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Processing There are 3 harvesting methods: stripping, hand-picking and mechanical. Stripping is commonly employed in regions with dry climate.  Harvesting begins when the majority of the cherries is in the over-ripe or partially dry stage, to prevent undesirable fermentation. Handpicking is generally used in regions with constant rain, where many flowerings occur throughout the year.  Only ripen cherries are picked into bags and taken for processing on the same day of harvest. Mechanical harvesting primarily involves vibration of the coffee shrub branches. In order to achieve homogeneous cherries, prior to processing, the harvested cherries will pass through water-separators to remove rocks and other impurities by densities.   Once harvested, the cherries will go through one of the 3 processing methods:  Natural/Dry process, Washed/Wet process, Pulped natural process Dry processing: Cherries are dried on patios or racks under the sun or mechanical dryers.  On patios, the cherries are turned several times daily to ensure consistent drying throughout the surface of the cherries.   As the most natural process, it is environmental-friendly and produces good body and aroma, suitable for espresso. In wet processing, ripe cherries pass through the washer-separators to separator the immature cherries from the ripe ones.  Next the cherries will go through the pulper to remove the pulp, followed by either dry or wet fermentation to remove the 0.5-2mm slimy mucilage from the parchment.  Fermentation takes about 12-36 hours depending on the ambient temperature.  Dry fermentation is faster than wet fermentation (where beans are immersed in water) and reduces the formation of ‘stinker’ beans.  Fermentation ends when the parchment loses the slimy feel of the mucilage.  Warm water contains more microorganisms thus it will speed up the fermentation process.  It has to be changed regularly to remove the concentrated mineral and sugar released from the beans, which otherwise will lead to ‘onion’ flavor that becomes stinkers and detected in the cup.   Formation of acetic acid increases as fermentation passes 20 hours, and this can also leads to production of off-flavors.  After pulping, the coffee beans have to be carefully washed, by friction, to remove any trace of mucilage.   Pulped natural process differs from natural and wet processes in that the cherries are pulped and dried with parchment and mucilage, without fermentation.  This process produces greater body than the wet process. Drying process Once the above process has completed, the beans are dried to a relative humidity of less than 12% to prevent the development of musty, earthy or fermented flavors, depending on the earlier processing method.   Prior to drying, coffee cherries can have the following humidity: Green immature cherries: 70%; Mature cheries: 50-70%; Over-ripe cheries: 35-50%; Dry cherries: 16-30%.  Because of this difference, the beans have to be separately dried by different methods. Naturally processed beans are spread out dried in thin layers of 2-3cm on drying patio where they can constantly turned throughout the day to speed up removal of external water and avoid appearance of moldy beans.  At night, they are heaped, thickened and covered with cotton or waxed fabric to prevent the morning dews from condensing onto the beans.   Pulped natural and wet processed beans are dried on patio or suspended tables, initially spread in 2-3cm layers, thereafter heaped when half dry.  At night the beans are covered, just like the dry-processed beans. For regions with adverse weather, mechanical drying is carried out until the beans reach a humidity of about 12%.  To speed up the drying process, beans dried on patio to 20-30% humidity also use this method.   Temperature in this drying process should not exceed 40-45°C, or 30°C if immature beans exist so as to prevent the beans from turning dark green. After the drying process, the dry-processed beans will be sent to the mill for grading process, including size grading, density separation and color sorting.  Wet processed coffee will be delivered to the mill for hulling. In the Mill The beans are cleaned in 2 stages.  In pre-cleaning stage, small and large impurities (eg, dust) sieved out.   Then, the destoning stage uses flotation of coffee to separate the beans from the heavier stones.  At either stage, rotary plates or magnets are used to remove any iron particles. Once cleaned, the beans are sent for hulling whereby the outer shell (husk) and ‘silverskin’ of parchment or dry cherry coffee is removed by friction and polishing.  The polishing process is commonly required for wet- processed coffee rather than dry-process coffee. Now the beans are ready for grading for marketing purposes as well as to provide roasters with consistent quality based on density and color.  Sieves of different sizes and shapes are used to separate the green beans according to their shapes and sizes.  Holes on sieves are usually measured in multiples of 1/64th of an inch.  Peaberries are separated by slotted (rectangular) screens of different sizes.  Below is a table to illustrate the classification of green beans based on the size of the beans:

