Maintaining Yeast Viability? Longer Storage

[arnobg]

I follow the procedures from the "Simple yeast storage procedures" thread by harvesting slurry from my fermenter without washing. I usually have about 2-3 different yeasts (US-05, 1318, 2206 for lagers) that I like to use but I only brew every 3-4 weeks at my current rate. As you can figure, this is probably an issue with keeping that stored yeast viable if I only brew a lager say every two or three months and alternate yeast strains.

I'm looking for tips/suggestions on keeping it viable for those longer periods. Should I make a small starter from the slurry every month in between batches if I'm not using it for a few months? To me this still costs way less than buying a new smack pack. I'm hoping I can do this and only use a strain 3-4 times but stretch it out to a year of use.

Is this doable or at I out of luck?

How big of a starter should I make if I'm just putting it back into storage?

 

[rhys333]

Its possible to store properly harvested yeast for many months without issue. I just store in pint size mason jars, filled almost to the top, taking care not to splash slurry above the beer line. I find the pint jars work well for a 5 gallon batch, as I get 3-4 jars of yeast each time. The first one or two I can usually direct-pitch a portion of one jar. Occasionally (happened last week) I'll open a jar and see slurry on the underside of the lid that turned funky due to air exposure. I just toss that one down the sink and grab another. 3 month old slurry usually just needs a small 1 L vitality starter. If you're approaching half a year, then yeah, probably wise to take a smaller amount of your slurry and build up mostly fresh cells.

Based off the Simple Yeast Storage authors notes, I estimate fresh slurry at 1.5B cells/ml and assume ~15% loss in viability per month of storage. I use this rule of thumb to decide how much slurry to use and/or how big of a starter to make and I consistently see fermentation activity between 8 and 24 hours.

I brew ales and not lagers, but here's how i would approach using 3 month old slurry for a 5 gallon 1.050 ale batch:

1.5B cells/ml fresh, estimating 45% loss in viabilty over 3 months:
1.5B x 0.55 = 0.82B cells/ml

To achieve the desired 200B cells:
Your pint jar contains about 400ml compacted yeast out of the fridge, which is about 328B cells. More than enough, but they're a bit tired at 3 months. You can just pitch, and I've done it without issue, but generally a good idea to do a vitality starter and build a few new cells.
So:
Pitch 200 ml of the slurry into a 1 L starter. You have about 160B cells. Using the no-shake set it and forget it method, you'll have about 200B cells when that sucker reaches high krausen in a day or so.

 

[arnobg]

Its possible to store properly harvested yeast for many months without issue. I just store in pint size mason jars, filled almost to the top, taking care not to splash slurry above the beer line. I find the pint jars work well for a 5 gallon batch, as I get 3-4 jars of yeast each time. The first one or two I can usually direct-pitch a portion of one jar. Occasionally (happened last week) I'll open a jar and see slurry on the underside of the lid that turned funky due to air exposure. I just toss that one down the sink and grab another. 3 month old slurry usually just needs a small 1 L vitality starter. If you're approaching half a year, then yeah, probably wise to take a smaller amount of your slurry and build up mostly fresh cells.

Based off the Simple Yeast Storage authors notes, I estimate fresh slurry at 1.5B cells/ml and assume ~15% loss in viability per month of storage. I use this rule of thumb to decide how much slurry to use and/or how big of a starter to make and I consistently see fermentation activity between 8 and 24 hours.

I brew ales and not lagers, but here's how i would approach using 3 month old slurry for a 5 gallon 1.050 ale batch:

1.5B cells/ml fresh, estimating 45% loss in viabilty over 3 months:
1.5B x 0.55 = 0.82B cells/ml

To achieve the desired 200B cells:
Your pint jar contains about 400ml compacted yeast out of the fridge, which is about 328B cells. More than enough, but they're a bit tired at 3 months. You can just pitch, and I've done it without issue, but generally a good idea to do a vitality starter and build a few new cells.
So:
Pitch 200 ml of the slurry into a 1 L starter. You have about 160B cells. Using the no-shake set it and forget it method, you'll have about 200B cells when that sucker reaches high krausen in a day or so.

Great reply thanks for taking the time to write that up!