View Full Version : Really stupid mistake (aeration & stuck fermentation)

01-21-2015, 09:08 AM
So, I noticed that my 25 L batch was starting to slow down (OG 1.092, SG 1.080) significantly, and I felt that it was on its way to becoming a stuck fermentation. The must I made comprised of water and honey. DAP was added regularly to compensate for the lack of nutrients in honey itself.

To prevent this, I have read that the must needs to be oxygenated, but such a thing is inadvisable during towards the end of the natural fermentation cycle. I decided to stir up the must for a few minutes and noticed tons of bubbles getting up into the surface (maybe degassing from accumulated CO2?). When I put the lid back on the fermenter, I waited for the airlock to start bubbling. Nada. I waited another half hour, and I saw that the water in the airlock actually retreated a little bit, but still no cigar.

Is this normal? Or did I just kill my fermentation by stirring the must up?

01-21-2015, 09:38 AM
OK, so I just checked my fermenter again, and it's bubbling like it did yesterday. It's just ever-so-slightly slower, but I predict that the speed will pick up a bit more over time. I am thinking that this lack of bubbling was caused by the fact that the lid on the fermenter is made of flexible polypropylene. This means that I had to wait a while before calling "Time of Death" so that the CO2 emitted by the fermentation process may accumulate enough to warp the plastic sufficiently that the gas will start pushing the water in the airlock. I have no idea whether what I said makes any grammatical sense.

bathtub brewer
01-22-2015, 01:43 PM
Well I don't know how things go for others, but I tend to see a significant slow down in fermentation after about 2 weeks. I don't worry about it. It will take some time to re build the pressure required to move the water in the air lock after you stirred.

Chevette Girl
01-23-2015, 01:13 AM
Regular stirring is good in general. I don't think it can kill your fermentation.

Aeration (like stirring, but splashy) for the first 1/3 to 1/2 of a fermentation is good, so you're fine until your SG is between 1.060 and 1.046, then you'd want to go back to just stirring.

What you do by stirring it is degassing, which will effectively knock a bunch of the CO2 out of solution (like stirring a carbonated beverage, it fizzes a bit then goes flat), so it takes a while after you've degassed it before the yeast can produce enough CO2 that it has to escape from the must and out your airlock.

In particulr to your fermentation, how long has it been going?