What could be wrong here - Stuck fermentation?

[Microphobik]

So I'm currently making a chocolate milk stout. Something pretty close to this. Only real difference is that I have a little more grain and I added half a pound of oats and cut a bit of the roasted barley and dropped the lactose by 25%.

I'm also using Windsor dry yeast and I added just a half teaspoon of wine yeast nutrient (about 1/6 what I would use for wine per the instructions).

I did a BIAB and my efficiency was much better than expected and the OG was 1.076 after lactose (1.068 before).

Within 3 hours of pitching the yeast I had such an intense fermentation that the air lock blew. Once corrected it was bubbling away twice per second and it looked like a sand storm in a Hollywood movie in there.

After just 22 hours I noticed that the bubbling had slowed to one bubble every 5 or 6 seconds and I got concerned so I took a sample reading at gravity was at 1.048. Pretty good but still got a lot of sugar in there. We can assume that if we subtract the lactose I still have 1.04.

8 hours later I'm getting just a bubble every 60 seconds or so, everything has settled to the bottom and there is little noticeable activity.

Is this possibly a stuck fermentation or could this be the yeast not being strong enough to handle the alcohol? It's a British style yeast meant to finish not very dry, but this is still obviously far to sweet. If it's the later I'm also wondering how this would effect priming.

Should I rest confident that the remaining sugar will get finished up over the next week or two regardless of visible activity, should I add some more nutrient, or should I throw in a different strain of yeast to help out?

Really not clear what may be happening here.

 

[gpack]

Pull out that trusty wine thief and your hydrometer and check it.

Oh. Sanitize it first.

What temp is it fermenting at?

I wouldn't be worried unless you got it too cool.

 

[Microphobik]

I actually did check it which was what made me nervous.

The OG was 1.076 after lactose (1.068 before).

After just 22 hours I noticed that the bubbling had slowed to one bubble every 5 or 6 seconds and I got concerned so I took a sample reading at gravity was at 1.048. Pretty good but still got a lot of sugar in there. We can assume that if we subtract the lactose I still have 1.04.

...unless you mean I should check it again after only 8 more hours.

It was fermenting at about 22 C (71.6 F) but since last night its dropped to 18 C (64 F). The thermometer is just a cheap stick to the carboy type in Celsius so there is probably some wiggle room there. But as you can see it's dropping, giving further concern that something is up.

Why might the yeast go so strong so fast and then stop so quickly? I'm sure I haven't dropped an entire 2 more points in only 8 hours with such sluggish fermentation in comparison to the first day.

 

[duboman]

Active fermentation will usually occur over the first 2-4 days and then slow which is exactly what you are describing and then things slow way down. You need to relax and leave the beer alone and let the yeast do what they do best-make beer! Don't even think of doing any thing until at least day 10 and then check for final gravity. Then wait two days and check again, it should be the same reading and it should then be done.

Fermentation has 3 phases:
1. Lag phase or growth meaning the yeast build up to begin fermenting
2. Active phase-vigorous fermentation with a lot of visible signs of activity
3. Cleanup phase-slow and usually not very noticeable when the yeast continue chewing through the sugars and cleaning up their own waste and then follows flocculation or dropping out.

 

[gpack]

Don't stress out too much. Are there signs of activity with the yeast- krausen/swirling particles?

If so, let it go.

An airlock is not always your best indicator of fermentation.

It is always good to keep your temps stable and in the known operation ranges of the yeast.

Sorry for the Gravity Check advice. Glazed right over that in your original statement.

How high did you mash? Tempwise.

 

[matt08wrx]

Wait a few more days before checking gravity again. Should keep eating unless it got too cold and the yeast dropped out.

 

[Microphobik]

Sorry for the Gravity Check advice. Glazed right over that in your original statement.

How high did you mash? Tempwise.

Thanks everyone for the advice, yeah, I'm definitely doing the classic stress out. I just got back into this after 15 years away and this is only my second beer. My first still in the carboy. So I'm really wanting them to turn out well.

I did a BIAB and mashed at 55. But it would drop a bit closer to 152 so I would goose it a bit up to 156 and then repeat. But with BIAB and a simple stainless steal thermometer it's hardly exact.

@gpack - no, I don't see much krausen swirling anymore at all. It was going crazy yesterday but everything is looking quite still aside from some small bubble trails here and there.

 

[Microphobik]

Just an update for anyone in the same situation who has stumbled upon the thread. Looks like I was mashing higher than I thought. Gravity never got below 1.036 (1.027 if you account for lactose). But surprisingly the beer was not overly sweet at all. In fact it just had a hint of sweet that most people don't even notice until you point it out. So the lesson learned, get a better thermometer. Until then, I have dropped my mash temps by a couple of degrees. Anticipating that it is a good deal warmer at the bottom of the BIAB pot than it is the top, even after a stir.

 

[Cyclman]

Thanks for the update. High Mash Temps will do that, a good digital thermo is a great investment. My guess is that the temp variations in your fermentation also sped / slowed the fermentation, based on high / low temps.