Processing methods of Coffee beans in Coffee Encyclopedia

1. processing method

The processing method chosen has a significant impact on the final price and quality of coffee. The first step in processing coffee beans is to dry the beans. There are two specific methods, the most comprehensive processing method is called "drying method", which is used for unwashed coffee beans to produce lower coffee beans, while the highest quality coffee beans are processed by "wet treatment", which is used for thoroughly washed or semi-washed coffee beans.

Most arabica beans are processed wet, except for drying, which is more common in brazil and ethiopia.

① Drying method

Drying is the cheapest, simplest and most traditional way to process coffee beans. When processing, the harvested fruit should be spread on concrete floor, brick floor or straw mat. Ideally in the sun and raked at regular intervals to prevent fermentation. If it rains or the temperature drops, the fruits must be covered to prevent damage.

After about 4 weeks, the moisture content of each fruit will drop to about 12%, when the fruit is dry. In Brazil, coffee beans at this stage are called cocoa. The skin is dark brown and brittle, and you can hear the coffee beans rattling inside the shell.

This process requires a lot of skill. Because coffee beans can be overdried, if this happens, the beans are vulnerable to damage at the next stage (i.e., during shelling). Conversely, coffee beans that are not sufficiently dried are also vulnerable to damage. The dried fruit is then stored in a cellar for a period of time during which the moisture in the fresh coffee beans continues to evaporate.

② Wet treatment method

The wet process requires more capital investment and effort, but it helps to maintain the quality of the coffee beans and reduce damage. The main difference between the wet and dry methods is that the pulp is immediately separated from the coffee beans during wet treatment, rather than drying them out as in the dry method.

The wet treatment method can be divided into the following four steps:

Step 1: Separation of pulp. In order to guarantee the quality of the coffee beans, the separation of the pulp must be carried out as soon as possible after harvest, ideally within 12 hours, but not more than 24 hours. If the coffee beans are left for too long, the pulp becomes difficult to separate from the coffee beans, resulting in incomplete separation and possible damage to the coffee beans (coffee beans are separated in pulp separators in such a way that the fruit is crushed in machines having a fixed area and a movable surface or in machines having movable rods, whereby the pulp is separated from the coffee beans).

Step 2: Rinse. The peel and pulp separated from the coffee beans will be washed away with water. The rinse tank is designed to have the function of separating light, tender coffee beans from thick, ripe coffee beans. Such separation can also be accomplished by an Ogau machine (Ogau, a coffee grower in Norway, designed a device to sift coffee beans through filters into a large container of water while growing coffee in Kenya, where the large, plump beans sink first and the lighter beans remain. Water can be recycled during this process).

Step 3: Fermentation. That is, the use of enzymes, separation of the coating on the endocarp creamy mucilage. Coffee beans are stored in the fermenter for about 12 to 36 hours, depending on the ambient temperature, the thickness of the slurry, and the enzymes. This process is mainly determined by ambient temperature, glue thickness and enzymes. When this process is complete, the endocarp around the coffee bean is no longer slimy but has a pebbly feel.

Quality control throughout the wet process is critical to prevent coffee beans from spoiling, as even one bean spoils, potentially damaging the entire bean. For this reason, the equipment used must be cleaned daily to ensure that no impurities remain before the next round of processing.

Step 4: Drying. After fermentation, coffee beans remain preserved within the endocarp shell, which still contains about 15% water. The endocarp must be dried to a moisture content of approximately 11% to ensure that the beans are stored in a stable and safe environment. Moisture content is critical because if arabica beans are dried quickly to 10% moisture, they lose their original blue-green color and their quality declines.

Coffee beans covered with endocarp should be dried on a concrete floor, slate floor, dry table or plate, similar to drying.

On larger plantations or in places where rain can disrupt the drying process, mechanical dryers are sometimes used, and the beans are placed in air-conditioned boxes where drying wind blows on the beans. Drying can also be done by sun exposure, turning the beans regularly to ensure complete drying, which takes 12 to 15 days. The most important thing is that the endocarp should not crack, and if the sun is too strong, the beans must be covered.

At this point, the whole process is complete, and the coffee beans become known as "parchment coffee beans"(because the outer endocarp of the coffee beans is very similar to parchment). In general, it remains in this form until the eve of export.

