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Agriculture > Plantation Crops > Coffee (Coffea arabica)
Crop Management

Processing

Irrespective of the harvesting method, green coffee beans and overripe coffee cherries inevitably end up mixed with the perfectly ripe cherries and must be separated. Overripe coffee cherries, undeveloped coffee cherries, sticks and leaves float in water. Ripe coffee beans and green coffee cherries are dense and sink. Therefore, the first separation step takes place by separating the floaters from the sinkers. The floaters are usually sent directly to the patio to be dried and are then slated for internal consumption. The ripe and green cherries can be sent to the patios to be dried using the natural (dry) process or can be sent to the pulping machines.

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The first stage of pulping is used to remove the green cherries from the ripe cherries. In the pulping machine the internal pressure is monitored to push the coffee against a screen with holes only large enough for a coffee bean (not cherry) to pass through. Since the ripe cherries are soft they break and the seed is released through the screen.

The green cherries are hard and cannot be pulped. Instead of passing through the screen, the green beans pass to the end of the barrel system and are separated from the ripe beans. The pressure inside the barrel controls how many cherries will be pulped. A very high pressure will cause all of the cherries including the green beans to be pulped. It is necessary to continuously monitor the pressure so that about 3% of ripe cherries are not pulped and are removed with the green cherries. This margin of error ensures that no green cherries are mistakenly pulped. The pulp and beans are then separated by centrifugal force and a barrel screen system.

The beans covered in the slippery mucilage can be sent to the patios to dry as pulped natural coffees or can be sent to fermentation tanks. The fermenting tanks are used to remove the mucilage before drying. The pulped beans are put into cement tanks with water and are allowed to ferment for 16-36 hours. On the way to the fermentation tanks another density separation can occur. The highest quality coffees are the most dense and should be separated and fermented in a different tank

The fermentation time depends on a number of factors including the amount of coffee fermenting, water temperature, and humidity. The mucilage is made up of pectin materials including protopectin (33%), reducing sugars including glucose and fructose (30%), non-reducing sugars such as sucrose (20%), and cellulose and ash (17%). Protopectin is not water soluble and will hydrolyze to pectinic acid in the fermentation tanks. Hydrolysis of the protopectin and degradation of the pectin by enzymes is the process that occurs to remove the mucilage during fermentation . Currently, the best way of determining the end of fermentation is to feel the beans to determine if the beans are still encased in mucilage. If the beans are fermented for 36-72 hours stinker beans develop. Lactic, acetic, and propionic acids are produced in this process and are believed to prevent the traditional fermentation taste by inhibiting mold growth that regularly occurs during drying on a patio in humid conditions.

From the fermentation tanks the beans are moved to drying patios and dried to 11-12% moisture content. A small portion of the lot is hulled and milled by a mini-huller. Three hundred grammes of coffee is classified for defects (100 g is often used), and the percentage of each screen size is determined. Then, 200-300 g of coffee is roasted in a sample roaster and cupped to determine quality. Ideally no lots will be mixed until the coffee has been classified and cupped. The coffee remains in pergamino until shipment time to help protect the flavor and aroma of the coffee.

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