Improvements in the Washing Operation of Coffee Harvested with Plastic Nets

Abstract

Coffee harvested with plastic nets presents a new processing problem during the cleaning and washing operations. Leaves and light extraneous matter are removed during the processing by a blower leaving a manageable material containing coffee beans ana berries in different stages of decomposition. To wash the coffee with a minimum amount of hulling and also reduce the amount of foreign materials to an acceptable level, a series of modifications were made to the commercially available coffee washer. The washer was complemented with a flotation tank to make the washing system satisfactory. The modifications consisted of enlarging the feeding opening, adding a one-and-one-half flight screw conveyor to the cylinder axle in the feeding end, and covering the axle spokes with canvassed rubber. The enlargement of the feeding opening permits continuous flow of coffee material into the washing cylinder. The screw conveyor section forces the material into the washing cylinder without hammering the coffee beans and reduces the coffee hulling action. Covering the axle-spokes with canvassed rubber diminishes the hammering action during the washing operation and also reduces coffee hulling. A flotation tank under the shaker-screen of the washer separates twigs and light material not eliminated during the washing operation. The overflow water used in the flotation tank is recovered in a screening tank and pumped back into the washing machine thereby saving water. In a more elaborate system a draining platform is added. Coffee is pumped from the flotation tank to the draining platform. The water drained is collected and piped back into the flotation tank. This washing system handles from 800 to 1,100 pounds of wet parchment coffee in 1 hour. The amount of water required varies from 600 to 700 gallons per hour. The removal of twigs is performed with 96-percent efficiency. When the flotation operation is conducted as suggested, the coffee that floats out is less than 1-percent.