Coffee is made from roasted coffee beans, the seeds of the coffee plant. When harvested, the seeds still look like red or yellow berries and before they are dried, roasted and ground, the skin and pulp has to be removed. This means that about half of the original total weight of the seeds becomes unused waste. But this so-called “pulp” contains many nutrients.
In order to make better use of the waste created by coffee production, researchers from the University of Hawaii conducted an experiment: on a 1400 square metre area in Costa Rica where coffee was once grown, the researchers spread around 35 truckloads of coffee pulp. In total, the layer was half a metre thick. What then happened on this experimental field was compared for two years with developments on a control area of the same size. The result, published in an article in the journal Ecological Solutions and Evidence, was even better than expected: “The area treated with a thick layer of coffee pulp turned into a small forest in just two years, while the control area continued to be dominated by non-native pasture grasses,” says Rakan Zak Zahawi, researcher at the School of Life Sciences at the University of Hawaii. He conducted the project together with researcher Rebecca Cole.
Coffee pulp generates heat and displaces the roots of unwelcome grasses
Coffee contains a lot of carbohydrates and raw protein, and when processed, the coffee pulp forms a valuable compost. Experiments have shown that non-native grasses are displaced by the pulp and the native forest can thrive. Zahawi explains how this works: “When the pulp starts to decompose, it generates a lot of heat which, combined with the deep layer, suffocates the grass and kills the roots by sort of baking them.” The coffee pod also enriches the area with soil nutrients, driving future rainforest recovery.
With the destruction of rainforests is rapidly increasing worldwide, we urgently need more findings like these. According to the WWF, more rainforest was even cut down in 2020 than in 2019 – even though everything was at a standstill in many areas due to the Corona pandemic. In total, a forest area of around 645,000 hectares is said to have been destroyed in March 2020, i.e. more than 900,000 football fields. Using conventional methods, it usually takes many decades until rainforests are completely renatured again – and we are highly dependent on the filtering function of these ecosystems.
Reusing waste residues from production could be a sustainable way to reduce waste and cut down on artificial fertilisers. “Although much research remains to be done, this case study suggests that agricultural by-products (or non-marketable products) can be used to accelerate forest recovery on degraded tropical lands. In situations where processing these by-products is costly for agribusiness, using them for restoration to meet global reforestation targets can be a ‘win-win’ scenario,” explains Zahawi.
Negative side effects: Coffee pulp develops intense odour and in some cases still contains pesticides from production
Alongside the positive results of the research project, however, there are also disadvantages to the fertilisation method. For one thing, the coffee pulp develops an intense smell that attracts flies and other insects and disturbs people who live nearby. For another, there are concerns that the fertiliser can have a negative impact on watersheds. “There may be some contamination,” Cole told National Geographic. Coffee pulp contains nutrients such as nitrogen and phosphorus that can negatively impact rivers and lakes by causing excessive algae growth, for example. The coffee pulp may also contain traces of pesticides used in its production.
The experiment in Costa Rica was conducted away from water sources, Cole said. Further research will look more closely at the possible effects on surrounding areas.