Green Coffee Processing

Timothy J. Castle and Joel Starr

Post-harvest coffee processing has historically involved trio goals. The first is to determine the method of processing that delivers the best tasting co/jee far a particular origin and the market where coffee is sold. The second is to process the coif e in the most efficient and least expensive manner The rerultatit process almost always owes its outline to both concerns. Joel Starr and Tin Castle report on these important goals that all coffee pvcess'ors, front the snallesrlarinurs to the largest mrillers, are concerned about.

hOver the years, advancements in coffee processing have generally been made in small incremental steps. The most striking feature of its history is the individualistic approach that farmers and millers ave taken to processing green coffee. While generalizations can certainly be made, processing methodology can change dramatically from one origion to another, not so much from a neighboring mill to another and from one farm to another in the same origin.

In surveying the broad outline of green coffee processing today, it's worth-while to review the basic processes and to assess their advantages.

The Dry Process Method

The traditional dry or "natural" process is the oldest and most straightforward method to obtain coffee beans. The cotcc elten'ies arc picked and then either spread out on patios to dry naturally in the sun or placed in machines called coffee driers, The cherries must be raked and turned often, to prevent mold and mildew from occurring during the duration of up-to-two weeks so they may lay to dry. Mechanical drying is faster, usually less than two days, but the cherries must also be turned often and hot air evenly distributed.

According to Carlos Brando, author of the coffee-processing chapter in the book Coffee: Growing, Processing, Sustainable Production. "The bins diy with their mucilage and pulp intact meaning the full cherry is dried as it leaves the tree becoming the black dry cherries common in Brazil and Ethiopia and known a s Wbuni in East Africa."

Dry processed Coffees can exhibit store variance from cup to cup and a slightly lower acidity but fuller body than their wet processed counterparts. According to Brando, "the drying of the whole cherry imparts full body and natural sweetness to the beans."

Dry processed coffees, while once viewed as inferior to wet processed coffees can no%% fetch significant premiums in their own right. Certain Sumatran eoflecs have become extremely expensive and man Brazilian estate coffees have i followed in this emerging pattern. Many as an essential element of a great espresso blend view natural processed coffees.

The Wet process method

The wet process owes its invention around 1740 to the Dutch in the West Indies. They realised that by stoning the pulp of the coffee off the cherry and then fermenting the remainder they could decompose and wash away the gelatinous and otherwise water-insoluble mucilage. When dry. the bean will become a beige-colored parchment.

Traditionally. "Washed" coffees were processed using a large .amount of water. Freshly picked cherries were first sent to water tanks for density separation. Overripe and partially dry cherries, having lower density, floated to the surface of the water tank whereas the denser, unripe and ripe cherries sank to the tanks hottorn.

The denser cherries were then pressed. again in water, between grated screens that removed the bulk of the cherry pulp. However. there was still another layer that needed to be removed-the mucilage. The beans were again immersed in water, and allowed to ferment for anywhere front a few hours to a few days. The fermentation does two things-it breaks down the cellulose of the mucilage layer covering the parehnient husk enclosing the beast, and, it is generally agreed. increases the acidity of the coffee. It stay also add increased complexity and elegance. After this fermentation step, the coffee could also he run through long channels that served to further separate the coffee according lo different densities.

Modern 'Wet' milling to produce "washed" coffee is now clone in an ecological manner that manages to consume 10 times less water than the traditional system. Water tanks may be replaced by mechanical siphons. patented by Brazilian machinery maker Pinhalense. These mechanical siphon tanks separate cherries according to density with very httlc water consumption. Machines can also sort out unripe cherries. Pinhalcnsc technical director Adclcio Piagentini claims "his company's immature cherry separators not only sort unripe cherries mechanically but also pulp the cherries in a gentle manner in order to preserve full quality with minimum damage to the eny ironment".

