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So last night I checked on my porter, 48 hours on fermentation with Wyeast 1968, bubbling away happily. My ferm chamber is a small chest freezer.

Got a blowoff tube running from the top of the bucket down to a quart or so of StarSan (leftovers from brew day). The sanitizer foams up, of course, and with all the bubbling and krausen coming down the tube a nasty pool of brown gunk had formed on the floor of the freezer. I grabbed a rag and reached down to mop it up...

And that's when I nearly died. My sinuses screamed in pain and I had to jerk my head out of the freezer. There was a knife-sharp effect on my nose by something in the air in the freezer.

I wouldn't say it's a bad smell, per se. There wasn't really a scent. It's that my nose hurt. A lot.

I managed to clean up the mess by pinching my nose shut before diving in, but man, what an experience.

What was that "smell"? Was it just CO2 buildup in the closed chest and my nose was reacting to a complete lack of oxygen? Could I possibly have an infection, in my beer or in my nose? Any good theories here?

Galapagos Jim
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3 Answers3

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It's the CO2 - I've had the same thing happen sniffing the top of a regular bubbler airlock. The CO2 enters the nose and dissolves quickly in the small capillaries creating carbonic acid, which stings. There's no real danger here since you don't stick about long enough to breathe in much CO2.

mdma
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    Yep, I've had the same thing happen when I overzealously whiff my fermentation chamber. Nose burns, eyes water, swear words fly. – JoeFish Jul 10 '12 at 20:59
  • Winner, winner, chicken dinner! +1's to everyone who said CO2, and green checkmark to mdma for the bonus biology lesson. My assumption was CO2, but having never experienced this I didn't know what to think. I feel like Columbus with my new "discovery". Thanks, all! – Galapagos Jim Jul 10 '12 at 22:11
  • I always thought CO2 would just suffocate you without any warning signs. Was I wrong? – Markus Jul 11 '12 at 07:22
  • @Markus, if you're completely surrounded by only CO2, such as in a confined space, then yes, you will asphyxiate from lack of oxygen. But that's not what's happening here - we're talking about a small amount of CO2, with plenty of O2 still being available form the surroundings. – mdma Jul 11 '12 at 08:42
  • @markus you are thinking CO, this is CO2 – brewchez Jul 12 '12 at 02:16
  • Most likely right. But does anyone else ever get a whiff of SO2 from the fermenter. I have noticed that a few times. Could be a combination of the two. – Chris Plaisier Jul 17 '12 at 14:19
  • A combination is possible. – mdma Jul 17 '12 at 18:13
  • To clarify. CO (carbon monoxide) produced by e.g. a faulty gas fire (and not present in air in significant quantities) is odourless and mixes well with air. CO bonds strongly to haemoglobin and makes it less efficient at carrying oxygen. Inhaling too much CO effectively renders your blood useless until it is replaced... hence the danger of asphyxiation.

    On the other hand, CO2 (carbon dioxide) is not "toxic" as such, your body just can't use it. You may asphyxiate if immersed but it the effects reverse almost immediately. In still air, CO2 generally drop harmlessly to the floor. Just sayin' :)

     – Doug Dec 16 '13 at 15:22
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Yep, it was more than likely CO2.

Denny Conn
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I've never experienced a "knife-sharp" smell, but I'm guessing it was just CO2. Maybe that was your brain's way of telling you that you were going to suffocate unless you get some fresh air pronto.

Breweries often use large 55-gallon drums half-filled with water as their blowoff tube airlock, and on more than one brewery tour I've heard the guide say that people will stick their heads in the bubbling drum to get a good whiff of the beer and will pass out.

I doubt you'd have a wild-running infection already.

Hank
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    Not a reaction from about to suffocate - a sudden excess of CO2 manifests itself as a lack of oxygen, resulting in a headache, thumping ears. Breathing CO2 through the nose hurts because of the carbonic acid created. – mdma Jul 10 '12 at 19:09
  • @mdma: Very interesting. – Hank Jul 10 '12 at 20:16