Coffee Production

Two different methods of processing the coffee beans have now been adopted worldwide: wet processing and dry processing.

Wet processing

iStock dryingWet processing, whereby the beans are washed, is mainly employed in Central America and parts of Africa (notably Kenya). This process is relatively expensive, but is beneficial to the quality of the coffee. The berries are first fed through a water channel to soak them and to remove any impurities. The unripe berries sink to the bottom, leaving the ripe fruit to float to the top. The ripe berries can then be processed further. The fruit flesh of the berries is removed with the help of a 'de-pulper', a machine that has a roller with a roughened surface. This scours away the fruit flesh (pulp) from the berries under a stream of water. Previously, the remaining pulp was treated as waste, but nowadays it is blended with minerals and turned into fertiliser.

In the second stage of wet processing the coffee beans are fermented in large water containers. The object of the fermentation process is not only to dissolve any remaining fruit flesh, but also to remove the sticky film surrounding the coffee beans, which is not water soluble. This part of the procedure, which lasts approximately two days, is very important. The long period of fermentation is what first gives the coffee its rich aroma and special flavour.

Washing

On completion of the fermentation process the coffee beans have to be washed. At this stage, the beans are still surrounded by their parchment husk, and for this reason the coffee is also referred to as 'parchment coffee'.

Drying

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The washed parchment coffee is then spread out on concrete slabs or drying racks and left out in the sun. To ensure that the beans dry evenly they are turned over several times a day. Depending on the weather conditions, this process takes five or six days. Cultivators operating on a medium to large scale make use of drying machines, huge metal drums inside which hot air circulates. Again, to ensure that the beans dry evenly the drums rotate continually. In the drums the drying process lasts about 24 hours. Dried parchment coffee has an attractive golden yellow colour and is known as pergamino coffee. At this stage the work of the coffee cultivators is largely at an end. The producer parts with his product, selling it to a wholesale distributor and/or an exporter.

Hulling

Next the pergamino is stored in bags, before being mechanically hulled by special machines. These peeling machines have grooved cast iron cylinders, inside which the husk of the coffee beans is scoured away as they rub against one another.

At the end of this process the beans are generally olive green in colour. Some varieties even have blue beans; these are the high quality so-called 'blue' coffees.

Sorting and gradi


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First the coffee beans are sieved to remove any foreign objects and damaged beans. Next they are mechanically graded according to size and shape. This is followed by a further selection process, this time carried out by trained workers. The coffee is sorted by eye as it passes in front of them on a conveyor belt into the different quality grades. There are also machines now that can perform this selection work.

Dry processing

In Brazil and across a large part of Africa, dry processing is used for lower quality Arabica and Robusta berries, a simple technique which is less labourintensive than wet processing. However, cheaper production costs must be offset against a loss in quality, since the length of the process (the drying of the berries) is dependent on the unpredictable climate. Once all twigs, leaves, stones and other foreign objects have been sieved out, dry processing can begin. Drying

The berries are spread out in the sun on cement or brick slabs in layers five to six cm deep. To ensure that the beans dry evenly, the berries are turned regularly for a period of two to three weeks. On smaller plantations drying mats made of wire netting are often used.

Hulling

Once the beans are completely dry, hulling begins. In a peeling machine similar to that used during wet processing, the dried fruit flesh (the pulp), the parchment skin and a part of the husk that surrounds the coffee bean are removed.

Cleaning and selecting

Finally, the beans are cleaned and then sorted according to size by mechanically operating vibrating sieves. The beans are then measured into sacks of a standard size (usually 60 kg).