So, I was brewing a nice IPA the other day. I walked in to check on the carboy and the stopper had popped out and there were hops everywhere! I stopped it back up and bottled it a few days later without problems.

But, I would like to know how this happened? I waited a little over a week to transfer to the secondary. The fermentation lock was bubbling once every couple minutes. So, I'm thinking primary fermentation was done.

I cleaned the secondary carboy really good (so I thought) and added the hops.

Any ideas here? Is this just a contamination issue?

  • 7
    Gotta stop brewing with C4. Commented Nov 9, 2010 at 16:42
  • 1
    Did you have an airlock on it or was it sealed? Commented Nov 9, 2010 at 17:31
  • This was in the secondary. I had a stopper on it. I'm using a 5 gallon carboy.
    – Scott P
    Commented Nov 9, 2010 at 19:47
  • 2
    try using a large gauge plastic hose into a bucket of water rather than an airlock until the ferment cycle settles down
    – BozoJoe
    Commented Dec 4, 2010 at 17:11
  • 1
    The first piece of advice I'd give is to not go by bubbles in the airlock to determine whether or not primary fermentation has finished, it's too prone to errors. My second piece of advice is to invest in a hydrometer and use a few days of stable SG readings to determine when primary fermentation has finished. Commented Dec 21, 2011 at 18:07

5 Answers 5


My understanding is that explosions are usually caused by the airlock getting clogged, usually by krausen. The pressure builds up and you get an explosion. The solution is to use a blow-off hose instead of an airlock, since it's wider and allows for krausen or whatever to escape.

On one hand, I haven't heard of this happening in secondary, but on the other hand, it's supposed to be more likely when you're using a fermenter with less head room (eg, a 5-gallon secondary vs a 6.5 gallon primary).

  • Fish is right on with the airlock getting clogged. When adding things like hops into the secondary it is easy to overfill and the hops probably blocked the bottom of the airlock. I had this happen with my very first batch (in the primary though). I have always used a blow-off hose after that. Commented Nov 9, 2010 at 17:25
  • It's exactly the head room problem. I'm onto a stout that is having a lot of problems in the secondary fermenter. The blow off tube seems to be doing the trick.
    – Scott P
    Commented Dec 7, 2010 at 1:32

Am I reading this right? Did you put a solid stopper in the carboy? If that's not the case, please ignore this answer.

Even though most of the fermentation is complete when you transfer to secondary, the beer is still releasing CO2 which needs some way of exiting the carboy. If you use an airlock instead of a solid stopper, you'll see a significant reduction in frequency of explosions.


I know your question is about contamination, but I figure your interested in how to prevent this in the future.

I recommend fermcap to reduce the volatility of big fermentation. Its a foam control product that really helps. I ferment 5.5 gallon batches in 6.5 gallon carboys, with this product I've been able to ferment 1.080 beers with only an airlock.

You can also use it to prevent boil overs.

  • I haven't had such good luck with fermcap. Seems like it only works for a day or two, then the krausen starts building back up. It does the trick in my boils though.
    – GHP
    Commented Dec 20, 2011 at 13:34

If you transferred to secondary after only a week, it's likely the fermentation wasn't finished. That would explain t he blowout on a sealed container. But in general, you don't need to use secondary. Just leave the beer in the primary for 3-4 weeks and you're good to go.


As a side note to this, I am DONE using whole leaf hops in the boil without a muslin bag or strainer into the primary. I have run into more problems leaving whole leaf hops in my brews (clogged/BROKEN siphons, this problem, etc)

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