"A blanket of CO2"

[muse435]

I am sure that this has been discussed somewhere but it has been really bugging me lately but I need to say some thing. This whole idea that CO2 and O2 just magically form a barrier and don't interact is pissing me off a little. By definition gasses move in random directions and will fill the volume of any fixed container. If there is any O2 in your carboy or bottle it will come into contact with your beer. All you can do is minimize to exposure to air to reduce oxidation.

"Diffusion is a process in which a gas enters a container with another gas and the two mix to form a uniform mixture."

All gasses diffuse!

I'm not trying to start a debate, I'm just venting.

 

[seabass07]

Isnt that the point of an airlock?

 

[HexKrak]

CO2 is heavier than O2, so while there would likely be some O2 in there, the concentrations of CO2 at the bottom will be much higher helping to protect your beverage from oxidation.

 

[muse435]

CO2 is heavier than O2, so while there would likely be some O2 in there, the concentrations of CO2 at the bottom will be much higher helping to protect your beverage from oxidation.

that is like saying water is heavier then alcohol so there is more alcohol in the top of your beer then the bottom. (since both will obey the laws of fluid dynamics)

 

[HexKrak]

That has to do with solubility. The alcohol and water mix. CO2 and O2 will mix as well, but to different degrees.

 

[muse435]

"Examining the mixing process on a molecular level gives additional insight. Suppose we were able to see the gas molecules in different colors, say the air molecules as white and the argon molecules as red. After we took the partition away, we would see white molecules start to move into the red region and, similarly, red molecules start to come into the white volume. As we watched, as the gases mixed, there would be more and more of the different color molecules in the regions that were initially all white and all red. If we moved further away so we could no longer pick out individual molecules, we would see the growth of pink regions spreading into the initially red and white areas. In the final state, we would expect a uniform pink gas to exist throughout the volume. There might be occasional small regions which were slightly more red or slightly more white, but these fluctuations would only last for a time on the order of several molecular collisions.

In terms of the overall spatial distribution of the molecules, we would say this final state was more random, more mixed, than the initial state in which the red and white molecules were confined to specific regions. Another way to say this is in terms of ``disorder;'' there is more disorder in the final state than in the initial state. One view of entropy is thus that increases in entropy are connected with increases in randomness or disorder. This link can be made rigorous and is extremely useful in describing systems on a microscopic basis. While we do not have scope to examine this topic in depth, the purpose of this chapter is to make plausible the link between disorder and entropy through a statistical definition of entropy." MIT

 

[muse435]

That has to do with solubility. The alcohol and water mix. CO2 and O2 will mix as well, but to different degrees.

The same laws apply to gasses, CO2 is soluble in O2 (or the other way around, i can't remember) but it is the same concept.

 

[LVBen]

Beers mix together... but you can still server up a black and tan with a distinct layer of stout and a distinct layer of pale ale.

Doesn't it take time for the CO2 to dissipate?

 

[seabass07]

Yes it isnt instantanious.

 

[muse435]

Beers mix together... but you can still server up a black and tan with a distinct layer of stout and a distinct layer of pale ale.

They stay separated for a little time but will eventually mix, (the beer being cold slows the presses as well as different initial densities) but if you shake a black and tan up it will mix (that's why I bought a turtle two days ago ), when you buy a Yuengling Black and Tan there is not two layers in the bottle.

Doesn't it take time for the CO2 to dissipate?

Yes, it is dependent on the energy (heat) of the system.

 

[LVBen]

So... what causes the burning sensation when I try to smell my beers during fermentation?

Is this not a dense layer of CO2?

 

[phenry]

Your fermenter is going to have a lot less O2 in it post-fermentation than it did pre-fermentation. To what degree, I don't know, but something's obviously coming out of the airlock. And since CO2 is heavier than O2, it would make sense that the majority of the gas evacuated through the airlock would be O2.

Sure, there's still probably some O2 that will contact your beer sitting in the fermenter, but the levels of CO2 are just so much higher.

 

[seabass07]

Im pretty sure the co2 would push all of the o2 through the airlock. The yeast will purge the o2. Im trying to figure out what context the blanket matters.

