OPINION
Q: My coffee cup says “compostable” on it. Can I actually put this in my compost?
A: The short answer is “no” and the long answer is a story about greenwashing that will inspire you to never use those cups ever again.
A coffee cup labelled compostable is generally made of PLA (polylactic acid); plastic most likely made from cornstarch or other fermented plant starch. PLA can only break down in certain conditions which are found at commercial compost facilities. A commercial compost reaches temperatures of up to 70 degrees Celsius and has controlled levels of nitrogen, oxygen, and carbon dioxide to ensure the composting process is happening as fast and efficiently as possible.
No matter how brilliant you are at composting in your own backyard, your compost is unlikely to reach temperatures of 60-70 degrees Celsius. Even if it does reach those high temperatures (my hot compost hit 65 degrees last year), it won’t stay that temperature for the amount of time PLA needs to break down. A commercial compost plant has carefully monitored stages, equipment, and advanced technology that ensures your coffee cup made from PLA can break down within 12 weeks.