Strange overcarbonation issues

[foxyaardvark]

I recently brewed a beer based off of the northern brewer bourbon barrel porter kit. I have a few bottles that are gushers, and the remainder of the bottles do seem overcarbonated by a bit, but not to the gushing level. I am perplexed by this. I am very careful with sanitation and the beer tastes good so I do not think it is an infection. I actually used only 3 ounces of priming sugar for this batch (5 gallon) so it should not have been too much. Before I bottled I took gravity readings a week apart and came up with 1.016 each time, so I went ahead and bottled. Out of curiosity, I tested the gravity of one of my gushers today (3 months after bottling). It is now reading 1.010. That is a big drop. What happened? Did I have a stalled fermentation that kicked back up when I added priming sugar? Is an infection possible? I am also wondering if I had uneven disbursement of the priming sugar in my bottling bucket.

I did add oak chips soaked in 16 ounces of bourbon about a week before bottling and I do not recall stirring it in. Could this have led to inaccurate initial gravity samples in the beer? I'm having trouble solving this one. Thoughts?

Strangely, my last few batches of beer have also been overcarbed for how much priming sugar was added. They have all tasted great and I always look for consistent gravity readings for at least 3 consecutive days. What is going on?!

 

[foxyaardvark]

I did notice that the carbonation on the gusher bottle disappeared from the beer very quickly. It now tastes flat, which makes me think that the CO2 had not been adequately absorbed into the beer yet. However that seems strange after 3 months of bottle aging. I did only have this one in the fridge for 20 minutes or so before opening it. This still wouldn't explain the significant drop in gravity though. strange...