Never ending fermentation

[CraptainWirtz]

Short version: why is my beer still generating bubbles after >5 weeks of fermentation? Temperature increase? Bacteria?

Long version:
What is going on with my beer? I brewed a stout over 5 weeks ago:
1.5 lb Munich
1.5 lb Maris Otter
1 lb black barley
1 lb flaked barley
2.75 lb light DME
1 oz Northern Brewer at 60 minutes

Accidentally mashed in at 158degF (was aiming for 150), so I left my brew kettle/mash tun uncovered for 45 minutes and let temperature drop to 152, covered and wrapped in towels and left for another 15 minutes. OG = 1.046. After boil and cooldown, pitched a 1 L starter of WLP007 at ~64degF and fermentation temp stayed at 66-67 for the next 3 days. I removed the carboy from my evaporative cooling system and let the temperature rise to ~70, and swirled the carboy twice a day for the next 6 days to ensure yeast were in suspension and fermented as much as possible. After 4 weeks, FG was 1.013 so I racked to secondary. I left it alone for another week and was planning on bottling but I see this:



Ugly iPhone video but hopefully you can see in the center-right, and at the bottom of the screen along the front side of the carboy, bubbles are coming to the surface. FG seems to have dropped a point to 1.012. After 5 weeks, I'm really surprised to see bubbles being generated. It was completely flat and completely still when I racked from primary. I'm thinking it's either due to warmer ambient temperatures over the past few days here (no air conditioner in my apartment) or bacterial contamination. Gravity sample tasted fine, but I'm still a little worried. Let's say I didn't sanitize my secondary or autosiphon/tubing well enough, would I be able to taste bacterial contamination by now, after a week? My instinct as a biologist tells me I would for sure - I've cultured plenty of bacteria in a laboratory, just not in beer. Can anyone give me any input and ease my fears? If I give it another week (4 weeks primary + 2 weeks secondary), the gravity doesn't change and it still tastes fine, do you think I'm safe to bottle?

Thanks for any help you can give,
Mark

 

[WoodlandBrew]

It is likely just CO2 coming out of solution after fermentation has completed. It is know an degasing.

Gravity will drop exponentially so seeing it change one point in weeks 2-3 is not uncommon. This corresponds to about one volume of CO2. (more info in my blog and book)

Agreed. If it tastes fine it is likely safe.

 

[CraptainWirtz]

Thanks for the reassurance. I just can't believe there's still either significant fermentation by yeast or CO2 degassing. It's been cooler the past couple days than the previous three or so. I took this video today:

[ame="http://www.youtube.com/watch?v=Cb-JfKJ7Je0"][YOUTUBE]Cb-JfKJ7Je0[/YOUTUBE][/ame]

That just seems like so much foam. Is it possible to have a slow-fermenting infection/contamination like this? Has anyone ever seen degassing this vigorous, even after the weather cools back down?

 

[WoodlandBrew]

I just watched your video. (I can't see them on my phone) What you have there is totally normal. You are just knocking the CO2 out of solution. Because it is at atmospheric pressure there is one volume of CO2 in solution. If you leave it alone that's one less volume you need to add when priming. (Most people add 5oz of sugar to 5 gallons of beer to add 2 more volumes to make a total of 3 volumes)

 

[CraptainWirtz]

Alright. I believe you. Thanks for your patience! I was just so shocked to see this for a few reasons: time elapsed since pitching yeast, the fact that I already knocked so much CO2 out of solution when I swirled the carboy to resuspend the yeast, and the fact that I didn't see this phenomenon with my last beer, which I also swirled the crap out of but racked to secondary sooner.

Anyway, thanks so much for your help. I'll try to forget about it until this weekend, take a gravity reading, and bottle if it hasn't changed. I guess I'm just anxious because I'm down to my last two bottles of homebrew so I'm looking at over a month of homebrewlessness as it is!

 

[DrunkleJon]

Generally speaking, the best way to know you are done fermenting is when you get the same gravity readings over 3 days. Basically take a reading then take one two days later. So long as you are in the temperature range where yeast is active, you are done enough to not worry about overcarbonation, etc. The airlock is most definitely not a sign of fermentation as depending on your seal you may not see bubbles or you can see bubbles from temperature swings, off gassing, or what have you. Relax, don't worry and all that.

 

[CraptainWirtz]

Generally speaking, the best way to know you are done fermenting is when you get the same gravity readings over 3 days.

Right, I get that. My concern is, shouldn't wlp007 be finished with a 1.046 beer after 4-5 weeks? Especially if I swirled the carboy enough to already knock most of the CO2 out of solution. So if my beer drops one gravity point between the 4th and 5th weeks, after I've taken it off the yeast cake, is this the beginning of an infection? Woodlandbrew says its normal off gassing so I'm going to do my best to RDWHAHB (last one I have ), forget about it until this weekend, and take another gravity reading.

 

[DrunkleJon]

It is most likely just the offgassing but you have to remember that yeast is a living organism, and if experience has taught me anything, anything living will find a way to surprise you when you think you have them figured out. Yes, after basically the 3 week point it is usually done as long as it didn't get too cold and put the yeast to sleep. Have you taken any gravity readings? Did you sample them? Infections are not all that easy to get. I had to leave the last half inch and trub in one of my fermenters unsealed for a month to get one. As long as you have rudimentary sanitation practices (I would still advocate you be extra clean but not to the point of retentiveness) infections are reasonably hard to get.

You should be fine.

 

[kh54s10]

Stop shaking the carboy and take some gravity readings. That beer probably fermented out 3 weeks ago. I ferment most of my brews for 3 weeks, check gravity and package.

What you are seeing is co2 coming out of solution. It will happen with atmospheric changes, possibly with temperature up or down and pressure up or down.

 

[CraptainWirtz]

I've taken several gravity readings:

OG = 1.046
"FG" at 4 weeks = 1.013, sample tastes OK, not great.
"FG" at 5 weeks = 1.012, sample tastes better than before, but kind of a hard-to-describe "sharp" flavor to it, not apparent at 4 weeks.

I only shook it to illustrate how much gas was still in solution at 5+ weeks, a major difference compared to how flat it was at 4 weeks (data not shown).

Regardless, we'll see what it's like this weekend.