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Coffee Processing

By :Hassan Mohamed 0 comments

After harvesting, coffee is then processed to remove the outer layers of the cherry and prepare it for sorting, grading, and export. Processing must begin immediately after harvesting.

There are two ways coffee is processed after harvesting, the Dry Method and Wet Method.

The ‘old’ and traditional methods of coffee processing

 

The Dry Method   ( Natural )

 

Also called Natural Process, this is the traditional way of processing coffee. The harvested cherries are spread over a concrete or brick patio, in full sunlight, and raked at regular intervals to prevent the beans from fermenting. If it rains or temperature drops, the beans are covered to protect them. After 7 to 10 days, when moisture levels within the cherries have fallen to 11%, the cherries are considered dry. The outer shell will have dried to a dark brown and become brittle. The dried cherries are then stored in silos.

The Wet Method

This method requires greater investment and more care than the dry method. The main difference between the two methods is that the wet method uses a pulping machine to remove the outer layers of the cherries from the beans within. This is done within 24 hours of harvesting. Cherries are carried by water, hence "wet method", and washed through the pulping machine which squeezes the beans from the cherry pulp, the beans are then carried through washing channels which separates the lighter, immature beans from the heavier, mature ones. The beans are then stored in fermentation tanks for 12 to 48 hours during which time enzymes work to naturally separate the remaining outer layer from the parchment covering ( the endocarp ). When the process is complete, the beans must then be dried to 11% moisture content. The beans will be dried either by sun on patios or by mechanical dryers.

Either way, the finished coffee is known as "parchment", referring to the final layer which remains on the beans.

The Difference

Wet Method coffee tends to have more acidity in the cup with a thinner body. Coffee process through the Dry Method will have a heavier body with not as sharp acidity. Most countries produce either wet or dry coffee, however a few do use both methods.

Wet Method Origins

Colombian, Java, Kenya, Mexican, Costa Rican, Guatemala, Hawaii, Jamaica, Nicaragua, Zimbabwe, Tanzania, and many more.

Dry Method Origins

Sumatra & Sulawesi

Origins Offering Both Methods

Brazil & Ethiopia

Coffee is next sorted by size and defects are removed. The size of coffee beans is expressed by a screen number. Coffee bean are passed over metal screens which are punched with holes. The first screen has holes 18/64 ths of an inch, beans smaller than that fall through the screen. The next screen has holes 17/64 ths of an inch, below that they are 16/64 ths of an inch, and so on. Beans are separated out by size and classified by the number of the screen they sort at. Our Colombian Supremo is always Screen 18+ which means all of the beans are 18/64 ths of an inch or larger. While we can purchase Colombian Supremo with a Screen of 16 , 17, or 17/18 mix, we require Screen 18+ to insure we have the best possible coffee.

Defects in coffee can be broken beans, black beans, pits of twigs or branches, or any foreign objects which make their way through processing and hulling. Defects are removed several ways depending to the technological investment at any given mill. Traditionally, defects have been removed by hand. Coffee passes in front of rows of sorters on conveyors, as the coffee passes by, defects are picked out. Some of the more advanced coffee farms, such as those on the Hawaiian island of Kauai, use color monitoring eyes that activate a blast of air to shoot bad beans out as they pass in front of the eye.

The final grade of coffee is determined by a random sample taken from a given lot of beans. The number of defects within that sample will determine the grade of the whole lot. The more time and care given by sorters the higher the grade will be since more defects will be removed.

modern methods of coffee processing

Anaerobic fermentation

The cherries are thrown into the de-pulper. The separated seeds are then placed in airtight fermentation tanks. The pulp and parts of the fruit that were obtained separately from de-pulping are added. The tank is then sealed and oxygen is sucked out. The process takes approximately twenty hours. During this time, the pressure in the tank increases due to the carbon dioxide produced during the fermentation. Its level as well as sugar level, temperature and pH are meticulously measured. The reactions must be stopped before alcohol is produced from the progressive fermentation.

 popular in Central American countries 

 in the cup:

  • complex, interesting, “wild” acidity
  • notes of cinnamon and flowers
  • creamy, silky texture

Lactic process

lactic acid bacteria cultures. The bacteria feed on the sugar contained in the pulp, which produces lactic acid. PH measurement is especially important in this case. At the right moment, fermentation is stopped and the beans are soaked in clean water to stop the growth of bacteria. The last step is drying, as with any other processing method.

 in the cup:


  • complex aroma and flavor
  • complex, pronounced acidity

             fruity notes


Carbonic maceration


 This type of processing stems from the method of processing grapes, combined with the movement of natural wines. In the context of coffee, it was first described by Sasa Sestic at the 2015 World Barista Championship. The whole ripe fruit is placed in an airtight tank. The tank is closed, then carbon dioxide is forced into it, which, as a gas heavier and denser than oxygen, “pushes” oxygen out  through a special valve. Characteristic for this process is the migration of substances called tannins and anthocyanins into the bean. Many chemical reactions take place there, the products of which are responsible for the original, unusual taste of the coffee processed in this way.




