Used Coffee Grounds Can Make Biodiesel, Study Finds

Every year, billions of pounds of coffee are brewed worldwide — and most of that coffee ends up as spent grounds, often discarded without a second thought. But what if those grounds could be more than waste? A team of US scientists asked that question and came up with a surprising answer: yes, you can make fuel from them.

Yes, used coffee grounds can be turned into biodiesel. According to a study by University of Nevada researchers, global coffee production yields over 16 billion pounds of grounds annually, which contain 11–20% bio-oil. That adds up to more than 340 million gallons of biodiesel per year.

How Coffee Grounds Become Biodiesel

The research, led by University of Nevada engineering professors Mano Misra, Narasimharao Kondamudi, and Susanta Mohapatra, focused specifically on spent coffee grounds — the leftover solids from brewed coffee. While scientists had long known that coffee contains some oil, this team conducted the first detailed analysis of actual coffee grounds. They collected 50 pounds of used grounds from several Starbucks locations, dried them in an oven, and then extracted the oil using chemical solvents. The solvents are reusable, and the leftover solids can serve as fertilizer, ethanol feedstock, or fuel pellets.

How Much Oil Is Really in Coffee Grounds?

The study found that the extracted coffee oil typically makes up around 15% of the weight of the spent grounds. That’s lower than oils from soybeans, rapeseed, or palm, which are more commonly used for biodiesel. However, coffee oil has a stability advantage: it contains more antioxidants, which help it resist degradation. The energy required for the extraction process is relatively low, and the resulting biodiesel could potentially be sold for around $1 per gallon.

Challenges to Large-Scale Production

Despite the promising numbers, there’s a big catch: collecting enough used coffee grounds efficiently at scale is difficult. The researchers noted that while the process works in principle, scaling it up would require a reliable, steady supply of grounds. To test the idea, they planned to establish a small pilot system the following year, sourcing grounds directly from Starbucks and sending them to a biodiesel processing facility. Even if every coffee ground in the world were converted to biodiesel, the total output would still be less than 1% of the diesel used in the US annually.

Why This Still Matters

"Using coffee grounds to produce diesel won’t replace petroleum," said Dr. Misra, "but it’s one way to reduce our environmental footprint. Our goal is to turn waste into useful fuel." An added curiosity? Vehicles running on coffee-based biodiesel may even emit a slight coffee aroma.

Frequently Asked Questions

How much biodiesel can be made from coffee grounds each year?

According to the University of Nevada study, global coffee production generates over 16 billion pounds of used grounds annually, which contain 11–20% bio-oil. This means the grounds could produce more than 340 million gallons of biodiesel per year.

What percentage of oil is in used coffee grounds?

The research found that spent coffee grounds typically contain around 15% bio-oil by weight. This is lower than oil content in soybeans, rapeseed, or palm, but the coffee oil is more stable due to higher antioxidant levels.

How did the researchers extract oil from coffee grounds?

The team collected 50 pounds of used coffee grounds from Starbucks, dried them in an oven, and then used chemical solvents to extract the oil. The solvents can be reused, and the remaining solids can be repurposed as fertilizer, ethanol material, or fuel pellets.

Can coffee biodiesel replace regular diesel?

No. Even if all the coffee grounds in the world were converted into biodiesel, the total output would be less than 1% of the diesel used in the US each year. It’s not a replacement for petroleum, but it can help reduce waste and emissions.

Is coffee biodiesel already being used?

Not yet at scale. The researchers planned to set up a small pilot system to test collecting grounds from Starbucks and processing them into biodiesel, but widespread use is not yet in place.

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