What is hulling in coffee processing?

Hulling is the mechanical removal of the parchment layer - the papery shell surrounding the green bean after the cherry skin and mucilage have been removed and dried. It happens at the dry mill and is typically the first step once dried parchment coffee arrives for export preparation.

The hulling machine applies friction or pressure to crack and strip the parchment without damaging the green bean inside. Calibration matters: too tight and beans get cut or chipped, raising the defect count; too loose and parchment fragments remain on the surface.

For wet-hulled Sumatran coffees, hulling happens much earlier - while the bean still has elevated moisture content, before it's fully dried. This early hulling is what produces the distinctive swollen appearance and dark opal-green colour of Sumatran green coffee, and is the defining variable that gives those coffees their characteristic earthy, full-bodied, low-acid cup profile.