How Coffee is Processed
Processing: Fruit Removal and Drying
The Dry Method:
In this, the oldest of processing methods, the coffee fruit is simply picked and put out into the sun to dry, fruit and all. It is spread in a thin layer and raked regularly to maintain even temperatures from top to bottom of the layer. Drying takes anywhere from ten days to three weeks, and, on larger farms, occasionally may be accelerated by putting the coffee into mechanical driers. The hard, shriveled fruit husk is later stripped off the beans by machine. Coffee processed by the dry method is called dry processed, unwashed, or natural coffee.
The Wet Method:
The fruit covering the seeds/beans is removed before they are dried. The wet method further subdivides into the classic ferment-and-wash method, and a newer procedure variously called aquapulping or mechanical demucilaging. Regardless of which of these procedures is used, coffee processed by the wet method is called wet processed or washed coffee.
In the classic ferment-and-wash version of the wet method, the fruit that covers the beans is taken off gingerly, layer by layer. First the outer skin is gently slipped off the beans by machine, a step called pulping. This leaves the beans covered with a sticky fruit residue. The beans then are allowed to sit in tanks while natural enzymes and bacteria loosen the sticky residue. Dry-fermented coffees usually are more complex and sweet than wet-fermented coffees, which tend to be brighter and drier in taste.
After the fermentation step the coffee is gently washed and then dried, either by the sun on open terraces, where the thin layer of beans is periodically raked by workers, or in large mechanical driers. This leaves a last thin skin covering the bean, called the parchment skin or pergamino. The parchment is then thoroughly dry and crumbly and easy removed. Coffee occasionally is sold and shipped in parchment or en pergamino, but most often a machine called a huller is used to crunch off the parchment skin before the beans are shipped.
Machine-Assisted Wet Processing:
The mechanical demucilage or aquapulp variation of the wet method is essentially a short cut a
pproach which removes the sticky fruit residue from the beans by machine scrubbing rather than by fermenting and washing. This mechanized short cut is increasingly popular for two reasons. Mechanical demucilaging cuts down on water use and pollution. Removing mucilage by machine is easier and more predictable than removing it by fermenting and washing. But machine demucilaging does limit the taste palate of coffee by prematurely separating fruit and bean.
The Semi-Dry or Pulped Natural Method:
This procedure is practiced regularly in only two regions of the world: Brazil and certain parts Sumatra and Sulawesi. The outer skin is removed as it is in the wet process, but the troublesome sticky fruit residue is allowed to dry on the bean and later removed by machine along with the parchment skin.
Processing: Cleaning and Sorting
The final steps in coffee processing involve removing the last layers of dry skin and remaining fruit residue from the now dry coffee, and cleaning and sorting it.
Removal of dried fruit residue:
The first step in dry milling is removing what is left of the fruit from the bean, whether simply the crumbly parchment skin in the case of wet-processed coffee, the parchment skin and dried mucilage in the case of semi-dry-processed coffee, or the entire dry, leathery fruit covering in the case of dry-processed coffee. The machines that do this range from simple millstones in Yemen to sophisticated machines that gently whack at the coffee.
Sorting by Size and Density:
Most fine coffee goes through a battery of machines that sort the coffee by density of bean and by bean size, all the while removing sticks, rocks, nails, and miscellaneous debris that may have become mixed with the coffee during drying. First machines blow the beans into the air; those that fall into bins closest to the air source are heaviest and biggest; the lightest (and likely defective) beans plus chaff are blown in the farthest bin. Other machines shake the beans through a series of sieves, sorting them by size. Finally, an ingenious machine called a gravity separator shakes the sized beans on a tilted table, so that the heaviest, densest and best vibrate to one side of the pulsating table, and the lightest to the other.
Sorting by Color:
The final step in the cleaning and sorting procedure is called color sorting, or separating defective beans from sound beans on the basis of color rather than density or size. Color sorting is the trickiest and perhaps most important of all the steps in sorting and cleaning.
Color Sorting by Eye and Hand:
With most high-quality coffees color sorting is done in the simplest possible way -- by hand. Teams
of workers, often the wives of the men who work the fields, deftly pick discolored and other defective beans from the sounds beans. The very best coffees may be hand-cleaned twice (double picked) or even three times (triple picked). Coffee that has been cleaned by hand is usually called European preparation. Most specialty coffees, since they are whole bean and consumers see what they get, are European preparation.
Color Sorting by Machine:
Machines now can mimic the human eye and hand. Streams of beans fall rapidly, one at a time, past sensors that are set according to parameters that identify defective beans by value (dark to light) or by color. A tiny, decisive puff of compressed air pops each defective bean out of the stream of sound beans the instant the machine detects an anomaly. These machines are not widely used to date due to their substantial capital cost, especially when compared to cheap labor costs in many coffee producing regions.
Processing: Grading
The last step in coffee's complex, approaches differ from country to country, but there are four main grading criteria: how big the bean is, where and at what altitude it was grown, how it was prepared and picked, and how good it tastes, or its cup quality. Coffees also may be graded by the number of imperfections (defective and broken beans, pebbles, sticks, etc.) per sample.
As the finest coffees move from the status of commodities sold by description to specialty products sold by specific lot, grading becomes less important, and origin (farm or estate, region, cooperative) more important. Growers of premium estate or cooperative coffees may impose a quality control that goes well beyond conventionally defined grading criteria, because they want their coffee to command the higher price that goes with recognition and consistent quality.
Even with fine coffee, however, government agencies in growing countries may impose grading standards to encourage and support quality and to attract and reassure foreign buyers. Coffee-growing countries like Kenya, for example, simultaneously promote high standards through imposing strict grading criteria while supporting growers by providing agricultural and social assistance.
The next Stage: Coffee Roasting
History of Coffee | How Coffee is Made | Where Coffee is Produced
Coffee Customs from around the world