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Old 04-08-2009, 12:17 PM   #11
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Originally Posted by giligson View Post
Wow that is impressive impermiability for saran. Maybe I should just wrap my plastic fermenters with it.
Saran (a trade name for polyvinylidene chloride) is somewhat hard to find these days--for instance, Saran Wrap isn't made of saran any more, since 2004 it's made of LDPE which has a much lower environmental impact in manufacture but is nowhere near as good an O2 barrier.


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Old 04-08-2009, 01:00 PM   #12
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Material


Oxygen Permeability cc-mm/m2-day, 23C
Wood, Oak 57
High-density polyethylene HDPE 18
Polypropylene PP 20
Polycarbonate PC 36
Nylon (not oriented) 0.62
Saran 0.02
Vinyl 20
Silicone 10600
Water 34400




Tank Volume [L] O2 cc/L.year
Burgundy barrel 300 8.5
Rodenbach tank, wood, small 12,000 0.86
Rodenbach tank, wood, large 20,000 0.53
HDPE bucket 20 220
Homebrew barrel 40 23
Glass carboy, 30cm vinyl immersion tube 20 0.31
Glass carboy, silicone stopper 20 17
Glass carboy, wood stopper 20 0.10
Unfortunately, I can't find the table I had linked to earlier. This is good stuff but it's missing the key number (for PET, which is what the argument is usually about since that's what Better Bottles are made of).

In particular it's missing the permeability of the exact kind of copolymer BBs use for O2 resistance (their site definitely confirms that they're made of some polyethylene terephthalate copolymer). BEHQ copolymer PET can have about 1/2 the O2 permeability of standard PET depending on concentration.

PET has _much_ lower permeability than HDPE does. See, for instance, the study of Vitamin C loss in orange juice packaged in plastic bottles Wiley InterScience which notes that there's substantially more O2 transmission through the HDPE cap on a bottle than through the PET walls, despite the latter obviously having much greater surface area: "The results showed that in plastic packaging materials, the loss of vitamin C was related to the oxygen permeability...The losses of aroma compounds by permeation through the bottle (PET) and the cap (high-density polyethylene, HDPE) have also been investigated. The results showed that permeation mainly took place through the cap."

http://www.chem.mtu.edu/~whanbing/NewBubbleWrap.htm notes the O2 permeability of several plastics in 10-10 g m / m2 s bar:

HDPE: 10
LDPE: 28
PET: 0.76

with a PET copolymer designed for low O2 transmission probably coming in at around half the figure for standard PET.

If you believe the relative permeabilities, it wouldn't be surprising if the Better Bottle's O2 transmission came in lower than the glass carboy with silcone or rubber stopper. Which is about what I recall from my earlier investigation: if you're really concerned about oxygen, it's _much_ more important to focus on the stopper/airlock setup you use than whether you're in a glass or PET carboy.

If you're really paranoid, you should probably go with something you can purge the headspace in that's made out of relatively impermeable stainless steel (ie a corney keg). If a standard glass carboy + stopper (possibly + airlock) setup is "good enough" for you, then a Better Bottle is probably good enough too (either slightly better or worse depending on the rest of the configuration and exactly what properties the BB copolymer have).


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Old 04-08-2009, 01:17 PM   #13
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Just to note one more thing:

Even the HDPE bucket there has a permeability of just 220 cc of O2/year. Think about the size of the headspace in your container--it's not too surprising to have a liter or so of head space, which would about the same amount of oxygen that the worst commonly use fermentor lets through in a _year_ (since air is about 1/5 oxygen)..

If you can't find a vessel you can purge, definitely use a carboy-shaped container and fill to the neck when you're bulk aging and worried about oxygen. And opening it once or twice during the year is going to let in enough oxygen to overwhelm the choice of materials, so resist the urge to peek/sample if you think O2 is that big a concern.
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Old 04-08-2009, 01:19 PM   #14
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Kinda ironical ain't it.

"Wood, Oak 57 vs High-density polyethylene HDPE 18"

Our much debated buckets have 3.16 time less permeability than a traditional wooden cask. Many of us go all schizophrenic about this plastic s inherent O2 permeability and strive to find any and every alternative to it.

But then, we go to the bottle shop and "pert near" bust a nut (or an ovary I suppose) when we find anything labelled "Oak Aged" and then can't say enough good things about our latest find.

The plain simple truth of the matter is that you can keep your beer in primary well over a month in the bucket and have no perceivable oxidation impacts whatsoever unless you are just beligerantly careless with your handling.
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Old 04-09-2009, 12:52 AM   #15
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Kinda ironical ain't it.

"Wood, Oak 57 vs High-density polyethylene HDPE 18"

Our much debated buckets have 3.16 time less permeability than a traditional wooden cask. Many of us go all schizophrenic about this plastic s inherent O2 permeability and strive to find any and every alternative to it.

But then, we go to the bottle shop and "pert near" bust a nut (or an ovary I suppose) when we find anything labelled "Oak Aged" and then can't say enough good things about our latest find.

The plain simple truth of the matter is that you can keep your beer in primary well over a month in the bucket and have no perceivable oxidation impacts whatsoever unless you are just beligerantly careless with your handling.
Personally when it comes to fermenters, I just find glass to be easier to keep clean and sanitized. O2 is of no concern.
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Old 04-10-2009, 01:30 PM   #16
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Personally when it comes to fermenters, I just find glass to be easier to keep clean and sanitized. O2 is of no concern.
I use reynolds turkey bags as liners. When fermentation is done, I rack off, pull the bag, tie a knot (to later pitch the cake in the compost), rinse the bucket, and I am done. Doesn't get any easier than that.
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Old 04-23-2009, 04:15 PM   #17
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I use reynolds turkey bags as liners. When fermentation is done, I rack off, pull the bag, tie a knot (to later pitch the cake in the compost), rinse the bucket, and I am done. Doesn't get any easier than that.
That's a pretty awesome idea.
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Old 04-23-2009, 08:28 PM   #18
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Personally when it comes to fermenters, I just find glass to be easier to keep clean and sanitized. O2 is of no concern.
I used to think this also, but I just soak a Better Bottle over night in OxyClean and its done. Rinse out with hot water and plug.


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