Coffee Grounds Contain High Levels of Antioxidants

Every day, billions of cups of coffee are brewed around the world, generating nearly 20 million tonnes of used coffee grounds. Most of that ends up in landfills—but some is repurposed as fertiliser. What many don’t know is that coffee itself is rich in antioxidants, and the grounds left behind might be too. So, do spent coffee grounds have untapped health benefits?

Yes. Research shows used coffee grounds contain significant amounts of antioxidants—but the amount varies by brewing method. Drip coffee makers, French press, and espresso machines leave grounds with higher antioxidant levels than moka pots. That’s according to a study led by Maria-Paz de Pena and published in the Journal of Agricultural and Food Chemistry by the American Chemical Society (ACS).

What Are Antioxidants, and Why Do They Matter?

Antioxidants are compounds that help neutralise free radicals in the body, potentially reducing oxidative stress and inflammation. Many of coffee’s health benefits—linked to reduced risk of certain diseases—are attributed to its natural antioxidant content, especially polyphenols like chlorogenic acids. When you drink coffee, you’re consuming those antioxidants. But what happens to them after brewing?

How Much Antioxidant Is Left in Spent Coffee Grounds?

The study analysed the antioxidant content remaining in coffee grounds after various common brewing methods. Researchers found that not all brewing techniques discard the same amount of antioxidants. Some methods leave behind more of these beneficial compounds in the spent grounds than others. This discovery opens the door to better utilisation of coffee waste—not just as compost, but possibly as a source for extracting valuable health-promoting substances.

Which Brewing Methods Leave More Antioxidants in the Grounds?

Not all coffee brewing methods are equal when it comes to antioxidant retention in spent grounds:

• Drip coffee machines (like standard filter or pour-over setups) leave grounds with relatively high antioxidant content.
• French press (plunger or cafetière) also retains a significant level of antioxidants in the used coffee grounds.
• Espresso machines produce grounds that still hold a notable quantity of antioxidants post-brewing.
• Moka pots, however, were found to leave behind coffee grounds with comparatively lower antioxidant levels.

In short, if you're brewing with a drip machine, French press, or espresso machine, the leftover grounds are richer in antioxidants than those from a stovetop moka pot. That doesn’t mean moka pot grounds are useless—they still contain some antioxidants and can be repurposed—but the highest residual antioxidant levels are found in grounds from other brewing methods.

What Happens to the Antioxidants After Extraction?

Importantly, the researchers emphasised that the antioxidants can be extracted from the spent grounds for potential use in dietary supplements or functional foods. Even after that extraction, the leftover biomass still has value—it can still be turned into fertiliser for plants. So the grounds serve a dual purpose: first as a possible source of bioactive compounds, then as a sustainable soil additive.

Frequently Asked Questions

Which coffee brewing method leaves the most antioxidants in the spent grounds?

According to the study, drip coffee makers, French press, and espresso machines leave behind coffee grounds with higher antioxidant levels. Moka pots leave the lowest levels among the methods tested.

Are the antioxidants in coffee grounds still usable after brewing?

Yes. The study confirms that antioxidants remain in the spent grounds after brewing, and they can be extracted for potential health or nutritional applications.

Can coffee grounds be used for anything after antioxidant extraction?

Yes. Even after antioxidant extraction, the leftover coffee grounds can still be used to make fertiliser, making them valuable for both health and agricultural purposes.

Is there a difference in antioxidant content based on brewing device?

Definitely. Brewing method affects how many antioxidants remain in the used coffee grounds. Drip, French press, and espresso brewing retain more antioxidants than moka pot brewing.

Does espresso brewing produce antioxidant-rich coffee grounds?

Yes. Espresso machine grounds were found to contain a relatively high level of antioxidants compared to moka pot grounds.

Why do moka pots result in lower antioxidant levels in the grounds?

The study did not detail the exact mechanism, but differences in brew pressure, temperature, and extraction efficiency likely result in more antioxidants being removed during the brew cycle in moka pots compared to other methods.

Recommended FrontStreet Beans for Antioxidant-Rich Coffee

For coffee lovers interested in antioxidant-rich brews, try FrontStreet Coffee’s Ethiopia Humbera – a bright Ethiopian single origin with notes of citrus, jasmine, and tropical fruit, known for its high natural antioxidant content from chlorogenic acids. Another great option is the Yirgacheffe, offering floral and lemony tones with a light body and vibrant acidity. For something deeper, their Classic Blend balances body and brightness with notes of dark cherry and cocoa, ideal for espresso or filter. All three are excellent choices for extracting maximum health benefits. Freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.