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How Coffee Is Processed

Posted by Jeremy Denny on 19th Feb 2021

How Coffee Is Processed

Coffee grows best in the warm climates near the equator from 25° North to 30° South, also known as the Bean Belt. The ideal coffee climates are within 1,000 miles of the equator and the higher the altitude the more sugar a coffee will produce. At about 7,000 feet (2,100 meters) above sea level coffee can no longer grow. Coffee goes from seed to seedling and then moved to the field for full growth cycle. It will take 3-5yrs for the coffee plant to produce fruit. With careful tending, some coffee tree can live to be up to 40 years old with proper care and maintenance, also variety dependent.

After the coffee is grown and ready for harvest, there are still lots of things that need to take place before it can be shipped out to a roaster to “cook” the coffee. After harvest coffee will be processed in one of 5 main ways. Wet, Dry, Natural, Semi-washed & Aquapulped, which we will be covered in detail.

WET / WASHED:

Wet processing involves washing the coffee beans of fruity material while the beans are still moist right after they are picked. In countries where water is plentiful, the cherries are usually passed through a pulping machine, sorted by weight, and deposited in a fermentation tank. Here, naturally occurring enzymes dissolve the pulp until it can be washed from the bean, a process that takes 12 to 72 hours depending on many factors such as temperature and humidity. Once fermented, the washed coffee, still in its parchment (filmy, paper-like covering) is spread out to dry until it reaches around 11% moisture content. At this point, the seed is stabilized and won’t germinate.

Most of the coffee that anyone drinks is washed coffee, or coffee that’s been wet processed. It is the more reliable of the two methods, producing coffee with higher acidity making a brighter cup of coffee.

The basic method begins with sending the just-picked coffee cherry through a pulping machine. This removes the outer skin while leaving the pulp known as the mucilage, clinging to the seeds inside. The pulp-covered seeds are then soaked in water and occasionally agitated to get the pulp to fall off. Fermentation follows, where the seeds sit in water for anywhere between a few hours to a couple of days, depending on the climate, equipment used, and desired final coffee characters.

Following fermentation, the beans are rinsed thoroughly and then dried, either outdoors on raised beds, or in a mechanical dryer. Climate and equipment dictate how many days this final step takes.

oThe wet processing method involves soaking the coffee cherries and allowing fermentation to take place to separate the cherry from the bean – or it can be run through a mechanical depulper to remove the coffee cherries. Once the green coffees are removed, they are washed once again to remove residue and placed outside to dry traditionally.

oBecause the wet processing method is quite invasive compared to dry processing, it is only used from Arabica beans for coffee forms. Robusta coffee beans are not processed with this system because of their low quality, low final price and consequently low profit.

oThe main characteristic of the wet process is that the pulp and all the skins in the coffee fruit are discarded before drying the beans. Wet processed coffee is more consistent and produces a more natural coffee flavor.

DRY:

Dry Processing involves first drying the coffee cherry in the sun while regularly raking the beans free of any dried fruit.

  • oDry processing is a type of coffee processing that involves drying the freshly picked coffee cherry in the sun for a period of time on large patios while repeatedly raking and turning the drying cherry until the green coffee beans are generally free of any dried fruit and the humidity content is about 10.5%. Sometimes automatic dyers are used.
  • oDry processed coffees tend not to have a vast array of flavors, as the coffee cherry always pushes the flavor toward fruity and sweet. Dry processing is particularly important for Brazilian, Ethiopian and Yemenian coffees.
  • oAnother key consideration is the amount of water required–dry processed coffees can use as little as one gallon per kilogram of dried parchment, whereas wet processing takes more than 10 gallons per kilogram of dried parchment. This also increases the body of the coffee in the final cup.

oIt is simply impossible to use the dry processing system for countries with heavy rain and high air humidity. So, coffee farmers from India, Indonesia, Vietnam and other places with similar climates have to use other methods, usually wet processing.