Milling



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. These steps are often called dry milling to distinguish them from the steps that take place before drying, which collectively are called wet milling.


Hulling

 

The first step in dry milling is the removal of what is left of the fruit from the bean, whether it is the crumbly parchment skin of wet-processed coffee, the parchment skin and dried mucilage of semi-dry-processed coffee, or the entire dry, leathery fruit covering of the dry-processed coffee. Hulling is done with the help of machines, which can range from simple millstones to sophisticated machines that gently whack at the coffee

Polishing

This is an optional process in which any silver skin that remains on the beans after hulling is removed in a polishing machine This is done to improve the appearance of green coffee beans and eliminate a byproduct of roasting called chaff. It is described by some to be detrimental to the taste. By raising the temperature of the bean through friction which changes the chemical makeup of the bean.

Cleaning and sorting


Most fine coffee goes through a battery of machines that sort the coffee by the 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, a 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. 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. With most high-quality coffees color sorting is done in the simplest possible way: by hand. Teams of workers pick discolored and other defective beans from the sound 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 have been cleaned and sorted in this way Color sorting can also be done by machines. 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. However, these machines are currently not used widely in the coffee industry for two reasons. First, the capital investment to install these delicate machines and the technical support to maintain them is daunting. Second, sorting coffee by hand supplies much-needed work for the small rural communities that often cluster around coffee mills. Nevertheless, computerized color sorters are essential to coffee industries in regions with relatively high standards of living and high wage demands

Grading

Grading is the process of categorizing coffee beans by various criteria such as size of the bean, where and at what altitude it was grown, how it was prepared and picked, and how good it tastes (cup quality). Coffees also may be graded by the number of imperfections (broken, under-ripe, or otherwise defective beans; pebbles; sticks; etc.) per sample. For the finest coffees, origin of the beans (farm or estate, region, cooperative) is especially important. Growers of premium estate or cooperative coffees may impose a level of quality control that goes well beyond conventionally defined grading criteria, as this allows their coffee to command the higher price that goes with recognition of consistent quality



Other steps

Aging

All coffee when it was introduced in Europe came from the port of Mocha in what is now Yemen. Importing the beans to Europe required a lengthy sea voyage around the Horn of Africa, which ultimately changed the coffee's flavor due to age and exposure to saline air. Coffee later spread to India and Indonesia but still required a long sea voyage. Once the Suez Canal was opened, shipment time to Europe was greatly reduced and coffee with flavor less affected by salt and age began arriving. This fresher coffee was, to some degree, rejected as Europeans had not developed a taste for unaged coffee.[citation needed] To meet the demand for aged coffee, some product was aged in large, open-sided warehouses at port for six or more months in an attempt to expose the coffee to the same conditions that shipments used to require.

Although it is still widely debated and subject to personal taste, certain types of green coffee are believed to improve with age- especially strains valued for their low acidity, such as beans from Indonesia or India. Several coffee producers sell purposely aged beans, some aging for as long as 8 years. However, coffee experts consensus is that a green coffee peaks in flavor and freshness within one year of harvest and that over-aged coffee beans lose much of their essential oil content

Decaffeination

Decaffeination is the process of extracting caffeine from green coffee beans prior to roasting. The most common decaffeination process used in the United States is supercritical carbon dioxide (CO2extraction. In this process, moistened green coffee beans are contacted with large quantities of supercritical CO2 (CO2 maintained at a pressure of about 4,000 pounds force per square inch (28 MPa) and temperatures between 90 and 100 °C (194 and 212 °F)), which removes about 97% of the caffeine from the beans. The caffeine is then recovered from the CO2, typically using an activated carbon adsorption system.

Another commonly used method is solvent extraction, typically using oil (extracted from roasted coffee) or ethyl acetate as a solvent. In this process, solvent is added to moistened green coffee beans to extract most of the caffeine from the beans. After the beans are removed from the solvent, they are steam-stripped to remove any residual solvent. The caffeine is then recovered from the solvent, and the solvent is re-used. The Swiss Water Process is also used for decaffeination. Decaffeinated coffee beans have a residual caffeine content of about 0.1% on a dry basis. Not all facilities have decaffeination operations, and decaffeinated green coffee beans are purchased by many facilities that produce decaffeinated coffee.

Storage

Green coffee is usually transported in jute bags or woven poly bags. While green coffee may be usable for several years, it is vulnerable to quality degradation based on how it is stored. Jute bags are extremely porous, exposing the coffee to whatever elements it is surrounded by. Coffee that is poorly stored may develop a burlap-like taste known as "bagginess", and its positive qualities may fade.

In recent years, the specialty coffee market has begun to utilize enhanced storage method. A gas barrier liner to jute bags, is sometimes used to preserve the quality of green coffee. Less frequently, green coffee is stored in vacuum packaging; while vacuum packs further reduce the ability of green coffee to interact with oxygen at atmospheric moisture, it is a significantly more expensive storage option.
















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