PET Permeability
Introduction
Many hundreds of thousands of BetterBottle's unique PET carboys have been sold since their introduction in July of 2003. Already widely available in the US, Canada, Europe, Australia, and New Zealand and distributed by all the major suppliers of premium wine kits and wholesalers of home winemaking and brewing supplies, BetterBottle carboys are clearly performing extremely well.

Discussion
BetterBottle PET carboys are made of plastic; however, they are not like other plastic carboys. First of all, they are made of a special PET and secondly they are made in a manner that packs the plastic molecules very tightly and creates a delicate balance between microcrystaline and amorphous regions.1 They are especialy well suited for home winemaking and brewing. So, why do rumors that no plastic is acceptable persist here and there? In the first place, many people have experienced failures attempting to use carboys made from types of plastic that are known to be too permeable to oxygen and to scalp flavors (see Flavor Scalping). Secondly, the mistaken belief that all plastics are the same is occasionally reinforced by sporadic reports of failures involving BetterBottle carboys. Making a good wine or beer is an art and results do not always meet expectations, regardless of whether the winemaker or brewer uses a glass carboy or BetterBottle carboy.


 

Yes, BetterBottle PET carboys are slightly more permeable than glass; however, it would be a mistake to assume that using a glass carboy will necessarily guarantee superior results. The minute traces of oxygen that penetrate BetterBottle PET carboys are incredibly difficult to measure and insignificant when compared with the amounts of oxygen diffusing through, or leaking past, many types of  carboy caps and stoppers (especially silicone stoppers), liquid-filled air locks, and many types of flexible tubing. Moreover, oxygen diffuses into, and reacts with, wine and beer so quickly that removing a closure from a carboy, even briefly, for testing and making adjustments can allow a relatively large amount of oxygen to enter. Wine and beer essentially suck up oxygen. And racking from one open carboy to another open carboy with a siphon, a pretty standard approach when glass carboys are used, will add a great deal of oxygen in an uncontrolled manner.

Breakthrough Technology - Exciting new instrumentation, has made it possible to measure oxygen concentrations from 0.001% to 25% in closed spaces,  quickly and easily. BetterBottle technicians used this technology to determine how permeable or leaky a wide variety of closures and air locks are. Many, perhaps even most, home winemakers and brewers have been fermenting and aging under conditions involving considerably more oxygen than they imagined. Click HERE to view the report (1.5Mb PDF).

The uncontrolled, excessive entry of oxygen is the real problem, because the addition of the micro amounts of oxygen, depending on the wine or beer, is can be beneficial.2,3,4 Wineries that ferment many hundreds of gallons of wine in a single tank may actually prefer polyethylene tanks, because the volume of wine is so huge compared to the surface area of their tanks. Polyethylene, or other similarly permeable material, cannot be used to make fermenters for small batches of wine and beer, because the volumes are small compared to the surface area of the fermenters. Using a BetterBottle fermentation system, even a novice will find it easy to rack or bottle cleanly under conditions that control oxygen exposure (Use the Products tab at the top of page to access How-To Tips).

1 Liu, R Y F. et al. Crystallinity and Oxygen Transport Properties of PET Bottle Walls. J. Applied Polymer Science. 2004 Vol. 94,671-677 (Accessed 01/15/12)
2 Kelly, M. and Wollan, D. Micro-oxygenation of Wine in Barrels. The Australian & New Zealand Grapegrower & Winemaker 2003, Technical Issue
3 Flecknoe-Brownn, A. Oxygen-permeable polyethylene vessels: a new approach to wine maturation. Grapegrower & Winemaker March 2005(Accessed 01/15/12)
4  Davis, K., Science trumps tradition at Napa wine-making facility.  Napa Valley Register 10/01/10 (Accessed 01/15/12)