Temp Control, Airlock ... Possilbe Oxidation Problem

[cosmo]

Just wanted to share what I noticed so others can avoid a possible problem. I was looking at my airlock bubbling yesterday and noticed that it was bubbling in reverse! Air was being sucked in instead of CO2 blown out! I noticed that it went back to normal after the temp controller cycled off. Apparently, each time the temp controller cycles on, it cools the headspace enough to cause the airlock to pull outside air in. It was bubling in reverse about once every few seconds for maybe a minute or two. I would think that as this happens continuously, a lot of air gets into the fermenter over time. I can see this because I am using a fermentation chamber with a hole in the lid that just lets the neck of the fermenter stick out. I use a 6 gal Better Bottle with 5.25 gal of beer, so that's 3 quarts of headspace. I don't know if this would be a problem with buckets or glass carboys. It probably depends on the headspace size and the insulative properties of the fermenter. The wall thickness on the Better bottle is quite thin, so maybe that is a big factor. My temp controller turns on/off with a 1F differential. The controller probe is taped to the fermenter with layers of paper towel and duct tape for insulation. Other than this problem, my temp control has worked flawlessly for years. For those with chest freezers or refrigerators, you might not notice this problem if you can't see the airlock while it is running. I usually switch from blow off tube to 3 piece airlock after fermentation slows down. I don't know how much this affects the beer. It may explain a slight oxidative flavor I ocassionally get. From now on, I'm keeping my blow off tube on until I rack to secondary or keg. Just a heads up.

 

[Hackrsackr]

So the top of the fermenter is out of the chamber? Wouldn't that be the cause of the suction? If the ambient air around the airlock would cool at the same rate as the head space( or close to the same rate), then it would dramatically decrease the pressure differential created between the two. Just a thought. We need someone with a glass door chamber to do some checking on this phenomenon for us! Great observation!

 

[Boleslaus]

Yea I would think that this could only happen if the entire fermenter wasn't inside the chamber. Theoretically, if it was totally enclosed, the air surrounding the fermenter would cool slightly faster or at the exact same rate as the air in the headspace, which means either a favorable pressure differential or no change in pressure.

 

[TopherM]

Either way, CO2 is heavier than O2, so the O2 sucked into your fermenter would stay on top of the CO2 layer and would never touch or oxidize your beer.

 

[cosmo]

Yea I would think that this could only happen if the entire fermenter wasn't inside the chamber. Theoretically, if it was totally enclosed, the air surrounding the fermenter would cool slightly faster or at the exact same rate as the air in the headspace, which means either a favorable pressure differential or no change in pressure.

The ambient air pressure inside the chamber is exactly the same as it is outside the chamber. The pressure is equal inside and outside the chamber since it does not have an airtight seal. The pressure differential exists between the ambient air and the air in the headspace. When the headspace cools down the gasses in the headspace contract. The lower pressure in the headspace pulls ambient air in through the airlock. It doesn't matter whether the airlock is inside or outside the chamber because the pressure is the same. We see this all the time even more dramatically when people have suckback when lagering.

 

[cosmo]

Either way, CO2 is heavier than O2, so the O2 sucked into your fermenter would stay on top of the CO2 layer and would never touch or oxidize your beer.

That is partially true and does help to prevent oxidation. However, there is diffusion and the laws of partial pressure which will allow some of the oxygen to get to the beer. The question is how much. I don't think this totally eliminates the concern especially over periods of days or weeks when fermentation is slowed and little or no C02 is being produced.

 

[Boleslaus]

The ambient air pressure inside the chamber is exactly the same as it is outside the chamber. The pressure is equal inside and outside the chamber since it does not have an airtight seal. The pressure differential exists between the ambient air and the air in the headspace. When the headspace cools down the gasses in the headspace contract. The lower pressure in the headspace pulls ambient air in through the airlock. It doesn't matter whether the airlock is inside or outside the chamber because the pressure is the same. We see this all the time even more dramatically when people have suckback when lagering.

If the headspace and the ambient air inside the fermentation chamber cool at the same rate though, how can there be a pressure differential? I would think the only way there can be a pressure differential is if the system is open to air outside the fermentation chamber (ie. through an airlock), where pressure would be higher.

