I was brewing a sour beer with Brett Bruxelensis, when my primary finished I harvested the yeast. The beer was fine.

When I subsequently added it to secondary with raspberries I ended up with vinegar due to aceto bacter.

I was wondering should I discard the harvested yeast or would it be safe to use?

I suspect the acettobacter was introduced by the fruits, but I am not sure (not a whole lot of experience with sours).

  • 1
    Was the beer sour after primary on Brett?
    – brewchez
    Commented Jan 8, 2020 at 18:23

2 Answers 2


Brettanomyces will make acetic acid in the presence of ethanol and oxygen. You'd need to determine if there is actually acetobacter present in the harvested slurry to know for sure if it was "clean". It is possible you picked up too much oxygen on transfer or had too much headspace in secondary.


To eliminate any risk at all, you could discard the harvested yeast. I agree with you, that most likely the acetobacter came from the raspberries. However, it's possible also that it simply flew in from the air or otherwise was incorporated as part of the racking to secondary. So there's no way to know for sure really.

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