What is a wet mill in coffee processing?

A wet mill is the facility where freshly harvested cherry undergoes initial processing: sorting, pulping, fermentation, washing, and the beginning of drying. It handles coffee in its most perishable state and makes the decisions most directly affecting cup quality.

Wet mills are found either on individual farms or as centralised stations serving multiple farmers - the latter is common in East Africa, where they're called washing stations or factories. Equipment at a wet mill includes flotation tanks, pulping machines, fermentation tanks, washing channels, and drying infrastructure.

The quality of wet mill operations is arguably the single most important variable in specialty coffee production. The decisions made here - about cherry selection, fermentation time, water quality, and drying management - cannot be undone downstream. An exceptional lot can be ruined by wet mill mismanagement; careful wet mill practice can coax remarkable quality from good cherry. Which is why when you see a lot traced to a specific washing station, that traceability is meaningful - it names the people and decisions behind what's in the bag.