Because coffee beans are exported from countries that produce them throughout the year, rather than just for about three months of harvest, they are stored in a perfectly stable environment in the form of parchment beans. High temperatures are the enemy of coffee beans, and humidity up to 70% is also easy to destroy coffee beans, for this reason,"parchment coffee beans" are generally not stored in the farm where they are produced. Highland-grown coffee beans should be stored at or near the same elevation as where they are grown because they are particularly susceptible to temperature. In this environment, Arabica beans should not be stored for more than 12 hours, and Robett beans can be stored for a slightly longer time.

(2)grinding or shelling

Coffee beans are ground before they are exported. This means that the endocarp is removed from Arabica and Robett beans ready for sale. Removing, washing the endocarp, and drying the shell of the coffee bean after the process is also known as shelling or peeling.

It is more difficult to remove the endocarp of coffee beans during wet processing than during drying, so different huskers need to be used. There are two main models: friction shell machine and compact shell machine. Engelberg and African models of friction huskers are suitable for dry or wet coffee beans: in a cylindrical box, coffee beans are squeezed between linear ribs and knives, and the shells are scraped by knives to expose the beans.

"Parchment coffee beans" are usually shelled on a Smoot friction huller. Smoot is Belgian, of Scottish descent. He was born in Kosberg, Prussia, and settled in Guatemala. In 1844, he developed a coffee peeling machine equipped with a rotating body with a screw, which rotates in a box equipped with a screw, and the screw rotates in the opposite direction. As the coffee bean is propelled along the rotor by power, the endocarp is stripped from the coffee bean. Because the rotor rotates relatively slowly, the rotor generates less heat than other types of huskers.

Other shellers include roll-type shellers (mainly used for dried coffee beans grown in South America) and crossbar shellers (equipped with knives).

Outside Brazil, parchment coffee beans are processed in a press sheller rather than a friction sheller. Coffee beans must have a moderate moisture content when shelled, otherwise they may crack. The press sheller consists of a horizontal disk rotating in a floral ring, around the rim of which are iron pins or irons. When the machine is running, the coffee beans come into contact with the iron needle due to centrifugal force, thus causing the endocarp shell to fall off.

(3)polishing

The silver-colored skin remaining on the beans after shelling must be removed by polishing. Most polishers work on a similar principle to Smoot huskers, except that copper rods are used instead of iron rods because copper rods do less damage to coffee beans. Copper also gives coffee beans their glamorous turquoise colour. Coffee beans processed with a press re-husker are usually polished because they always look messier than coffee beans shelled by rubbing.

Polished coffee is thought to be superior to unpolished coffee beans, but in fact, the final brew makes little difference when tasted in a cup. There are also those who insist that the value of polishing will be affected by the quality of the cup, but it is difficult to find conclusive evidence.

(4)Grading and classification

Coffee beans are graded first by size and then by density. All coffee beans have a fairly regular size and the same proportions, except for the more elliptical pea beans at the beginning and the larger giant beans (i.e., marago peel beans), one side of which is flat and the other is semi-elliptical.

In general, larger coffee beans produce better coffee. The size classification of coffee beans is usually expressed as 10 to 20, but some countries classify coffee beans according to a certain size, such as AA. The way to determine the size of coffee beans is to let them pass through a sieve.

It is important to note that coffee beans of the same size can vary in weight, and bad, shriveled coffee beans that must be eliminated can still survive.

The best way to separate unwanted coffee beans from good coffee beans is to use gravity and air. Compressed air is hand-operated and requires a high degree of skill. It uses jets to separate heavy and light coffee beans. Another method, gravimetric separation, is to place coffee beans on elevated plates and let air pass through them to drop heavy coffee beans. This is also a technically demanding method. If used properly, it can separate coffee beans more accurately and effectively.

The next step is to sort the beans. Remove rotting, dark, sour and overfermented or unshelled coffee beans. This process depends on the eye, put the beans on the moving belt inspection.

Other methods include electronic color classification (mainly for Roscoff beans) and dichromate (using light detection to look for bad beans). However, by far the best test classifier is still the human eye.

Different countries classify coffee beans according to different grading systems. Some of them, like the classification methods commonly used in Haiti, are too complicated to be effective, while the classification devices used in Brazil, although complex in structure, are indeed necessary. Generally speaking, there are six export grades, the highest grade is SHB(strictly hard bean), or highland coffee beans, produced at an altitude of not less than 400 meters.