High temp fermentation suck back

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gan

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Hey guys, I have a saison in the ferm chamber right now set at 90F, and I have to continuously top off the airlock with vodka because every time the heating function cycles, the airlock sucks back into the wort. I think my issue lies in the fact that I have the temperature sensor insulated against the carboy so it's measuring the temp of the liquid and not the ambient temp of the ferm chamber. The heater stays on for a while until the wort warms up enough, but the ambient temp must get pretty high during that time, creating a pressure differential between the chamber and the headspace and forcing the suck back. My ferm chamber is just an old mini-fridge with a hair dryer set on low for my heat source (and obviously the fridge's cooling system as the cold source).

A few primary questions/observations:

1. I'm not entirely convinced that setting the temp sensor to read the chamber's ambient air will make a big difference here. There would still be a decent temperature/pressure gradient between chamber air and headspace air, and I imagine suck back would still occur. Does anyone have any familiarity with temp sensor placement and this issue?

2. I don't think I could just use a rubber stopper or piece of foil or something like people do when cold crashing, since I'm raising the temps during fermentation. I guess foil would potentially work, but then during the hot cycle it would just be pushing all that oxygen back in (although that's essentially what it's doing now...).

3. For people that don't experience this: do you use a different heat source? I bet a carboy belt would not cause the same problem but I'm trying to keep the ferm chamber system as cheap as possible and we had a spare hair dryer on hand.

4. :pipe: Epiphany: If I put a piece of insulated foam to separate the neck of the carboy and airlock from the bulk of the carboy (and hair dryer), would that solve my problem?

Lend me your thoughts and personal solutions!

Cheers,

Gan
 
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gan

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Very clever, I had no idea those existed. Thanks for the tip!
 

acidrain

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You must be using a three-piece air lock. Those are for wine. Try using an S shapes one.
 
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gan

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I can see how the S-shaped airlock (and the foam stoppers, obviously) would limit liquid suck back into the beer, but both options still allow oxygen through. Now that I'm really thinking about it, I don't care about a couple of ounces of vodka getting into my beer, but I am a bit worried about oxygen getting in there. So, a couple more pertinent questions:

Is the amount of oxygen getting in something to worry about? Currently it looks like a fair amount bubbles through every time the hair dryer cycles on, so I don't think it's negligible. (glad I'm using WLP500 since the fermentation just started back up and is hopefully eating any oxygen that gets into the beer)

If so, what's the best way to minimize the pressure differential between the ferm chamber atmosphere and the carboy headspace--should I just suck it up and buy a brew belt? How high can a brew belt effectively raise a ferm temp? I'm in SD so ambient garage temp is usally around 65, as low as 55.

Cheers,

Gan
 

IPA-Hole

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Generally speaking, it's safe to say that any O2 getting in there would be sequestered to the top of the fermenter; CO2 being heavier would blanket and protect the wort/beer.
 
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