When the coffee beans are ripe, it is time to harvest them. Here begins the long series of processes that will end with our much-loved cup of coffee and its taste. Each processing step involves critical specifications, which must be managed correctly to ensure the best possible result. During the harvesting, it will be necessary to ensure that the best chemical qualities of the beans are preserved and that their degradation is avoided, averting the risk of either drying the fruit on the plant, or triggering an uncontrolled fermentation.
The Harvest begins when most of the fruits of a plantation’s coffee plant are ripe. It usually takes place only once a year and can last for a few months, just to guarantee the complete ripening of the fruit. There are three collection methods: picking, stripping and the mechanical method. Picking, or manual selection, is carried out fruit by fruit by pickers, who take from the plant only the ripe drupes they consider perfectly ripe. To complete the harvest they will, therefore, need to return several times to each plant. This method is used to produce high quality washed and natural coffees, as we will see below.
The second harvesting method is stripping. It is made by passing the hand in a comb-like fashion from the base to the end of a branch and tearing off all the berries, together with leaflets and twigs. At the end of this type of harvest, to ensure the best quality, the fruits that are too dry and too green are discarded. Only in the flat areas and in plantations where the perfect ripening of the fruits is practically simultaneous, is it possible to use the third method of harvesting, that is the mechanical harvest. The harvesting machines, taller than coffee plants, are equipped with brushes that move in such a way as to shake the tree and make the fruits fall to the base of the machine itself, where they are then collected.
The freshly picked ripe fruits must be processed immediately, on the day of the harvest, to prevent fermentation processes that would damage irreparably the quality of the coffee produced.
The main processing methods are: dry, wet and semi-washed. The natural or dry processing requires that the freshly picked cherries are dried in the sun on barns, racks, or a concrete patio, thus bringing the moisture content of the fruits to around 12% in a short time. Subsequently, hulling machines separate the shell, the pulp and the parchment from the grain.
The dry-treated beans will have a green-yellow color and their roasting will be less uniform than those treated wet; the silvery film that remains in the groove of the grain will take on a dark brown color during the roasting. The coffees produced with this process are called natural. Wet processing involves five phases:
- During the separation, the dry and immature drupes are identified and eliminated with a separating machine, or through the soaking in tanks of water, where the overripe and dry cherries will float, while the immature ones will lie on the bottom;
- the stripping eliminates peel and pulp from the grain in parchment. Also, this phase is mechanized and allows the two beans to separate from the pulp through a light crushing of the drupe;
- fermentation, which is a period varying from 6 up to 72 hours, the parchment grain rests while micro-organisms trigger the fermentation of the mucilage present on the parchment, facilitating its removal. The duration of this phase is correlated to the climatic conditions: higher temperatures accelerate the fermentation processes, shortening their duration;
- washing takes place by sliding freshwater onto the beans arranged on cement channels and which allows you to clean the beans in parchment and select them by density;
- drying, which consists of drying the beans in parchment, can be done in the sun or using dryers.
The stewed beans assume a green, blue-green or gray-green color. They toast uniformly and, once roasted, have a silvery yellow straw-colored film in the furrow of the grain. The coffees produced with the wet processing are called washed coffees and are particularly suitable for producing filter and espresso coffee, because this process enhances the acidity and the most precious flavors, such as florals and fruity ones.
The semi-washed method simplifies the processing of washed coffee as it skips the fermentation phase. In this case the mucilage is removed mechanically by rubbing between the beans, produced by jets of water under pressure. Among these methods it is not possible to prioritize, draw up a ranking or determine which is the absolute best. The existence of so many procedures is not linked to the degree of development of the producing countries, but climatic requirements. The amount of annual rainfall, humidity and water availability strongly affect the choice.
If we chose to use the natural method in countries such as Indonesia, Guatemala or Colombia, we would consider ourselves crazy, because they are countries that traditionally treat coffee with the washing method, having large quantities of freshwater available all year round and rates of humidity so high as to make it impossible to dry the coffee drupes in the sun without generating fermented and defective beans.
This does not mean that the natural processing method is less valid and this is demonstrated by the high quality of natural coffees produced in Brazil and some countries of East Africa. Countries characterized by drier climates and which do not have sufficient water sources to process coffee with water, traditionally choose the natural process.
With the processing of the beans, the complex chemical-physical modification begins, which will produce a surprising variety of flavors and smells of the different types of coffee in the cup. In general, a natural coffee from the Arabica plant has a uniform and thick cream, hazelnut-colored with slight streaks of a darker color. The taste is not very acidic, with sweet and bitter notes, rather full-bodied and has an aftertaste that recalls the smells of bread and pastry products. While a grain of Arabica, that has undergone the washing process, produces instantly a light hazelnut colored cream, more striped and quite thick but not very consistent. The acidic taste is more accentuated, the sweetness prevails over bitterness, the coffee is not very full-bodied and has a floral and fruity aftertaste.