Happy HolidaySs Giveaway - Last Sponsor Giveaway of the Year!

Come Enter the BrewDeals/FastFerment Giveaway!


Home Brew Forums > Home Brewing Beer > Fermentation & Yeast > Composition of gasses in the headspace during active fermentation?
Reply
 
LinkBack Thread Tools
Old 04-05-2013, 02:58 PM   #1
DSorenson
HBT_SUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Mar 2013
Location: , Connecticut
Posts: 787
Liked 116 Times on 86 Posts
Likes Given: 541

Default Composition of gasses in the headspace during active fermentation?

More out of curiosity than anything, but I was wondering if anyone has found out how the gas composition changes within the carboy, assuming perfect seal and that it started out with regular air composition?

I know CO2 is heavier than O2. My theory is that as fermentation is happening, the CO2 produced forces the less dense O2 out of the airlock.

I guess I'm kind of interested to know, because this means that fermentation does it's own CO2 purge, which should mean that taking the airlock on and off, or testing the SG is less intrusive than it would be otherwise.

__________________

Ever have trouble getting a "big beer" to carbonate in the bottle? Read the "rules" and please add your story to the list!

DSorenson is offline
 
Reply With Quote Quick reply to this message
Old 04-06-2013, 05:13 AM   #2
GSul
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2012
Location: East Haven, CT
Posts: 43
Liked 3 Times on 3 Posts
Likes Given: 5

Default

Good question. Remember that the key to a healthy yeast fermentation is plenty of O2. But indeed a good thought in where does that O2 go...

__________________
GSul is offline
 
Reply With Quote Quick reply to this message
Old 04-06-2013, 07:14 AM   #3
Beaker
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2013
Location: San Francisco, CA
Posts: 30
Liked 1 Times on 1 Posts
Likes Given: 3

Default

Not entirely correct, the yeast only needs O2 in the very beginning, so to say it's needed for fermentation is actually false.

That O2 gets used during the yeast cells lag phase, eventually being used to build healthier cell walls. it's no longer in the fermentor in the same way free O2 is.

The CO2 produced by the fermentation does displace the lighter residual air out of the carboy and essentially blankets the surface of the bitter wort.

__________________
Beaker is offline
 
Reply With Quote Quick reply to this message
Old 04-06-2013, 02:22 PM   #4
passedpawn
Waste Allocation Load Lifter - Earth Class
HBT_MODERATOR.png
Feedback Score: 0 reviews
 
passedpawn's Avatar
Recipes 
 
Join Date: Apr 2009
Location: ☼ Clearwater, FL ☼
Posts: 19,619
Liked 3601 Times on 2221 Posts
Likes Given: 3105

Default

Quote:
Originally Posted by DSorenson View Post
More out of curiosity than anything, but I was wondering if anyone has found out how the gas composition changes within the carboy, assuming perfect seal and that it started out with regular air composition?

I know CO2 is heavier than O2. My theory is that as fermentation is happening, the CO2 produced forces the less dense O2 out of the airlock.

I guess I'm kind of interested to know, because this means that fermentation does it's own CO2 purge, which should mean that taking the airlock on and off, or testing the SG is less intrusive than it would be otherwise.
CO2 is heavier than O2, but they are gasses and they will mix. The idea of a "blanket of CO2" is not completely accurate. If you remove the airlock, O2 immediately and slowly begins to mix with the other gasses in the headspace. Given enough time, the headspace would be room air due to this mixing.
__________________
Hey goomba I love how you dance the rumba
But take some advice paisano learn-a how to mambo
If you're gonna be a square you ain't-a gonna go anywhere.
passedpawn is offline
 
Reply With Quote Quick reply to this message
Old 04-06-2013, 04:13 PM   #5
Beernik
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jun 2009
Location: salt lake city, ut
Posts: 3,161
Liked 335 Times on 275 Posts
Likes Given: 25

Default

The gases mix, but don't mix instantaneously (not a lot of wind movement in a primary). Plus you have a source of CO2 generation from the fermenting wort.

For these reasons, I would tend to think of the headspace in a primary during fermentation as being more of a plug flow reactor (PFR) than a Continuously Stirred Tank Reactor (CSTR). What ever off gasses from the top of the wort is going to march it's way up and out of the primary.

This changes when active fermentation ends. Then its more like a Batch Reactor and random Brownian Motion can mix gases (like if oxygen is introduced by opening the carboy). But Brownian Motion still isn't an instantaneous process.

__________________
People tell me that if they lived near a beach they would run on the beach every day.

If I lived near a beach, I'd drink beer and look at the beach every day.
Beernik is offline
 
Reply With Quote Quick reply to this message
Old 04-06-2013, 05:04 PM   #6
passedpawn
Waste Allocation Load Lifter - Earth Class
HBT_MODERATOR.png
Feedback Score: 0 reviews
 
passedpawn's Avatar
Recipes 
 
Join Date: Apr 2009
Location: ☼ Clearwater, FL ☼
Posts: 19,619
Liked 3601 Times on 2221 Posts
Likes Given: 3105

Default

Partial pressures of the gasses move the gas molecules in/out of the fermentor.

