Blow-off Tube vs Air Lock

[A1sportsdad]

Okay, so I ran into something I had not considered. I switched over from using an air lock to using a blow-off tube. I did it originally because I had an overactive fermentation that blew off the lid and had krausan all over when I woke in the morning. Ever since then I have only used a blow-off tube. Works just as well and much better in the case mentioned above.
The problem I ran into recently caught me off guard. I recently started doing temperature control on my fermentation, so I was able to do a controlled 64 F fermentation then I sent it up to 69F for an diacetyl rest. In the process the temperature would cycle up and down and I imagine the air space temperatures in the fermenter probably cycled even higher and lower as this space would change temperature faster than the volume of wort. The head space would expand and contract a lot more being a gas. All of this expansion and contraction, with the production of CO2 from active fermentation being over, caused a lot of the water in the blow-off reservoir to suck up into the blow-off tube and into the fermenter. The amount of water sucked up would increase with increased head space since you would have more volume of gas expanding and contracting.
It kind of left me wondering the best way to deal with this. I thought maybe I start with the blow-off tube and once the really active fermentation is over, swap it out for an air lock, but I am still going to have the issue of the expansion and contraction, so it will still draw in air, so now I have to worry about oxidation. I suppose the best thing I could do is just skip the diacetyl rest, but I really wanted to give it a try. Anybody have any thoughts on the issues.

Thanks

 

[videojunkie1208]

Are you ramping the temperature daily? or are you doing several days at 64*F, and then slowly raising it to 69*F for a final diactyl rest?

 

[Nate R]

Wouldn't it still suck back from the air-lock? Until the little bit of starsan was gone, then it would just suck oxygen?

 

[Jag75]

Going from 64 to 69 shouldnt create suckback

 

[jack13]

^yes.

Also, fermenting at 64F will not result in diacetyl, so you don't need to do a d-rest.

 

[videojunkie1208]

Going from 64 to 69 shouldnt create suckback

Wouldn't raising the Temp create more volume of gas? unless I am not remembering basic physics right.

 

[Jag75]

Wouldn't raising the Temp create more volume of gas? unless I am not remembering basic physics right.

I'm no science guy but the warmer it gets it will expand , the colder it contracts . This is why people who cold crash have to be set up for it .

 

[RM-MN]

Your beer only needs temperature control until the fermentation dies down. After that you can just take the fermenter out of the controlled space and let it rise to room temp. No suckback that way.

http://www.brewgeeks.com/the-life-cycle-of-yeast.html

 

[A1sportsdad]

Are you ramping the temperature daily? or are you doing several days at 64*F, and then slowly raising it to 69*F for a final diactyl rest?

Just a ramp after about 5 or 6 days of fermentation. Then left there for the duration, but the temperature does fluctuate as I have to heat to get to 69 F (in my basement). I have it in a minifridge with a heater as well. If it hits 70F the fridge turns on. At 68F the heater turns on.

 

[A1sportsdad]

Wouldn't it still suck back from the air-lock? Until the little bit of starsan was gone, then it would just suck oxygen?

Yes, that's why I'm concerned. Either way I get the oxygen, but with the airlock I only get limited liquid sucked in.

 

[A1sportsdad]

Going from 64 to 69 shouldnt create suckback

The problem is when you cycle to your high temp and I will guess the air may get up to 72 or 73, then you cool back down. That's when you create the vacuum in the fermenter and suck back into it.

 

[A1sportsdad]

Wouldn't raising the Temp create more volume of gas? unless I am not remembering basic physics right.

Certainly, but you overshoot some and cool back down. That's when you create the vacuum.

 

[A1sportsdad]

Your beer only needs temperature control until the fermentation dies down. After that you can just take the fermenter out of the controlled space and let it rise to room temp. No suckback that way.

http://www.brewgeeks.com/the-life-cycle-of-yeast.html

Yes. I will probably do this in the future. I was trying to eek out a few more degrees with the heater.

 

[A1sportsdad]

^yes.

