Mechanics of oxidation

[brewbama]

Pardon me if this has been answered before, if it has I overlooked it In my search.

When beer ferments, it is in a closed system expelling CO2 from an airlock of some sort. When that airlock is broken (say I pull the blow off tube out of the liquid solution in a jar) and the spigot at the bottom of the fermenter is opened, as the beer fills a CO2 purged keg it pulls air thru the tube into the headspace of the fermenter. This air mixes with the CO2 and begins to oxidize the beer. Here’s the question(s):

Is the top layer oxidize slightly at first, then gradually more and more saturated and begins to slowly work its way lower and lower into the beer? If so, how long does this take? Filling a keg with 5 gallons takes about 15 minute. If the fermenter was filled to 5.5 gallons will the oxygen have reached the half gallon depth (or more) in that 15 minutes or is the underlying 5 gal of beer protected by this top sacrificial half gallon layer resulting in a keg filled with near zero O2 beer?

 

[JAReeves]

I can’t help, but I really want to know the answer.

 

[effeffe]

Pardon me if this has been answered before, if it has I overlooked it In my search.

When beer ferments, it is in a closed system expelling CO2 from an airlock of some sort. When that airlock is broken (say I pull the blow off tube out of the liquid solution in a jar) and the spigot at the bottom of the fermenter is opened, as the beer fills a CO2 purged keg it pulls air thru the tube into the headspace of the fermenter. This air mixes with the CO2 and begins to oxidize the beer. Here’s the question(s):

Is the top layer oxidize slightly at first, then gradually more and more saturated and begins to slowly work its way lower and lower into the beer? If so, how long does this take? Filling a keg with 5 gallons takes about 15 minute. If the fermenter was filled to 5.5 gallons will the oxygen have reached the half gallon depth (or more) in that 15 minutes or is the underlying 5 gal of beer protected by this top sacrificial half gallon layer resulting in a keg filled with near zero O2 beer?

I don't know the exact answer but I suspect it doesn't really matter as the transfer will cause some movement/turbolence and the beer will mix.

Airlocks don't really make a close system anyway, indeed they suck air in if wort/beer temperature drops.

I assume you're purging kegs with CO2 fermentation and have no gas tank, otherwise you could use that.

If you're concerned with oxidation at this stage, spunding is an alternative.

 

[Tallgrass]

I would like to know the answer as well but in the meantime...
Connect the gas post from your keg to the blow off tube on your fermenter. As you fill the keg, co2 will be pushed into the headspace of the fermenter.

 

[day_trippr]

15 minutes seems like a long time - is this a gravity transfer? I do CO2-push racking and it's closer to 5 minutes.
And if there's concern the atmospheric suck-back is a problem time certainly matters.

Also...it takes a lot of CO2 to purge a keg - like the entire CO2 blow-off from a 5 gallon fermentation...

Cheers!

 

[brewbama]

The Low O2 guys have done some research with a bioreactor that is wired for these kind of what-ifs. I thought one of them would chime in with a data driven answer or someone could cite a research paper I have overlooked.

When I close transfer, I return the CO2 from the keg to the top of the fermenter and let gravity do the work. I guessed at 15 minutes. I’ve not timed it.

….but the question is ‘why?’. What non-emotional reason do we do this if the underlying beer is protected by a sacrificial half gallon layer?

 

[Bobby_M]

The function of oxygen entering a liquid from a gas mixture is solution. How fast that happens is a function of surface area, pressure and liquid temperature. Oxygen is more soluble in liquid that his warmer.

The function of a molecule moving around from an area of high concentration to an area with low concentration is called diffusion. Different gases diffuse at different rates and the liquid's temperature and viscosity also matters quite a bit. The warmer something is, the more active movement of molecules. I'm not smart enough to say how fast it permeates through a gallon of beer.

 

[Bassman2003]

The exchange of gasses is a complex topic and something I am looking to learn more about. What makes this more complicated is the addition of flavor impact. It does seem that a little amount of O2 has a large flavor impact over time. What I do not know is if the O2 inside the keg gets used up upon contact or does it keep on affecting flavor beyond your sacrificial 1/2 gallon? Given bottled beer seems to be ruined to its entirety even though it is sealed and purged makes me think the odds are against us!

 

[hopjuice_71]

The function of oxygen entering a liquid from a gas mixture is solution. How fast that happens is a function of surface area, pressure and liquid temperature. Oxygen is more soluble in liquid that his warmer.

The function of a molecule moving around from an area of high concentration to an area with low concentration is called diffusion. Different gases diffuse at different rates and the liquid's temperature and viscosity also matters quite a bit. The warmer something is, the more active movement of molecules. I'm not smart enough to say how fast it permeates through a gallon of beer.

Oxygen as actually more soluble at lower liquid temperatures. However, the rate of dissolution is greater at higher temperatures. There is more potential for oxidation of beer at lower temperatures but it will take longer. Just wanted to make sure that was clear.

 

[Bobby_M]

Oxygen as actually more soluble at lower liquid temperatures. However, the rate of dissolution is greater at higher temperatures. There is more potential for oxidation of beer at lower temperatures but it will take longer. Just wanted to make sure that was clear.

I don't know how I got that mixed up.

 

[Bilsch]

When beer ferments, it is in a closed system expelling CO2 from an airlock of some sort. When that airlock is broken (say I pull the blow off tube out of the liquid solution in a jar) and the spigot at the bottom of the fermenter is opened, as the beer fills a CO2 purged keg it pulls air thru the tube into the headspace of the fermenter. This air mixes with the CO2 and begins to oxidize the beer. Here’s the question(s):

Is the top layer oxidize slightly at first, then gradually more and more saturated and begins to slowly work its way lower and lower into the beer? If so, how long does this take? Filling a keg with 5 gallons takes about 15 minute. If the fermenter was filled to 5.5 gallons will the oxygen have reached the half gallon depth (or more) in that 15 minutes or is the underlying 5 gal of beer protected by this top sacrificial half gallon layer resulting in a keg filled with near zero O2 beer?

This, as Brewbama has alluded to, has been measured and the answer is yes some oxygen gets in. Does it make a difference? That depends on a LOT of factors not the least of which being what style of beer, temperature and duration of storage, if there are any other antioxidants such as SO2 or yeast derived sulfites in solution etc. Another huge factor is the palate of the consumer and his or her preferences. A lot of people actually prefer/are used to beer with some amount of staling.

Fortunately, if a brewer wishes, it's a problem that can be easily solved by closed transfer or even better.. spunding.