Unless you’re one of the lucky few who have the extra cash and space for a stainless steel cylindroconical fermentor, chances are you ferment your homebrew in glass or plastic. The debate over which is better is as old as the hobby itself, and you’ll find loyalists on both sides of the divide. As with most things, choosing one over the other is largely a matter of personal preference, but here are a few things to keep in mind.
Glass
A 6.5-gallon glass carboy is the time-honored fermentation vessel of choice, while 5-gallon carboys are favored for aging. Glass is rivaled only by stainless steel for ease of sanitation and, with proper care, a glass vessel can last a lifetime.
Pros
- Glass is impermeable to oxygen.
- Glass doesn’t readily scratch and is therefore less prone to contamination than plastic.
- Tough surface residue may be scrubbed off with stiff brushes that could damage plastic.
- The transparency of glass lets you observe fermentation.
Cons
- Glass vessels are heavy and can be awkward to carry, especially when full of liquid.
- Glass is usually more expensive than plastic and can incur high shipping costs.
- Wet, heavy carboys need to be handled with care. Some homebrewers have ended up in the emergency room after dropping slippery carboys.
- Glass needs to be kept in a dark location or draped with a cloth to prevent skunking from direct sunlight.
Fermenting in glass used to imply narrow carboy necks that could make cleaning and dry hopping difficult. But new products such as the Big Mouth Bubbler make this less of an issue than it used to be.
Plastic
Homebrewers have long relied on plastic fermentation buckets for their ease of use and light weight. Ported buckets remain the most popular vessels for bottling, and now some carboys such as the BetterBottle are made of plastic as well.
Pros
- Plastic is lightweight and inexpensive.
- Most plastic buckets feature convenient carrying handles and are easy to move around.
- It’s easier to pour liquid into a wide plastic bucket than into the narrow neck of a glass carboy.
Cons
- Plastic scratches more easily than glass, which may promote contamination.
- Because of the potential for cross-contamination, plastic may be less suitable than glass for beer brewed with wild yeast and bacteria such as Brettanomyces and Lactobacillus.
- Plastic buckets are opaque, so you can’t visually monitor fermentation (plastic carboys do not have this issue).
- Plastic is permeable to oxygen, making it less suitable than glass for long-term aging.
With respect to that last point, although plastic can theoretically allow beer to oxidize over a period of time, I’ve left beer in plastic carboys for months without issue. Nonetheless, beer that requires very long aging may benefit from the impermeability of glass.
Excellent fermentation vessels are made from both glass and plastic, and you can ferment great beer in either material. Think about how you like to brew beer, and choose the option that best suits your process and lifestyle.