Dry hopping - Re-starting a stuck fermentation

[Aaron]

I thought i'd post this to see if anyone has had a similar experience.

I'm on the bandwagon and I've been making a few NEIPA style beers recently. I've been using a few different yeasts such as WY1318, Vermont ale, and some belgians. Sometimes the fermentation stalls out. It can usually be completed by merely raising the temperature but my last fermentation, using Ardennes yeast, stopped at 1021 and didn't restart even after raising the temp up to 26C. I tried agitating the fermentor, nothing. About 4 days passed - still 1021. I thought i'll dry hop and cross my fingers. About an hour after dry hopping, low and behold, the airlock is bubbling again.
I have noticed a similar uptick in fermentation after dry hopping on a few other occasions, but not quite so stark as this time, where i'm absolutely convinced it was the dry hops that re-started the fermentation.

Has anyone else had this experience? I'm assuming it must be happening through oxygen getting in with the dry hops.

[orlando]

I thought i'd post this to see if anyone has had a similar experience.

I'm on the bandwagon and I've been making a few NEIPA style beers recently. I've been using a few different yeasts such as WY1318, Vermont ale, and some belgians. Sometimes the fermentation stalls out. It can usually be completed by merely raising the temperature but my last fermentation, using Ardennes yeast, stopped at 1021 and didn't restart even after raising the temp up to 26C. I tried agitating the fermentor, nothing. About 4 days passed - still 1021. I thought i'll dry hop and cross my fingers. About an hour after dry hopping, low and behold, the airlock is bubbling again.
I have noticed a similar uptick in fermentation after dry hopping on a few other occasions, but not quite so stark as this time, where i'm absolutely convinced it was the dry hops that re-started the fermentation.

Has anyone else had this experience? I'm assuming it must be happening through oxygen getting in with the dry hops.

I have heard about this phenomenon before. It usually turns out to be hops providing a nucleation point for CO2 to evolve from. The test is a gravity check a day or so later. Doesn't necessarily account for the difference in the two hops, so that is interesting. Let us know.

[MTW]

I agree that the airlock is no sort of sign; it's the gravity that matters.

However, the diastatic activity of hops and the presence of maltase in them, has been shown to create further fermentation after dry hopping. Here's a link to the research, which is very old:

http://onlinelibrary.wiley.com/doi/10.1 ... 6070.x/pdf

BTW The Ardennes yeast (WLP 550/WY3522?) is usually a monster, so if it's getting stuck at 1.021 you should probably review your process.

[Aaron]

I didn't aerate the wort, just chucked the yeast in, which may account for the stall. The yeast was healthy as it was freshly harvested from the krausen of a prior brew. I'll update when I take a gravity reading. Cheers.

[TheSumOfAllBeers]

Some yeasts stall, for a few reasons like underpitching or lack of aeration. Some fickle yeasts will also stall if CO2 becomes too concentrated.

Dry hopping can alleviate this by :
- nucleation, which will agitate and remove some CO2
- o2 introduced with hops
- diastatic power of the hops