I racked a beer into a secondary about a week or so ago. I monitor the frequency of the bubbles with a stopwatch from time to time. Once it hits 3 minutes between bubbles, I usually bottle it. Well, I was down to a bubble every 4 minutes on one batch and could not tend to it that day. The next day, it was bubbling at a rate of once every minute again!
After thinking about it really long and hard, I came to the conclusion that the whole time the beer was in the secondary, we were getting hammered every day by rain. We were under a huge low pressure system. The day I was at a bubble every 4 minutes, was the first nice sunny day we had in over a week. Mile high blue sky. High pressure system. Well, this led me to believe that this was the source of my rapidly changing bubble frequency through my s-trap air lock. Does this make any sense to anyone else? I now use a hydrometer to determine when it's time to bottle and not time.