From Palmer's online book, discussing fermentation that just won't stop. Something to consider....
Cause: Gusher Infection
The sustained bubbling is often due to "gusher type" infection. These infections can occur at any time and are due to wild yeasts or bacteria that eat the higher order sugars, like dextrins. The result in the fermentor is a beer that keeps bubbling until all of the carbohydrates are fermented, leaving a beer that has no body and very little taste. If it occurs at bottling time, the beer will overcarbonate and will fizz like soda pop, fountaining out of the bottle.
Cure: Improve your sanitation next time.
If the beer seems to be bubbling too long, check the gravity with a hydrometer. Use a siphon or turkey baster to withdraw a sample from the fermentor and check the gravity. If the gravity is still high, in the teens or twenties, then it is probably due to lower than optimum temperature or sluggish yeast. If it is below 10 and still bubbling at several per minute, then a bug has gotten hold. The beer will not be worth drinking due to the lack of flavor.