Several companies have developed a new generation of pulpers that consume little and even no water. Unlike Pinhalcnsc, which has machines to handle cherries with any degree of maturation. front fully mixed to ICO% ripe, and to pulp only the high quality ripe ones. Colombian Penagos Clausen I.tda believes in selective picking. Owner Alphonso Periagos-Consuegra states that. "of course, to pick and process only ripe cherries in the right way is our ultimate goal. There is no doubt that our ecologic wet coffee processing units have improved the quality of coffees processed".

Ecological wet milling proposes the removal of the mucilage by friction in machines called mucilage removers that consume and contaminate much less water than the traditional fermentation tanks. Mucilage removers can also be used after partial fermentation to complement the removal of mucilage. Whether to use fermentation or mechanical means to remove (lie mucilage is today the topic of heated arguments by quality experts. I lowever the need to protect our environment may hold the last word in favor of mechanical removal.

Alphonso Pcnagos Consucgra favors a light approach and a delicate touch to preserve the integrity of the green beans through the processing stages. According to Penagos Consuegra, "What is important is to preserve the quality of the coffee throughout the productive line, that is, to grow the best and adequate variety in the best soil, climate and the necessary overall conditions". Pinhalensc's Adclcio Piagentini believes that "because conditions vary from counts to country. not to say from one farm to the other, modern wet milling must be flexible and take into account local conditions, like the flex-line wet milling we are about to launch".

The Semi -washed Method

The semi-washed "pulped natural" Arabica coffees are considered a good base for the best espresso blends. which is important to note since espresso is the fastest growing coffee preparation system in the world. 'this method of processing uses the density separation method and de-pulping without the use of the mucilage removal step. In some cases, partial removal of mucilage is done mechanically. "The beans are dried w ithout the pulp but enveloped by all mucilage or some of it (when dl-v. it will be brownish colored parchment, the darker the brown. the store mucilage is left behind)." stated Brando.

According to Brando. "'I he sentiwashed system produces the same cup as natural coffee along with the advantage that there is no risk of unripe cherries interfering with the cup." Either method. it is understood, will yield coffees that arc sweeter and somewhat less acidic than those that undergo a fully washing process. The semi-washed "pulped natural" sy stem has been introduced in Brazil by machinery maker Pinhalenw. whose director I'iagentini claims. "that the country will soon produce up to five million bags of this type of coffee". I le adds that "the semiwashed system is now being used in Central America by suppliers of coffee to companies that set I espresso coflccs".

The critical aspect of post harvest coffee processing is to understand that almost every processing operation has a unique set of challenges and opportunities front both a quality and cost control perspective, and that almost every situalion will yield a totally unique result. It is therefore critical for farmers and processors to be aware of all the appropriate choices at their disposal in order for them to achieve the maximum quality at the lowest possible cost.

Parchment Drying

Wet Parchment coffee conuning out of a wet mill must be dried to about an I I-12% moisture content. This is accomplished by letting the parchment beans dry in the sun or through some type of mechanical drying. The beans. as in the dry process, require constant raking to avoid mold and bacterial growth if they are dried on pations or screens.

It is pretty well established it this point, that no particular drying method is superior front a quality point of view. Each method has its own risks and advantages. I Mechanical methods can overheat the beans and dull their flavor if file machines are not properly designed or operated. Suit drying can take too long and also dulI and/or muddle flavors or introduce bacterial and fungal taints. The method chosen depends on the resoures of the processor and the costs ofthe various inputs in a given situation. Ambient temperature and humidity. in addition to naturally present microbes, can also impact the drying method that is finally chosen. "Tire full wash helps to enhance the acidity at the expense of some of the body. "stated Brando.

Once the coffee is dried to the appropriate moisture level it can either be stored to await shipment, or in Nome situations to cure in a reposado step that some farmers and millers believe improves and integrates the coffee's flavor by mellowing it and reducing the potential harshness that many newly harvested and processed coffees can have.

