Hi guys, after many years of homebrewing I recently have noticed this issue : I have always used the left model of airlocks until yesteday that I set an airlock like the one of the right, then when I put the secondary fermenter inside a glass door fridge I figured the airlock starts to work backwards, I mean the alcohol fills the inner little vessel of the airlock and bubbles air inside the carboy. I am abosolutly ignorant in regards physics so I would like someone to give an explanation , I think could be something regarding sudden temperature change but I don´t know how this air is expelled to avoid oxidation. I guess it has always been like this , the difference now is just I could see the moment when this takes place.
When the temperature drops, so does the pressure. This creates a vacuum, and since the carboy is not sealed, air is drawn in to balance the pressure with the outside. There isn't a good way to avoid it other than cold-crashing in a sealed container like a keg. Personally, I gradually raise the temperature throughout fermentation and conditioning to avoid this issue, then cold crash in the keg or in bottles once carbonated.
If the fermenter is cooled after being sealed, the gas(es) in the fermenter will contract, tending to suck air in from outside. Is any fermentation still occurring? Is so, the release of CO2 as the some fermentation continues will tend to ‘scrub’ the air (oxygen) out of the fermenter. If no fermentation is occurring then air (oxygen) is indeed entering and staying when this suck back condition is occurring. Cheers!
Yes, unfortunately it is possible that the air (oxygen) will accelerate oxidation processes and thereby premature staling. if you drink your beer quickly you will likely not notice these effects. As @CurtFromHershey posted above, it is beneficial to cold crash in a sealed vessel (e.g., a keg, bottles, etc.) since this eliminates the possibility of suck back (air getting into the vessel). Cheers!
I have never had this matter very clear in my mind, I have always thought oxidation would occur if air gets into beer when a splash takes place but not just because there is beer in contact with the air(like the air in the bottle space)
But if you have a layer of air (oxygen) on top of the beer some of those oxygen molecules will dissolve into the beer. The action of splashing will most certainly accelerate the amount (rate) of oxygen diffusion into the beer but by just simply allowing air (oxygen) to contact the beer this will happen as well. The other thing to keep in mind is that oxidation processes (i.e., the process that creates stale flavors such as cardboard) take time; it does not happen the moment that oxygen gets into the beer. That is why I mentioned that if you consume your beer quickly you might not even notice this effect. How long it takes for oxidation processes to become perceptible flavors is a function of many things: How much oxygen is in the beer (e.g., the Dissolved Oxygen level in units of ppb) The temperature of the beer (warm temperatures accelerate oxidation processes) The style of the beer (e.g., AALs seem to 'showcase' staling flavors more quickly) etc. Cheers!
MacGyver probably would have come up with some way to avoid this issue without having to use a sealed container. Here's a thought: If you know ahead of time that you're going to cold crash with the airlock still in place, put vodka in the airlock and then put a baggie over the airlock to trap escaping CO2 for a few days, then put the entire fermenter and the baggie with airlock, into the refrigerator. Hopefully the suck-back air will then be CO2 from the plastic bag. Anyone have any thoughts about whether this is realistic?
That would help get rid of some O2 in the headspace that hasn't yet dissolved into the beer. But how would you do the purging? In a non-pressurized system, you'd never rid of all the headspace O2 that's already in the headspace.
Your event has already occurred, so I was just suggesting this idea to the community for comments for future use to see if it is realistic. For now, I don't think the baggie idea will do you any good.
Personally, I wouldn't bother. A visual analogy: Take a bucket filled with red Kool-Aid, insert a garden hose, and turn it on. How long until the bucket contains just water?
In other words, you could push CO2 into the unpressurized fermenter all day long, but it wouldn't push out all of the O2.
This happened to me for the first time this year. When I soured my wort, and placed the fermenter in a fridge to control the heat, the airlock began sucking air in. It eventually started pushing out the correct way, but for a while there I was thoroughly confused.
