bourgeoisbee said:
I know plastic is obviously more permeable than glass, but are there studies that test permeability of the plastic in a bucket compared to the plastic in a better bottle? Many people have secondaried beers with one or more of brett, lacto, pedio in plastic with great success. Take
Oldsock for example, he uses lots of better bottles and has made tons of great funky beers in them. Cantillon, Russian River, etc age in oak barrels, which far are more permeable than glass/stainless.
Depending on the barrel sizes used, compared to a 20L (roughly 5gal) HDPE plastic fermentor, the permeability of the plastic allows a LOT more oxygen to diffuse into a given volume of beer, for instance (roughly):
* 415 times and 256 times more than the large (~5,300gal) and small (~2,200gal) wooden tuns that Rodenbach uses, respectively
* 26 times and 10 times more than 80gal and 10gal oak barrels, respectively
*for the hell of it... 13 times and
2,200 times more than a 5gal glass carboy with a silicon stopper and a wooden stopper, respectively
*and to get things from a slightly different perspective, these 3 things have roughly the same permeability: 5gal glass carboy w/ silicone stopper, 10gal oak barrel, and a 53gal HDPE plastic fermentation tank (same plastic as an "Ale Pail")
As for the Better Bottles, which are made of PET rather than HDPE plastic, the manufacturer claims that there is negligible/no oxygen permeability. But MANY people have raised serious doubts about the veracity of these claims, and still more have suggested, with some degree of evidence, that it somehow becomes increasingly permeable over time.
As far as I know though, there are no completely reliable figures available to substantiate anyone's claims on the matter, let alone allow it to be directly compared to pretty much every other kind of fermentor, for which the numbers not only exist, but are widely available.
Basically, a Better Bottle may be (and I would even say probably is) a decent choice, but I prefer being able to calculate roughly how much gas exchange is occurring in order to be able to be able to modify it in a deliberate manner, should I choose, or even adapt recipes to new conditions. But I would never, ever, use a HDPE plastic bucket (or anything made of that plastic smaller than 2bbl) to ferment a sour/wild beer. So for now, I stick with glass carboys and do what I can to control the oxygen based on what I'm making.