I just finished fermenting a brew and I forgot to remove the blow off tube which is a tube sitting in a 500 ml bottle of water. So when I started sucking beer out of my fermenter, I sucked all the water from the bottle. I decided to carbonate one of the 2 kegs at 2'C and store the other keg at 16'C. My question is: will these beers be contaminated?

2 Answers 2



Depends on what bugs were in the water and whether they can reproduce fast enough to flavour the beer before your drink it.

My advice is to keep the beer as cold as you can to limit microbe growth, and drink it quickly. The beer stored at 16 C is much more at risk because the elevated temperature will accelerate microbe growth. If you can keep both kegs close to freezing, that's optimal.

  • So you don't think allowing the beer to sit around 16'C will let any yeast eat away at any bacteria? Thanks
    – Scott
    Feb 6, 2013 at 3:32
  • 1
    Yeast doesn't 'eat' or fight off bacteria in any way... Depending on the beer strenght and hop content it may be harder to bacteria to grown (the more alcohol and the more hops the harder). Feb 6, 2013 at 7:34

Maybe, but probably not. Several things are working against contamination post-fermentation.

  1. Post-fermentation your beer is attenuated and has alcohol in it, a natural anti-microbial. This higher the ABV, the less likely something bad can grow in it.
  2. Beer also contains hops, which is another natural anti-microbial.
  3. You are immediately cooling the beer down to carbonating/serving temp. Low temperature also inhibits growth of microbials.

Was your blowoff tube pumping krausen into the water or just basically operating as an extended airlock? If it was pumping krausen that increases the chances of something growing in the water, but does not necessarily mean it will continue to grow in the keg. If it was just an extended airlock, then the only thing that went into the water was CO2. Even IF something was growing in the water, it would have had to produce off-flavors BEFORE going into your beer since due to the reasons above, it shouldn't continue growing.

Comment response:

Sure water sitting at room temp for 10 days could grow something, but generally sugar or something else is required for bad stuff to grow since they need something to eat. Bacteria can't just eat water. Given that this was also in a fermentation fridge (enclosed space) for the 10 days, it is even less likely that something landed in there and started to grow so I'd bet that you are perfectly fine with just very slightly diluted beer.

Again, the fact that your beer had alcohol and hops in it at the time the water was added will prevent almost anything else from growing in it. The biggest risk for contamination is pre-fermentation, not post. Like another comment said, yeast doesn't eat bacteria. Yeast only eats sugar. Chilling the beer causes the yeast to go dormant and settle out of the beer at the bottom so yes it stops working, but it wasn't "eating" the bacteria in the first place.

Yeast outcompetes other bad stuff in your beer simply because it reproduces so fast in wort. When you start fermentation, I guarantee there is contaminating bacteria in there no matter how good your sanitization practices are. The yeast just goes to work immediately and outcompetes the bad stuff, producing alcohol as a byproduct which in turn kills the bad stuff. Hopefully this clarifies things.

  • Thanks for your thoughts August, It was just an extended airlock. (Blichman Conical Fermenter) And yes just plain water, the only reason I asked the question was the water was sitting in my fermenting fridge for 10 days at 20'C. Nice place for bacteria to grow. Should I chill both kegs, my thoughts were remaining yeast would eat any bacteria left in the keg. Am I correct in saying once you chill beer yeast stops working?
    – Scott
    Feb 6, 2013 at 23:29
  • Thanks for your thoughts, that clarifies alot for me. Certainly a mistake not worth making again. Cheers.
    – Scott
    Feb 7, 2013 at 23:17

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