View Full Version : Airlock backflow

01-30-2010, 03:24 PM
I'm relatively new to mead making (mostly a beer brewer), but have pulled off a couple fairly successful batches.

I have a batch going right now that's about 7 weeks in and just now I noticed that the airlock was actually sucking the water backwards into the carboy. there's probably 2 1/2 gallons of mead in this 3 gallon carboy, and I've racked it twice since I started, though it's been a week or so since the last racking, but I haven't mucked with it in any other way. I purged the new carboys with CO2 before each racking. The original gravity was 1.099 and the fermentation was fairly quick and the mead has already cleared a couple weeks ago and been steady at 1.004 so it's more or less ready to be bottled (which I'll hopefully do in this coming week)

The question is, what would cause the pressure to reverse like that and is there anything I should do to make sure it hasn't been contaminated?

I'm planning to make it sparkle, so I'm not planning to stablize it with anything so I can bottle condition it. I always sanitize my airlocks when I rack and use clean water in them, but by now (a week or more since the last rack) I wouldn't consider them totally sanitary. The only reason I can come up with is that slight temperature fluctuations cause it to push air out when it's warmed up and hence suck back when it cools (the carboy is at the mercy of our home's thermostat, though it doesn't fluctuate much: 61-65 degrees). But this seems like a somewhat week hypothesis.

Oh, and the style airlock I'm using is the kind with the little inverted cup sitting on top of the air tube. If that matters at all. And the recipe was a simple 7 lbs wildflower honey boiled briefly with a little grapefruit juice for acidity and some yeast nutrient and redstar champagne yeast.


Medsen Fey
01-30-2010, 03:42 PM
Welcome masterhaleco!

The suck back question is easy - You have a large space in your fermenter with a gas (CO2) that not only shrinks, but also dissolves more readily into solution at colder temps. That will create a reduced pressure inside the carboy that may suck liquid or air in.

You also have a fermentation that hasn't quite finished - it should be bone dry with a gravity less than 1.000. You may want to take it someplace a bit warmer to finish before you prime and bottle it, otherwise you may not only have bottle fermentation of the sugar you add, but also of the remaining sugar at 1.004. That extra sugar is enough to create potential bottle bombs.


01-31-2010, 04:55 AM
Thanks. I figured that might be the case, but I didn't think about the CO2 being absorbed back into the liquid. I just wanted to make sure there isn't some contaminant in there that might cause that effect. But your point about the incomplete fermentation is on my mind. Since I'm used to brewing beer, I'm used to bottling whenever the gravity stabilizes and the beer clears and never usually see gravities below 1.010. This gravity has been steady for over a month so I just figured it was done. Think maybe I'll post for some advice in the newbie section about knowing when it's done. A warmer place isn't really an option til summer comes.

Medsen Fey
01-31-2010, 09:53 AM
A warmer place isn't really an option til summer comes.

Brewbelt? Heating pad? A spot closer to the furnace?

01-31-2010, 12:26 PM
I've got it near a radiator now, but I didn't want to put it too close as I figure the fluctuating temperatures of going off and on would be detrimental. I was hoping to avoid purchasing more equipment, as my homebrew equipment budget is significantly in the red, but that may be the way to go.

01-31-2010, 03:56 PM
Isn't it amazing how temperatures can fluctuate between spaces as far as 3 or 4 feet?

Last night my wife had her beer against one wall and my mead was against the adjacent wall. The carboys are only about 4 feet apart. When we checked our brew's respective temps her's was about 3 degrees higher than she wanted it to be and mine was 2 degrees colder than I wanted it to be. We switched the carboy's places and mine went up to where I wanted it and hers went down to where she wanted it.

It was later that I really thought about it and I realized that we have a radiator against the wall in the room next to our brew-room. Having the radiator against the wall, in the other room, is enough to change the temp by 2-3 degrees.