Valorization of coffee crop residues
The Tierras de Montaña project is a social and environmental project that envisages the manufacture of between 15,000 and 17,000 tonnes of Biochar for its marketing, management and generation of puro-earth CO2 elimination certificates (CORC).
A replicable project whose pilot will be carried out in the region of Tolima, Planadas in collaboration with the municipality of Planadas and Asopap, an association of 54 coffee-producing families.
TDM’s activity is the production of Biochar, taking into account a total area of 3,500 hectares, including 1,000 hectares of forest restoration and 2,500 hectares of agroforestry dedicated to coffee.
The beginning of the project is segmented and offers the possibility to start producing biochar using the region’s coffee harvest residues, in exchange for the pulping process, fermentation, drying, and/or composting, or simply by purchasing biomass directly.
Starting coffee production and forest regeneration, followed by waste recovery through the establishment of a pyrolysis unit is the other possibility that could be explored.
Valorization of residues
ANATOMY OF THE COFFEE CHERRY
What is a coffee bean?
The coffea is a plant and the coffee beans are coming from dark red coffee cherries.
Inside the cherry is where you find the material that contributes to the quality of your cup, the beans grow with this material which makes up over 80 percent of the cherry, we call it waste and it is underutilized and unfortunately in many circumstances contaminating.
Each part of the coffee cherry impacts the processing method and final profile of your coffee.
The beans we roast, grind, and use to make coffee are the seeds of a fruit.
The coffee plant produces coffee cherries and the beans are the seeds found inside the cherries.
Coffee trees can grow naturally and reach heights up to 9 meters.
But growers keep the plants low by pruning and topping them to conserve energy and make harvesting easier.
Smaller trees have better quality and yield in limited space. Each tree is covered in waxy green leaves that grow in pairs and coffee cherries grow along the branches.
Depending on the variety, a coffee tree takes between three and four years to bear fruit.
A typical coffee tree produces 10 lbs of coffee cherries per year, which is equivalent to about 2 lbs of green beans.
But there are different varieties of coffee and their beans have many different characteristics.
Size, flavor and disease resistance vary, among other factors.
THE LAYERS OF A COFFEE CHERRY
The skin or shell of the coffee cherry is called the exocarp or epicarp and is green until ripe and turns red, yellow, orange or even bright pink, depending on the variety.
Green coffee cherries should not be confused with green coffee beans , which are the unroasted seeds from the ripe coffee cherry.
Under the skin of each cherry is a thin layer called the mesocarp, also known as the pulp. The mucilage is the inner layer of the pulp.
There is also a layer of pectin under the mucilage. These layers are rich in sugars, important during the fermentation process.
Next are coffee seeds, whose technical name is endosperm, but which we know as beans. There are usually two beans in a coffee cherry, each of which is covered with a thin layer of epidermis called silver film (a paper-like covering, which we call parchment (technically the endocarp). Typically, the parchment is removed during pounding, which is the first step in the dry grinding process.
Machines or stone mills are used to remove remaining fruit and dried parchment from the grains.
But sometimes (not for export), green beans are sold with this layer intact as parchment coffee.
The silver film is a group of sclerenchyma cells tightly attached to the grains. These cells form to help and protect the bean and are shed during roasting. In this phase they are known as cascarilla.
Sometimes there is only one seed inside a coffee cherry and it is rounder and larger than normal.
This occurs in about 5% of cherries and the pits are called caracolillos (or snails). Snails may be an anatomical variation of the plant or may form when there is not enough pollination and an ovule is not fertilized.
Sometimes the seed simply won’t grow, either for genetic or environmental reasons. Snails usually appear in parts of the coffee tree exposed to terrible weather conditions.
THE IMPACT OF ANATOMY ON YOUR MUG
The fruit and skin of the coffee cherry are usually discarded, but they are sometimes allowed to dry to make shells for tea and other products.
It is difficult to remove the skin and mucilage from coffee beans and several processing methods have been developed to achieve this. Each method has an effect on the flavor and profile of the final coffee.
1/ For washed coffee, all the pulp is removed before drying.
2/ In the case of natural coffee, the pulp is removed after drying.
3/ The honey process consists of removing the skin and sometimes part of the mucilage before drying, but the remaining mucilage and other layers are then eliminated.
The producer moves the coffee beans to washing channels. Washing the coffee beans.
Leaving the mucilage behind produces a sweeter coffee with more body.
Washed coffees have clean, more consistent flavors that can be highlighted by their acidity.
Natural coffees are much fruitier, sweeter and have more body.
The sugars in the mucilage also ferment during dry processing and washing, which impacts the final flavor.
If not carefully monitored and drying is inconsistent, the unpredictable fermentation process can produce undesirable characteristics.
