Oh No, My Yeast is Foaming Out of my Airlock! Is it Comtaminated? What Should I Do?
Celebrate! Foamy fermenters are most likely not comtaminated by bacteria during foam-overs because carbon-dioxide escaping from the fermenter as a part of the foam is preventing anything from getting into the fermenter and contaminating the wort or must. Foam volume is a result of several variables including yeast strain, pitching rate, and dissolved oxygen. Weizen and wit beer yeast strains take the grand prize for foam production. In general, increased pitching rate with sufficient dissolved oxygen results in more aggressive fermentation resulting in more foam. But, the yeast must be pitched viable or alive and healthy.
Rapid and aggressive fermentation is one of the best ways to reduce the risk of contamination. Slow, sluggish fermentation taking several days or long lag times increase the risk of contaminatin. Ph reductions and the production of alcohol are two keys to supressing the growth of bacterial competitors especially during the early stages of fermentation.
If your airlock is filled with foam remove it, clean it and put it back on. This may need to be done several times a day during vigorous fermentation to prevent clogging. The pressure buildng up in a fermentor with a clogged air lock may result in the airlock being shot out of the vessel like a rocket spraying the ceiling with brown yeast and hop resins or pink yeast and purple grape juice. The worst case sinerio is that the airlock is fitted to tightly that the pressure actually causes the carboy to break.
The best solution to foam in the airlock is switching to a blowoff hose during vigorous fermentation. This is a 1 inch inside diameter hose which fits snuggly in the neck of the carboy and runs down into a bucket of water. The blowfoff hose is less likely to become clogged and if foam does blow off during fermentation, the bucket of water can be changed without removing the airlock. Once vigorous fermentation subsides, replace the blowoff hose with a traditional airlock.
A foamy fermentation can be a healthy sign of a good beer or wine to come.