 

[cervezarara]

I believe the yeast consume a lot of O2 during the adaptive phase of fermentation. During the primary phase, they are consuming sugars and producing primarily ethanol and CO2. The amount of CO2 produced is related to the Brix of the wort, or grams of sugar per 100ml of wort. A typical 1.050 SG wort has a Brix of 12.37. The conversion to CO2 is 48.9% (each glucose molecule is reduced to two ethanol molecules and two CO2 molecules- molecular weight of glucose is 180 and molecular weight of CO2 is 44. (44X2)/180 = 48.8888.) Thus, for every 100g of sugar (12.37 in the 1.050 wort.) 6.05g of CO2 is produced. Since this CO2 production reduces the amount of solution, the final beer will produce 6.44g of CO2 per 100ml of wort (6.05/(100-6.05)*100). Or, we can say each liter of wort produces 64.4g of CO2. Thus, for five gallons of wort (18.93 liters) roughly 1200g of CO2 are produced. Remember that one mole of CO2 weighs 44g, so 27.7 moles of CO2 are produced. And each mole of gas at STP occupies 22.4 liters (our beer is warmer that standard temperature with an airlock and 65C fermentation temp, but suffice it to say gas occupies more volume at higher temperature) or >619 liters of CO2 are produced (assuming 100% attenuation.)

This gas has to go somewhere, so it gradually fills the headspace of the fermentation vessel and eventually makes its way through the airlock. Since this is not done all at once, the O2 in the headspace air (~20%) is gradually diluted and displaced through the airlock along with the Co2, N2 and other gases in the air. Over time, the air becomes so dilute in the headspace as to become negligible, and some of the 619 liters of CO2 that were produced remain (depending on the headspace volume.) I could use calculus to approximate the volume of air that remains, but I think it is very small. I am also assuming that yeast consumed the O2 dissolved in the wort during the adaptive phase. Some of the CO2 will remain dissolved in our beer (about 0.9 volumes at 65F), as bottle priming calculators are aware.

Of course, if open fermentation is allowed, these calculations become meaningless. And every time you remove the airlock, air is allowed to mix with the headspace CO2, as muse states in his original post.

 

[unionrdr]

Well said. I figured that some of the air being in contact with the surface of the wort would be used to some extent by the multiplying yeast. Then whatever remains,even if it does mix with the co2 would eventually be displaced by the growing volume of co2 in a given head space. Otherwise,it seems to me that infections &/or oxidation would happen far more frequently.
The airlock also seems to keep a certain amount of pressure in said head space,before it builds up enough to vent. It seems blow off tubes reduce this pressure build up quicker do to less back pressure from the airlock's center piece being absent.

 

[Bobby_M]

CO2 is heavier than O2, so while there would likely be some O2 in there, the concentrations of CO2 at the bottom will be much higher helping to protect your beverage from oxidation.

This is only true for a short period of time, like for the time it takes to rack from primary to keg.

If CO2 really could form a protective layer above beer, you could lightly cover the opening of a bucket full of beer and let it sit for months without it getting oxidized. Of course this isn't true.

 

[KayaBrew]

People often forget how much exposure to air our beers get when we bottle. The empty bottle is full of ambient air, that air is then purged by the rising level of beer in the bottle as it is filled. Not to mention how much beer comes in contact with air from racking from primary or secondary to an open bottling bucket. According some of the "oxidation paranoia" theorists out there, bottled homebrew should then be horribly oxidized...but it isn't. Don't worry so much about oxidation.

 

[unionrdr]

Another reason I started using the o2 caps. They really do work. I get about 3 more weeks from bottled beers now. They improve with age for a longer time before finally going south. Here's a weird one in regard to this. We had 2 bottles of my wife's BB summer ale (Belgian wit clone) That were some 8-10 weeks old. The hop,spice,malt flavors that had been fading started coming back again. Strange. O2 caps strike again!

 

[Yooper]

I am sure that this has been discussed somewhere but it has been really bugging me lately but I need to say some thing. This whole idea that CO2 and O2 just magically form a barrier and don't interact is pissing me off a little. By definition gasses move in random directions and will fill the volume of any fixed container. If there is any O2 in your carboy or bottle it will come into contact with your beer. All you can do is minimize to exposure to air to reduce oxidation.

"Diffusion is a process in which a gas enters a container with another gas and the two mix to form a uniform mixture."

All gasses diffuse!

I'm not trying to start a debate, I'm just venting.

I said the same thing myself a few weeks ago. I mentioned that this magical "co2 blanket" isn't there forever, and once fermentation slows down it disipates and will strive to reach equilibrium. This is especially true of extra long time in the fermenter- the reason why winemakers top up and/or flood the carboys with co2, as well as using campden as an antioxidant.

I was beat down pretty severely by the "magical co2 blanket believers" and just gave up.

