Reused Yeast Fermentation. How?

[Middleton_Brewing]

I just checked on a batch of yeast that I washed on June 11th and both jars were carbonated. Carbonated to the point where they dented the tops. The seals were still in tact, but there was obvious fermentation. I wash my yeast with 2 cycles of boiled water and am crazy about sanitation. My only guess was that since I kegged the beer a little before it reached its FG there were still some fermentables in there. Could that have caused it even though I washed the yeast? Any help would greatly be appreciated. Thanks!

 

[motorneuron]

What exactly is your setup here? You had a beer in the carboy, and when it finished you harvested and washed the yeast, by adding boiled cooled water to the carboy, swishing it around, and dumping it into sanitized jars? And then you repeated that a second time after the yeast settled a bit, and you decanted off the nasty stuff? Now it's two weeks later and you have some additional CO2?

If that is what happened, then yes, I think you're almost certainly seeing a little additional fermentation from the sugars in the mostly-finished beer, and there's no reason to worry. I've had additional fermentation many times from harvested yeast. No biggie. It doesn't actually take that much additional CO2 to make a jar or bottle bulge. You can cool it before you try opening the lid--that will reduce the pressure.

 

[glick]

The same thing happens to me all of the time. I just used some WLP300 that had been in my fridge since January and when it warmed it did the same thing. It's nothing to worry about.

 

[BigFloyd]

Same here recently on a couple jars, one ale (1968 ESB) and one lager (2124 Bohemian) while still cold.

I just released the pressure, gave them another rinse with sanitized/chilled water and replaced the lids with others I had sanitized. One thing I was more mindful of this time was to try and fill each jar up all the way to reduce head space as much as possible.