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Yeast and Fermentation / Over Attenuating Yeast - How is it Possible?
« on: May 17, 2013, 06:56:32 AM »
Confused ... :confused:
I brewed a Rogue Double Dead Guy clone, mashed at 152F - it started at 1.084 and finished at 1.010, fermented with Wyeast Pacman. No mash out.
Beersmith calculates that as a 82.7% attenuation. OG measured with a refractometer and FG measured with two hydrometers.
Wyeast's stats are 72-78% attenuation for this strain.
The yeast was about 11 months old, smelled and tasted good, and pretty creamy white. I made a 2L starter with the decanted slurry and it took off in about 4 to 6 hours.
I hit the wort with O2 and pitched the decanted starter. Within 4 to 8 hours it began to show signs of fermentation.
The beer fermented @ 65F in a refrigerator (measured by a thermowell) for about 3 weeks. I let it sit on the yeast cake @ 45F for another three weeks. Approximately 6 weeks total.
This recipe should have finished around 1.018 - 1.020, mine however continued to 1.010. As a result, it is much drier with an alcohol bite. At 6 weeks old, it's not so green anymore.
With that being said, what in your opinion might account for the higher attenuation?
If anything, I suspect old/aged yeast would be less attenuating, unless it mutated.
What about sitting on the yeast cake for an extended period? After three weeks @ 65F, the yeast should have been entirely done, and at 45F, the yeast should be dormant and inactive.
Would over pitching push it lower?
Would no mash out increase attenuation?
Any ideas?
I brewed a Rogue Double Dead Guy clone, mashed at 152F - it started at 1.084 and finished at 1.010, fermented with Wyeast Pacman. No mash out.
Beersmith calculates that as a 82.7% attenuation. OG measured with a refractometer and FG measured with two hydrometers.
Wyeast's stats are 72-78% attenuation for this strain.
The yeast was about 11 months old, smelled and tasted good, and pretty creamy white. I made a 2L starter with the decanted slurry and it took off in about 4 to 6 hours.
I hit the wort with O2 and pitched the decanted starter. Within 4 to 8 hours it began to show signs of fermentation.
The beer fermented @ 65F in a refrigerator (measured by a thermowell) for about 3 weeks. I let it sit on the yeast cake @ 45F for another three weeks. Approximately 6 weeks total.
This recipe should have finished around 1.018 - 1.020, mine however continued to 1.010. As a result, it is much drier with an alcohol bite. At 6 weeks old, it's not so green anymore.
With that being said, what in your opinion might account for the higher attenuation?
If anything, I suspect old/aged yeast would be less attenuating, unless it mutated.
What about sitting on the yeast cake for an extended period? After three weeks @ 65F, the yeast should have been entirely done, and at 45F, the yeast should be dormant and inactive.
Would over pitching push it lower?
Would no mash out increase attenuation?
Any ideas?