The Coffee Cherry
Coffee is a deciduous, shrub-like tree. Most cultivars used in commercial production are pruned back each year to less than 8 feet in height, and every 8-10 years the tree is pruned nearly to the ground. The life of the tree in terms of good coffee production can be 50 years, and it will live much longer but will probably stop producing coffee with good organoleptic qualities at some point.
The coffee cherry matures for about 5-6 months on the branch! At any time in this period it is susceptible to damage from weather, rain (or lack thereof), hail, insect damage, etc. Changing from green, to ripe, to rotten. The cherry must be ripe when picked, which is why all quality coffee is harvested by hand. At any given time a branch contains ripe and unripe fruit simultaneously so picking is done with continuous passes on the same trees.
Bad coffee is picked less discriminately, and the cup quality bears this out. Green cherry is unacceptable in good coffee. Yellow to red cherry is not necessarily going to ruin a cup, but ideally all fruit is deep red to crimson. Overripe cherry can give interesting nuance to a cup in small amounts and ruin it if there is too much. In the wet-process method, cherry must be depulped within 6-12 hours after picking or it will began to rot.
In dry-processing, the whole ripe coffee cherry is laid out on patios to sun-dry. Then the seed is milled out of the cherry once the moisture content is down to about 12%.It can be done in remote areas without water or electric, one reason this is ideal for small-plot farms. But only coffee for local markets is processed this way in Central America.
In wet-processing the coffee cherry is harvested by hand, and brought to the wet mill in baskets. In Guatemala a full basket is called a Quintal. The cherry enters a deep water flotation tank. Ripe cherry sinks, unripe cherry floats. The floaters are skimmed off the surface and the ripe cherry enters the pulper. At this stage the external skin of the fruit is removed/abraded and the fruity, pulpy muscilage is exposed. The coffee then enters a water tank to ferment. Fermentation is natural and it begins to break down the remaining musilage and makes the wall of the parchment (the tough blonde-colored inner layer surround the seed) thin. Fermentation is carefully controlled to avoid giving the coffee any off flavors, and lasts between 12-48 hours, sometimes as much as 72 hours in colder, high altitude locations. Then the coffee is channeled in a water stream to the drying patio. Drying is anywhere from 4-8 days depending on the weather, until the coffee reaches about 12% moisture content, and it will shrink a bit in size. It is now ready for the dry mill where it is removed from parchment, sorted by density and screened, hand prepped, and bagged for export.