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?