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Old 06-20-2010, 02:49 AM   #1
ksbrain
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Default Yeast Cross-Contamination?

Today I kegged my American Wheat. Simple 5% beer half wheat fermented @ 66 F with US-05. When I sampled it two weeks ago (1 week after brewing), it was perfect and normal. Today it tastes Belgian.

The beer before the wheat in this carboy was my Dubbel. I'm thinking somehow some yeast made it from the Dubbel to the Wheat. Anyone ever had something like this happen before?

The worst part is I was going to use that yeast for a big pitch for my IIPA. Good thing I had two packs of US-05 sitting in the bottom of my fridge!

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Old 06-20-2010, 03:23 AM   #2
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IF you sanitized your fermenter properly there is no way active yeast made it between batches. Perhaps it has to do with esters created by the temps its been held at? Beer does change as it ages, and there is a very pronounced difference between green beer (one week after brewing) and properly matured bottles or kegs of beer.

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Old 06-20-2010, 04:45 AM   #3
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There is no way a few left-over yeast would result in any detectable flavour in such a beer. Maybe if it was bret and you fermented it for 6 months but not a wheat beer that is 3 weeks old.

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Old 06-21-2010, 06:09 PM   #4
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Then maybe it's mutation of the yeast? This was maybe 3rd or 4th generation. But if it were mutation I'd expect it to have the flavor even after a week.

This is a beer I make all the time, and it has never had any Belgian taste to it before at any time during the life of any previous batch. Fermentation was same as ever, controlled to 66 degrees F in a fridge.

I did turn up the temperature for the last two weeks to try to get the Stout that was fermenting alongside the wheat to drop some gravity points. Maybe that was it...

At any rate, that yeast is gone, and let's hope the IPA comes out clean.

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Old 06-21-2010, 06:18 PM   #5
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Quote:
Originally Posted by ksbrain View Post
I did turn up the temperature for the last two weeks to try to get the Stout that was fermenting alongside the wheat to drop some gravity points. Maybe that was it...
Between that and the yeast being 3-4 generations old, I would say you had some stressed and/or "genetically drifted" yeast that gave you the flavors you tasted.
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Old 06-22-2010, 03:06 AM   #6
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Quote:
Originally Posted by ksbrain View Post
Then maybe it's mutation of the yeast? This was maybe 3rd or 4th generation. But if it were mutation I'd expect it to have the flavor even after a week.

This is a beer I make all the time, and it has never had any Belgian taste to it before at any time during the life of any previous batch. Fermentation was same as ever, controlled to 66 degrees F in a fridge.

I did turn up the temperature for the last two weeks to try to get the Stout that was fermenting alongside the wheat to drop some gravity points. Maybe that was it...

At any rate, that yeast is gone, and let's hope the IPA comes out clean.
Maybe it is not only cross contamination with your other yeast but also contamination with wild yeast. You should go back to your frozen stocks every so often to be sure you are pitching uncontaminated yeast.
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Old 06-22-2010, 01:00 PM   #7
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Maybe it is not only cross contamination with your other yeast but also contamination with wild yeast. You should go back to your frozen stocks every so often to be sure you are pitching uncontaminated yeast.
Yeah...my frozen stocks. You must mean the LHBS!
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