I understand but bubbles cannot in fact convincingly or unquestionably suggest that a fermentation is still active. It could have stalled. So, you ask, if it has stalled where are the bubbles coming from? Well, those bubbles come from CO2 and while it is possible (and even likely) that the bubbles are being produced the gas may have been produced hours or days or even weeks before - if something in the environment provides for a change in the equilibrium of the contents of the fermenter then gas that was suspended in solution can fall out of suspension and bubble up and out and I can think of several things that could cause that to happen - a rise in the air pressure; an increase in the ambient temperature; particles (fruit, tannins, proteins) that were in
solution dropping out and creating what are called points of nucleation (Add any powder to fermenting mead or wine and you can see the gas roil out of suspension pushing all the liquid above it up and out of the fermenter and if you are fermenting in a carboy with a narrow neck that gas will use the neck to rifle the liquid and it will shoot up with so much energy that it can paint your ceiling.. ) - so bubbles are amusing to watch and listen to but the information they offer is really very limited... ;D