 

[Hackrsackr]

I guess I'm confused as to you chamber setup. Not sure how the warmer air above the air lock can not have a higher partial pressure than the cooling co2 in the headspace (some of which will be going back into solution) Pics would be great. Seems crazy that one degree differential setting would even cycle on for very long. Ive seen auction in an airlock but only during cold crashing where you're dramatically cooling the solution quickly. Still believe my confusion is based on your chamber set up. If its not air tight then what method of cooling are you using. Not doubting you at all. Would just like to wrap my head around it! Late fermentation o2 pick up is just plain awful! Unless you like cardboard I guess...

 

[cosmo]

Okay. Let's see if I can explain it better. It has nothing to do with the chamber setup except for the fact that I can see the airlock without disturbing anything. It would be the same as a refridgerator or freezer. In all cases, there is no difference in pressure inside or outside the chamber. If there were a difference, then air would rush in our out when you open the door or lid. The pressure can be the same even though the temperature is different.

Now on to the fermenter. Normally C02 gas is produced which causes gas to escape through the airlock by bubbling up through it. Assuming CO2 generation has stopped, the airlock will only bubble if you increase or decrease the temperature of the headspace. The beer will also expand and contract, due to temperature, but this is a much smaller effect so we can ignore that for illustrative purposes. When you heat up a gas, two things can happen; it can expand in volume or (if constrained) it can increase in pressure. The same is true in reverse. If a gas is cooled it can either contract in volume or decrease in pressure. If you periodically increase and decrease the temperature of the headspace, the gas will expand and contract pushing and pulling the liquid in the airlock in either direction. If this expansion and contraction is large enough, gas will be transported in both directions throught the airlock. This will happen regardless of the temperature surrounding the fermenter since it is always at the same pressure due to the fact that air is free to move into and out of the chamber (or refridgerator) without any restriction.

As I explained earlier, I don't know how much of a problem this is, but I just wanted to make people aware that it can occur and may possilby have an effect on the finished product (YMMV).

Hopefully that helps. Sorry for the long drawn out explaination.

 

[Hackrsackr]

Ok yeah I get the ideal gas law and all, but I don't get how you can have a gas constricted by an air lock decrease in temperature but not pressure. If the temp of the gas in the headspace decreases it will decrease in volume AND pressure.

Also, I've never seen air sucked though the water of an air lock. If there would be a suction created, then wouldn't it suck the water back first (assuming that the water level covers the holes of the inner piece)?

One last thing is in your OP you stated that co2 was still being produced, and pushing out through the lock. If that's the case the I would think that the co2 generation would be vastly greater than any suction force created by a one degree differential. Maybe I'm just dense and not getting it. However, if you can document this phenomenon and prove it, then I would assume that data would drastically decrease 3 piece airlock production. They basically have one purpose and you would be proving it an ineffective design.

Anyway I hope your occasional oxidative flavors disappear forever and the world is filled even more good beer.

Cheers!

 

[Wynne-R]

Good observation. I’ll bet this happens a lot, people just don’t see it happen. With the probe on the BetterBoy you’re cooling the beer a whoppin’ degree F every cycle. Your air temperature is going to be way more than one degree cooler than the beer when the compressor is running. It’s a lot easier to cool the gases in the headspace than the beer. The headspace is probably cooling something like ten degrees. The result, as you know, sucks.

You’re right about the partial pressure. Absent substantial out gassing from the beer, air gases in headspace will diffuse into the CO2 and then into the beer. My guess is that this process is really slow. Think about open fermentors.

Try moving the temperature probe higher up on the carboy to measure the gas rather than the beer. You should actually get tighter regulation that way, now that the fermentation is mostly complete. Your compressor will be running more often for shorter periods of time.

 

[cosmo]

Ok yeah I get the ideal gas law and all, but I don't get how you can have a gas constricted by an air lock decrease in temperature but not pressure. If the temp of the gas in the headspace decreases it will decrease in volume AND pressure.

The volume in the fermenter is relatively fixed. As the pressure drops, air is pulled into the fermenter.

