Millions of people around the world drink coffee to boost their energy. Researchers in South Korea have now given new meaning to the concept of coffee as fuel.
The team from the Korea Institute of Geoscience and Mineral Resources (KIGAM) report a way to convert soggy coffee grounds into a high-quality coal-like fuel. The process, reported in the journal Chemical Engineering Journal, takes just 90 seconds from start to finish. And the final product has fuel performance comparable to conventional charcoal, according to the researchers.
The world generates almost 10 million tons of waste coffee grounds each year. Most of this ends up in landfills or gets incinerated. The spent grounds hold a lot of energy because of their high calorific value. But they have a high moisture content, so using them as any kind of biofuel would first require a long drying process or oil extraction.
But the KIGAM researchers eliminated the pre-drying step. Instead, they developed a way to use the moisture to accelerate the reactions and improve the quality of the solid fuel.
In the new technique, called flame plasma pyrolysis, the researchers start with coffee grounds containing around 55% moisture. They create a plasma flame by burning liquefied petroleum gas and compressed air. This creates a plasma as hot as 900°C and puts the coffee waste under immense pressure.
The pressurized heat rapidly vaporizes the moisture, triggering hundreds of tiny explosions in the coffee grounds, reducing the mass of the grounds by 83.3% and transforming them into a dry, porous biochar, all within 90 seconds.
The process boosts the calorific value of the coffee gounds by about 33%. The biochar exhibited a heating value of 29 megajoules per kilogram, comparable to that of coal.
According to a press release, the new process should work on any high-moisture organic wastes, such as food waste, sewage sludge, and agricultural residues. “We plan to expand the technology to various types of high-moisture organic waste and further optimize the process for industrial-scale commercialization,” said Taejun Park, lead author of the study.
Source: Taejun Park et al. Rapid conversion of wet spent coffee grounds into high-calorific biochar via drying-free flame plasma pyrolysis for process intensification. Chemical Engineering Journal, 2026.