Dry processing

TO say that hulling, grading and sortie_ coffees is a "hands on" process is easily an under statement. requiring the efforts of multiple people to obtain a good. clean sort. However, over the years, technological advancement. as well as the rising costs of labor in most countries (both in terms of pay and training), has helped to integrate various types of machinery into the processes. Therefore, we talked to a few people from exporters to roasters to manufacturers, to get some idea of the history and the current status of dry coffee processing today. This is not a comprehensive survey. or even an overview, but an attempt to grasp the scope of a discussion that should be ongoing and certainly will never be concluded!

When the coffee is ready for shipment. the cherry or parchment husk is removed along with some of the silver skin by mechanically grinding it off.'I'bis process can also overheat the coffee. It is important to set and maintain the milling machines in order to remove parchment without subjecting them to undue friction.

Alphonso Penagos states that" our Apolo coffee hullers. well known all over the world. remove the parchment and polishes the green coffee in two stages, without over healing the beans." Pinhalense recommends its CON cold hollers for dry cherry coffee and two-stage hulling and polishing in several it lternative arrangements for parchment beans.

Tire Gravity of the Situation

For both the dry and wet methods, the coffee roust be graded before it is bagged and shipped. In most situations today, grading is usually done mechanically using equipment that separates according to bean size, density and color. In rare circumstances, probably accounting for much less than I % of the world's production. some coffees arc sorted by hand.

We'll start with a bit of history that is still being made today, with the ubiquitous and hardy machine that is the "Oliver--a vibrating table that shakes coffee beans into groups of varying densities. Denser beans shake to the top portion and lighter beans shake to the bottom right of the table. The Oliver was invented in 1930 by Oliver Steele in St. Louis, Missouri, Many companies make similar devices but we are the originators." said Dan Peters. Sales manager for Oliver Manufacturing, based in Rocky Ford, Colorado since they moved there in 194'. "Now we manufacture about a dozen different de-stoners, gravity sepatators and Iluidizcd bed-dryers which are mainly surface dryers for washed coffee.'.

Size grading must be done before density and colorseparation in order to make the most out of these machines. According to plagentini, "Pinhalense, a long -time leader im size grading, has recently launched an upward flocc size grader that has greater precision than conventional down-flow grader;. As such it indirectly contributes to improve the performance of' gravity separators and color sorter;'.

Optical Sorting

Another type of sorter is the optical or color sot lei. Optical sorters use a small CCD camera to look at each bean as it passes through. They can identity and remove foreign matter and defective beans-(hose exhibiting cuts, fungal growth, and insect damage. ifa bean passes, it doc.just that and passes through: if a bean is identified as a defect. a puff of air blasts it into a reject pile. Optical sorters are manufactured by Xcliron in Costa Rica and Sortex in the U.K.

Alan Ilillarv. sales director for Sortex. remarked on the evolution of the optical sorter. "There was a horticulture seed producer called Gun son who had a germirnuion problem and they identified darker seals as being infertile. A couple of men there created an optical sorter that could identify the two. They created the Sortex brand name in 1949. At that time, the sorter was used for sorting rice, and that first model was distributed in 1953 to remove discolored rice grains. These days, sorters use CCD cameras similar to what you buy in a shop. They used to use a photo diode until about 15 years ago when Sortex became the first producer to use CCD chips. They're about the size of one pixel on your computer screen and they enable the detection of a different lit iehincxs all the way down to 5 of a millunetc,,.

Optical sorters, White useful for Arabica Producers. are far store common on Robusta mill. According to I I i l lary. "For robusta coffee. pretty much all millers will use an optical sorter, 'fhc defects to look for are very dark and it's quite easy for an optical sorter to do. The use of our sorters for Arabica is a lot less. Defects tend to be subtle differences in color, like a slightly different green color from immature beans. They don't won)' about that with Robusta, but with Arabica it makes a big difference in the cup. "In South Anicrica the big, problem is a whole drilled by a larvae or broca. We just call it insect damage. Banging around AraBica also causes bruises and Arabica bleaches very easily, all of which have an undesirable affect on the flavor." Optical sorters. although not a replacement for human labor. can greatly aticet output production if added to a human hill(,[ force.

