For at least 500 years, humans have turned to coffee for a variety of purposes. Whether it’s a pick-me up in the morning, or over ice to cool down, many rely on this magical bean every single day. Yet researchers have suggested that coffee might have an additional use beyond simply being consumed in a mug.

According to a new study, it could also help reduce the waste from 3D printing.

That’s the vision behind a new project led by Michael Rivera, an assistant professor in the ATLAS Institute and Department of Computer Science at the University of Colorado Boulder. He and his colleagues have developed a method for 3D printing a wide range of objects using a paste made entirely out of old coffee grounds, water and a few other sustainable ingredients.

The team has already experimented with using coffee grounds to craft jewellery, pots for plants and even, fittingly, espresso cups. The researchers claim that the technique is also simple enough that it will work, with some modifications, on most low-cost, consumer-grade 3D printers.

“You can make a lot of things with coffee grounds,” Rivera said. “And when you don’t want it anymore, you can throw it back into a coffee grinder and use the grounds to print again.”

The group presented its findings this summer at the Association for Computing Machinery’s Designing Interactive Systems conference in Pittsburgh.

For Rivera, the project is part of his mission to make 3D printing more sustainable—allowing artists, designers, engineers and more to quickly make graspable prototypes and other household objects without adding to landfills.

“Our vision is that you could just pick up a few things at a supermarket and online and get going,” Rivera said.

How do you even get to the point of trying coffee in a 3D printer though? Well, somewhat predictably, it began in a coffee shop.

When Rivera was a graduate student at Carnegie Mellon University, he often worked out of a café in Pittsburgh called Arriviste Coffee Roasters. The coffee shop contracted with a local group to pick up its used coffee grounds for composting, but during the COVID-19 pandemic, that wasn’t possible. The waste began to pile up.

“The owner told me, ‘I don’t know what to do with it. So I just throw it away,’” said Rivera, who joined CU Boulder as a postdoctoral researcher in 2022. “I looked at the grounds and said, ‘Maybe I can do something with them.’”

Rivera explained that most consumer 3D printers on the market today print with thermoplastics of some kind. The most common is polylactic acid, or PLA. This material is, theoretically, compostable, but only a fraction of composting facilities will accept it.

“If you throw it in a landfill, which is wher the majority of PLA ends up, it will take up to 1,000 years to decompose,” Rivera said.

Rivera his colleagues mix dried coffee grounds with two other powders that they buy online: cellulose gum and xanthan gum. Both are common additives in food and degrade easily in a compost bin. Next, the researchers mix in water.

“You’re pretty much shooting for the consistency of peanut butter,” Rivera said.

“We’ve made objects with a ton of usage,” he continued. “We’ve dropped them, and they haven’t broken yet.”

He sees a lot of potential for turning coffee grounds into tangible objects. Rivera, for example, has made small planters out of coffee grounds, which can be used to grow seedlings for acid-loving plants like tomatoes. once the plants get tall enough, you can plant them, pot and all, in the soil. The team can also add activated charcoal to its grounds to make parts that can conduct electricity, such as buttons for sustainable electronics.

Rivera noted that printing with coffee grounds may never become a widespread practice. Instead, he sees the project as a step toward discovering other kinds of sustainable 3D printing materials that could, one day, replac plastics.