Also, fermenting at 64F will not result in diacetyl, so you don't need to do a d-rest.

It was more of an experiment. I had heard John Palmer say that even with ale temps it still has benefits to help clean things up. Probably will not do it in the future. I'll probable just take it out of the fridge at that point.

 

[Jim R]

I don't think it is an issue with a 4-5 degree temperature change for a diacetyl rest (ie going from 69 to 65 degrees as you cool back down). When I use some of the formulas posted here for calculating the volume and pressure changes for cold crashing (ie going from 65 degrees to 35 degrees for several days), the amount of suck back from a 5 degree change is a small fraction of the change with cold crashing. Depending on your fermenter headspace, the difference would be something like a volume change of 1-2 oz for 5 degrees compared with 12-30 oz for a prolonged 30 degree temp drop for a cold crash. Maybe just using a wider and longer blow-off tube for safety would compensate for this small 1-2 oz volume change.

Practically, I don't think I have seen any Star San suck back with my 5 degree dactyl rests but I have seen a 1 quart suck back with a fermenter cold crash. I learned that lesson the hard way and now cold crash in my keg.

I also don't think there is anything to lose by doing a dactyl rest for ales. I do it slowly in my mini refrigerator by adjusting my temperature controller slowly.

 

[RM-MN]

It was more of an experiment. I had heard John Palmer say that even with ale temps it still has benefits to help clean things up. Probably will not do it in the future. I'll probable just take it out of the fridge at that point.

Warming the beer at the end of the fermentation does help clean things up but diacetyl isn't the major item to clean up. Acetaldehyde would be more likely to need cleaned up in an ale. Diacetyl rests are used for lagers where the fermentation temperature is lower.

 

[Nate R]

All of the above are great excuses to go blow some MORE money on this obsession/hobby and get a pressureable fermenter!!!

 

[A1sportsdad]

I don't think it is an issue with a 4-5 degree temperature change for a diacetyl rest (ie going from 69 to 65 degrees as you cool back down). When I use some of the formulas posted here for calculating the volume and pressure changes for cold crashing (ie going from 65 degrees to 35 degrees for several days), the amount of suck back from a 5 degree change is a small fraction of the change with cold crashing. Depending on your fermenter headspace, the difference would be something like a volume change of 1-2 oz for 5 degrees compared with 12-30 oz for a prolonged 30 degree temp drop for a cold crash. Maybe just using a wider and longer blow-off tube for safety would compensate for this small 1-2 oz volume change.

Practically, I don't think I have seen any Star San suck back with my 5 degree dactyl rests but I have seen a 1 quart suck back with a fermenter cold crash. I learned that lesson the hard way and now cold crash in my keg.

I also don't think there is anything to lose by doing a dactyl rest for ales. I do it slowly in my mini refrigerator by adjusting my temperature controller slowly.

Well, I had a gallon and a half of head space and I really have no idea how warm the head space got since the temp probe is in the wort, so maybe I got much warmer than I thought. I'm also not sure how much or if any actually got sucked in. When I noticed, the tube was full of water. It's 1/2 inch silicone tubing about 3-4 ft long. If it didn't actually suck into the fermenter, then it was really close. In the future, I will just let it warm up naturally as warm as it will get.

 

[Jim R]

I usually adjust my Inkbird temp controller by 1 degree every few hours or so when I am making temperature changes up or down. You are right that you can easily be chasing your tail where the wort is changing temperature very slowly but the refrigerator is going full bore at 30 degrees or the heater is at 80-90 degrees. Changing 1 degree at a time should minimize this and is probably even better for the yeast health.

 

[ncbrewer]

This thread discusses suck-back: https://www.homebrewtalk.com/forum/threads/suck-back-from-blowoff.642598/

 

[A1sportsdad]

This thread discusses suck-back: https://www.homebrewtalk.com/forum/threads/suck-back-from-blowoff.642598/

That is brilliant. I was trying to think up something similar to break the suction without letting in oxygen. Gonna have to make one of these up. Thanks for the link.