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WLP004 Low Attenuation - How long do you keep yeast?

What’s the age limit on your use of harvested yeast?

I brewed a dry irish stout 3 weeks ago using WLP004. The yeast was harvested from a previous batch in late May so I know viability was low. I made a 1L starter which was very active and ended with a nice 3/4 inch or so cake in my 1 gallon jug. OG was 1.053, fermentation kicked off a few hours after I pitched at 63 degrees. Kept the temps low for 3 days then let it rise to ambient of 68-70.

Only got 1/2 inch or so of krauesen at most during ferm.

Checked SG after 1 week and it was 1.018. Shook the carboy a bit to try and roust the yeast. Checked SG last Sunday, same and again today, same…

The beer tastes good. A little sweeter and not as dry as expected. I’ll definitely keg and drink it soon.

66% attenuation if my calculations are correct. Not great. Just for future reference…should I have done a 2 stage starter since my yeast was so old? I know some people say they don’t even try to use harvested yeast after 3-4 months.

WLP004 is a low attenuator. The one time I used it for a Smithwick’s clone, I got just 64% attenuation, and that was with an all-grain mash at 153 F for 45 minutes. Finished at 1.020. Your fermentation is finished, regardless of age of the yeast. It’s just a poor attenuating yeast.

To answer your question about how long to keep yeast… I have reused yeast after up to 8 or 9 months without issue. It needs a two-step yeast starting process to get woken up again but it works. I wouldn’t go much beyond that point though. I think after about a year it is roughly 95-100% dead and usually not worth the extra effort to bring it back.

[quote=“dmtaylo2”]WLP004 is a low attenuator. The one time I used it for a Smithwick’s clone, I got just 64% attenuation, and that was with an all-grain mash at 153 F for 45 minutes. Finished at 1.020. Your fermentation is finished, regardless of age of the yeast. It’s just a poor attenuating yeast.

To answer your question about how long to keep yeast… I have reused yeast after up to 8 or 9 months without issue. It needs a two-step yeast starting process to get woken up again but it works. I wouldn’t go much beyond that point though. I think after about a year it is roughly 95-100% dead and usually not worth the extra effort to bring it back.[/quote]

Thanks for your response Dave!

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