The Night Brett Snuck in Through the Air Lock

Almost exactly one year ago Luke Gottlieb and I brewed a Belgian style ale that included one quart of local raw gamble oak honey. The beer was left to ferment in the secondary for the school year, and when I got home from Maine the first thing I did was run down stairs to check on my baby. It looked unchanged, but as I examined further I noticed that something unusual was floating on the surface. Near the edge of the carboy there was a scattered mess of hard bubbles. These bubbles are not a byproduct of normal fermentation--from Saccharomyces that is--but more likely a result of a wild yeast contamination. In this case I believe the culprit belongs to the the Brettanomyces genus. I am obsessively sanitary when brewing, so there is a very slight possibility that the Brettanomyces--Brett--made it into the beer during handling; what is more likely is that this wild funk snuck in through the air lock--the plastic contraption on the carboy that contains water to allow CO2 to escape but keeps air out.

When this beer was first fermenting, it was in a room that fluctuated in temperature. Each night the temperature would drop, and a pressure differential would be created between the inside of the carboy and the rest of the room. In the morning, the air lock would be empty and air would be allowed to flow into the carboy. It is most probable the intruder came in during this time.

The carboy at a distance

The funk on the side

I once read that no known pathogens have been found in infected beers, so I wasn't afraid to taste it--in fact, I was excited. Being a lover of sour beers I began to imagine a tart treat. What if Luke and I had created what beer aficionados salivate over? On the other hand, it could turn out to be a band-aid ale, which thanks to Matt McElwee, I have had the displeasure of trying. I withdrew a sample and did a one handed drum role as I sniffed and then poured the liquid over my tongue.

Looking a little better outside the carboy

The taste was........... lacking any resemblance to an infected beer. In fact I couldn't pick out any off-flavors other than a slight burn of alcohol and some esters that tasted like bananas. It almost tasted like a light after dinner liqueur, but the taste of band-aids and tartness was absent. The Brett might have attempted to establish itself but the high alcohol percentage probably restricted its growth.

Even though Luke and I were lucky our beer wasn't ruined, the problem could have been avoided by using a different style of air lock. The standard 3-piece air lock that I usually use does not account for any changes in pressure but the "bubbler" style does. The bubbler air lock allows water to pass into two chambers to offset any differences in pressure. I have since outfitted all of my carboys in Colorado with the bubbler style to keep out any more unwanted yeasties.

Below are the two styles with blue dye added to the water.

The 3-piece

The "bubbler"