Wet Processing

Coffee beans are the product of coffee “cherries” composed of skin, pulp, mucilage, parchment, silver membrane, and the pit (bean), normally two symmetrical halves to each cherry. Wet processing is an industrial technique for removing the fruit skins and pulp mechanically, removing the mucilage covering the coffee beans through a soaking, fermentation and washing process, then drying and sorting the coffee in its parchment covering on raised tables. When carried out carefully, in a coffee washing station (CWS), a.k.a., wet mill or depulpery, wet processing produces a coffee that, when dry milled and roasted properly, has superior cupping qualities.

In Burundi there are over 160 coffee washing stations spread out across the higher elevations of  nearly every province in the country, though with concentrations in the northern provinces, particularly in Kayanza and Ngozi. Associated with each coffee washing station in Burundi are one or more farmer associations, as well as a population of non-associated coffee farmers in the vicinity of the CWS. Burundi’s larger coffee producer associations have increasingly split into smaller associations, often as groups of “hillside neighbors.” From the perspective of specialty coffee traceability these smaller associations offer Burundi an important opportunity for producing smaller, high value lots of coffee with distinct flavor profiles.

During harvest season farmers transport their cherries, normally on foot or by bicycle, to the washing station(s) in their areas. The average distance from producers’ farms to washing stations is approximately 5 km (3.1 miles), and for those located in more distant areas coffee cherries are often transported through a network of small coffee traders/rural collectors. For all fully washed coffee in Burundi the goal is to transport coffee cherries to the washing stations in less than six hours after harvest to help ensure coffee quality.

Before their cherries are weighed and passed on to the managers of the CWS for processing they are sorted by hand and by flotation. Burundi’s more advanced and progressive washing stations have installed banks of concrete flotation tanks in which farmers dunk their cherry using wire mesh screens with the purpose of skimming off the “floaters.” Cherries that do not sink are removed from the process as they lack the proper density due to a variety of defects.

Once the cherry has been washed, dried and hand sorted, trucks collect the parchment coffee from the washing stations and transport it to the dry mill.

Dry Milling

After Burundi coffee is dried at the washing stations arrangements for dry milling are made between the owner of the coffee and one or more of the country’s dry mills. Because specialty coffee needs to be segregated and often processed in smaller lots, this is a critical and often challenging step.  Before the parchment coffee is milled it is stored, at high elevations where it is produced, either at the SOGESTALS or in licensed warehouses at the coffee washing stations.

Also prior to dry milling Burundi coffee is classified by the coffee authority in Burundi (ARFIC). Samples of coffee are taken and evaluated (inspection and cupping) to officially determine coffee quality. Even when there is a contract between a buyer and seller an official quality certificate is issued by ARFIC.

Once coffee is classified a sample is retained by ARFIC and exporters or owners are free to transmit coffees to prospective buyers and negotiate with millers about the timing and price of milling. A contract is signed to formalize their agreement and initiate the milling plan.

Dry milling of specialty coffee is a step-by-step process.  Equipment and capacity to mill specialty coffee in Burundi is varied. Optimally the dry milling of specialty coffee undergoes each of the following steps:

  • Pre-cleaning
  • Hulling, removal of chafe and polishing
  • Spinning, grading and separation according to 5 screen sizes set by ARFIC
  • Separating by density using catadors or densometric tables
  • Color Sorting
  • UV sorting