fermentation stalling

[Booker140]

Hi Everyone,

I'm making 2 new batches of cider one my own recipe and one from this site.
I have both in a 6Gal carboy and after about 2 weeks fermenting they both stop bubbling. The temp is about 15C; so I know I'm not cold crushing them.
I read on one of the posts that the head space during the fermenting stage doesn't matter too much but I'm wondering if that might be the problem. Both are a little bit below the shoulder of the carboy. Could fit another 1/2 Gal. I know if I shake them they will bubble for a bit and then stop completely again. My previous batches had the same amount of head space and fermented right out no problem. Any ideas?

Booker

 

[MarkKF]

Once fermentation slows you have to eliminate headspace. Either transfer to a smaller vessel or top off.

 

[Revvy]

Stopping bubbling doesn't mean fermentation is stalled... an airlock is NOT a fermenation gauge, it's a VENT to bleed off excess Co2. As fermentation slows down from the initial concentration of sugars that the yeast are orgying on, less EXCESS co2 is produced, meaning it doesn't need to VENT... But that doesn't mean that there's not still fermentation going on.

Gas expands and contracts due just as much from environmental reasons such as a change in temp or barometric pressure as from anything being wrong. It often stops or starts because the dog tried to hump the fermenter, or the vacuum is running OR a truck drives by and disturbs any trapped co2 in the trub at the bottom....If you look at an airlock for what it is, a vent, then you realize that all an airlock bubbling means......


Is that an airlock is bubbling. *shrug*

If you live in most of the United Sates, you experienced an unseasonable WARM UP over the weekend which could very easily result in gas expansion in your fermenter or secondary...In other parts of the states you had storms, which meant a change in barometric pressure...It was an active weekend weather wise.


Ciders, wines, meads, have a LOT of fermentation to do... they do a lot initially, but then the it slows down... and may take weeks to finish out... with nary a blip....


The ONLY "fermentation gauge" is taking a grav reading. That will tell you more of what is going on than what a cheap piece of plastic will ever do.

 

[Scrumpy!]

Wait for dark or turn off the lights in a closed room then shine a flashlight through your cider. You will likely see a steady stream of bubble rising even when fermentation is nearly finished. The headspace in your carboy is so large, changes in temp and atmospheric pressure will mask any pressure generated by fermentation at the end of the cycle. Large headspace also puts your cider at risk of oxidation or contamination. Top up your carboy with fresh juice until it gets to the neck or rack to a smaller carboy (5 gal?).

 

[GeneDaniels1963]

I recommend getting a refractometer and using it for testing SG. They only cost $20-30, and they take only a tiny sample to test the wort. I know they are not as accurate as a hydrometer, but they are more than close enough for home brewing. There are several online sites to converter the BRIX reading to SG. I use one from NorthernBrewer: https://www.northernbrewer.com/learn/resources/refractometer-calculator/