At a time when the issue of food waste is garnering headlines for its burden on our planet, reusing or "upcycling" organic waste such as coffee grounds can be both environmentally-friendly and help save money too.
Here are some of the ways in which coffee grounds (including from Cultured Coffee) can add value by being recycled and contribute to a more sustainable food system:
Rich in nitrogen and phosphorus, elements microbes need to synthesize proteins for energy to fuel the conversion of organic matter into compost, coffee grounds can support the ecosystem that underpins gardens and farms.
While coffee beans are naturally slightly acidic, the action of brewing coffee renders the resulting grounds relatively neutral. This makes coffee grounds unlikely to significantly alter soil pH and cause problems for growing plants.
Coffee grounds can be spread directly as an organic garden mulch or, better still, worked into compost. Here, microbes release nutrients from the grounds as they decompose which in turn supports microbial diversity that helps break down all the organic matter in the compost.
Compost then acts as a fertilizer when mixed into soil, releasing nutrients back into the environment for plants and other living organisms to reuse.
Caffeine in Compost
One problematic aspect of using coffee grounds in the garden however is tied to their caffeine content.
An organic compound produced by coffee plants, caffeine is a secondary metabolite that acts as a natural allelochemical to deter germination in other nearby plants by stunting root growth. It also has some antimicrobial effects.
While microbes can help break down some of the caffeine in compost, a high ratio of grounds to other organic matter may disable the action of microbes and create compost that hinders growth in other plants.
As a result coffee grounds should only form a small portion of the overall organic matter used in the compost.
A Clean Source of Power
In London, United Kingdom, the city's famous red buses are running on biofuel made from coffee grounds, which account for 500,000 tonnes of landfill waste in the country each year. The goal is to turn a large source of food waste into a renewable source of energy.
To produce the fuel, coffee grounds are heated to 60°C (140° F) for around two hours to extract the oil from the grounds. Residual hexane, a natural alkalane, is evaporated to leave pure oils. These oils are mixed with methanol and a chemical catalyst to create a fuel.
A new process has also been developed by researchers in the country to achieve the same results in fewer steps via a process known as transesterification.
The aim is to develop rapid and cheap ways to convert coffee grounds and other organic waste matter into sustainable biofuel, which is still a contentious issue around the world including the United States.
Biofuel and Beyond
Produced by a British company, coffee biofuel is one of a set of products made by recycling grounds sourced from local cafés and coffee chains including: biomass pellets for commercial heating and barbecue briquettes. This way energy stored in the coffee plant is reused as a clean source of power without the need to grow crops exclusively for fuel.
While these coffee-based experiments are still relatively limited, other forms of biofuel derived from plant matter such as sugar cane and corn or animal fat are being trialed across the globe.
These alternative biofuels are produced using enzymes derived from microbes, for example, which support the hydrolysis of polysaccharides in plant cell walls. This process converts carbohydrate molecules into monomers. Microbes such as yeast then ferment the monomers into ethanol, which is used as a biofuel in some countries.
Whether coffee-, plant- or animal-based, the use of biofuels across the world is forecast to grow by 16% between 2017-2022.
Natural Odor Absorber
Used coffee grounds have the capacity to absorb surrounding odors much like baking soda.
Sodium bicarbonate, the pure form of baking soda, neutralizes acidic volatile compounds (odors) released by different foods and organic substances. Comprised of natural amphoteric molecules, these molecules react with and reduce the volume of acidic compounds.
Coffee grounds can be carbonized to behave the same way as baking soda. The grounds' caffeine content (specifically the natural nitrogen in caffeine) then activates carbon atoms in the grounds. This helps them mop up unpleasant sulfur odors from the air through adsorption.
Coffee grounds can also be used to dye textiles. Using natural dyes could reduce the water and chemical pollution attributed to the textile manufacturing process, which accounts for 20% of global water pollution and the release of up to 72 different chemicals into the environment.
By mixing one tablespoon of water to each cup of grounds, the resulting mixture can be spread onto moist fabric and allowed to air dry for the dye to permeate the fabric. This process lends a long-lasting dark yellow color to textiles without the need for chemicals as well as using food waste.