Over carbonation analysis

I have been trying to identify why some of my beers are coming out over-carbed while others are fine. They all were fine after inital bottle conditioning, but then over time they got really too carbed. One batch turned into bottle bombs.

I have ruled out infections for the most part, and also the yeast strain (i.e. different yeasts used in different batches). The only similarities I can find is that out of the 4 batches that were over carbed, 2 were pumpkin ales and 2 were porters. One of the porters was aged on bourbon soaked oak chips.

So for the pumpkin ales, I am thinking that the sugars from the pumpkin were not consumed by the yeast during normal fermentation, but later were consumed by the yeast little by little, after bottling.

For the porters I have no idea. Would the yeast have started working on the bourbon after bottling?

Its strange because all of my lighter beers - IPAs, Pales, etc. - have been fine. I am trying to improve my fermentation regimine. Just bought an aeration system and also a chest freezer/temp controller. So I will see if that helps. But in the mean time if anyone has any ideas I would appreciate it.

How have you ruled out infections? Most of the time a late onset gusher, is an infection.

I had a few batches of beers do that to me as well. I think i had figured my issue out which was my bottling process. I used to pour the sugar solution in the bottling bucket and then rack my beer on top without stirring. It seemed when i did this a few of my bottles would explode after conditioning for a while while the rest were fine. Im trying a new method by pouring the sugar water gently on the top after i had racked and then stir slighlty to make sure it is mixed well. I never did that before because i didnt want to cause oxidation. The one batch i did recently seemed to have been fine and evenly carbed without any bottles exploding. I hope that was my issue and not an infection. Only way to tell is to try it a few more times and hope for the best.

How long from yeast pitch to bottle? What yeast? How much and what type of sugar? Any honey in the recipes? If you want help, please provide a few details.

Pumpkin has very little sugar, and it certainly is not complex sugars. If you don't mash, I don't think you will extract any sugars from pumpkin (but I could be wrong about that).

My guess would be either you bottled before fermentation was complete, or you used too much sugar.

While not always, an infection will tend to leave a ring around the bottle at the top of the liquid.

I ruled out infection because the beer tasted fine in most cases. However in retrospect I think the bottle bomb batch was an infection after all. These batches were over the past few years, so I don't have a lot of the details. However I always go at least 3 weeks before bottling.

I am beginning to think that the fermentation may have stopped and then re-started when I added the bottling sugar. I've done one batch since making the fermentation improvements so I think I will wait and see if it happens again in the next few batches.