Author Topic: Yeast viability of store bought vs. starter yeast stored in fridge at home  (Read 723 times)

Offline bdrinkrow

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First, my process for making starters and stretching my dollar on yeast is to make 4L starters and separate the yeast into even, pitchable amounts and store it.  So, if I need 300 billion cells, I make a 2L, then 4L starter and will split that into thirds, using one, or even using one for another starter if it were a big pitch.

This is the first time since I've started this process that I have yeast that has sat idle for over 4 weeks.  I have an approximation of the number of cells, and I keep my keezer at 36-38 degrees so I can store yeast and cold crash/lager in it as well as serve beer.  So, that's the temp the yeast has been stored at.

I'm going to use my last jar of month old yeast to make another 4L starter and had intended to figure it's viability with the calculator I use.  But, I'm wondering if the yeast would die more quickly being stored in my fridge under starter beer.  I don't wash it, since there are no hops and it is a low alcohol environment, it's just stored under maybe 50ml of starter beer.

Would I be wrong to figure the viability of my yeast as stated based on this information?  I realize it's an inexact process to begin with, but I also know there are more people on here with a lot more experience than I and I haven't been able to find an exact answer or thoughts on this question by googling.
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Re: Yeast viability of store bought vs. starter yeast stored in fridge at home
« Reply #1 on: February 04, 2014, 10:52:12 AM »
For yeast stored under starter "beer" at fridge temperatures, a good rule of thumb is 25% viability loss per month. I've never done a count on a pack that was more than a few weeks old, but I suspect the number is much lower in that case, maybe 10%/month. Those yeast have been propagated aerobically in very low-gravity media with plenty of nutrients, and stored in an alcohol- and oxygen-free environment.

Short answer, a month isn't a big deal, assuming your cell count was actually close to the target. What I personally would do in that situation is get a liter or so of low-gravity wort on the stir plate as early in the brew day as possible (during lautering, generally) and pitch it late in the day, hopefully as the starter is nearing high krausen.

Offline bdrinkrow

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Re: Yeast viability of store bought vs. starter yeast stored in fridge at home
« Reply #2 on: February 04, 2014, 11:10:04 AM »
The number the calcs give for new yeast stored in a LHBS's fridge is around that number.  I think it is actually .7% per day, but about 20% per month.  I've been farming these into jars of approx. 300 billion cells, and I'm down to 1 jar of this particular yeast.  So, I wanted to make another big starter and try to approximate it into 300 billion cell jars.

I also just blended this yeast with another so I wanted to keep them isolated in jars so I can mix them at the same ration on brew day.

I didn't think a month would be too big of a deal, and I always use yeast energizer and nutrient in my starters, partially because I store them.  With that being said, I also figured the medium the labs store them in are better than mine, and their yeast are healthier.  But, I've always read and heard, "if it's a month old, make another starter".  But that always applies to brewing with it, not what I'm doing.

I guess, since I'm dividing it by 3, my errors would be reduced anyway.  So, even if I estimate it at 300billion at start, and consider it 66% viable, I could assume I'd be starting with 200 billion cells and make my starter as I normally would to get me to that 850-950 billion number I shoot for, then store in 3 jars, I'd be OK.

If I had the money to make the investment I would just start slanting as I have a hard core pressure cooker.  But, as they say.. You can wish in one hand and.. nevermind...
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Offline ynotbrusum

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Re: Yeast viability of store bought vs. starter yeast stored in fridge at home
« Reply #3 on: February 05, 2014, 05:31:52 AM »
For yeast stored under starter "beer" at fridge temperatures, a good rule of thumb is 25% viability loss per month. I've never done a count on a pack that was more than a few weeks old, but I suspect the number is much lower in that case, maybe 10%/month. Those yeast have been propagated aerobically in very low-gravity media with plenty of nutrients, and stored in an alcohol- and oxygen-free environment.

Short answer, a month isn't a big deal, assuming your cell count was actually close to the target. What I personally would do in that situation is get a liter or soof low-gravity wort on the stir plate as early in the brew day as possible (during lautering, generally) and pitch it late in the day, hopefully as the starter is nearing high krausen.

