8 replies to this topic

[SchwanzBrewer]

https://beerandwinej...form-a-blanket/

 

 

The blanket of CO2 atop an active fermentation is not a solid barrier. Gas diffusion is occurring constantly as CO2 diffuses into the air above it and oxygen (and nitrogen) dissolve into the region of high CO2 concentration. And, of course, a strong air current can blow this blanket away. It is the fact that CO2 is constantly being replaced that keeps the “CO2 blanket” intact during fermentation and able to protect the fermenting liquid from the vast majority of the oxygen exposure it would have suffered, if it had not been fermenting.

 

When I was using the plastic barrels to ferment 10 gal batches I was having a problem with appears to be acetaldehyde. It's was really annoying. I wasn't always prudent with getting the beer out of the fermenter very quickly after it was done fermenting and after it was cleared. I wonder if I was having air lock problems and was getting air intrusion into the fermenter post fermentation which was oxidizing the beer and during the clean up stage while there was still some active yeast, turning the ethanol back into acetaldehyde.

 

The last batch I fermented at home I used a big mouth bubbler, and I used vodka in the air lock instead of starsan. I ended up with acetaldehyde again. I let that one stay in the chamber longer than it should have and the vodka evaporated. This article suggests that the beer shouldn't be left in the fermenter because it has a CO2 blanket, when in actuality it doesn't after equilibrium has been reached - unless the air lock is true and there is no air left in the fermenter. Anecdotally this suppors what has happened to my beers over the last couple years at home.

 

I've not had any problems with acetaldehyde on the bigger system and I think it's because my air lock is better sealed and also because I slightly pressurize the fermenter (so I don't get a vacuum) and close it off completely when I cold crash.

[Big Nake]

In the past year or so, I have been a little slower to get my beer out of primary. I'm not trying to see if I can get some autolysis or other adverse condition, it's just happening this way. 4, 5, 6 weeks in the primary for some of these ales and lagers. I do check my airlock to make sure there is Starsan solution in there and my guess is that a well-fastened lid and a full airlock is going to protect me. I even have some buckets where the lids don't match up that well... the lid is securely on but it's like a loud burp might pop it off of there. I haven't had any issues with these batches from that prolonged time in the primary. I would think a dry airlock could cause a problem but I wouldn't be overly concerned about it.

[SchwanzBrewer]

In the past year or so, I have been a little slower to get my beer out of primary. I'm not trying to see if I can get some autolysis or other adverse condition, it's just happening this way. 4, 5, 6 weeks in the primary for some of these ales and lagers. I do check my airlock to make sure there is Starsan solution in there and my guess is that a well-fastened lid and a full airlock is going to protect me. I even have some buckets where the lids don't match up that well... the lid is securely on but it's like a loud burp might pop it off of there. I haven't had any issues with these batches from that prolonged time in the primary. I would think a dry airlock could cause a problem but I wouldn't be overly concerned about it.

 

The only other explanation I would have for my off flavor is some sort of contamination in or near my garage and in the fermentation chamber causing a local terroir.

[HVB]

You were using the red top fermenters correct?  I have been pretty lucky with them and I have not had an issue.  Most of the time I use an "S" style airlock and always have positive pressure on it.

[Big Nake]

I know you have experienced this before and I feel like I'm in deep water with this topic because I don't experience it. I just went and looked at the description again to see what would be causing it. I assume you're pitching large enough volumes of active, healthy yeast into well-oxygenated wort, right? Do you still use the "shake-the-bejesus-out-of-the-primary" method of aerating? Can you get your hands on an O2 setup and pick up a small O2 canister and try oxygenating the wort... or have you already gone down that road?

[No Party JKor]

I would think any tiny amount of O2 that's coming in during fermentation would be used by the yeast.  After active ferment you could certainly get oxygen in there if you aren't protected by the air lock.  I wouldn't expect this to be a huge issue though, unless where you have the fermenter is going through a lot of temp swings, causing it to 'breathe'. 

[SchwanzBrewer]

It didn't seem to matter. I was making starters, I was using filtered O2, I tried shaking, every beer was getting acetaldehyde. I changed out fittings, I threw out old hoses and got new ones, I threw out fermenters. Nothing mattered. The only thing I didn't try was closed transfers. I used a new autosiphon each time, I purged the kegs with CO2 prior to filling, I cleaned and sanitized the bejesus out of the kegs, still ended up with that flavor. Drove me nuts. It's one of the reasons I'm a complete sanitation freak when it comes to the bigger system. I don't leave hoses with fittings on them, I completely disassemble everything and clean it. If it's on the cold side it gets cleaned even more so. I break down valves and reassemble with new parts after a while, I boil some parts, basically anything to ensure the beer is it's best.

[Big Nake]

I only mention the O2 thing because everything I see says that you might get this flavor (notice I'm just trying to avoid spelling acedwuwoiw89hyde) when yeast is not at optimum health or is otherwise disrupted. Pulling the beer off the yeast too quickly was one issue mentioned. The yeast might produce this flavor but clean it up given the proper amount of time and the right temp. All of my beers sit at room temp for some amount of time after primary fermentation is complete. That includes "in the primary" and then again in secondary. This reminds me of an issue I used to have where I would take a lager out of primary (48-50°) and send it to secondary and directly to cold lagering without letting it warm up first. The resulting beers had a funny wine-like, medicinal flavor.

[SchwanzBrewer]

This is apple or apple and melon.