This happend to me the other day for the first time. Thats why I would like to have a bigger primary, and a conicle one day, but anyway I caught it as it was happening I was able to remove the airlock and sanitize it and place it back in but I did not stick the airlock as far into the rubber stopper, and I got lucky this time. I refilled the airlock and I used a started for the first time which could have contributed. It was ferminting so vigourously, I had to fill the airlock twice. But anyway I cleaned up the mess, and its in the secondary now, has been for about 4 days, and no signs of contamination....Good luck If your not familiar with a blow off tube, just run a tube from your rubber stopper into a container with water. It will be fine.Janx said:Well, it's gonna smell like that because the stuff that escaped almost certainly *is* "infected". After all, it's out in the great wide world.
Your beer in the fermentor should have no problems, since none of that foam went back into the fermentor.
No worries. As long as you were clean, it won't get infected because of blow-off. It's possible to successfully ferment in an open-topped primary if you want and some of the world's great breweries do that. The outflow of CO2 tends to keep the nasties at bay.