If you drink soda — pop, Coke, or whatever you call fizzy sugar water in your neck of the woods — you know what PET bottles are. These plastic bottles are used in the soda industry because they are lightweight and retain carbon dioxide (CO2) in carbonated beverages. Many homebrewers wonder if these would make suitable beer containers. There certainly would be a variety of benefits to using them.
Environmentally-conscious homebrewers may like that they could reuse a bottle rather than throwing it away (if they live somewhere without recycling). If they drink soda, cost-conscious homebrewers might see a source of essentially free bottles. Homebrewers who like hiking and camping would have a lightweight container that could easily be packed in and packed out of a campsite. In fact, most homebrewers can probably think of a time when having beer in a lightweight, disposable package would be a benefit. For example, if you’re going to a party and don’t want to bring a full keg, or lug a case of beer in glass bottles, you could bring a couple 2-L or 3-L bottles. And when you leave, you could just leave the bottles behind. You might not want to do that with “nice” bottles of homebrew (heavy, dark bottles with the labels removed).
In addition, PET bottles are essentially unbreakable; if you drop one, you won’t be cleaning shards of broken glass off the floor. So, if they are such a great container, why don’t commercial breweries use them?
PET and Oxygen Permeability
PET bottles (sometimes called PETE bottles, and bearing the #1 recycling code) are made from polyethylene terephthalate. There are lots of different variants of PET bottles. For this article, I’ll limit the discussion solely to the “regular,” thin-walled soda bottles. As I mentioned, one reason to use PET bottles for soda is the ability of PET containers to retain carbon dioxide (CO2). However, the permeability of PET with regards to oxygen is a concern of brewers. Keeping CO2 in is a necessary feature of a beer bottle, but keeping oxygen (O2) out is also important. If oxygen can enter the bottle, the beer will go stale faster. And this is why you don’t see commercial beer packaged in “ordinary,” thin-walled PET bottles — they are permeable to oxygen. (There are thicker bottles and specialty bottles that use a layer of polyvinyl alcohol between layers of PET to lower oxygen permeability.) In addition, many PET bottles are clear and most brewers would prefer a dark bottle to prevent the beer from becoming lightstruck.
On the Other Hand . . .
Commercial breweries don’t sell beer in regular PET bottles because the shelf life of their product would be lowered. Likewise, if you are a homebrewer who is bottling a beer you intend to age, I would not recommend putting it in PET bottles. However, there are some times when bottling in PET would be acceptable.
Oxygen permeability isn’t an all-or-nothing kind of thing. The rate of oxygen ingress is important. As mentioned before, PET bottles retain CO2 very well. Oxygen gas (O2) is a slightly smaller molecule and some can cross through the plastic. The rate at which this occurs is sufficiently high to rule out long-term storage of beer (as long as commercial beer might reasonably sit on a store’s shelf). However, over shorter terms, the rate is small enough that it shouldn’t cause a problem.
Certainly, beer can be stored in PET bottles for very short amounts of time, hours or a few days. If you fill a few bottles from a keg to bring to a party, homebrew club meeting or weekend camping trip, your beer will be fine. The amount of oxygen exposure from transferring the beer to the bottle would greatly exceed the amount of oxygen that reached the beer by passing through the walls of the bottle.
In my homebrew club, lots of brewers bring their beer to the meetings by filling a PET bottle from the keg, then attaching a Carbonator Cap. This is a cap that screws onto a 2-L soda bottle and connects to a standard Corny keg gas in fitting (ball lock). Storing the bottle for a short time under regular keg CO2 serving pressure ensures that any carbonation lost when filling the bottle is replaced. (The manufacturer recommends not exceeding 40 PSI when using the cap on plastic bottles.)
Beer can even sit for a few weeks in a PET bottle — long enough to bottle condition before being served — and still not taste recognizably different from homebrew bottled in glass or kegged.
The maximum length of time that beer would stay good in a PET bottles depends on a few things — temperature, how careful the brewer was to exclude oxygen when transferring the beer to the bottles, and how sensitive the beer drinker is to oxidized notes in their beer. In graduate school, I bottled a fair amount of beer in 2-L PET bottles out of necessity. Also, I had far more beer than I had fridge space. Based on my experiences, I would tentatively say that you can store beer in PET bottles at room temperature for 2 months and still have it taste reasonably fresh. (Fresh enough that someone who knows what oxidized beer tastes like isn’t going to be offended.) Keep the beer in a box or closet to shield it from light. Stored cold, it should stay fresh longer, but not the 6 to 8 months that ordinary homebrew (in glass bottles) remains fresh.
So, if you think your beer might sit around for awhile, either keg it or put it in glass bottles. However, if you know of an event in the next couple months for which having beer in a lightweight, disposable (or recyclable) bottle would be a benefit, don’t be afraid to bottle however much you think you’ll use in PET bottles.
The Best Use for PET Bottles in Homebrewing
I have found one very good use of PET bottles in homebrewing — as a yeast starter container. The 3-L soda bottles have a wider mouth than the 2-L bottles. A #6.5 or #7 stopper — the same size used in most carboys — fit’s the 3-L bottle’s opening. In a 3-L vessel, you can ferment about 2.5 L of starter wort. This is enough volume to raise sufficient yeast for 5.0 gallons (19 L) of ale up to OG 1.070. Soda bottles are sanitary until opened, so a light cleaning followed by a quick soak in sanitizing solution is all you need to prepare the bottle. Be sure to cool your starter wort before transferring it to a PET bottle.