Oxygen Permeation and Fermentation Speed

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cdubbaya

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I have a question that I think I know the answer to, but who better to tell me I'm right or wrong than the best homebrew community on the interwebs?

So recently, we bought a stainless conical to serve as both a primary and secondary fermentation vessel. Previously, we've used buckets and carboys (both plastic and glass).

I've noticed that in our conical, fermentation takes much longer, sometimes an extra week or two for primary.

With the same amount of yeast, we've noticed our primary schedule for a light ale is:

- Plastic Bucket: 7-10 days
- Glass Carboy: 14 days
- Conical 14-21 days (dumping yeast every 4-5 days)

My guess is the length of fermentation has to do with Oxygen Permeation in each vessel?

Obviously the plastic bucket allows a bit of oxygen in, which would make the yeast move a bit faster through the sugars. The conical, on the other hand, is completely air tight, so after the initial 2-3 days of fermentation, CO2 would be the only gas left in the vessel.

Note - we do oxygenate the wort as it goes into the fermentation vessel, but I'm specifically referring to the time it takes for primary fermentation to end.

Any thoughts? Am I thinking about this too much?
 
I've never used a conical but I wouldn't think that there would be enough permeation through any of the vessel walls to make that much difference on fermentation. My "guess" would be that the shape of the chronicle may have more impact than anything. I'm only guessing so we will see what other posters say.
 
Oxygen permeation in all 3 vessels is so minuscule as to be practically nonexistent. My best guess is that you now have less surface contact with the yeast cake AND you are drawing off the yeast cake before it even gets rolling.
 
Holy guacamole, it takes you up to three weeks to hit your FG in your conical? There's something very odd going on here. A proper does of oxygen at the beginning is all that's really necessary. As others have said, permeation is trivial on this kind of scale.
 
I would guess that's an effect of pulling off the yeast every few days. You are removing the very things that converts wort to beer...of course that is going to muck with how fast it gets to FG.
 
Interesting, thanks for the replies. I was under the impression that oxygen permeation was a factor, due to the comments from others who brew wild ales. They say that leaving a beer in a bucket is a bad idea due to the oxygen that can get in versus a glass carboy, but maybe that's just for long-term storage?

I would guess that's an effect of pulling off the yeast every few days. You are removing the very things that converts wort to beer...of course that is going to muck with how fast it gets to FG.

I only pull the yeast that has already settled out, so that the trub and other stuff in there is gone. Blichmann says to dump the trub/yeast when primary fermentation has slowed, which is normally 5 days in. I normally only get a cup or two of yeast in my 10 gallon batches.

I'm really not sure why it takes so long to ferment, at a loss. The last batch I kegged was fermenting for about 15 days or so, and I noticed it hadn't cleared up much yet, still a lot of yeast in suspension. This was after a few consistent FG readings, so it was mostly done.

I've brewed many great batches using buckets and carboys, but the last couple with the new conical have been a challenge.
 
cdubbaya said:
Interesting, thanks for the replies. I was under the impression that oxygen permeation was a factor, due to the comments from others who brew wild ales. They say that leaving a beer in a bucket is a bad idea due to the oxygen that can get in versus a glass carboy, but maybe that's just for long-term storage?

Right, exactly. Wild brewers are concerned about very small amounts of oxygen over very long periods of time. Whatever amount permeates is trivial compared to your initial dose.
 
I only pull the yeast that has already settled out, so that the trub and other stuff in there is gone. Blichmann says to dump the trub/yeast when primary fermentation has slowed, which is normally 5 days in. I normally only get a cup or two of yeast in my 10 gallon batches.

I'm really not sure why it takes so long to ferment, at a loss. The last batch I kegged was fermenting for about 15 days or so, and I noticed it hadn't cleared up much yet, still a lot of yeast in suspension. This was after a few consistent FG readings, so it was mostly done.

I've brewed many great batches using buckets and carboys, but the last couple with the new conical have been a challenge.

An easy test would be to not pull off any yeast and see if things are faster (if not you can tell me I'm wrong).

It sounds like the initial stage of fermentation is going pretty much to plan (4-5 days of vigorous activity), its just that last bit to FG is the problem. I've seen something very similar with fermentations in my 55F basement in the winter. The beer basically keeps itself warm enough during the initial fermentation, but cools off too much to keep the yeast active in order to drop that last few points. Is that what is going on?
 
An easy test would be to not pull off any yeast and see if things are faster (if not you can tell me I'm wrong).

I would do this test, but we left our first batch sit for over a week without pulling yeast, and it became almost impossible to dump the yeast and harvest. We literally had to suck the yeast out through the hose. Needless to say, weren't saving that yeast yet. We learned quickly to pull the yeast sooner.

It sounds like the initial stage of fermentation is going pretty much to plan (4-5 days of vigorous activity), its just that last bit to FG is the problem. I've seen something very similar with fermentations in my 55F basement in the winter. The beer basically keeps itself warm enough during the initial fermentation, but cools off too much to keep the yeast active in order to drop that last few points. Is that what is going on?

We thought about the temperature as well. Our first fermentation was done around 62F, but the others have been closer 65-68F consistently. Fortunately, even with temperature swings, we didn't see a lot of fluctuation with the wort temp, due to the 10 gallon volume.

We've got a milk stout fermenting right now, has been there for 13 days. It's still got quite a bit of yeast suspension and fermenting slowly. I think it's almost done, but the cloudiness concerns me.
 
....but we left our first batch sit for over a week without pulling yeast, and it became almost impossible to dump the yeast and harvest.

Is it possible to bubble CO2 up through the bottom of the conical every day or so? That would re-disperse the yeast cake, preventing caking up on the bottom and increase the exposure of the yeast to the sugars in the wort.
 
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