Only 30% of a coffee bean is soluble in water, and many brewing methods aim to extract significantly less than that. So of the 1.6 billion pounds of coffee Americans consume in a year, more than 1.1 billion pounds of grounds are knocked from filters into compost bins and garbage cans.
While watching the grounds from her own espresso machine accumulate, Danli Luo , a University of Washington doctoral student in human centered design and engineering, saw an opportunity. Coffee is nutrient-rich and sterilized during brewing, so it's ideal for growing fungus, which, before it sprouts into mushrooms, forms a "mycelial skin." This skin, a sort of white root system, can bind loose substances together and create a tough, water-resistant, lightweight material.
Luo and a UW team developed a new system for turning those coffee grounds into a paste, which they use to 3D print objects: packing materials, pieces of a vase, a small statue. They inoculate the paste with Reishi mushroom spores, which grow on the objects to form that mycelial skin. The skin turns the coffee grounds — even when formed into complex shapes — into a resilient, fully compostable alternative to plastics. For intricate designs, the mycelium fuses separately printed pieces together to form a single object.
The team published its findings Jan. 23 in 3D Printing and Additive Manufacturing.
"We're especially interested in creating systems for people like small businesses owners producing small-batch products — for example, small, delicate glassware that needs resilient packaging to ship," said lead author Luo. "So we've been working on new material recipes that can replace things like Styrofoam with something more sustainable and that can be easily customized for small-scale production."
To create the "Mycofluid" paste, Luo mixed used coffee grounds with brown rice flour, Reishi mushroom spores, xanthan gum (a common food binder found in ice creams and salad dressings) and water. Luo also built a new 3D printer head for the Jubilee 3D printer that the UW's Machine Agency lab designed. The new printer system can hold up to a liter of the paste.
The team printed various objects with the Mycofluid: packaging for a small glass, three pieces of a vase, two halves of a Moai statue and a two-piece coffin the size of a butterfly. The objects then sat covered in a plastic tub for 10 days, during which the mycelium formed a sort of shell around the Mycofluid. In the case of the statue and vase, the separate pieces also fused together.
The process is the same as that of homegrown mushroom kits: Keep the mycelium moist as it grows from a nutrient rich material. If the pieces stayed in the tub longer, actual mushrooms would sprout from the objects, but instead they're removed after the white mycelial skin has formed. Researchers then dried the pieces for 24 hours, which halts the fruiting of the mushrooms.
The finished material is heavier than Styrofoam — closer to the density of cardboard or charcoal. After an hour in contact with water, it absorbed only 7% more weight in water and dried to close its initial weight while keeping its shape. It was as strong and tough as polystyrene and expanded polystyrene foam, the substance used to make Styrofoam.
Though the team didn't specifically test the material's compostability, all its components are compostable (and, in fact, edible, though less than appetizing).
Because the Mycofluid requires relatively homogeneous used coffee grounds, working with it at significant scale would prove difficult, but the team is interested in other forms of recycled materials that might form similar biopastes.
"We're interested in expanding this to other bio-derived materials, such as other forms of food waste," Luo said. "We want to broadly support this kind of flexible development, not just to provide one solution to this major problem of plastic waste."
Junchao Yang , a UW master's student in human centered design and engineering when completing this research, is a co-author, and Nadya Peek , UW associate professor of human centered design and engineering, is the senior author. This research was funded by the National Science Foundation.
