Which U.S. industry is worth $350 billion per year and employs 2.2 million people spread across every single state and territory? Think espressos, lattes and cappuccinos; lots and lots of them, according to the National Coffee Association (NCA).
Although the figures were published before the latest administration took office — and changes in consumption since then could perhaps form an interesting investigation in its own right — that’s still 1.6 million pounds per year of roasted coffee beans.
As processes go, however, it’s wasteful. 1.6 million pounds of roasted beans leave about 1.1 billion pounds of grounds. It makes a good compost; some coffee shops here in Ireland give away the grounds for free, but the vast majority here and almost everywhere else ends up in landfills.
It was the familiar sight of a filter filling with grounds in her own espresso machine that prompted Danli Luo, a doctoral researcher at the University of Washington (UW), to investigate potential uses for them.
The outcome, described in the Jan. 23, 2025, issue of 3D Printing and Additive Manufacturing, is a process that turns grounds into a resilient, fully compostable alternative to plastics.
The title gives away the key ingredient: 3D-printed mycelium biocomposites: method for 3D printing and growing fungi-based composites.
What Luo and her colleagues in the department of human-centered design and engineering at UW did was develop a system to turn her grounds into a paste that could be used to 3D print objects.
To get to this point, the team had to create what they dubbed a mycofluid paste which could be 3D printed.
This consisted of coffee grounds (54.9% wt), water (24.7% wt), brown rice flour for the carbs (13.7% wt), ground grain spawn — mushroom mycelium grown into a certified organic grain (5.5% wt) to act as the spawning substrate, and xanthan gum (1.1% wt) as a homogenizer and binder.
This paste was first inoculated with Reishi mushroom spores.
Long used in East Asian countries to help reduce stress, improve sleep and lessen fatigue, the mushroom is well studied. However, the team was most interested in the stage before the mushroom sprouts.
In a suitable medium such as coffee grounds, the fungus puts out a root-like structure that contains a huge mass of branching, thread-like structures called hyphae. It is these that can bind loose substances together and, in this case, create a tough, water-resistant, lightweight material.
First, the mycofluid paste is shaped using a standard 3D printer with a modified head (Figure 1).
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 forming the white mycelial skin. Researchers then dried the pieces for 24 hours, which halts the mushroom fruiting.
The team printed various objects with the mycofluid, including packaging for a small glass (Figure 2), a vase and a small statue.
The objects then sat covered in a plastic tub for 10 days, during which the mycelium formed a shell around the mycofluid. In the case of the statue and vase, the separate pieces also fused together to provide even greater protection.
Using the workflow presented in this paper, the researchers believe it is possible to expand the library of mycelium-laden materials with accessible, local and recycled biomass other than spent coffee grounds.
Even so, they do acknowledge some drawbacks and limitations with the initial process.
For one, sterility must be maintained throughout the 3D-printing process and during the spawn run to avoid the growth of unwanted molds.
The mycelium on the bottom layer of the packaging needs air exchange for growth, but it is still malleable during incubation, so operators must work carefully when exposing it.
Printing quality is influenced by both the material and the machine: there are no sensors to detect clogs, excessive material flow or other factors that might affect the final print, for example.
Fabrication is slow; it typically takes over a week in incubation for the mycelium to form robust and sustainable products.
The study also did not include a formal compostability test. However, the team points out that all the components involved are indeed compostable. “In fact, edible, though less than appetizing,” they admit.
Luo added that the team now is further investigating the self-fusing properties of mycelium, which opens exciting possibilities for creating more complex structures and functionality without traditional assembly methods.
“The broader vision for our project is to develop pathways for small-scale production and experimental fabrication using renewable biomaterials. We see this as an opportunity to democratize access to sustainable material production rather than focusing on industrial-scale optimization at this stage,” she told Chemical Processing.
