Coffee Pulp

May 21, 2004

A layer of soft pulp surrounds coffee beans when they are harvested. This pulp is removed with abrasive rollers and a flow of water. The bean that remains is dried and, later, roasted.

For at least twenty years, Vincent has had inquiries about processing the wet pulp into a by-product. Generally, the goal was to convert the pulp into animal feed by dewatering and drying it. For economic reasons, none of their projects have gone ahead.

During the last few years, a new system has been developed in conjunction with Swisscontact. Swisscontact is a foundation based in Switzerland, dedicated to environmental projects in developing nations. Their office in Costa Rica has focused on coffee pulp.

At present, coffee pulp is landfilled. As rainwater seeps through the rotting mass, groundwater contamination becomes a problem. At the same time, rainforests are being harvested and used as firewood for drying the coffee beans. The Swisscontact idea was to dewater the pulp sufficiently for it to be used in place of firewood for drying the beans.

Efforts to dewater the pulp with a screw press were futile. After the free water was expelled, the press cake still had 80% moisture. In general, organic matters need to be reduced to 50% moisture before they will burn.

The bitter, acid nature of the coffee pulp reminded us of orange peel. Only because of this similarity did we suggest trying to react the pulp with hydrated lime. To our delight, it worked the same as it does with orange peel: the chemical reaction with the lime broke down the pulp. This done, the screw press was able to produce press cake with 65% moisture.

This press cake is tumbled in a duct that carries the flue gasses from the bean dryer. These gasses dry the pulp to 50% moisture, after which it is burned as fuel.

A problem remaining with the system is disposal of the press liquor. The liquid is loaded with solids, which kill vegetation and load up wastewater treatment plants.

Issue 149