Jan 19

Written by:
19/01/2012 3:39 PM 

Far more is done on a coffee plantation than just growing and harvesting the fruit. 

When coffee cherries ripen, they must be picked almost immediately, not an easy thing to time when a single tree’s fruit is in various stages of maturity simultaneously. In most Arabica-growing areas the ripe cherries will be carefully hand-picked and dropped into the picker’s basket, the weight of which determines the picker’s pay and, in areas of smoother terrain and shorter trees, can be as heavy as 100kg by the end of the day. The same tree will be visited on several different days as more cherries ripen.

A harvester will “strip-pick” the entire tree when the majority of its cherries are ripe, by sliding his or her fingers down the branches, causing all the cherries, ripe or not, to fall to the ground. Alternatively, a large vehicle will be driven slowly down the row of coffee trees, and its revolving arms will knock the looser, and hopefully riper, fruit to the ground. Harvesting machines are used primarily in Brazil, where the immense, flat terrain of the large estates allows the trees to be planted in even, widely spaced rows.

If the fruit is on the ground, it must be raked up and “winnowed” by workers who, using large meshed hoops, fling the sweepings into the air several times; twigs, leaves, cherries and dust are tossed up high, and the worker, like a juggler, catches the cherries as the lighter weight materials are blown aside. A major problem with the hand stripping and machine methods or harvesting is that many cherries are included which are not at a point of perfect ripeness; these under or overripe cherries must be removed by extra sorting or else they will lower the grading quality.

The Coffee Cherry

The coffee fruit is called a cherry primarily because it is about the same size, shape and colour as an actual cherry. Beneath the bright red skin is the pulp, a sweet, sticky yellow substance, which becomes slimy mucilage towards the centre of the fruit where it surrounds the coffee beans, which are actually the seeds.

There are normally 2 beans per cherry, facing each others flat side, like peanut halves. On the surface of the beans is a very thin, diaphanous membrane, called the silver skin. Each bean (and it’s silver skin) is encased in a tough, cream coloured, protective bean shaped shell, or jacket, called parchment, or pergamino, which serves to keep the beans separate from the mucilage. Beans destined to be seed beans for growing new coffee plants must remain in their parchment if they are to sprout.

Processing the Cherry

The next step after harvesting is to remove the beans from the surrounding fruit pulp, which is done by either the washed (wet processes) or the unwashed (dry process). The latter, dry processing, is the separation method, used where there is a shortage of water or equipment, or both.

Dry Processing

In spite of its description, dry processing begins with the washing of the newly harvested cherries, not only to clean the cherries but to implement another sorting procedure, as the floaters – defective beans due primarily to insect infestation or over ripeness- are easily picked out at this stage.

The cherries are then spread out to sun-dry; if on patios they are raked and if on matting stretched across trestles, or on another raised platform, they are hand turned, for about three weeks. They are protectively covered from any night condensation or rain –the unwashed process tends to be used in drier regions anyway – and the drying process may be finished with hot air machines.

When only about 12 percent of their moisture content remains they are either stored in silos or are sent on for final processing at a mill or factory. Here they undergo hulling, which in one operation removes all of the dried skin, pulp, and parchment from the beans.

From this point the procedures are the same for both washed and unwashed beans: they are polished, screened and sorted, processes usually done with more sophisticated equipment, including electronic sorting machines; and then graded and bagged. After this the bags of green (unroasted) beans may go into storage or exported.

Wet Processing

Before any fermentation can begin in the freshly picked cherries, they are immediately washed in large tanks, from which the water then carries them into a system of channels. Staying in contact with the fresh-flowing water helps to loosen the outer skin, while the cherries are carried towards a depulping machine. Here they lose their skin and some of the pulp, but the flowing water takes the beans, still wearing a lot of the sticky mucilage, through various screens, sieves and sluices, which further sort the beans by size and weight. 

At last the beans arrive in a fermentation tank, where any remaining mucilage is broken down by natural enzymes during a 36 hour soak. The fermentation is monitored and controlled as it must only remove the mucilage and not develop off flavours in the beans themselves. The parchment beans, once clear of mucilage, are rinsed, drained and spread out on patios or wire mesh platforms, and left to dry in the sun.

As in the dry method, the parchment beans are turned and raked for between one and two weeks, or they may go into low temperature drying machines, until their moisture content is about 11-12 percent: the last stages are critical because overdrying  makes them brittle and they can lose quality, under drying means vulnerability to unwanted fermentation, fungi and bacteria or bruising during subsequent hulling.

Wet Hulled

In this method, the farmer picks ripe coffee cherry, pulps off the skin and either dries it immediately for one day, or lets it sit overnight in a bucket (with or without water), then washes it the next day and dries it. In either case, the coffee is partially dried with some or all of the mucilage clinging to the parchment covered seed. It is then sold to a coffee processor at 40-50% moisture content, who then dry it to 25-30% and run it through the wet hull machine. Friction strips off the parchment, and the bean emerges swollen and whitish green. Then it is dried on the patio down to 11-14% moisture, ready for sorting, grading, bagging and export.