Also, I've never seen air sucked though the water of an air lock. If there would be a suction created, then wouldn't it suck the water back first (assuming that the water level covers the holes of the inner piece)?

This is what I saw. No speculation here. Those with better bottles and 3 piece air locks will tell you that if you squeeze and release, air can bubble both ways. Not all of the liquid in the airlock gets sucked into the fermenter. You can try it yourself. put an airlock on an empty beer bottle or flask. Put it in the fridge. You will see maybe some but not all of the liquid gets sucked in along with some air. Then take it out of the fridge and watch as it warms up. Since there is now more air in the bottle, as it expands it will bubble out again. You can keep repeating this as many times as you want and still have liquid in the airlock.

One last thing is in your OP you stated that co2 was still being produced, and pushing out through the lock.

Here is what I said:

I usually switch from blow off tube to 3 piece airlock after fermentation slows down.

Obviously the heating/cooling effect is enough to overcome the miniscule amount of C02 being produced. This is what I saw. You are right that it will only occur once fermentation is done and CO2 generation is very small. After noticing this, I moved the fermenter to a cooler with a small frozen ice bottle in it to keep the temperature relatively constant 68F for a long period of time. At that point the airlock was bubling about once every 120 sec.

If that's the case the I would think that the co2 generation would be vastly greater than any suction force created by a one degree differential.

there is much more than a one degree change in air temperature when the beer temperature is being controlled to within 1 degree. For example, when controlling the temp to 68F, just before the cold cycle kicks on, the air temperature is probably close to 68F or maybe a little higher. Then, when the thermostat trips the cold cycle on, cold air at about 32F comes out of the cold side until the beer tempeture drops back down enough to trip the thermostat off. So the air temperature differential between cycles is about 32F. A chest freezer may have a higher temperature variation since it is designed to go way below 32F. I don't have a chest freezer so I'm just speculating on that. The headspace temperature is probably not cycling that widely, but I'm sure it's significantly over 1 degree.

However, if you can document this phenomenon and prove it, then I would assume that data would drastically decrease 3 piece airlock production. They basically have one purpose and you would be proving it an ineffective design.

I wouldn't go that far. Everyone's setup is different and I only saw it happen on mine. In my OP I said I didn't know if this is a problem and YMMV. I just wanted to point out that it is possible and I think people should be cognizent of it. I didn't know it could even happen until I witnessed it for myself and gave it some thought. My solution for my system is to keep the blowoff tube on until I rack to secondary and then put the airlock on. Believe me I have nothing against airlocks.


Thanks to all that contributed to this thread, It helped me think through what was happening. Fun stuff.

 

[free]

Hello- I have the SS brewtech chronical and 6 days into brewing / fermenting a pumpkin ale I'm noticing the same problem: with slowed but still ongoing primary fermentation -- when the temperature control system cycles on it sucks air In. Now- when it cycles off it goes back to bubbling co2 every 45 sx or so. So I'm not worried TODAY. My question is: as I typically like to patiently ferment and allow longer sit times in what would be considered secondary fermentation-- once the normal fermentation has reached terminal, do I even need to worry about temperature control if the highest my house would get would be the mid 70s ? I set the control to ferment at 68 degrees-- but if I do t want to keep sucking oxygen in to the tank once fermentation has generally stopped, do I risk more to turn the ftcs off? Or to leave it running and continue to suck outside air in ?

 

[Dcpcooks]

Hello- I have the SS brewtech chronical and 6 days into brewing / fermenting a pumpkin ale I'm noticing the same problem: with slowed but still ongoing primary fermentation -- when the temperature control system cycles on it sucks air In. Now- when it cycles off it goes back to bubbling co2 every 45 sx or so. So I'm not worried TODAY. My question is: as I typically like to patiently ferment and allow longer sit times in what would be considered secondary fermentation-- once the normal fermentation has reached terminal, do I even need to worry about temperature control if the highest my house would get would be the mid 70s ? I set the control to ferment at 68 degrees-- but if I do t want to keep sucking oxygen in to the tank once fermentation has generally stopped, do I risk more to turn the ftcs off? Or to leave it running and continue to suck outside air in ?

Just use a blow off tube. You never want 02 post fermentation