Quote:
Originally Posted by Beernik View Post
The gases mix, but don't mix instantaneously (not a lot of wind movement in a primary). Plus you have a source of CO2 generation from the fermenting wort.

For these reasons, I would tend to think of the headspace in a primary during fermentation as being more of a plug flow reactor (PFR) than a Continuously Stirred Tank Reactor (CSTR). What ever off gasses from the top of the wort is going to march it's way up and out of the primary.

This changes when active fermentation ends. Then its more like a Batch Reactor and random Brownian Motion can mix gases (like if oxygen is introduced by opening the carboy). But Brownian Motion still isn't an instantaneous process.
__________________
Hey goomba I love how you dance the rumba
But take some advice paisano learn-a how to mambo
If you're gonna be a square you ain't-a gonna go anywhere.
passedpawn is offline
 
Reply With Quote Quick reply to this message
Old 04-06-2013, 06:06 PM   #7
feinbera
Feedback Score: 0 reviews
Recipes 
 
Join Date: Aug 2012
Location: San Francisco, CA
Posts: 590
Liked 120 Times on 96 Posts
Likes Given: 55

Default

For the practical purposes of homebrewing, you can treat the headspace as an impermeable blanket of CO2 -- while some minuscule amount of oxygen will diffuse through if you pop your carboy bung or bucket lid, as long as you're careful not to slosh things around and disturb the blanket, that amount will be so small as to have no detectable effect on your beer.

Oxygen also diffuses through the water in your airlock, and, if you really wanna geek out, straight through the walls of your fermentation vessel via quantum tunneling -- but, again, in amounts so tiny in the scale of a few-week fermentation that the effects are not detectable, so, we happily pretend these effects do not exist at all, without our beer suffering any adverse effects for the pretending.

__________________
feinbera is offline
2
People Like This 
Reply With Quote Quick reply to this message
Old 04-06-2013, 06:27 PM   #8
passedpawn
Waste Allocation Load Lifter - Earth Class
HBT_MODERATOR.png
Feedback Score: 0 reviews
 
passedpawn's Avatar
Recipes 
 
Join Date: Apr 2009
Location: ☼ Clearwater, FL ☼
Posts: 19,619
Liked 3601 Times on 2221 Posts
Likes Given: 3105

Default

Quote:
Originally Posted by feinbera View Post
For the practical purposes of homebrewing, you can treat the headspace as an impermeable blanket of CO2 -- while some minuscule amount of oxygen will diffuse through if you pop your carboy bung or bucket lid, as long as you're careful not to slosh things around and disturb the blanket, that amount will be so small as to have no detectable effect on your beer.

Oxygen also diffuses through the water in your airlock, and, if you really wanna geek out, straight through the walls of your fermentation vessel via quantum tunneling -- but, again, in amounts so tiny in the scale of a few-week fermentation that the effects are not detectable, so, we happily pretend these effects do not exist at all, without our beer suffering any adverse effects for the pretending.
That's perfect. I didn't mean to suggest that removing the airlock momentarily was a problem.
__________________
Hey goomba I love how you dance the rumba
But take some advice paisano learn-a how to mambo
If you're gonna be a square you ain't-a gonna go anywhere.
passedpawn is offline
 
Reply With Quote Quick reply to this message
Old 04-06-2013, 10:30 PM   #9
DSorenson
HBT_SUPPORTER.png
Feedback Score: 0 reviews
Recipes 
 
Join Date: Mar 2013
Location: , Connecticut
Posts: 787
Liked 116 Times on 86 Posts
Likes Given: 541

Default

Wow guys... Thanks! It's reassuring homebrewers are so scientifically inclined.

__________________

Ever have trouble getting a "big beer" to carbonate in the bottle? Read the "rules" and please add your story to the list!

DSorenson is offline
 
Reply With Quote Quick reply to this message
Old 04-07-2013, 12:40 AM   #10
Beernik
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jun 2009
Location: salt lake city, ut
Posts: 3,161
Liked 335 Times on 275 Posts
Likes Given: 25

Default

Quote:
Originally Posted by passedpawn View Post
Partial pressures of the gasses move the gas molecules in/out of the fermentor.
Partial pressures do not move gasses into the fermentor unless you don't have an airlock on it. The airlock works as a one-way valve allowing gas to exit and not enter.
__________________
People tell me that if they lived near a beach they would run on the beach every day.

If I lived near a beach, I'd drink beer and look at the beach every day.
Beernik is offline
 
Reply With Quote Quick reply to this message
Reply



Quick Reply
Message:
Options
Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Fermentation chamber gasses Kayos Fermentation & Yeast 3 03-04-2013 01:32 AM
Active 2nd Fermentation w/pic opengun Fermentation & Yeast 9 03-07-2012 02:22 AM
Day 5 and still Active Fermentation Shepherd5 Fermentation & Yeast 2 05-25-2010 08:46 PM
Fermentation gasses..possible fix.. smokinghole Cider Forum 20 11-22-2009 08:21 AM
Which is better? A fast, very active fermentation, or a slow steady fermentation? cerberus9 Beginners Beer Brewing Forum 6 09-24-2009 05:56 PM



Newest Threads

LATEST SPONSOR DEALS