The outer cover of the seed is formed by a hard-pale brown endocarp that becomes the “parchment” after drying. The endocarp contains an enclosed seed, which has a thin, green testa known as the spermoderm or “silver skin”, which is a remnant of the perisperm.
Measurements made with a large number of seeds of Coffea arabica indicate that the seeds are 10 to 18 mm long and 6.5 to 9.5 mm wide.
The endosperm, which is a living tissue, contains a hard-external region and soft internal region, which surround the embryo. It is formed by polygonal and rectangular cells in different parts of the seed with the endosperm cap being formed by smaller and thinner cell walls compared to the rest of the endosperm where the radicle ultimately protrudes.
In terms of chemical composition, the endosperm contains proteins, lipids and minerals, but the main storage reserves possess high levels of polysaccharides, cellulose and hemicelulloses commonly deposited in the cell walls.
The cell walls are composed of cellulose and hemicelluloses, mainly insoluble mannans. The lateral endosperm is extremely hard because the mannan is deposited there as very thick cell walls; in the micropylar region, however, the walls are much thinner.
Morphology of coffee bean
