Ethically Kate: Can I really put ‘compostable’ coffee cups in my compost?

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.

You may be thinking “Okay cool, I’ll just find a commercial compost factory then,” but there are several issues with this. Firstly, you’ll struggle to find one. Also, the function of a takeaway coffee cup is to use it on the go and get rid of it. How many people do you think would carry it around for the entire day until they find a bin they can trust will take it to a commercial compost facility?

Secondly, the coffee cup will not add any nutrients to the soil created by the commercial compost plant. Now that PLA is being used so prolifically, there is growing research and concerns around how large quantities of decomposed PLA could negatively affect the health of our soils.

Lastly, a single-use coffee cup made from anything is, in my opinion, a silly idea. Take your “compostable” cup for example. Chances are you felt better getting a coffee from a place with “compostable” on their cups because you try to do the best thing for the environment. Unfortunately, that cafe and packaging company has just greenwashed you.

That cup took resources (from a planet with finite resources) to create, it travelled to the cafe most likely in a petrol-guzzling vehicle for thousands of kilometres, and you used it for five minutes before throwing it away. Most PLA cups end up in landfills (which is a big issue to discuss another day) but if they do end up being transported to a commercial composting plant this takes more resources, more time, more fuel, and could have all been avoided with the “no cup, no coffee” rule. Single-use cups, compostable or not, do not make logical sense in most situations.

Next time you need a coffee, bring a mug from your office, take a cup from your car, sit down to have your cuppa, or go without.

- Kate Hall, The New Zealand Herald