Author Topic: Viability of Harvested Yeast  (Read 1303 times)

Offline TeeDubb

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Viability of Harvested Yeast
« on: October 18, 2017, 10:17:46 PM »
After wanting to try and re-use yeast for many years I finally gave it a shot.  My previous IPA fermented very quickly using fresh purchased WLP090 (San Diego Super Yeast) so I harvested about a pint from the bottom of the fermenter as I was draining the beer to the keg.  I turned the dip tube down and got essentially a mix of whatever was at the bottom.  WLP090 flocs well and I did not used any hops in primary, so I'm confident that it was a clean sample.  I washed 3 times with distilled & boiled water to get rid of trub, and saved a 35ml sample (re-using an old White Labs plastic vial).

Here is my question: the next batch of beer needs about 260B cells.  I made a 1.6L starter using the 7 week old harvested yeast.  Normally with fresh yeast the starter takes off within 4-8 hours but this one took about 18-20 hours to get creamy and show evidence of fermentation. With the way I took my sample and the lag noted, will I have a low cell count in the finished starter? I'm assuming I had 1B cells/ml in the sample.

I'm trying not to fuss about this, but want to learn and get an opinion.  I think I will pitch the 2nd gen WLP090 starter and if I see a huge lag maybe pitch a packet of US-05. OG on the second batch is 1.068

Offline Todd H.

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Re: Viability of Harvested Yeast
« Reply #1 on: October 19, 2017, 09:12:25 AM »
You should be fine.
When I collect yeast after fermentation I just swirl the yeast up in whatever beer is left at the bottom of my carboy and pour that into sterile mason jars(s) and store under that beer.
Even though yeast has a cell wall and can survive distilled water for a period of time, no cells really like sitting in a hypotonic solution.  Most cells (like mammalian cells) lyse right away.  Yeast doesn't because of the cell wall, but I guarantee that the viability over time drops faster than if you were to store in a beer slurry without rinsing or whatever.  I'd guess that's why you saw a lag in your starter.
(Source: did my PhD in a yeast genetics lab a long time ago.)

Offline TeeDubb

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Re: Viability of Harvested Yeast
« Reply #2 on: October 19, 2017, 09:26:52 PM »
Thanks Todd - that makes a lot of sense.  I will keep the sample on beer next time and try and use it within 1-2 weeks for the next batch.

Offline Hooper

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Re: Viability of Harvested Yeast
« Reply #3 on: October 28, 2017, 09:26:21 AM »
Or...you could pour a small portion of your starter into a small mason jar on brew day and store in the fridge for a week or 2 until you are ready to make another starter...
“Stay with the beer. Beer is continuous blood. A continuous lover.”
—   Charles Bukowski

Offline el_capitan

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Re: Viability of Harvested Yeast
« Reply #4 on: October 30, 2017, 04:38:40 PM »
Or...you could pour a small portion of your starter into a small mason jar on brew day and store in the fridge for a week or 2 until you are ready to make another starter...

After years of successful yeast harvesting and repitching, I've recently switched to overbuilding the starter and saving pre-fermentation yeast.  It's great to have a clean sample that is absolutely pure.  I try to rebuild the culture every 3 months.  My general method is this:

Reculture:  Overbuild a starter and save yeast to reculture in about 3 months.  Pitch most of the yeast into a standard-gravity batch.

Repitch 1:  Pitch 1/3 of the yeast cake from the batch into a second batch.

Repitch 2:  Pitch 2/3 of the yeast cake into the third batch. 

Repitch 1 and 2 happen about a month apart, which is why I save the bigger portion of the yeast cake for a second repitch.  If I'm brewing two more beers with that yeast at about the same time, I'll split the yeast cake into the other two batches.  Once the yeast has gone through the second batch, I may choose to pitch the whole cake into a high-gravity batch, or just retire that yeast and go back to the reculture step. 

Hope this makes sense!  I have 5 yeast strains in my bank and try to reculture every 3 months.