Turning used ground coffee into biodegradable coffee bags

Paul Clearfire
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April 2, 2024
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Breakthrough developments suggest plastic materials made from spent coffee grounds (SCG) might be used to create genuinely biodegradable coffee bags. Worldwide, coffee consumption generates about 60 million tons (58 million tonnes) of spent coffee grounds each year. In a landfill, each ton of SCG can generate an estimated 340 cubic metres of methane, a greenhouse gas that is far more destructive than carbon dioxide. 

Fortunately, progress is being made in keeping SCG out of the waste stream. For instance, used coffee grounds can help make concrete up to 30% stronger. Another example is Coffee-eco, a company in Greece, that collects SGG from local hotels and then sells extracts from the grounds back to the hotels as beauty products. 

Beyond this, several studies prove the value of SGG in producing high-grade biodiesel and biogas, which are helpful for cooking fuel and producing electricity. Kickback Coffee, a runner-up for MTPak’s 2023 Circular Economy Grant, has been working with local farmers to see if a mix of farm waste, chaff from the roaster, and SGG from the café can be used to make methane. This, in turn, could replace the propane used to fire the brand’s coffee roaster.

A recent study from associate Professor Srinivas Janaswamy and his team at South Dakota State University’s Department of Dairy and Food Science (SDSU) focuses on their process of using coffee grounds to make truly biodegradable plastic films. These films could replace the plastic used in many everyday products, such as single-use shopping bags and perhaps even biodegradable coffee bags.

I spoke with Professor Janaswarmy about his work with this breakthrough material, how he and his team hope to use it, and what work remains to bring it to market. I also spoke to Richard Ali, CEO of Tigray Coffee in Nigeria, about why the brand uses biodegradable coffee bags. 

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The pressing need for biodegradable coffee bags

People worldwide face pollution problems caused by single-use plastics. Many plastics do not degrade well on land or in water and are a particularly persistent problem in rivers and oceans. Richard describes the intense problems faced by Nigerians dealing with an ironic plastic waste disaster in their rivers and lakes. 

Many Nigerians have limited access to fresh drinking water. Thus, many rely on inexpensive and readily available purified water sold in plastic sachets. “However, people discard them on the streets,” says Richard, “All over Abuja, you can see waterways clogged by plastic.” 

Single-use shopping bags pose an even greater threat. “I’m so tired of them,” Richard admits. “Within the course of a week, you get probably 20, and you don’t know what to do with them.” He adds that the problem really hits home when he visits his local lake and sees plastic bags everywhere. 

A solution based in science

Interestingly, this is precisely the problem Professor Janaswarmy set out to solve. Srinivas started his career as a physicist with an interest in studying the molecular structures of food materials. In particular, he wanted to learn how interactions among those structures can modify macroscopic properties. He and his team were studying the properties of cellulose when a colleague came up with an idea. 

People have been solubilising cellulose for years, and they thought perhaps they could use solubilised cellulose to make plastic films. “We came up with some new ideas for using inorganic salts to solubilise the cellulose to make films. That was the first step,” Srinivas explains. 

Initially, the team was using cellulose from trees, “However, we knew trees and forests are the lungs of the planet. So, we shouldn’t chop them down just to use the cellulose.” Therefore, the team began looking for a sustainable source, which led them to agricultural waste.

The team at SDSU trialled many crops as farms regularly discard masses of biomass from crops, such as corn and wheat. This waste material contains a significant amount of cellulose. That said, much of the waste from these crops also goes right back onto the ground, which is good for the soil. 

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Spent coffee grounds: A sustainable source

While searching for an abundant, reliable source of agricultural waste, Srinivas mentioned the project to the store manager at his regular coffee shop. He explains that she noted he was trying to solve a problem they all faced and expressed a desire to help. “She stored a whole week’s supply of SCG instead of throwing it in the garbage,” Srinivas says. “She gave me bags and bags! I even acknowledged her in my paper.”

Srinivas says that cellulose in these plants grows in an impure form called lignocellulosic fibres. Thus, the team had to extract it from the caffeine and other chemicals in the coffee. Eventually, they were able to use their inorganic salt process to solubilise the cellulose and make films.

The resulting film is slightly golden brown but otherwise looks just like a piece of plastic cut from a supermarket shopping bag. As he stretches it, Srinivas notes, “See how strong this is? 24 to 30 megapascals (MPa).” By comparison, a typical supermarket shopping bag made from high-density polyethylene (HDPE) has been found to have a tensile strength of 15 to 20 MPa. 

And unlike HDPE, the plastic film produced by the team at SDSU will biodegrade completely on moist soil. They measured the degradation to more than 80% within 45 days on soil with 30% moisture. On soil with 12% moisture, the plastic degraded to 80% within 100 days. That puts this material within reach of being certified as “readily biodegradable”. 

This means that it will fully break down into organic material without the use of an industrial composter. However, when left free from contact with water, the plastic will maintain its integrity for many years. The sample Srinivas displayed during our interview was two years old. 

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A promising future for biodegradable coffee bags

There is still progress to be made. Issues with oxygen barrier and moisture resistance must be solved before this plastic can be used for food storage. Beyond this, the team must complete full Life Cycle and Techno-economic analyses to verify the environmental impacts and economic viability of the manufacturing processes. As with many academic research and development efforts, the end goal merely awaits sufficient funding.

In recent years, growing demand from consumers for eco-friendly products has made biodegradable packaging more of a necessity than a choice for specialty coffee roasters. By switching to biodegradable coffee bags, you are showcasing your commitment to environmental sustainability to your consumers. It also demonstrates an ability to keep abreast of new trends, giving people confidence and trust in the quality of your product.

At MTPak Coffee, our biodegradable coffee bags are made from the following sustainable materials:

  • Kraft paper
  • Polylactic acid (PLA)
  • Rice paper

We guarantee that all our paper-based coffee packaging, including our kraft paper bags, is sourced from forests that have been certified by the FSC.

Images courtesy of Tigray Coffee and Professor Srinivas Janaswamy

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