Processing of coffee beans after harvest

Coffee beans must be processed immediately after harvest to avoid spoilage. Producers use two treatments: solarization and cleaning. An effective sun-drying method is to spread the berries evenly in the yard and stir the dehydrated berries occasionally to heat and aerate them evenly. The dried berries are then put into a machine that crushes the outer shell and simultaneously removes the outer shell and the parchment film that surrounds it, separating the beans from the inside, sorting and bagging. Alternatively, the berries are mechanically pulped, washed, and finally dried and separated from the parchment outer membrane. Either way, the goal is one: to reduce the water content of coffee berries from 65% to only 10 - 12% green coffee beans.

One of the biggest challenges in making good coffee is making sure to start with good green beans. Top manufacturers, such as illy coffee in trieste, italy, use sophisticated birth-management techniques to reduce the proportion of defective beans. These include UV fluorescence analysis to identify moldy beans and a three-colour map (yellow, green, red and infrared) to create a colour fingerprint for each batch of beans. Illy teamed up with Sotex to develop a two-color sorter system that provides final quality control before green coffee beans are roasted. The method is to pick out the bad beans from the beans falling on the plate by photoelectric detector, and then use a blow from the air nozzle to eliminate them individually. The sorting works at speeds of up to 400 beans per second, which is unmatched by any human, and with an accuracy that even the most trained human eye can't match.

A perfectly ripe green coffee bean consists of unusually thick cells, which can be 5 to 7 microns thick and are rare in the plant world. During the roasting process, these cells, 30 to 40 microns in diameter, act like microreactors, where all the important chemical reactions driven by heat take place; the fascinating taste and aroma of coffee are also produced. Immature coffee beans have thin cell walls and lack important aroma protein precursors produced in the final stages of maturation. After fermentation by bacteria or mold, the beans and cells are emptied of these important substances.