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Old 08-12-2012, 04:36 PM   #1
Sep 2010
San Francisco
Posts: 9
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Lately, Iíve been noticing a large difference in attenuation between yeast vials, based upon their age.

My LHS sells a lot of yeast and for the more popular yeasts, I usually get vials with manufacturing dates less than 1 week old. For me, vials this fresh have been consistently outperforming vials that are over 3 weeks old. For example, in my last batch, the WL English (1 week old) had a 4% higher attenuation than the WL British (3.5 weeks old) and 2% higher for the WL Scottish (2 months old). Both are rated with higher attenuations than the English, the Scottish significantly so.

I do make large starters (2L per 5 gal. for ales , 4L for lagers). But the difference remains. Maybe Iím not bringing the older yeast back up to prime condition with my starters (I donít use a stir plate, just oxygen injection). But, given my results, Iím beginning to believe that there really is no substitute for very fresh yeast. The difference between 1 week old vials and 3 week old vials seems to be significant.

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Old 08-12-2012, 04:44 PM   #2
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Apr 2011
Minneapolis, Minnesota
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Do you account for the manufacture date when calculating starter size/no. of vials/packs per starter? I find to be really helpful.
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Old 08-12-2012, 06:07 PM   #3
AmandaK's Avatar
Feb 2010
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Originally Posted by jayfaustini
The difference between 1 week old vials and 3 week old vials seems to be significant.
You are correct. The viability of yeast diminishes quite rapidly after production. has a good calculator in it as well.
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