This paper from the MBAA Tech. Quarterly may shed some light on the situation:
Tech. Q. Master Brew. Assoc. Am., 1986, 23(2), 37-43. English
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The effect of trub on fermentation.
Siebert, K.J., Blum, P.H., Wisk, T.J., Stenroos, L.E. and…
if your vile of yeast was within the sell-by date then it's unlikely to be a problem of yeast viability.
It's probably an aeration issue unless you're using an oxygen injector or aeration pump. If it's still alive the yeast will move into exponenti…
June 8, 2009
Kyle Carney is now a member of ALEiens Homebrew Club
Things are great. Got a great job working at Showtime and just gearing up for the summer. Plans to expand our brewing capacity, so thats really fun. Hows the Brew Master program going? soo cool. Maybe we'll run into each other at an event when you get back to the states.