My airlock blew off. What causes a ferment to be so violent?

There are usually a few contributing factors to a violent blow off of your airlock. First is the yeast selection. Certain yeast have a greater propensity to create a "big fluffy head". The yeast that are known for big head productions are White Labs Trappist, WLP300 Hefeweizen, and WLP002 English. Certainly the first two are the most infamous. However, once in awhile we will hear of a yeast like the normally calm WLP001 California busting out of a carboy. A second factor is heat. They yeast go wild when they get hot. Fermentation above 73 degrees are candidates. Another factor is starting gravity. Higher gravity beers have more violent ferments. Sometimes a beer will start to ferment and come to a near halt shortly after starting because of a rapid drop in ambient temperature. When it suddenly becomes warm, because the weather heats up or the carboy is moved to a warmer location, it can cause a yeast breakout. If you plan on brewing with actual fruit in the primary (when lots of sugar are left) you should use a blow off that has a tube inner diameter of at least 1/2". As you can see there is no solid rule for when it will happen but there are certain factors that can be avoided. Don't ferment in a 5 gallon carboy with only an airlock as your primary fermenter. Keep an eye on your fermenter when in doubt.

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