Degassing to complete fermentation

thecolin · 03-14-2011, 09:21 PM

So I've never really seen this mentioned, I'm curious if everyone else does it. When I started out, I wasn't getting complete fermentation, I tried all the standard solution with no results. The only thing I've discovered that really works every time is swirling the fermenter to expel all the gas. Since CO2 is toxic to yeast, once it's forced out, fermentation starts right up again within a day or so. (My latest wheat beer started at 1.050 and has finished at 1.006).

So is this an uncommon practice for a reason? Should I be avoiding doing this? I know that mead and wine makers do this, so why not beer brewers?

**Yooper** · 03-14-2011, 09:22 PM

Quote:

Originally Posted by thecolin

So I've never really seen this mentioned, I'm curious if everyone else does it. When I started out, I wasn't getting complete fermentation, I tried all the standard solution with no results. The only thing I've discovered that really works every time is swirling the fermenter to expel all the gas. Since CO2 is toxic to yeast, once it's forced out, fermentation starts right up again within a day or so. (My latest wheat beer started at 1.050 and has finished at 1.006).

So is this an uncommon practice for a reason? Should I be avoiding doing this? I know that mead and wine makers do this, so why not beer brewers?

Because oxidation is the death of beer. Co2 won't harm the beer- not in the volumes in a typical fermenter.

Mead makers degas ONLY at the very beginning of fermentation. Not after fermentation slows, as to avoid oxidation.

**Golddiggie** · 03-14-2011, 09:26 PM

I'm going to agree with Yooper here...

As a side note, when mead makers degass/aerate it's only until 1/3 of the sugars in the must have been consumed by the yeast. Once that point has been reached, it's strictly hands off. Some only aerate at the very start, adding nutrients before pitching the yeast in. Others will do step feeding along with degassing and aerating... Often the 1/3 break is achieved within the first 7-10 days (or less, depending on the OG)...

thecolin · 03-14-2011, 09:35 PM

Quote:

Originally Posted by Yooper

Because oxidation is the death of beer. Co2 won't harm the beer- not in the volumes in a typical fermenter.

Mead makers degas ONLY at the very beginning of fermentation. Not after fermentation slows, as to avoid oxidation.

I've thought about that, but once fermentation has started, isn't the top of the fermenter full of CO2 and the oxygen has been pushed out (since CO2 is heavier than air)?

**Golddiggie** · 03-14-2011, 09:39 PM

Gentle swirling can sometimes be used to rouse the yeast up again. But, I think it's a double edged sword... While you might want to do it sometimes, I don't think you want to use it every time. Chances are, proper fermentation temperatures, and pitching rate, will take care of that for you.

thecolin · 03-14-2011, 09:53 PM

I understand that's the general consensus, I'm just trying to understand where the oxygen comes from in a sealed fermenter. I don't really understand oxidation yet, and I'm trying to get a better grasp on it.

Also, you mentioned that mead makers stop degassing once 2/3 of the sugar are consumed. So the same rule wouldn't apply to beer?

**Golddiggie** · 03-14-2011, 10:14 PM

thecolin, it's once 1/3 of the sugars have been consumed, NOT 2/3...

Mead making methods don't translate to beer brewing methods... Completely different processes are involved.

For oxidation, anytime you introduce air into a wort, you risk it. Gentle swirling CAN be safe IF you do it right. I wouldn't recommend it as part of your normal process though. I've used it in maybe 2-3 of my beers so far. Even then, it's only with high OG worts. With yours being lower, I wouldn't try it.

You introduce oxygen into the wort at the very start, before pitching the yeast. This is so that the yeast can replicate initially, then get down to eating the sugars, producing alcohol and CO2 for you. You vent the CO2 while fermenting so that you get alcohol. Without venting the CO2 (via the airlock) you won't get the alcohol you desire.

I'm not a biologist, or yeast expert by any stretch... I just try to follow BKM for brewing beer and making my mead... If they say don't F with it during this stage, I leave it the F alone.

giligson · 03-15-2011, 12:27 AM

Quote:

Originally Posted by thecolin

I understand that's the general consensus, I'm just trying to understand where the oxygen comes from in a sealed fermenter. I don't really understand oxidation yet, and I'm trying to get a better grasp on it.

Also, you mentioned that mead makers stop degassing once 2/3 of the sugar are consumed. So the same rule wouldn't apply to beer?

Do you mean: how does oxygen get in there when there is a cozy blanket of Co2 covering the surface?
If that's the question, then the answer is diffusion - there is always some mixing of gasses goin on in the interface ( so if you want to avoid oxygen then you keep this mixing of the gas phase to a minimum.

**Yooper** · 03-15-2011, 12:30 AM

Quote:

Originally Posted by giligson

Do you mean: how does oxygen get in there when there is a cozy blanket of Co2 covering the surface?
If that's the question, then the answer is diffusion - there is always some mixing of gasses goin on in the interface ( so if you want to avoid oxygen then you keep this mixing of the gas phase to a minimum.

Right. The co2 blanket we talk about isn't a permanent thing. Sure, it's protective to a point, but once fermentation slows/stops, equilibrium will be attempted to be reached. That's why we use an airlock, to keep air exchange at a minimum while allowing excess co2 to vent. The co2 "blanket" won't be in there indefinitely. If you swirl/shake/stir the fermenter, it'll go away sooner rather than later.

thecolin · 03-15-2011, 06:08 AM

Quote:

Originally Posted by Golddiggie

thecolin, it's once 1/3
I'm not a biologist, or yeast expert by any stretch... I just try to follow BKM for brewing beer and making my mead... If they say don't F with it during this stage, I leave it the F alone.

I always like to understand why I shouldn't 'F' with something, because maybe the conventional wisdom is wrong. I'm not saying that's the instance in this case, I'm not out to prove anything. If I wasn't open to the information, I wouldn't be asking. But until I have what I feel to be complete understanding, preferably with some direct experience, I'll keep F'ing' with stuff until my understanding is complete. Just doing something because somebody said so, doesn't make for a very informative process.

Thanks for the information guys, I'll keep it in mind as I go forward.