Billions of pounds of coffee grounds go to waste each year. Now, scientists from the University of Washington are aiming to put those wasted beans to use. (Photo by KATY TOMEI on Unsplash)
New water-resistant material also made with mushroom tissue can be created using a 3D printer
In a nutshell
- Researchers have developed a way to turn used coffee grounds into durable, water-resistant materials by combining them with mushroom tissue in a 3D printing process. This could help address the more than 1.1 billion pounds of coffee grounds Americans discard annually.
- The resulting material performs similarly to Styrofoam but is fully biodegradable. When printed objects are placed together during a 10-day growth period, the mushroom tissue naturally fuses the pieces, enabling complex shapes that would be difficult to create as single prints.
- While currently best suited for small-scale production, the technology is accessible and open-source, with a complete printing system costing around $1,700. This makes it particularly promising for small businesses needing custom sustainable packaging or product displays.
SEATTLE — Every cup of coffee leaves behind a problem: wet, used grounds that typically end up in landfills. However, in a University of Washington laboratory, discarded coffee grounds are getting an unexpected second life. Rather than heading to landfills, these spent grounds are being transformed through an innovative combination of 3D printing and mushroom biology. Researchers have created a new way to transform spent coffee grounds into 3D print sustainable objects that can actually grow stronger over time.
Each year, Americans consume 1.6 billion pounds of coffee, but only 30% of each coffee bean actually dissolves during brewing. This leaves more than 1.1 billion pounds of coffee grounds destined for compost bins and landfills annually, enough to fill roughly 2,000 Olympic-sized swimming pools. While many coffee shops and home brewers try to compost their grounds, much still ends up in landfills where it generates methane, a potent greenhouse gas.
This innovative solution, discovered in research published in 3D Printing and Additive Manufacturing, was inspired by an everyday observation. While watching grounds accumulate from her espresso machine, doctoral student Danli Luo recognized an opportunity. Coffee grounds, being nutrient-rich and naturally sterilized during brewing, provide an ideal growing medium for fungi.
“We’re especially interested in creating systems for people like small business owners producing small-batch products — for example, small, delicate glassware that needs resilient packaging to ship,” says 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.”
Luo et al./3D Printing and Additive Manufacturing)
How do you make this susatainable new packaging?
The key to this transformation lies in mycelium, the root-like network of fungal threads that mushrooms use to grow and digest nutrients. Before a mushroom ever sprouts its familiar cap, mycelium spreads through its food source, creating a dense network of tiny white fibers. This natural process effectively binds loose materials together while creating a water-resistant outer layer, properties that make it ideal for manufacturing.
Moving beyond traditional petroleum-based plastics in 3D printing, the team developed a material called “Mycofluid” by combining recycled coffee grounds with carefully selected ingredients. Their recipe uses spent espresso grounds (54.9%), brown rice flour (13.7%), Reishi mushroom spawn (5.5%), and a common food thickener called xanthan gum (1.1%), the same ingredient that gives salad dressings and ice cream their smooth texture. Water (24.7%) brings everything together into a printable paste.
To work with this unique material, the researchers created a specialized 3D printer called “Fungibot.” Unlike conventional 3D printers that work with solid plastic filaments, Fungibot is designed to handle thick pastes. They modified a Jubilee 3D printer from UW’s Machine Agency lab, adding a custom printhead that can hold up to a liter of Mycofluid. At about $200 for the extruder and $1,500 for the motion platform, the system remains relatively affordable for research and small-scale production.
Once an object is printed, it enters a crucial 10-day growth period in a covered container, similar to the environment used for growing mushrooms at home. During this time, the mycelium colonizes the coffee ground structure, spreading throughout the material and creating what researchers call “mycelial skin.” This living process transforms the printed object from a fragile coffee paste into a durable, water-resistant material.
How strong is the material?
Though heavier than Styrofoam, closer to the density of cardboard or charcoal, the resulting material proves surprisingly resilient. When submerged in water, the mycelium-enhanced material only absorbs 7% more weight and returns to nearly its original weight upon drying while maintaining its shape. Traditional coffee-based materials, in contrast, would simply dissolve. Testing showed strength and toughness comparable to polystyrene and expanded polystyrene foam (Styrofoam), making it a viable alternative for many applications.
