Homebrewer's Guide to Plastics - by genthree
The quickest way to determine what kind of plastic something is made of is by looking at its recycle code (if it has one).
Here's a typical code shown left.
Plastic Codes
RC 1 - polyethylene terepthalate (PET)
Most commonly seen as plastic coke bottles, this is a form of polyester. It has high heat resistance and is an excellent oxygen and moisture barrier, making it excellent for homebrewing. One thing to watch out for, though, is that at high temperatures or sunlight exposure, it can degrade and release potential harmful products like phthalates and heavy metal catalysts.
Good properties for homebrewing, but keep out of sunlight and don't pour extremely hot wort into it. Do not use if it is discolored (yellowed)
RC 2 and 4 - high and low density polyethylene (LDPE and HDPE)
Extremely common plastic. High density (RC 2) is what is used in plastic bottle caps and hardhats. Low density (RC 4) is what milk jugs are made of. From a chemical point of view, this is the simplest plastic possible. This is good because it is pretty much completely inert in your body and poses no health threats. The downside is that it has limited heat resistance. RC 4 begins to deform at around 85C (below water's boiling point) and RC 2 begins to deform around 110C (above the boiling point, but I'd still be careful).
Excellent from a health point of view, but poor temperature resistance. Choose RC 2 when possible and do not pour boiling hot wort into it.
RC 3 - polyvinyl chloride (PVC)
This is most commonly seen as PVC pipe, but is used for a wide variety of things. There are a number of different forms and some are better for homebrewing than others. As a general guide, the more rigid the plastic is, the safer it is for homebrewing. In order to make them more flexible, chemicals are added which can leach into your beer and potentially cause problems. There is still a large amount of debate about the safety of PVC.
While a useful plastic, there are many forms that can be hard to tell apart. It may be best to avoid using PVC unless you are confident that the form you have is safe.
RC 5 - Polypropylene (PP)
Very similar in structure to polyethylene, PP is most familiar to homebrewers as the hard plastic used in a flip top bottle. It is also used as the lid for tic-tacs and is the material used in those large plastic barrels. PP is very chemically inert and does not pose a significant health concern. It has slightly better heat resistance than polyethylene, but should be kept out of sunlight as this can cause it to degrade.
Safe and useful. Slightly higher melting point than polyethylene. Keep out of sunlight.
RC 6 - Polystyrene (PS)
Polystyrene is used in a wide variety of places. It is used to make styrofoam as well as in take-away food containers and plastic flower pots. It is relatively brittle at room temperature , but begins to get soft at 100C (water's boiling point) and can release styrene monomer when heated. Styrene monomer has been linked to cancer, but the FDA has approved the use of PS for food packaging claiming that the styrene is at low enough levels to not cause concern. Personally, I would be uncomfortable heating polystyrene, but you can take whatever risks you would like.
Brittle at room temperature, melty at boiling temperature, releases cancerous chemical. Probably best to avoid for homebrewers.
RC 7 - Other (most commonly polycarbonate)
RC 7 is the catch-all for other plastics and tells pretty much nothing about the chemical structure. The most common plastic seen with RC 7 is polycarbonate (hard nalgene bottles/baby bottles). This was the plastic that caused the whole BPA scare. It's generally fine for room temperature liquids, but I would not put hot liquids into it. That said, I think BPA has been blown out of proportion.
This code tells you little. Generally best to avoid the unknown.
Most commonly seen as plastic coke bottles, this is a form of polyester. It has high heat resistance and is an excellent oxygen and moisture barrier, making it excellent for homebrewing. One thing to watch out for, though, is that at high temperatures or sunlight exposure, it can degrade and release potential harmful products like phthalates and heavy metal catalysts.
Good properties for homebrewing, but keep out of sunlight and don't pour extremely hot wort into it. Do not use if it is discolored (yellowed)
RC 2 and 4 - high and low density polyethylene (LDPE and HDPE)
Extremely common plastic. High density (RC 2) is what is used in plastic bottle caps and hardhats. Low density (RC 4) is what milk jugs are made of. From a chemical point of view, this is the simplest plastic possible. This is good because it is pretty much completely inert in your body and poses no health threats. The downside is that it has limited heat resistance. RC 4 begins to deform at around 85C (below water's boiling point) and RC 2 begins to deform around 110C (above the boiling point, but I'd still be careful).
Excellent from a health point of view, but poor temperature resistance. Choose RC 2 when possible and do not pour boiling hot wort into it.
RC 3 - polyvinyl chloride (PVC)
This is most commonly seen as PVC pipe, but is used for a wide variety of things. There are a number of different forms and some are better for homebrewing than others. As a general guide, the more rigid the plastic is, the safer it is for homebrewing. In order to make them more flexible, chemicals are added which can leach into your beer and potentially cause problems. There is still a large amount of debate about the safety of PVC.
While a useful plastic, there are many forms that can be hard to tell apart. It may be best to avoid using PVC unless you are confident that the form you have is safe.
RC 5 - Polypropylene (PP)
Very similar in structure to polyethylene, PP is most familiar to homebrewers as the hard plastic used in a flip top bottle. It is also used as the lid for tic-tacs and is the material used in those large plastic barrels. PP is very chemically inert and does not pose a significant health concern. It has slightly better heat resistance than polyethylene, but should be kept out of sunlight as this can cause it to degrade.
Safe and useful. Slightly higher melting point than polyethylene. Keep out of sunlight.
RC 6 - Polystyrene (PS)
Polystyrene is used in a wide variety of places. It is used to make styrofoam as well as in take-away food containers and plastic flower pots. It is relatively brittle at room temperature , but begins to get soft at 100C (water's boiling point) and can release styrene monomer when heated. Styrene monomer has been linked to cancer, but the FDA has approved the use of PS for food packaging claiming that the styrene is at low enough levels to not cause concern. Personally, I would be uncomfortable heating polystyrene, but you can take whatever risks you would like.
Brittle at room temperature, melty at boiling temperature, releases cancerous chemical. Probably best to avoid for homebrewers.
RC 7 - Other (most commonly polycarbonate)
RC 7 is the catch-all for other plastics and tells pretty much nothing about the chemical structure. The most common plastic seen with RC 7 is polycarbonate (hard nalgene bottles/baby bottles). This was the plastic that caused the whole BPA scare. It's generally fine for room temperature liquids, but I would not put hot liquids into it. That said, I think BPA has been blown out of proportion.
This code tells you little. Generally best to avoid the unknown.