Residues from coffee cultivation
By analyzing the various nutritional elements and physico-chemical properties of the biochars studied. (Zawada-Ospina Pereira 2020), it was identified that the coffee pulp biochar manages to have similarities with some of the data described in the macronutrient elements , micronutrients and physicochemical characteristics of the different biochar, serving as a reference to determine the variables that can be considered the most important for the characterization of the uses that coffee pulp biochar has or can valorize, this was of vital importance because it made it possible to identify the possible agricultural uses of biochar from coffee pulp, where it was possible to identify that the biomasses of leaf waste, bush waste, tree waste, wood chips pallets, food waste and hazelnut shells have similarities when it comes to the uses of coffee pulp biochar, these being mainly soil fertilization, climate change mitigation, nutrient delivery and contaminant retention. Considering a daily biochar production of 150 kg and a monthly production of 3,600 kg, the production costs were estimated which gave values of 73,024 COP and 1,649,611 COP respectively; which leads to a production cost of COP 458.23 per kilogram, which is considerably low for this type of product due to its low number of inputs and low cost. This allows the farmer to be assured of employment and decent remuneration which will be reflected in the improvement of his quality of life and in his work performance thanks to the satisfaction and security that this work generates. .
The conditions for improving environmental quality were determined due to the reduction in pollution and environmental degradation produced by the inadequate disposal of coffee pulp after processing.
Economic profitability will depend on the benefits already mentioned and could be reflected in the medium term, therefore, socio-economic and environmental benefits become reciprocal dynamics where “receiving” or “winning” requires effort and implies “giving in”, thus formalizing the principles of action of the circular economy.
It was possible to demonstrate that pulp biochar is postulated as a sustainable product and at the same time as a cleaner production strategy meeting the specifications given by the circular economy approach, an organic waste that is taken as raw material to be transformed and finally reincorporated into the different processes of the agricultural industry as an organic product capable of contributing to the improvement and productivity of the physical, chemical and biological characteristics of the soil, minimizing the negative impacts coming from the use recurring use of inorganic fertilizers, generating environmental and sometimes socio-economic benefits. This allowed us to establish that agricultural practices can be developed effectively without the presence of chemicals, which ultimately have the opposite effect on the environment and people’s well-being. The study of biochar has gained relevance in recent years in countries such as the United States and Brazil because it is an innovative product; in Colombia this is still a relatively new area of research to which we must continue to provide not only information but also application possibilities.
Coffee pulp’s biochar
Energy production from coffee waste is an alternative with great potential to contribute to the energy sustainability of the sector.
Additionally, producing biofuels from coffee waste would position this industry as zero waste and help solve the problem of climate change.
Some of the studies carried out on this topic are discussed below.
Water extracted from coffee cherry extract is a potential source of biogas production; the cherry extract which is collected and heated, and will become a boiling mass of micro-organisms of all kinds which will act on the sticky fruit juices released. Proper fermentation and other procedures reduce the pH, and the subsequent neutralization process will give rise to CO2 foam; the evolution of CO2 at this stage allows the subsequent production of biogas (Rathanivelu and Graziosi, 2005).
The biogas produced can be burned to generate electricity and all the waste heat can be used to dry the coffee. The biogas yield would be between 0.500 and 0.598 m3/kg of dry organic matter, with a methane concentration of between 55 and 61% (Neves et al., 2005; Neves et al., 2006; Vitez et al., 2016). ; Luz et al., 2017; Girotto et al., 2018).
Another energy alternative is fuel pellets, which are biofuels densified from pulverized biomass from forest cleaning, forestry industries, agro-industrial waste and lignocellulosic biomass. To make pellets, the waste must be crushed, then dried and finally pressed into small cylinders. The pellet is used as biofuel to generate electrical and/or thermal energy in a clean way. Currently, studies have been carried out for the production of fuel pellets from grass, corn stubble, hay, garden waste, as well as straws from different cereals such as barley, rice and wheat ( Pradhan et al., 2018). Regarding coffee waste, mixtures were made with eucalyptus wood waste, which gave rise to pellets with greater durability, hardness and net energy density.
However, the production of fuel pellets from coffee waste has not been studied and could be used in the same coffee production process, making this industry sustainable and low environmental impact. Therefore, more research is needed on how to utilize waste or by-products generated by the coffee industry.
Potential for producing fuel pellets from coffee waste
As mentioned previously, according to the International Coffee Organization, Colombia had a production of 813,420 tonnes of green coffee in 2018 (ICO, 2019); This is equivalent to 2,323,940 tonnes of cherry coffee produced in the country’s coffee lands, over a harvested area of 974,000 hectares (FNC 2019). A large quantity of waste is generated in Colombia, which can be recycled for the manufacture of fuel pellets; These pellets are used as a clean biofuel to generate heat and/or electrical energy. The energy potential of industrial waste biomass (a category in which coffee waste is considered) is estimated to be 0.003837 TJ/ton.
The energy potential of waste is therefore estimated at 3,155 TJ. Therefore, fuel pellets from coffee waste in Colombia would generate 3,155.00 TJ (320.83 GWh); It is worth mentioning that this figure does not take into account losses in the production process and that the necessary infrastructure exists for the transfer of waste. In a particular way.
Given the geographic distribution of coffee producers, it is important to note that in many cases there is no infrastructure necessary to transport waste to production centers. It is therefore necessary to carry out a supply chain study that takes these aspects into account. However, one solution could be the creation of pellet production centers for 3 or 5 relatively close communities; These pellets could be used by producers themselves to meet the thermal energy needs of their homes or in the coffee drying process.
