Okay, it’s definitely NOT the biggest fermentation mess I’ve encountered before.
First, I deviated from the original plan: the Wyeast French Saison “smack pack” did not activate, so I pitched a different yeast: US-05 from Safale, a dry yeast with which I am familiar. The “lag time” (length of time between addition of yeast and start of active fermentation) was a little longer than with most of the beers I brew.
There are occasions where beer (or in this case, cider) ferments so robustly that the foam that forms at the type “blows through” the airlock, and begins to ooze like a terrible monster or spreading contagion. It’s normal, and harmless, but can be quite messy. I noticed the possibility that it would happen with the cider yesterday, so I took precautions. I moved the carboy out of the fermentation chamber so I could keep an eye on it, and I removed the airlock to allow the cider to ferment “open” for the time being.
Normally, open fermentations can be risky. You keep the carboy closed with an airlock to prevent the infiltration of contaminants that will either infect or flavor the final product. I’ve had varying success with open fermentations. Some yeasts (like the California Lager) are good to use for open fermentation. But the possibility of something going wrong is much higher anytime you leave the fermenter open to air.
In this case, I’m not terribly concerned about leaving the airlock off for this phase. The reason is that the cider has a thick, bubbly, foam completely covering (and protecting) the cider itself. The CO2 being created by the yeast in the fermentation process creates a “layer” that protects the cider from air and contaminants. I cleaned off all the sludge that I found around the opening of the carboy this morning, but if I left it in place, it would further protect the beer while providing a means for CO2 to escape.
If you closed a carboy fermenting like this without using an airlock (assuming you could keep a “bung” inserted — you’d need a wire cage contraption like they use on sparkling wine bottles), the pressure that would develop inside the carboy would likely cause the whole thing to explode.
Yeast are living organisms, and the amount of carbon dioxide they produce is significant.
Another reason to marvel at God’s creation.