1/64 inch mm Classification Central America and Mexico Colombia Africa and India 20 8 Very Large Superior Supremo AA 19.5 7.75 19 7.5 18.5 7.25 Large 18 7 A 17 6.75 Excelso 16 6.5 Medium Segundas B 15 6 14 5.5 Small Terceras C 13 5.25 Shells Caracol   12 5 11 4.5 Caracolli 10 4 9 3.5 Caracolillo 8 3

Apart from bean size, green coffee beans are also classified by: Species and variety - arabica & robusta Number & types of defects Density - Specific weight of the beans Appearance & humidity (dryness) - bean uniformity; humidity should be 11+-0.5%. Colour - Coloration of the beans.  Eg. bluish-green color is very desirable in washed coffee Processing - Natural (dry), pulped natural & washed (wet).  Washed beans are shiny, translucent & green-bluish color.  Natural beans are semi-opaque color with yellowish or even brown skin.  Pulped natural beans has an intermediate aspect. To further remove defects associated with less dense beans, such as malformed beans, insect-damaged beans, fermented beans, some types of black beans, etc., mechanical and electronic sortings are used. Mechnical sorting uses traditional catadors or densimetric tables (also known as gravity separators) to separate the light, defective beans from the heavier sound beans.  Densimetric tables blows air located below the deck of the table to separate the lighter and heavier beans, and with vibration, the beans leave the deck separately. Electronic sorting removes the defective beans based on the colors of the bean.  As such, several complex optical measurement techniques are required to address different types of defects.  For example, Monochomatic sorting removes beans lighter or darker in hue than average beans Bichromatic sorting remove unripe, waxy, chipped, insect-damaged or broken beans as well as white and black beans Trichromatic sorting enhances bichromatic sorting by sorting according to different size and shape to remove foreign materials eg. glass, stones and insects UV fluorescence sorting to remove stinkers and non-visible defects eg. mould or bacteria Latest optical sorting deploys the use of laser to eliminate the need for optical band pass filters for the various defect detection. Defects There are basically 5 categories of defects found throughout coffee processing: Non-coffee defects (foreign matters, eg. stone, twig, leaves, wood fragments, metal, etc.).  These defects are removed by sieving. Defects of non-bean origin (husks/hull).  Such defects are removed by sieving or by air classifying. Irregular formed beans (shells, ears, broken beans, nipped beans bruised by pulper, bean fragments, broken beans, insect-damaged beans).  These are removed via densimetric and optical sorting. Beans with irregular appearance (eg. black bean)  that may influence the cup taste.  Such defects are removed visually by hand or by optical sorting. Off-taste(eg. Stinker beans, rio beans), that is only identifiable during cup tasting.  The only way to detect is by cupping a sample of roasted and ground coffee.

Defect/ Appearance Cause Effect on Cup Light-green bean, unripe Unripe Increased bitterness due to phenolic acids (17% in unripe beans compared to 7% in ripe beans)Reduced lipid content Dark-green bean, unripe Unripe beans exposed to temperature > 40°C Astringent taste. Separated by densimetric sorting Black bean Over-ripe beans fallen from trees Harsh and ashy flavor Sour bean Excessive fermentation or over heating leading to sour smell & taste Sour smell and taste Stinker bean Over-fermented, over-heating, contamination by moulds/bacteria, abrasion during pulping leading to loss of protective layer Sour and foul rotted Rioy bean, look same as normal bean Cherries contaminated by moulds/bacteria while still on plant, drying too slow or drying patio soil contaminated by microorganism Medicinal, iodine-like Whitish bean Excessive humidity Reduces aroma, slightly bitter and woody Mouldy bean Contaminated by mould Mustiness taste Earthy bean Presence of mould Earthy, musty, robusta-like Peasy bean Cherry contaminated by bacteria Strong reminiscent of fresh peas

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processing & grading