Bubbling doesn't really mean anything other than the airlock is bubbling. And airlock is not a fermentation gauge, it's a vent to bleed off EXCESS gas, be it oxygen or EXCESS co2. It shouldn't be looked at as anything else, because an airlock can bubble or stop bubbling for whatever reasons, including a change in temperature (gas expands and contracts depending on ambient temps) changes in barometric pressure (You can have bubbling or suckback in the airlock, depending on pressure on the fermenter) whether or not a truck is going by on the street, the vacuum cleaner is running, or your dog is trying to have sex with the fermenter. Or co2 can get out around the lid of the bucket or the bung...it doesn't matter how the co2 gets out, just that it is.
And bubbles don't coordinate with anything concrete within the fermenter either, "x bubbles/y minute" does NOT TRANSLATE to any numerical change in gravity....if an instruction says do something when bubbles do something per something, throw the instructions out.
The only way to know how your beer is doing is to take a hydrometer reading.
Your hydrometer is a diagnostic tool. You're not sure what your beer is doing, right? Then if that's the case, you taking the reading will tell you what your beer is doing, and therefore either ease your mind, or will till you if there's a problem.
I always make the analogy that taking a gravity reading is like a doctor using a tool like and ekg or an x-ray- you can't always rely on your senses to know what's going on. An airlock may or stop bubbling due to everything from barometric and temp changes, a leak in the bucket, to a truck rolling down your street, so it's NEVER a reliable indicator of what's happening.
But a hydrometer reading is. Until then, all you have is a bubbling airlock.