Coffee is one of the most important commodities in the world, which is reflected in the sustained growth of its global production. Its production process generates a large amount of waste, which can be revalued for the generation of value-added products, as well as biofuels.
In particular, the conversion of this waste into biofuels would allow the coffee sector to migrate towards a circular economy with low environmental impact.
The residues from coffee cultivation
In coffee cultivation, a large amount of waste is generated during the processing from fruit to cup, approximately 350 grams of dry residue for each kilogram of coffee beans; Depending on the method used to obtain the coffee bean, the type of waste released will be different. The two basic methods of processing coffee are the wet method and the dry method. Wet-processed coffee is also called washed coffee or parchment coffee. This method involves removing the fruit pulp that covers the grains using a pulper before they dry out. On the other hand, the dry method is considered the oldest and simplest; In this method, the newly harvested fruits are dried then graded and bagged. If the processing is carried out dry, the main waste generated is the skin, pulp, mucilage and husk; All this waste is grouped into the same fraction called coffee hulls or pods. While wet processing allows the skin and pulp to be recovered in a single fraction, the mucilage and soluble sugars in a second fraction, and the envelope in a third fraction. Among the different wastes from coffee processing, coffee pulp is the one that is generated in the greatest quantity (43% during wet processing) (Mussatto et al., 2011). Coffee hulls and pulp make up approximately 45% of the cherry and are the main by-products of the coffee industry, Figure 3.
figure 3
In coffee-producing countries, waste and by-products constitute a source of pollution, which poses a serious environmental problem. In most coffee plantations there are coffee processing units, in which improper disposal of coffee pulp, hulls and effluent is carried out; This causes contamination of water and land around processing units. This waste contains tannins, attributed to low biodegradability and which have even been described as recalcitrant agents; in addition to being perceived as reducing nutritional quality.
Coffee pulp is the main crop waste, accounting for 29% of the dry weight of the whole fruit, and its high moisture content makes it difficult to dispose of.
In contrast, coffee cherry hulls represent approximately 12% of the whole fruit and are composed of water (15.0%), cellulose (24.5%), hemicellulose (29.7%), lignin (23.7%) and ashes (6.2%). ) (Gouvea et al., 2009; Bekalo and Reinhardt, 2010).
In 2018, 10,256,220 tonnes of green coffee were produced worldwide, around 10% of which was in Colombia.
Knowing that, for each kilogram of coffee, 350 g of waste are produced. Thus, in Colombia, 358,985.6 tons of waste were generated by this industry in 2018.
Considering that the biodegradation processes of coffee waste require very long times and a high demand for oxygen, it is clear that their direct incorporation in the environment represents a high risk. for the flora and fauna of these ecosystems.
In this regard, in Colombia, very few or no industries control the waste generated by coffee production, which continues to pose a pollution problem (Wong et al., 2013). Therefore, strategies are needed to enable its reassessment, a topic discussed in the next section.
Valorization of coffee harvest residues
Recycling is defined as the process by which waste is transformed into new products that can be inserted into the market; These products may include high value-added products, chemicals, biotechnology and cosmetics, as well as biofuels. Through revaluation it is possible to eliminate the waste that generates the pollution problem, and at the same time improve the profitability of the process through the commercialization of the products, or in the case of energy products, their use in the process.
In coffee waste, coffee pulp and peels were only used as fertilizer, livestock feed, compost, as well as an adsorbent for the removal of toxic compounds for the manufacture of gibberellic acid; However, in these applications only a small fraction of the available amount of waste is used, as they are not technically very efficient.
It is therefore necessary to find other uses for this solid waste.
Below are some alternative uses of coffee waste and by-products that have been reported in the literature.
One of the alternatives considers the solid fermentation of coffee pulp using the fungus Aspergillus niger; Through this process, the levels of polyphenols, fiber and caffeine in the pulp are significantly reduced and its protein content is increased by 10%. Another option is to ensile coffee pulp for use as feed for certain dairy or farm animals.
On the other hand, the pulp can be used as an organic fertilizer, due to its content of potassium, phosphorus, calcium and other micro-minerals that contribute to the development of soil fertility. Currently, coffee pulp fertilizer is used in various plantations, preferably in new coffee plantations. Recently, studies have been carried out on the use of coffee by-products for paper production.
Coffee residue such as skin and residue after brewing are materials rich in cellulose and hemicellulose; These wastes could be used for the production of different types of paper (Wong et al., 2013).
Another option is to use waste coffee residue as an inexpensive and highly available adsorbent for the removal of cationic dyes in wastewater treatment. In 2009, Nakamura et al. studied the production of activated carbons from the endocarp of coffee; This proposal helps reduce waste in the Portuguese coffee industry by creating an economic surplus.
The applications mentioned so far are of great interest.
Here are the two most recommended.
Biochar or biocarbon soil amendment with high added value.
Pellets for energy in rural homes.
Energies and pellets generated by the valorización of coffee residues
Coffee cookie and a smile!