Theory concerning primary fermentation

[abracadabra]

The theory goes like this:

The gas permeablity of a plastic primary fermenter is of no real concern. Here's why:

if a little bit of oxygen gets to the wort before fermentation starts it is of no consequence because you areate or oxygenate the wort anyway so a little more won't hurt and might help the yeast.

Once active fermentation starts the CO2 production creates positive pressure inside the fermenter so any gas should be flowing outward from the fermenter not inward.

I intend to prove or disprove this theory by doing a primary fermentation in a #7 other plastic container at some time in the not to distant future. I might just try a 1 gal. container to start.

 

[Bobby_M]

Ok, but oxygen permeability is not my primary concern with #7 other. That is a nasty catch all for unidentifiable recycled plastic which might be made up .72% of ****** tips for all I know.

I know a lot of water companies us it for water, but then wort/alcohol is probably a bit more capable of leeching something out of the plastic. Maybe I'm just a little more paranoid. Besides, those bottles are 5 gallon and you'll need at least 6 for primary.

 

[Fiery Sword]

I could be totally wrong here, so be warned. But I'm not sure that oxygen diffusion into the fermenter is terribly dependent on pressure of the CO2 pushing out of the fermenter. My way-back-hat from high school bio/chem is teling me that the two are not directly related - oxygen's desire to diffuse into the carboy, where oxygen density is less, is not inhibited by CO2's desire to do the same in the opposite direction. Both will occur.

...But again, I could be totally wrong.

 

[Orfy]

I could be totally wrong here, so be warned. But I'm not sure that oxygen diffusion into the fermenter is terribly dependent on pressure of the CO2 pushing out of the fermenter. My way-back-hat from high school bio/chem is teling me that the two are not directly related - oxygen's desire to diffuse into the carboy, where oxygen density is less, is not inhibited by CO2's desire to do the same in the opposite direction. Both will occur.

...But again, I could be totally wrong.

I think you are right.

 

[FlyGuy]

You are wrong. While there is osmotic potential for 02 to enter the vessel, osmotic pressure can be offset by gradients in atmospheric pressure/vessel pressure. That's how reverse osmosis works (e.g., as used to create RO water).

But that is not to say that abracadabra is necessarily right either.

 

[Fiery Sword]

So people's concerns about oxygen diffusing through plastic are, in a brewing setting, bunk? I have trouble believing this, but I'm listening!

 

[Shockerengr]

You are wrong. While there is osmotic potential for 02 to enter the vessel, osmotic pressure can be offset by gradients in atmospheric pressure/vessel pressure. That's how reverse osmosis works (e.g., as used to create RO water).

But that is not to say that abracadabra is necessarily right either.

It's a bit of each, but in a primary fermenter, we aren't talking very much pressure, so osomsis will likely still be the stronger force.

 

[psymn]

It's a bit of each, but in a primary fermenter, we aren't talking very much pressure, so osomsis will likely still be the stronger force.

For osmosis to occur the membrane must be permeable and there must be a common solute on either side of the membrane. I might be wrong, but plastic buckets don't seem to be very pourous in my experience.

I thought the major concern with long-term storage in plastic was the seal at the top of the bucket. The lids are not perfectlly matched to the bucket, and there is no positive force closure other than the edge of the lid. I think if the lid could be tightened onto the bucket there woudl be little concern of oxidation after primary fermentation.

Matt

 

[FlyGuy]

It's a bit of each, but in a primary fermenter, we aren't talking very much pressure, so osomsis will likely still be the stronger force.

Actually, what I meant was that he was wrong when he said that the diffusion of oxygen is not affected by pressure. It is.

However, the pressure inside a primary is never more than the force required to force air through the airlock/blow-off tube. So yes, in this case the pressure is actually negligible and there will be osmotic pressure for oxygen to diffuse into the wort if the plastic is permeable.