Yesterday I brewed our highest gravity beer to date – it measures at 19 °P (Degrees Plato) which, I plan, will produce a beer just under 8% ABV. It is a ‘doubling’ of our popular “Domestic Short Hair” American Stout (“Double Domestic”). There are some special considerations to be made when brewing and fermenting a beer of this gravity, and after this batch of “Double Domestic” was in the fermentor for 24 hours, I was confronted with one of those issues – the beer was bubbling in to the airlock.
Because I use plastic as a primary fermentation vessel, I didn’t have to worry about the rupture that can happen in a situation like this with a glass carboy. But there’s a sanitation issue. As the yeast ferments the wort into beer, a head of foam rises called krausen. The higher the gravity the beer, the more sugar there is to be eaten by yeast, the more fervent the fermentation, the more serious the krausen.
There is only so much head-space in a fermentor, and if the krausen rises into the airlock, the barrier between the sanitized environment of the fermentor and the bacteria-riddled air of everyday is broken, you vastly increase the risk of your beer being contaminated and producing off-flavors. It won’t kill you, it will just taste… ‘off.’
So I sanitized some tubing in iodophor, poured some bleach into a growler and set up my first blow-off hose using an airlock hack I read about. I also sanitized the existing airlock, so there was no beer/air barrier for about three minutes. Hopefully the CO2 being generated by the fermentation is enough to keep most of the air out.