An early demucilager from the 1950s, developed at the Kona Branch of the Hawaii Agricultural Experiment Station.
The oldest patent we have found for a machine capable of removing coffee mucilage was the Urgelles Device, patented in 1912, which used sand and sawdust as abrasives (E. T. Fukanawa, 1957). Widespread use of demucilager machinery began in the 1950s after the invention of the Raoeng pulper. It was designed for removing the pulp and mucilage of robusta coffee. As millers came to realise these machines were far more efficient if they were used only as demucilagers and not pulpers, their use became widespread and they came to be known as aquapulpers. Up until the 1980s, many versions were produced by different manufacturers around the world (J. N. Wintgens, 2004, pg. 642).
Aquapulpers remove mucilage by pushing beans through a rotating horizontal drum that is surrounded by a sleeve. Pressurised water pushes the parchment through the pulper, and mucilage is removed by the parchment rubbing against parchment and against the perforations of the drum and sleeve. Whilst this technology increased the efficiency of wet processing, it was very water intensive, requiring an estimated 9.3 litres of water per kilogram of green coffee (C. H. J. Brando, 2018).
In the early 1980s, demucilager technology was revolutionised by the introduction of a machine known as an ELMU. This machine was designed with a vertical demucilaging mechanism wherein wet parchment was fed into the top of the machine. Like the aquapulper, it used friction between the beans to remove the mucilage. Parchment travels from the top to the bottom with the help of rotors shaped like fingers, which keep the parchment moving. A version of the Penagos Ecoline combines a drum pulper, a disk pulper, and a vertical demucilager. This system is designed to remove 95% of the coffee mucilage.
This video from Colombian farm equipment fabrications company Panagos,