Post-harvest

After picking, the coffee berries are ready for processing. The flowchart below shows common post-harvest processing techniques.

The Dry Method

This is the traditional method of processing coffee. The harvested berries are spread out to dry in sunlight, or sometimes in driers during the wet season. The techniques for drying berries are same as those used for drying beans. After 7 - 10 days, the berries are dried to 10 - 12% moisture. Then, they are stored.

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Pre-cleaning and floating:

The harvested products (including the berries, flowers, sticks and leaves) are soaked in a water tank. The over-ripe, undeveloped cherries, leaves and flowers float since they are lighter than water, and are termed "floaters". The "sinkers" include ripe and green cherries, which sink to the bottom of the tank. The floaters are sent to the patio to be dried, and then slated for internal consumption, while the sinkers are processed further.

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Pulping

Pulping refers to separating the beans from the berries. This is done using a pulping machine. The internal pressure of the machine is monitored to ensure that it is just right to break open the ripe, soft berries. The coffee beans that are released easily pass through a screen and are collected for further processing. Green berries cannot be pulped since they are harder. These berries are too large to pass through the screen. Together with the pulp, they pass to the end of the barrel system and will eventually be used as compost.

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Demucilating

The mucilage is the wet, slippery outer layer of the bean. This layer is removed by friction as the beans move against each other in a machine. This process is termed "demucilating". Removing the mucilage mechanically allows the fermentation step to be shortened or even skipped, thus reducing total water consumption and processing time.

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Fermentation

The mucilage is the wet, slippery outer layer of the bean. Fermentation tanks remove the mucilage by biological fermentation. The enzymes in fermentation bacteria convert the mucilage, which is made up of sugar and pectin, into acids. Fermentation time varies from 16 - 36h, depending on the acidity, temperature, and oxygen level. Over-fermentation can affect the taste of the beans; hence it is important that fermentation conditions are well controlled and monitored.

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