The living nature of mycelium enables a unique manufacturing capability: parts can grow together. The team demonstrated this by printing complex objects in sections, such as a decorative vase in three parts and a Moai statue in two halves. When the pieces are placed together during the growth period, the mycelium bridges the gaps, naturally fusing them into a single, solid object. They even created a small butterfly-sized coffin in two pieces that fused into a seamless whole, showcasing the potential for creating biodegradable alternatives to traditional materials.
Bringing the Fungibot to a business near you
The technology shows particular promise for small-scale manufacturing and custom packaging. A local pottery studio, for instance, could print custom protective packaging for shipping delicate pieces, knowing their packing materials would break down naturally after use. Small businesses could create tailored product displays or packaging that align with their sustainability goals without investing in expensive mold-making equipment.
While scaling up presents challenges due to the need for relatively uniform coffee grounds, the researchers are already exploring other recycled materials that could form similar bio pastes.
“We’re interested in expanding this to other bio-derived materials, such as other forms of food waste,” says Luo. “We want to broadly support this kind of flexible development, not just to provide one solution to this major problem of plastic waste.”
As researchers continue exploring new applications for this technology, the implications extend beyond just coffee grounds. The same principles could potentially apply to other forms of food waste, creating a network of local, sustainable manufacturing systems. Each innovation in bio-based materials brings us closer to reducing our dependence on petroleum-based plastics.
Paper Summary
Methodology
The process begins with collecting spent espresso coffee grounds, which are already partially sterilized through the brewing process. Researchers mix these grounds with brown rice flour, Reishi mushroom spawn, xanthan gum, and water to create Mycofluid. The team modified a Jubilee 3D printer with a custom printhead capable of handling up to a liter of this paste. After printing, objects are placed in a covered plastic tub for approximately 10 days – similar to the environment used for home mushroom growing kits. During this period, the mycelium forms its characteristic white “skin” around the structure. The process concludes with a 24-hour drying period that halts any further fungal growth, preventing actual mushrooms from sprouting.
Results
Testing revealed several significant performance metrics. The final material, while denser than Styrofoam, achieved comparable strength and toughness to traditional polystyrene materials. In water resistance tests, the colonized material only absorbed 7% additional weight when submerged and returned to nearly its original weight after drying, all while maintaining its structural integrity. The team successfully demonstrated the material’s versatility through various applications, including a three-part vase, a two-piece Moai statue, and custom packaging for delicate glassware. The density of the finished product proved similar to cardboard or charcoal. It was heavier than Styrofoam but still practical for many applications.
Limitations
Several practical constraints emerged from the research. The process requires relatively homogeneous coffee grounds, which could present challenges for large-scale production. While the ingredients are all technically compostable and even edible (though unappetizing), formal compostability testing wasn’t conducted. The 10-day colonization period plus drying time means this isn’t a rapid manufacturing process. Additionally, the need to maintain proper moisture levels and sterile conditions during growth limits production environments.
Takeaways and Discussion
This research addresses multiple sustainability challenges simultaneously: utilizing the over 1.1 billion pounds of coffee grounds Americans dispose of annually, creating biodegradable alternatives to petroleum-based packaging materials, and developing accessible manufacturing methods for small-scale producers. The team’s open-source approach and focus on small business applications suggests a path toward more sustainable, localized production methods. While not a complete solution to plastic waste, the research demonstrates the potential for bio-derived materials in manufacturing.
Funding and Disclosures
The project received support from the National Science Foundation under Grant No. 2029249. The research team included Danli Luo (lead author), Junchao Yang (who was a UW master’s student in human centered design and engineering during the research), and senior author Nadya Peek, UW associate professor of human centered design and engineering. No competing financial interests were declared.
Publication Information
This research, titled “3D-Printed Mycelium Biocomposites: Method for 3D Printing and Growing Fungi-Based Composites,” was published on January 23, 2025, in the journal 3D Printing and Additive Manufacturing (Volume 00, Number 00, 2025) by Mary Ann Liebert, Inc. The work was conducted at the University of Washington’s Human-Centered Design and Engineering department, specifically utilizing the Machine Agency lab’s facilities and equipment.
