Oxygen Permeability Of Plastic Fermenters?

[mfdes]

I have been wondering for a while, since I started brewing in glass, whether plastic fermenters are permeable to oxygen and could promote oxidation if the beer spends a bit too long in them.
I have noticed that the long-term stability of my beer is better when I've fermented in in glass all the way through. Once fermentation ceases and there is no longer positive CO2 pressure in the fermenter, are plastic fermenters allowing oxygen in? I always make sure I have a good airlock seal and the lid is airtight, but I still seem to get more oxidation in plastic-fermented brews over the long term. I like to leave the beer in the primary at least 4-5 days after active fermentation ceases so the yeast can mop up after itself (and to dry hop if it's required), and this may be the time that problems are occurring.

Does anyone know what the oxygen permeability of food grade plastic fermenters is?

Cheers!

MFS

 

[Tseay]

I have been wondering for a while, since I started brewing in glass, whether plastic fermenters are permeable to oxygen and could promote oxidation if the beer spends a bit too long in them.
I have noticed that the long-term stability of my beer is better when I've fermented in in glass all the way through. Once fermentation ceases and there is no longer positive CO2 pressure in the fermenter, are plastic fermenters allowing oxygen in? I always make sure I have a good airlock seal and the lid is airtight, but I still seem to get more oxidation in plastic-fermented brews over the long term. I like to leave the beer in the primary at least 4-5 days after active fermentation ceases so the yeast can mop up after itself (and to dry hop if it's required), and this may be the time that problems are occurring.

Does anyone know what the oxygen permeability of food grade plastic fermenters is?

Cheers!

MFS

Good place to start - has a pdf of permeability readings


http://www.flextank.com.au/Technical.htm

 

[mfdes]

This is not a bad source either.

http://www2.parc.com/emdl/members/apte/flemishredale.shtml

You'll notice that the normal, HDPE fermenters and cubes are in fact very oxygen permeable. This may be the reason that leaving beer in a plastic fermenter for too long will adversey affect its long term storage, at least in my case.
I kinda feel bad because I've given a fair bit of advice to leave the beer in the fermenter a while to clarify and for the yeast to mop up its by-products, because this works very well for me, but many people will not be doing a primary fermentation in glass like I am...

Oh, well.

MFS.

 

[voota]

Was reading about this in Wild Brews the other day...

oxygen diffuses into the beer at 20 cc/l/year in a typical plastic fermenter, 17cc/l/year in a glass fermenter with a silicone stopper, and 8.5cc/l/year in a wine barrel. It should be noted that you can bring the diffusion down to 0.10cc/l/year by using a wooden stopper in a glass fermenter, and the book states that glass lets in no oxygen... oxygen will only come in through the stopper.

Hope that helps you a bit.

Edit : Ergh, you've pretty much already covered it in that article mfdes

 

[technobabble66]

I just posted this in another thread, then discovered this one where it's more relevant & easier to find in a search, so i'll repeat it here in necroland. Maybe the moderators can clean this up for me
Also thought it worthwhile posting here as the above links no longer seem to work :angry:

http://www.mocon.com/pdf/optech/Closures%20-%20Oxygen%20Passage%20Study.pdf

It's a study looking at the O2 permeability of different bungs & airlocks (primarily for glass carboys). I thought it particularly interesting as it gives a nice summary of the oxygen permeability of various plastics, etc.

In particular:
HDPE (fermenters) = 44-91
LDPE (glad wrap) = 98-138
PET = <1-1

Also, with the bungs/airlocks, it seems Silicon is very permeable to O2 (well, i didn't know that) and the problem with water trap airlocks is not only the permeability of the plastic, but that the water can allow easy transfer of O2. Still water apparently allows significantly less O2 transfer, but still some.

So if we're concerned with O2 getting into our fermenting/conditioning beer, maybe we should be moving to glass carboys with dry/mechanical air-locked non-silicon bungs.

I should probably say i don't think i've yet experienced any problems with my brews i'd attribute to O2 getting into them (i've done 9 brews in plastic ferms), but the findings above are interesting nonetheless.