Coffee Production and Trade

Coffee processing

Introduction

Coffee passes through various stages of primary processing in the country of production before it is exported as unroasted 'green' coffee. The main aim of primary processing is to separate the coffee beans from the skin and the pulp of the coffee cherry. The beans are then dried (which is the most critical element of primary processing from both a quality and an OTA formation perspective) - only then can the resulting green coffee beans be traded, and, ultimately, roasted.

Beneath the red skin of a ripe coffee cherry (the exocarp) lies the pulp (the mesocarp), containing (usually) two beans, each surrounded by a parchment-like covering (the endocarp). When the fruit is ripe a thin, slimy layer of mucilage surrounds the parchment. Underneath the parchment the beans are covered in another thinner membrane, the silver skin (the seed coat). Each cherry generally contains two coffee beans - if there is only one it assumes a rounder shape and is known as a 'peaberry'.

There are two methods for removing these outer layers, known as the 'wet' method and the 'dry' method. Essentially, in wet processing, ripe cherries are harvested, pulped, fermented and washed, dried, peeled and then polished. This is known as 'washed' or 'Mild' coffee, and normally applies to arabica coffee¹.

In dry processing cherries are harvested, dried whole and then mechanically decorticated (hulled) in order to extract the green coffee bean. This is also known as 'natural' coffee.

Correct and proper primary processing is one of the key determinants of coffee quality, along with farm practices, prevailing weather conditions, plant vigour and fertility.

It is important to minimise any delay between harvesting and processing, as this helps reduce the opportunity for mould growth and the risk of OTA contamination.

Click here to view a generic processing flow-chart showing the key steps in the wet and dry processing of coffee cherries, and subsequent processing of green coffee beans.

¹ Some washed robusta is also produced, but it accounts for a small volume of the total international coffee trade.