Worried about airlock suckback in plastic carboy

[Matt3189]

I have noticed that the water in my plastic carboy filled with apfelwein has slowly started creeping back to the point where it looks like it may be sucked back in soon... Should I remove the airlock and replace it or is this a normal occurance? I am assuming this ahs something to do with using a plastic carboy because I have never had this problem with my glass carboy.

If this means anything the apfelwein has been in there for 2 1/2 weeks...

Thanks!

 

[UpstateMike]

I have noticed that the water in my plastic carboy filled with apfelwein has slowly started creeping back to the point where it looks like it may be sucked back in soon... Should I remove the airlock and replace it or is this a normal occurance? I am assuming this ahs something to do with using a plastic carboy because I have never had this problem with my glass carboy.

If this means anything the apfelwein has been in there for 2 1/2 weeks...

Thanks!

Suckback is one of the reasons some people fill the airlock with vodka instead of water. I wouldn't worry too much about a little water getting in your cider though. I would be worried about air, so I don't suggest removing the airlock. Just make sure you have the correct amount of fluid in it.

 

[zeg]

This can happen in any fermentor if the temperature drops. The contents of the fermentor contract, lowering the pressure inside, causing suckback. I'd actually expect (perhaps naively) that if it makes any difference, this would be a bigger effect in a rigid fermentor (like a glass carboy) since a flexible vessel can squeeze itself slightly, taking some of the pressure off the air lock. In any case, I'd think the air lock would suck back long before such a deformation was significant.

The vodka in the airlock is one way to mitigate this. If you're using a 1-piece S-shaped airlock, you can avoid this by never filling past the max-fill line. That is a level low enough that all of the liquid will fit comfortably in either one of the bubbles, so the airlock can run in either direction without liquid escaping. (This is only true for gradual pressure changes, if you do something sudden like lift the carboy, it can suck or blow hard enough that liquid will be expelled before it can bubble.)

I don't know how well other types of airlock handle this, I seem to recall that one-piece airlocks are better than the others at this, but I'm not sure.

 

[Matt3189]

If you're using a 1-piece S-shaped airlock, you can avoid this by never filling past the max-fill line. That is a level low enough that all of the liquid will fit comfortably in either one of the bubbles, so the airlock can run in either direction without liquid escaping. QUOTE]

I am using the 1 piece airlock, I didnt know that was why the max lines were there, good to know!

Would I not have to worry about air passing through the water back into the carboy, even if no water is coming back through? Wouldnt this have a similair effect as taking the airlock off?

Thanks for the help!

 

[zeg]

The chances of having a problem from the air sucking back are extremely small. It's safer than removing the airlock (in a relative sense, anyway; neither is a very big risk for a short time). There's not a whole lot of air going in and out (each burp is something like an mL of air), so oxidation is a miniscule concern. As far as contamination goes, it's extremely unlikely any airborne particles would make it around the bends in the airlock and also not get trapped in the liquid. If you remove the airlock, there's more chance of dust falling in.

But there's really nothing significant to worry about. I'd let it run backward simply to opening things up, because the biggest risk in any of these scenarios is that the brewer does something stupid and drops something into an open fermentor.