In Sam Calagione's book, "Extreme Beer: An Enthusiast's Guide to Brewing Craft Beer at Home," he notes some very good points regarding glass or plastic in brewing:
- Glass is a lot easier to clean and has less chance for contamination than plastic.
- Plastic fermenters work fine, but can be difficult to clean because they have a flat bottom.
- Plastic is usually more porous than a glass carboy.
- On rare occasions, ingredients may be larger than the opening of a glass carboy (especially when adding ingredients that are used in brewing extreme beers), and plastic buckets work better because of their large openings.
- Many types of plastic are permeable by oxygen.
- If using plastic, a newer type of carboy made from plastic called PET (polyethylene terephthalate) has recently been introduced to the homebrewer. PET is not permeable by oxygen.
- PET carboys are lightweight(1 1/2 lbs. vs. 14 lbs. for a 6 1/2 gallon glass carboy)
- PET carboys won't break.
- You can more easily see how well your beer is fermenting and when it is done if you use a glass carboy.
- Plastic buckets do not seal as well as glass carboys.
Even with the pros and cons of each, Sam recommends an upgrade to a glass or PET carboy.