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After harvesting, the coffee beans are transported to the factory. After the arrival, the coffee beans are cleaned. Stones, dust and other foreign particles are removed. The coffee beans can be stored in silos for several days.
The taste of the coffee beans depends on the quality of the ground, the weather, the moment of picking etcetera. To keep the quality of the coffee as constant as possible, beans of different batches are mixed.
After mixing, the beans are roasted for 1,5 to 10 minutes. The beans are exposed, by direct or indirect heat, to temperatures from 100ºC in the beginning of the process, to 200-260ºC at the end of the process. The effect of heating is increased by roasting at lowed pressures. There are five methods of roasting the beans:
- Drum roasting: continuous or discontinuous processing are both possible. The drum itself or a stirrer tumbles the beans in the drum. Hot air of 400-550ºC is added. The process takes 8,5-20 minutes.
- Centrifugal roasting: discontinuous process. The drum is turning around a vertical axis. Heat exchange is possible through a closed wall (air temperature is 480-550ºC, the process takes 3-6 minutes) or addition of hot air through a perforated wall (air temperature of 280ºC, this process takes 1,5-2 minutes).
- Jet roasting: possible in continuous and discontinuous process. Several tubes are put in a layer of coffee beans. Hot air is blown through the tubes, and moves the product. The air temperature is 260-300ºC, the process takes 3-6 minutes.
- Fluid-bed-roasting: possible in continuous and discontinuous process.
- Stationary: hot air is blown through a layer of beans, the product moves, air temperature is 260-300ºC and the process takes 5 minutes.
- Pneumatic movement: hot air is pressed through the layer of beans with pneumatic movement. Air temperature is 230-360ºC, process duration is 1,5-20 minutes, depending on the temperature of air.
- Shake roasting: semi continuous process. A layer of beans is put on a floor with open parts. Through the holes hot air of 240-270ºC is blown, and shakes the beans on the floor. This process takes 5 minutes.
The roasting process has several influences on the bean:
- Water evaporates from the bean. During evaporating the intern pressure in the bean increases and the volume of the bean doubles
- The skin of the bean is released and falls off
- The colour of the bean changes from yellow green to dark brown
- Depending on the temperature oil steps out
- Due to chemical reactions the specific coffee aroma is developed. More than 800 aroma components are identified with the help of a gas chromatograph.
- A coffee bean contains 1-2% carbon dioxide and some carbonmonoxide. Depending on the temperature these gases release
- Due to the loss of water the bean looses 11 to 20% of its weight
On a given moment an exothermic reaction starts. This reaction is unwanted and should be prevented. Therefore the temperature should be monitored carefully.
To stop the roasting process and exothermic reaction the beans are cooled fast. Cooling is possible by means of cold air or addition of cold water. Adding of cold water is most effective. When exactly dosed all chilled water evaporates and the beans do not have to be dried. The roasting process stops straight away.
Extra cleaning and grinding/milling
Sometimes the beans are cleaned or mixed for a second time after grinding. After cooling a the beans can be packed straight forward or stored and later milled before packing.
The most used package for ground coffee is vacuum packaging with plastic-laminated foil. This packaging form gives the best keeping qualities. It gives a long closed shelf life of minimum 18 months. Deep frozen coffee has an even longer shelf life. It is also possible to pack the coffee at atmospheric pressure, with specific gas composition or air. These packages give a less good quality and taste.
After harvesting, the coffee beans are transported to the factory. After the arrival, the coffee beans are cleaned. Stones, dust and other foreign particles are removed. The coffee beans can be stored in silos for several... read full description