PULPED NATURAL / SEMI-DRY / HONEY:

Pulped Natural Processing involves initially pulping the coffee but without a fermentation stage like the wet processing method, then dried with much of the mucilage still attached.

Honey processing method is unique in that it uses actually honey to pull the moisture of the beans. This creates an intense clean sweetness that comes from coffee cherries being partially washed, with a portion of the sticky mucilage left on the cherries. At this point, the coffee is spread out to dry in the sun and the fruit adheres to the bean.

oThe pulped natural or “semi-dry” process involves extracting various portions of the coffee cherry– between Wet Processing and Dry Processing. Recently, these varying amounts have become known respectively as “black honey,” “red honey” and “yellow honey”–more of the coffee cherry left on the outside results in more caramelizing and darker color. Less coffee cherry, on the other hand, means less sugar and a light hue.

oPulped Natural processing is a procedure that removes the coffee cherry’s outer skin to reveal the fruity layer and then helps it to dry in the sun or with a mechanical dryer. Between dry processing and wet processing, it is called halfway–taking more processing time and consuming more water than pure natural processing, but also providing a potentially overall higher quality cup.

oThe pulped natural method exhibits features of both wet processing method (good acidity) coffee and dry processed green coffees (sweetness, body), with some of the full flavor of dry processed coffee in the cup, comparable to a wet processed coffee.

SEMI-WASHED:

Semi-Washed processing a demucilaging machine is used to remove the coffee cherry’s skin and most of the mucilage,

  • oA demucilage machine strips coffee cherry skin from the green coffee bean itself as well as some or most of the mucilage.

oSemi-washed coffees are similar to coffees processed using the natural pulped method and like wet processed coffee. They feature a bright, clean and have less body than most dry processed coffee.

oNext the mucilage of the coffee cherry is removed via fermentation of the cherry for up to a day in a fermentation tank. Sometimes certain beans are double fermented to bring out even more character.

oThen the coffee beans are dried either by forced-air drying or spread over decks or patios to dry naturally in the sunlight. They are dried until they have a moisture weight of about 10%.

AQUAPULP:

Aquapulp is another method which cleans the coffee cherry initially and has recently been adopted by many areas that formerly used wet processing.

  • oAquapulp removes the sticky pulp or mucilage of the freshly picked coffee cherry. This is usually done mechanical to demucilage, using machines to clean the cherry.
  • oGradually but consistently, the aquapulp process replaced the long standing and common wet processing methods for extracting mucilage through fermentation and washing.
  • oThis method is an expensive investment but can save labor in long run and also be faster and more consistent under proper conditions. The initial cost of aquapulping systems keeps many smaller farms from moving to this processing method.

POST PROCESS:

After processing the coffee is complete the coffee still has a long way to go before it can be brewed to a delicious nectar. Immediate after processing is finished the coffee is then hulled & graded, explained below. Finally, the coffee is packaged and shipped to a coffee roaster where they will use chemistry, physics, experience and general knowledge to get the best character out of the green coffee bean.

HULLING:

Immediately after processing hulling takes place. This removes the parchment from bean. Methods for hulling range from old world primitive hand mills to modern sophisticated equipment. Once hulled, coffees are sorted into by size and then defects are eliminated from the batch. Often 50-100 people visually inspecting and removing defects, other farms have cutting-edge laser sorters performing this important step.

GRADING:

The coffee beans are sorted and graded based on local standards and industry standards after processing & hulling is finished. The beans are sorted into grades of quality based on size, shape, and other many other key character factors.

oGraduated hole sizing screens assist in completing the grading process. Also used are vibrating air tables, using gravity to divide the beans by density and to isolate damaged coffee beans that can affect the final product’s taste.

oCommon grading criteria includes bean size, bean hardness, rising altitude, color, smell, imperfections or defects, bean type / plant type purity, number of underripe beans and/or overripe beans, and also type of processing used.

oCommon imperfections in coffee grading include coffee beans that are hollow, deformed, chipped, nicked, or broken. Also, consistency of batch and many other factors that may change season to season like rainfall and other weather oriented issues.