 

[muse435]

I believe the yeast consume a lot of O2 during the adaptive phase of fermentation. During the primary phase, they are consuming sugars and producing primarily ethanol and CO2. The amount of CO2 produced is related to the Brix of the wort, or grams of sugar per 100ml of wort. A typical 1.050 SG wort has a Brix of 12.37. The conversion to CO2 is 48.9% (each glucose molecule is reduced to two ethanol molecules and two CO2 molecules- molecular weight of glucose is 180 and molecular weight of CO2 is 44. (44X2)/180 = 48.8888.) Thus, for every 100g of sugar (12.37 in the 1.050 wort.) 6.05g of CO2 is produced. Since this CO2 production reduces the amount of solution, the final beer will produce 6.44g of CO2 per 100ml of wort (6.05/(100-6.05)*100). Or, we can say each liter of wort produces 64.4g of CO2. Thus, for five gallons of wort (18.93 liters) roughly 1200g of CO2 are produced. Remember that one mole of CO2 weighs 44g, so 27.7 moles of CO2 are produced. And each mole of gas at STP occupies 22.4 liters (our beer is warmer that standard temperature with an airlock and 65C fermentation temp, but suffice it to say gas occupies more volume at higher temperature) or >619 liters of CO2 are produced (assuming 100% attenuation.)

This gas has to go somewhere, so it gradually fills the headspace of the fermentation vessel and eventually makes its way through the airlock. Since this is not done all at once, the O2 in the headspace air (~20%) is gradually diluted and displaced through the airlock along with the Co2, N2 and other gases in the air. Over time, the air becomes so dilute in the headspace as to become negligible, and some of the 619 liters of CO2 that were produced remain (depending on the headspace volume.) I could use calculus to approximate the volume of air that remains, but I think it is very small. I am also assuming that yeast consumed the O2 dissolved in the wort during the adaptive phase. Some of the CO2 will remain dissolved in our beer (about 0.9 volumes at 65F), as bottle priming calculators are aware.

Of course, if open fermentation is allowed, these calculations become meaningless. And every time you remove the airlock, air is allowed to mix with the headspace CO2, as muse states in his original post.

I agree completely with cervezarara. I have not read to many threads discussing this issue with the primary, The active fermentation should take care of it, as said above. It is in the secondary that people have this crazy idea. Thanx to all who listened, agreed, and disagreed, I just wanted to vent.

 

[seabass07]

That is why you minimize head space in secondary. It occurred to me that cold crashing in primary could be beneficial. If you transferred cold beer to secondary and minimized head space, the warming beer would release co2 and help to purge the head space of o2. Is this feasible? It seems that it would only take a 10 or 20 degree difference.

 

[moti_mo]

This is one of those myths of homebrewing that I've always been amazed that people hold onto.

 

[muse435]

That is why you minimize head space in secondary. It occurred to me that cold crashing in primary could be beneficial. If you transferred cold beer to secondary and minimized head space, the warming beer would release co2 and help to purge the head space of o2. Is this feasible? It seems that it would only take a 10 or 20 degree difference.

I like that thinking, if you could fill with cold CO2 that would help further, due to the expansion of gas.

 

[GoHawks]

muse - are you a chemist or physicist?

 

[muse435]

muse - are you a chemist or physicist?

I have a BA in physics

 

[GoHawks]

Alrighty - then your postings on O2 have more value in my eyes. Thanks.

 

[muse435]

Alrighty - then your postings on O2 have more value in my eyes. Thanks.

I am not pretending to be an expert in fluid dynamics but I remember a thing or two about it :fro:

 

[iaefebs]

See this is why I never truly believed in tropopause or stratopause.

 

[Beerrific]

Here:

Someone solve it.

But, I agree with muse435. I think it is over rated and used as a crutch for otherwise poor brewing technique. I mean if this separation of CO2 and oxygen was so pronounced, you would probably die from the "CO2 blanket" in your lungs.

 

[remilard]

People often forget how much exposure to air our beers get when we bottle. The empty bottle is full of ambient air, that air is then purged by the rising level of beer in the bottle as it is filled. Not to mention how much beer comes in contact with air from racking from primary or secondary to an open bottling bucket. According some of the "oxidation paranoia" theorists out there, bottled homebrew should then be horribly oxidized...but it isn't. Don't worry so much about oxidation.

A very good proportion, say 1/3, of homebrew entered in competitions is distinctly oxidized. Homebrewers have a tolerance if not a preference for oxidized beer. According to Fix and Bamforth, many consumers do do (think of the preference for import beers which are uniformly oxidized and/or skunked).