It'll be done when it's done.
I brew outside, and ferment in a shed that might as well be outside. When the chilly weather started to hit this year, we had a couple or three beers that took a month and were still bubbling in the secondary. If you have a clean ferment going on, it's absolutely no big deal. Let it go and bottle/keg it when it's done.
Don't worry about the low fermentation temp. It will definitely make for a slower fermentation. But it doesn't endanger your beer. If you have a clean fermentation going on, it's all good.
Another thing to consider is the way CO2 in solution and bubbles work. When the yeast actually start munching sugar and *ahem* excreting C02, that CO2 largely dissolves into solution, since the yeast have such tiny CO2 farts. It takes a while before the CO2 saturates the solution. Then, finally, quite a while after CO2 began being produced, larger bubbles form from the smaller bubbles and rise to the surface.
Well, at the end of a fermentation, the reverse it true. A beer can take seemingly *forever* to stop bubbling. But bubbles are hiding everywhere. The solution is at saturation, and, even though no more CO2 is being produced, and the yeast is settling to the bottom, CO2 is still bubbling out of solution slowly. It also bubbles out of the yeast cake at the bottom. If you move your container, you knock a lot of it out of solution, and it bubbles like mad, like a soda.
In any event, hopefully I gave you something to read for a while, so your beer can finish fermenting. Because as long as you have a nice clean fermentation going, all it needs is a little more time until it settles out and is nice and calm on top. Cool, slow fermentation produce excellent, clean beer, so don't shortchange yourself by drinking it young.
Happy New Year, y'all!
Janx