Second runnings, Sean, or made from scratch with DME? Probably doesn't matter?
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Offline Jeff M

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Re: Yeast viability of store bought vs. starter yeast stored in fridge at home
« Reply #4 on: February 05, 2014, 07:12:39 AM »
Are you keeping track of the generations of yeast?  Ive been reading the yeast book and iirc after 5-10 generations you may end up with some gene mutations.  Im sure someone with a better memory and more yeast experience will say something but there may come a point that re-pitching this may not be a good idea:)

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Offline a10t2

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Re: Yeast viability of store bought vs. starter yeast stored in fridge at home
« Reply #5 on: February 05, 2014, 08:19:34 AM »
Second runnings, Sean, or made from scratch with DME? Probably doesn't matter?

First runnings taken as soon as the vorlauf clears, diluted to 8-10°P, boiled for a couple minutes, then chilled in the sink. DME would be almost the same thing, I just don't keep any on hand. I do like the idea that it's the same wort as the batch, just lower in gravity, since I pour the whole starter in.
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Offline bdrinkrow

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Re: Yeast viability of store bought vs. starter yeast stored in fridge at home
« Reply #6 on: February 05, 2014, 08:29:19 AM »
I do keep track, but I don't get to ten before I buy new anyway.  Because of splitting it, I get maybe 30 batches before ten generations.  Which is enough to last the winter, then my cellar is warmer and I use different yeasts. I've really been thinking about using this kolsch as a house yeast, and for some reason, it's the easiest ECY to get.  It's closer to the WL kolsch as far as being highly flocculant. Nothing like WY's kolsch. Love 2 brew still has some in fact.

But, I've never worried about mutants too much, considering that's how all these great yeasts came about anyway.  If I ever had a batch that tasted off, I'd get new yeast.
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Offline a10t2

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Re: Yeast viability of store bought vs. starter yeast stored in fridge at home
« Reply #7 on: February 05, 2014, 08:50:09 AM »
Ive been reading the yeast book and iirc after 5-10 generations you may end up with some gene mutations.

I don't think it's mutation per se, just drift in gene expression over time. The odds of a section of DNA that actually codes for an active protein mutating within a few generations is astronomically low; most of the genome is "junk". I think it's more likely that the yeast are altering which codons are active in response to environmental stresses, and that's why a culture "gets used" to a particular wort after a few generations.

I've repitched yeast over 20-30 generations many times, and worked with a culture that was in the 80s, but only used for one beer. If you're hitting your targets and flavor performance is consistent, I wouldn't throw out a culture based on an arbitrary number of pitches. On the other hand, yeast at the homebrew scale is so cheap that it may be worth it, especially if you don't have a way to quantify yeast health.
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Offline bdrinkrow

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Re: Yeast viability of store bought vs. starter yeast stored in fridge at home
« Reply #8 on: February 05, 2014, 12:21:45 PM »
Great info to know, thanks. 
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Offline Jeff M

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Re: Yeast viability of store bought vs. starter yeast stored in fridge at home
« Reply #9 on: February 05, 2014, 12:44:02 PM »
Ive been reading the yeast book and iirc after 5-10 generations you may end up with some gene mutations.

I don't think it's mutation per se, just drift in gene expression over time. The odds of a section of DNA that actually codes for an active protein mutating within a few generations is astronomically low; most of the genome is "junk". I think it's more likely that the yeast are altering which codons are active in response to environmental stresses, and that's why a culture "gets used" to a particular wort after a few generations.

I've repitched yeast over 20-30 generations many times, and worked with a culture that was in the 80s, but only used for one beer. If you're hitting your targets and flavor performance is consistent, I wouldn't throw out a culture based on an arbitrary number of pitches. On the other hand, yeast at the homebrew scale is so cheap that it may be worth it, especially if you don't have a way to quantify yeast health.

Thanks Sean, I knew someone with more experience would explain it correctly:D
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