At the Mills
Once picked, there is a short window of time to process coffee before the cherry begins to decompose. Processing methods and environmental variables at the wet mill have huge impacts on the quality of the final cup.
At the Wet Mill
Wet mills are usually geographically close to the farms where the coffee is grown. Cherries arriving at the wet mill are allowed to ferment for 6-72 hours in fermentation tanks with or without water. A naturally occurring enzyme called pectinase breaks down the gelatinous fruit structure of the coffee cherry and softens it. Processors have several options for how to dry the beans: They can completely wash off the cherry fruit (washed process), they can wash off most but not all of the cherry (honey process), they can dry the cherry with all the fruit attached (natural process), among other less common methods.
About 95 percent of the coffee we buy is washed process coffee. Once coffee is washed, it is dried down to between 9 to 11 percent moisture. This makes the coffee more stable during shipping and storage. Method and speed of drying makes a difference in the overall flavor and longevity of the coffee. Drying in Latin America is often done by raking coffee over concrete patios in open air. In East Africa, coffees are often dried on raised beds, allowing air to pass around the coffee as it dries. Both methods are affected by uncontrollable weather elements, but the ideal drying time is between two to four weeks.
At the Dry Mill
Dry mills are usually close to exporting ports and are often owned by the exporters themselves. Dried coffee beans are brought in on trucks and sorted on a vibrating gravity table to separate the higher quality dense coffees from the lower quality coffees. A dry mill may remove anywhere from 10 to 15 percent of the lower-quality coffee depending on whether the gravity sorter is calibrated for greater quality or greater volume.
From the gravity table, coffee is sent through a quality control machine with electronic eyes that remove defects like broken beans, black beans, insect damaged beans at lightning fast speed.
Coffee is then weighed and bagged in lined burlap sacks and organized on pallets and shipping containers to export to roasteries around the world.
Learn more about coffee in the next section: At the Roastery.