Let's start with the standard food grade high density polyethylene (HDPE) container. HDPE is somewhat permeable to oxygen and other gases. This will provide for a slow and continuous gas exchange during the lengthy fermentation and may aid in the growth of the Brettanomyces and subsequent flavor development and maturation. This is purely speculation based on the fact that wood is also gas permeable and is the traditional material used for lambic fermentation.
Another type of plastic container commonly used by homebrewers is the 5 gallon water bottle made of polycarbonate (PC) plastic. PC is harder and more rigid than HDPE and has about twice the gas permeability for both oxygen and carbon dioxide(17). As mentioned for HDPE this gas permeability may be of some advantage in the long term aging of lambic-style beers. PC being a plastic has the same perceived disadvantage as HDPE in that it can be scratched and thus harbor bacteria and wild yeast. PC has the advantage of being able to withstand boiling water without melting unlike HDPE. This allows one to thoroughly sanitize such a container since the whole vessel can be heated to a temperature that will kill all bacteria and yeast. This can be done using boiling water or an autoclave. Remember, be very careful when pouring boiling water into a container to avoid personal injury. PC is a clear plastic that allows observation of the fermentation process over time. This quality seems to be important for those first time lambic- style ale brewers who worry whether or not their beer is developing a pellicle or ropiness.
Ref 17. Nalgene Labware Catalog 1995, Nalge Company Rochester NY.