Hillary continued. "Robusta mills tend to he quite big and stilling call go through six tons per hour. You put a color sorter into it you can get good grades of coffee without human intervention. Arabica mills are smaller and it takes about 200 people to sort about one ton per hour. We've put a color sorter in a still in Ethiopia to grab the gross defects and they were able to increase the output to about three tons per hour. The operator has a lot of control of exactly hat he wants to reject and he can be very. very precise. Repeating simultaneous sorting can virtually create different grades of cofTce on the fly".

The Art of the Process

Aleco Chigounis, roaster for the Venice. California-based Groundwork Coffee. spent four years in Costa Rica working with "The Coffee Source," where he worked an entire tan e.t at the farm and the mill. then moved to the Neumann Coffee group to source coffees from Costa Rica. El. Salvador. and Guatemala.

Chigounis noted that while the vast majority of Costa Rican coffee is now washed, there is some experimentation happening with pulped Naturals and a trend toward mass milling. "The mills in Costa Rica now are mega-mills, a small mill could be built for $5000 but a mega-mill requires about a 5300.000 to $400,000 dollar investment. Hand sorting is very rare:: they use electronic sorters after the Olivers. To me, coffee processing is one of (he finer arts of coffee. The miller has the opporumit> to leave their mark on the final cup quality of the bean over the course of the many hours that coffee will be sent through his or her processing plant. Acidity, body and sweet ness can all be altered or enhanced with decisions made by the stiller. Many millers al oriftin think that acidity can be increased by washing coffee in a Delva machine instead of letting the coffee sit in fermentation tanks. By choosing to not remove the coffee's mucilage, a miller can increase the depth and sweetness of the flavor profile. These are just a couple of the many ways that entice nuance is manipulated at the mill."

Mechanically grading CoJee?

Alejandro Candena works closely wish many farmers in Colombia, sourcing fine coffees for Virmax, an exporter of Columbian coffee. "Our experience is that hand sorting is the best way to reduce physical defects to an absolute minimum. Color sorters can't do miracles, as they have at most 50-60% efficiency. And, there are sonic defects, like beans with one broca perforation or damaged by de pulpers that are impossible to eliminate with color sorters. The best result would be to have a coffee with no detects at all. which in reality is difficult to find. If we have a very good physical quality for example, a very low number of blacks and vinegars. we wouldn't use color sorters at all. It just depends on the physical quality of the coffee."

Accord in,- to Brando, "The farmer can make money using technology in his favor by doing as much processing as he can. For example, in addition to post-harvest processing (dry, semi-washed, or washed systems) and drying. the farmer can hull and separate his coffee. This not only produces fuel for the driersthe coffee husk-but, roost importantly. allows the btmer to approach the market with full knowledge of the features of his product."

"Another way to use technoloeo to increase profits is for _rowers to have access to cupping laboratories or stations staffed with experienced suppers. This will avoid the repetition of processing mistakes as coffee is harvested and processed and the harvesting season carries on" Brando expounded.

The Evolution of Green Coffee Prrttoessing

Green coffee processing will continue to evolve with the changing tastes and needs of the coffee market. The market for equipment will develop unto a great number of niches and sub markets as coffees become more specialized. Higher volume capabilities and great quality control will continue to evolve. sontetuucs together sometimes in opposite directions ? bulk shipment for commercial cofees and bar-coded customized jute bags for specialty coflce ? just as the coffee market continues to evolve in general. Today, the coflce industry depends on the ability of equipment manufacturers to advance technologically, in order to provide the right coffees at the right price.

for growing global demand of both store coffees and better coffees. We should all be rooting for them !