Silicone Tubing CO2/O2 diffusion

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BasementArtie

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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.
 
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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.
 
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
 

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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.
 
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.
 

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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.
 
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?
 
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.
 
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?

Screenshot_2023-03-19-21-36-31-94_e2d5b3f32b79de1d45acd1fad96fbb0f.jpg
 
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.
 
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.
 
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.
 
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?
IMG20230322172504.jpg
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IMG20230322172525.jpg
 
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Thought I'd just update. I decided to to buy a stainless steel bulkhead with barbs and stainless washers + Viton washers to remove the need for a bung! For the silicone seal inside I got some quotes for FDA Nitrile and Viton to replace the lid gasket this was looking to be anywhere between £50-120 so I took a raincheck and went with an alternative option of nitrile bands bonded sealing the lid from the outside.
 

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It looks like you are going down the oxygen rabbit hole - which is a choice, and not necessarily bad. But Alexkay makes a good point - the fermenter is the lowest risk area unless you leave the beer on the yeast after fermentation is complete. Active yeast protect you from oxygen damage.

Unless you are addressing oxygen on the hot side during your brew day, there is little to "protect" in your fermenter. The beer has already been exposed and oxidized. Low oxygen brewers try to bring wort from the brewhouse that has not been oxidized into the fermenter. This is when you need to pay more attention to everything.

But for all beers, as he stated, once the yeast stop being active your duties begin.
 
This more to stop any cold side oxygenation and flavour / aroma changes to styles such as NEIPAs. I don't think I'm likely to get into the LODO just yet on the hotside.
 
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