct me if I'm wrong.

I guess what I was describing is like adaptive mutation, since I don't think there are any known mutagens formed by chilling on trub (that I can imagine). I don't subscribe or un-subscribe to that applying to petite mutation (not really qualified to) but I guess at least Jamil and likeminded people think it's real and a factor. Sounds kind of sketchy, really, the more I think about it.

My point is I don't think there's any way you're getting real, actual mutations in a fridge, with no reproductive activity. I am not even sure you're doing anything to the yeast that could cause mutations in offspring, I just hold that it's not something I can rule out with my limited expertise. But I can say it doesn't sound very likely. It sounds way more likely that "mutation" is just a sexy enough word that even some experts are misapplying it (Jamil is an expert, but he is definitely a lay expert).

 

[cjgenever]

Think we're getting off topic here. no, you can't store your cake with trub and beer for months and expect good viability.

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[XXXBrewDude]

Think we're getting off topic here. no, you can't store your cake with trub and beer for months and expect good viability.

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Thanx, yes the mutation debate was a bit side tracked but from both your inputs I learned a lot about yeast storage and appreciate the insight.
"There are those who must portray the leg up, and there are those who genuinely are" xxxbrewdude


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[fearwig]

Think we're getting off topic here. no, you can't store your cake with trub and beer for months and expect good viability.

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Aaaand you also can't store it without beer and trub for months and expect good viability. Make a starter, or adjust for viability. Good luck!

 

[cjgenever]

In his book "yeast" jz suggests using slurry within two weeks with a maximum storage time of six months. He advocates for removing from the trub and beer as soon as possible.

FWIW...
"the problem with long term storage is not viability, but maintaining a mutation free culture" (White, C., & Zainasheff, J. (2010).Yeast: the practical guide to beer fermentation. Boulder, CO: Brewers Publications.).

the lower the temperature and the less amount of fermentables, the lower the rate of metabolism. hence, the lower the rate of mutation. the storage media and temperatures we are speaking of here will result in the highest rate of mutation. mutation occurs over time in storage and does not apply to slurries being used in a time frame as suggested by professionals. Chris White (White Labs) states in his published work that mutation does occur in storage.

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