Silicone Tubing CO2/O2 diffusion

[BasementArtie]

Just a hypothetical question for a silicone blow off tube (ID 9mm OD 13mm), at roughly what rate would the blow off tube filled with 100% CO2 diffuse to atmospheric air / O2 and then eventually be fully replaced.

Let's assume the length of silicone is 1m, the internal length of tubing holds 63.6ml of CO² which (I think) would roughly equate to (1.847mg/ml) 114.514mg of CO2 at 15C.

 

[balrog]

paging @doug293cz

 

[day_trippr]

42

 

[BasementArtie]

42

I was hoping for more than the hitchhiker's guide to the galaxy answer to the universe

 

[AlexKay]

You didn't specify the units!

Or the wall thickness of the tubing. That's going to matter.

Even for fairly thick-wall tubing I think you're looking at a few days (assuming a ~1e-5 cm2/s diffusion constant). Luckily, during active fermentation you're continually purging the space with CO2, so oxygen will not build up.

But after fermentation stops ... not so much. Short answer is to use a different kind of tubing for blow-off.

 

[BasementArtie]

You didn't specify the units!

Or the wall thickness of the tubing. That's going to matter.

Even for fairly thick-wall tubing I think you're looking at a few days (assuming a ~1e-5 cm2/s diffusion constant). Luckily, during active fermentation you're continually purging the space with CO2, so oxygen will not build up.

But after fermentation stops ... not so much. Short answer is to use a different kind of tubing for blow-off.

Thanks Alex. The wall thickness is 3mm so not huge.

I've wrapped the tube in yellow PTFE tape around my silicone tubing as I love silicones flexibility hopefully this will act like an O2 barrier

 

[MaxStout]

It's not like a blowoff tube needs to be overly flexible. All you need is for it to bend from the fermenter to some other vessel. Plain old vinyl tubing is less porous and works fine.

 

[BasementArtie]

Also what material should I be looking at for my air lock bung (tapered type) the one that came with my fermenter is a red silicone one which again I feel like should be replaced

Attached picture of similar bung.

 

[AlexKay]

Once you start down this path ...

I want to say that basically anything will be ok as long as it isn't silicone. McMaster sells EPDM, though they're not specifically food grade.

 

[BasementArtie]

Once you start down this path ...

I want to say that basically anything will be ok as long as it isn't silicone. McMaster sells EPDM, though they're not specifically food grade.

My question is if they know that silicone is rubbish for the specific task why do they continue to use it? Is it that much cheaper than anything else?

 

[AlexKay]

My question is if they know that silicone is rubbish for the specific task why do they continue to use it? Is it that much cheaper than anything else?

Well, people on a home-brew forum are a nutty bunch, and probably worry about oxygen rather a lot more than anyone else.

Also, there's the simple question, "does oxygen diffuse through material X?" which has a simple answer (for silicone, it's "hell yes, and fast.") and the much harder question of "will this make any sort of difference in my beer?"

Even if you leak a lot of oxygen into your fermenter, active yeast will metabolize it, and they'll metabolize (decarboxylate) many oxidation products that form. So your stopper material and blow-off-tube material may not matter at all. I'm not sure anyone actually knows. Once the beer is off the yeast and cold, I absolutely would not leave it to the mercies of a silicone tube or stopper.

I'll go a step farther and say that if you're using a stopper at all, that means you're probably not fermenting in a keg or unitank and not doing closed transfers, and that any difference the stopper makes at that point is probably wholly theoretical.

 

[BasementArtie]

Well, people on a home-brew forum are a nutty bunch, and probably worry about oxygen rather a lot more than anyone else.

Also, there's the simple question, "does oxygen diffuse through material X?" which has a simple answer (for silicone, it's "hell yes, and fast.") and the much harder question of "will this make any sort of difference in my beer?"

Even if you leak a lot of oxygen into your fermenter, active yeast will metabolize it, and they'll metabolize (decarboxylate) many oxidation products that form. So your stopper material and blow-off-tube material may not matter at all. I'm not sure anyone actually knows. Once the beer is off the yeast and cold, I absolutely would not leave it to the mercies of a silicone tube or stopper.

I'll go a step farther and say that if you're using a stopper at all, that means you're probably not fermenting in a keg or unitank and not doing closed transfers, and that any difference the stopper makes at that point is probably wholly theoretical.

No I am not fermenting out of those things unfortunately.

I've got a stainless fermenter with clips on the side to seal the lid but it was provided with a silicone bung which in my mind defeats the point in the seal lid!

I've read natural rubber as a material is better than silicone and quite drastically. Is there any down side to using an old demijohn natural rubber bung instead?

 

[tracer bullet]

A consideration for stoppers is how thick they are compared to a tube wall. Even a "bad" material might still be pretty good if the thickness is high. A #10 stopper as an example is what, maybe 1.5" tall?

I use a stainless blow off tube. A place like Brewhardware will make them custom for you.

 

[mac_1103]

I've got a stainless fermenter with clips on the side to seal the lid but it was provided with a silicone bung which in my mind defeats the point in the seal lid!

If you're this worried about that little silicone plug, you might want to check what the big old gasket is made out of.

 

[BasementArtie]

If you're this worried about that little silicone plug, you might want to check what the big old gasket is made out of.

Didn't even think of the lid gasket tbh. Yeah probably silicone

 

[AlexKay]

I've asked pro brewers whether they've ever considered replacing their tri-clamp O-rings with Viton, and they've looked at me like I have two heads.

 

[BasementArtie]

Okay I'm probably taking this a bit far but I love a bodge. It's in its early conceptual phase but I'm thinking about the bung being silicone (1 I'll probably update this rubber at some point although that's still not very good) is covering the bung in a boiled SMB deoxygenated solution. It should allow the co2 to come through the silicone but there shouldn't be any return of oxygen, especially as water is much better at mixing with co2 than oxygen!

I have included some pictures. What do you guys think?