The stages of the coffee processing process along the supply chain that brings the seeds from the field to our tables are long and complex and often some phases escape the eyes of even the most passionate and attentive consumers. In fact, after harvesting the drupes, at least two fundamental processes take place: cleaning and drying.
Processing must begin on the same day as harvesting, to avoid fermentation and mold contamination. Dirt and impurities are separated from the cherries, which are subsequently washed and separated by density: the light ones (dry or overripe cherries) and the heavy ones (ripe cherries). They are then separated by humidity level to facilitate the drying phase.
The processes can be:
- Dry (natural): after harvesting, the whole fruits are dried in the sun or mechanically. This method allows you to obtain a good coffee in terms of body and aroma.
- Washed (wet): only fairly ripe cherries are selected and the mucilage is removed (mechanically or by fermentation). They are then washed to remove the last traces of pulp.
- Natural stripped: the drupes are selected stripped and dried with parchment. Cost and quality are intermediate between the other two techniques.
The used water and solid residues must be disposed of properly to avoid damage to the environment. The natural process is practically sustainable: the water only serves to separate the fruits, which do not release anything into the fluid. The natural pulping method produces organic substance that can be used as a fertilizer. The wet method, especially if it includes fermentation in water, produces large volumes of water polluted with organic substances. Wet processed beans lose an average of 1% of soluble solids, but are facilitated in the drying process.
This phase is followed by the necessary drying phase, in fact, the humidity in cherries is around 60% for ripe ones and tends to decrease with ageing. The elimination of water is a slow process so to have an adequate yield it is necessary to have a uniform coffee mass and a long drying time. The process can take place by exposure to the sun, with mechanical dryers or a combination of the two and leads to humidity around 25%.
With exposure to the sun, the grains are selected based on their point of ripeness and are spread over several days in thin layers on large farmyards, slightly sloping to encourage water flow. Every hour or so they are turned in order to make the exposure to light as uniform as possible and to expel the water which can cause fermentation.
The stripped coffees are placed on suspended shelves and the drying phase is completed in just one day. Mechanical drying is used when the climate is adverse and often to push the humidity to around 10%. . The heat is transmitted through radiators to avoid contact with smoke. The temperature must not exceed 50°C to avoid the formation of unpleasant flavors and the death of the embryo in the grain. To make the process greener, coffee peels and parchment are also used as fuel.
The coffee is now peeled, if necessary, cleaned, polished and separated by shape, color and size, in order to have a final product as homogeneous as possible.
The sieving selects the grains by size with a series traditionally based on 1/64 of an inch. Round peaberry seeds from single-seeded cherries do not pass through specially oblong holes. Defective, damaged or fermented grains, therefore lighter, are separated by gravity.
Fans placed under a shelf make the light grains float and the heavy ones separate and fall due to vibration. The selection by color is carried out manually by operators, where the cost of labor is affordable.
To improve the general quality and automate the process, electronic selection machines have been introduced which exploit the reflectance of particular wavelengths, IR and UV fluorescence. Once this processing phase is completed, the grains can be stored in controlled humidity and temperature environments and, upon request, transported to the roasters for the roasting and grinding phase.
The roasting process, or roasting, constitutes one of the fundamental phases in coffee processing: it is irreplaceable because in addition to making green coffee edible, it gives the aromatic and organoleptic profile characteristic of each coffee blend.
During roasting, through the administration of heat to the beans, transformations take place that form and develop a complexity of components and aromas.
Roasting consists of providing heat to the coffee beans by increasing the temperature and cooking time according to specific profiles.
According to the traditional roasting process, in a large rotating drum, the beans are subjected to a heat source which progressively increases up to temperatures oscillating between 200 and 230°C for 12-15 (in some cases even 20) minutes.
In particular, the thermal steps perform different transformations:
At 100°C the beans dry and acquire a golden color. The aroma of roasting is starting to make itself felt.
Above 150-180°C the beans gain volume and become larger, shiny and take on their characteristic brown colour.
At 200-230°C the roasting is at an optimal level, the beans have lost weight, have become crumbly and their color is darker. The coffee takes on its characteristic aroma. The bean also begins to lose carbon dioxide, a process that continues for days after roasting.
For more intense roasting, you can reach a maximum of 240°C as beyond these temperatures the dangerous threshold of spontaneous combustion of the coffee would be reached.
As the roasting time lengthens, the balance between acidity and bitterness shifts. However, if the times are too long, the volatile aroma compounds are destroyed, impoverishing the coffee. This is why, as soon as it is extracted from the roaster, the coffee is quickly brought to room temperature with air flows. Air cooling is as important as roasting because it stops cooking, leaving the best aromas intact and preserving the coffee.
If you want to know more about the coffee processing process or other topics, do not hesitate to contact us and always remember to follow us on our Facebook and Instagram pages.