Overcarbonation

[ncbrewer]

I've had two batches recently that have been overcarbonated - the first one was slight gushers. They were both primed for 2.65 volumes - pretty normal for me. To see if these continued to ferment after bottling, I checked the gravity of a bottle after conditioning - ready to drink. In both cases the gravity dropped after bottling - by 6.2 gravity points in one and by 3.6 gravity points in the other. Gravities at bottling were 1.0151 and 1.0128. The samples were decarbonated before reading by pouring back and forth between glass and pitcher 20 times. These were both fermented with US-05 and were bottled after 23 days in the fermenter. Temp for both was 67F during active fermentation and 72 - 75 after that. Checked gravity with a narrow range bottling hydrometer two days before bottling and again on bottling day - it was steady. I'm a little concerned that maybe the fermentations stalled, and restarted after bottling. But I've never checked the gravity of bottled, conditioned beer before. I just assumed it should be the same as before bottling since the priming sugar would all ferment. The gravity would go down a little due to the alcohol being lower gravity than water, but that should be negligible.

Does anybody have ideas about what's happening here?

 

[day_trippr]

If these were in fact bottle conditioned they would have gained enough alcohol to increase the ABV by ~ 0.5%, which ain't bean bag.
In turn that alcohol would have reduced the Specific Gravity by some mathematically related number of points.
I'm not doing that math for you but there's likely a calculator out there that'd provide the "final final" specific gravity

Cheers!

 

[IslandLizard]

In both cases the gravity dropped after bottling - by 6.2 gravity points in one and by 3.6 gravity points in the other. Gravities at bottling were 1.0151 and 1.0128.

Those are substantial drops. After 23 days I wouldn't expect any more attenuation either, although the FG of 1.0151 at the time is definitely highish. What were their OGs?
All Grain?
Anything in the recipes that was very chewy for them?
Lots of Maltotriose possibly?
Or longer, more vigorous boils causing more caramelization?

Is it possible a small infection was introduced during bottling? A wild yeast perhaps?
Bucket as fermenters? Spigots?

 

[DuncB]

Any suspended hops in the transfer to bottles?
If so could be hop creep secondary to the diastase enzyme in the hops. Doesn't take much enzyme to do this.

 

[ncbrewer]

If these were in fact bottle conditioned they would have gained enough alcohol to increase the ABV by ~ 0.5%, which ain't bean bag.
In turn that alcohol would have reduced the Specific Gravity by some mathematically related number of points.
I'm not doing that math for you but there's likely a calculator out there that'd provide the "final final" specific gravity

Cheers!

I agree, the additional alcohol reduces the sg, but a quick search didn't turn up a good calculator. I didn't spend much time looking because IMO the sg drop I got was way beyond any difference the additional alcohol would make. (I hope I understand your comment correctly.)

 

[ncbrewer]

Those are substantial drops. After 23 days I wouldn't expect any more attenuation either, although the FG of 1.0151 at the time is definitely highish. What were their OGs?

[Fixed reply inside quoted text -Mod]

	OG	FG	Bottled	AA	Style
1st	1.0549	1.0151	1.0089	72.5	Nut Brown
2nd	1.0555	1.0128	1.0092	76.8	American Brown

All Grain?
LME. Notorious for finishing high, but I haven't heard of having this type of problem.

Anything in the recipes that was very chewy for them?
Lots of Maltotriose possibly?
Victory, crystal, chocolate, and other malts (Williams Brewing Nut Brown LME)

Or longer, more vigorous boils causing more caramelization?
40 minute boils, fairly low boil

Is it possible a small infection was introduced during bottling? A wild yeast perhaps?
One case of the bottles from the first batch was used again without issue, so it doesn't seem to be bottle infection, unless it's a random infection while bottling, but I haven't changed the process. And they taste the same as always (same beer several times before). Still, this could explain it.

Bucket as fermenters? Spigots?
I use a bucket fermenter - no spigot. I only open the fermenter twice - once to get an early gravity sample and again on bottling day.

 

[ncbrewer]

Any suspended hops in the transfer to bottles?
If so could be hop creep secondary to the diastase enzyme in the hops. Doesn't take much enzyme to do this.

Some hops in the last few bottles of the batch, but the overcarbonation has been uniform through the whole batch. There are no dry hops in these. One batch had a hop stand at 180F - I think that would denature any enzymes???

 

[IslandLizard]

Can we simply conclude your fermentations stalled and resumed after bottling?

Are your ferm temps steady (temp controller) or can they fluctuate? A temp drop at the wrong point can stall a fermentation, especially when it happens on the low side of her range.

 

[day_trippr]

I have a suspicion the 3.6 point drop reflects bottle conditioning to 2.65 volumes, and the excess of that in the batch with the 6.2 point drop reflects additional fermentation of the original beer...

Cheers!

 

[ncbrewer]

Can we simply conclude your fermentations stalled and resumed after bottling?

Are your ferm temps steady (temp controller) or can they fluctuate? A temp drop at the wrong point can stall a fermentation, especially when it happens on the low side of her range.

That's exactly my concern. If fermentation will stall, and resume in the bottle, it's a safety issue.

My ferm temps are reasonably steady but not perfect. Targeting 67, temp will vary from 66 to 69. Using a swamp cooler, adding ice jugs as needed. I'm retired and can watch the temp closely. But it's possible that it might vary a little more than I'm aware of at times.

After this experience I'm thinking about going to kegging. I don't really have room, but I'll give it some thought. It's my impression that kegging eliminates the issue with overpressure.

 

[ncbrewer]

I have a suspicion the 3.6 point drop reflects bottle conditioning to 2.65 volumes, and the excess of that in the batch with the 6.2 point drop reflects additional fermentation of the original beer...

Cheers!

I did a rough calculation based on specific gravity of ethanol. The second batch, with a 3.6 point drop, lowered the gravity by about 0.8 gravity points just due to the alcohol content. It seems that both had continued fermentation in the bottle. Papazian stressed "Don't worry", but I'm worried.

 

[IslandLizard]

Papazian stressed "Don't worry", but I'm worried.

You could lightly crack the caps and let some pressure off. Then recrimp.

 

[ncbrewer]

You could lightly crack the caps and let some pressure off. Then recrimp.

This batch is just overcarb'd, but not gushers, so not a big problem there. My concern is about an ongoing safety problem since I had two stalled fermentations, two batches apart. I don't like the trend.

 

[IslandLizard]

This batch is just overcarb'd, but not gushers, so not a big problem there. My concern is about an ongoing safety problem since I had two stalled fermentations, two batches apart. I don't like the trend.

No, these aren't happy surprises.

After this experience I'm thinking about going to kegging. I don't really have room, but I'll give it some thought. It's my impression that kegging eliminates the issue with overpressure.

Now, that's a novel idea!
Since they're stored cold (usually), refermentation is rare. Those that happen to over-pressurize (as you just experienced or for other reasons) are easily remedied by pulling the PRV: Done!

After I started kegging I've only filled a few bottles, mostly from "leftover" kegs, to free up the kegs.

I can clean 3 kegs (by hand, don't have a keg washer, yet) in about an hour, 100% Starsan pre-purged, ready to be filled. Filling each takes 10-20 minutes, tops, including prep work. That beats cleaning, sanitizing, filling, and capping 3 cases of bottles.

 

[ncbrewer]

I'll be watching everything related to this problem. Thanks to all who commented.