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From Farmer to Roaster

Coffee trees produce berries that are called coffee cherries.  Inside these cherries are the coffee seed (bean).  They turn bright red or yellow depending on the variety when they are ripe and ready to pick.  The skin (exocarp) is thick and bitter although the fruit beneath (mesocarp) the skin is sweet with the texture of a grape. The next layer is the parenchyma that is slimy and helps to protect the beans.  The beans are also covered by another thin membrane called the spermoderm or silverskin.

coffee cherry diagram

Anatomy of a coffee cherry

 Among the 73 species of coffee shrubs there are two main species which are commercialized: Robusta and Arabica.  Arabica coffee accounts for 75-80 % of the world’s coffee  production. Robusta coffee accounts for 20% and differs from Arabica in terms of taste. The robusta bean is smaller and rounder than arabica beans. It is a heartier plant and  can sustain warmer temperatures. Robusta beans produce bitter tasting coffee with more caffeine than arabica. 

A coffee farmer propagates a red ripe coffee cherry by pulping and removing the mucilage by fermentation. The bean can then be planted immediately or dried for later use.  Properly stored dried coffee seeds can be used up to a year.

Planting

 It takes on average 3-4 years before a coffee plant will start to produce sweet smelling flowers and 5 years before you see your first coffee cherry.  After the initial 5 years has  passed then it only takes 6-9 months for the flower to ripen into a fruit.   Arabica plants are self-pollinating whereas Robusta depend on cross pollination.   The roots of the  coffee tree can extend 20-25 km in length. The tap roots extend no further than 30-45 cm below the surface.   The leaves of the coffee tree are shiny, dark green, and waxy.

When the farmer is ready to plant more trees he must first germinate the seeds; also known as the bean.  There are two ways to germinate the seeds.  In the first  method the seeds are pre-germinated by spreading them on a sand bed and covering with moist burlap bags or straw.  The second method is to mix seeds with moist vermiculite and  keep them in a polythene bag.  Once the beans have sprouted the seedlings are moved to a nursery bed or poly bag for the next stage of growing.  The soil for planting is a combination of soil and compost.   The beds need to be shaded  part of the day during the first couple months and then slowly weaned off as the seeds prepare to be planted in the fields. If polybags are used they are filled with a mixture  of topsoil, well rotted cattle manure, coarse sand, gravel, coffee pulp and coffee husks.  A top dressing of nitrogen is also used.

There are two optimal growing climates for Arabica beans; subtropical and equatorial regions.  The rainy and dry season should be well defined and altitude should be between 1800-3600 ft.  This provides one coffee growing season and one maturation season.  Examples of these subtropical growing regions are Mexico, parts of Brazil, and Zimbabwe.   The equatorial regions are at latitudes lower than 10 degrees and between 3600-6300ft.   Frequent rainfall causes almost continuous flowering which results in two coffee harvesting seasons.  The period of highest rainfall determines the main harvest while the period of least rainfall determines the second harvest season. Rainfall in these areas are too frequent for patio drying so mechanical dryers are used. Examples of these growing regions are Kenya, Colombia, and Ethiopia.

coffee-plant

 Harvesting

There are four methods of harvesting: stripping, combing, mechanical, and picking.

Stripping as a method of harvesting is just that – taking the branch and stripping off everything. That includes the flower, leaves, ripe and unripe berries.
Combing is using a wide flexible brush to “comb” the branch. This method leaves the unripe fruit, leaves and flowers on the trees.  It only pulls off the ripe cherries.
Mechanical harvesting uses tractors to pick the fruit with a brush that also removes the flowers and leaves.  Brazil is a common user of the mechanical method.
Picking requires manual laborers to hand pick each ripe cherry.

Most countries have one harvest per year.  A good picker averages 100-200 lbs of picked coffee cherry per day which will produce 20-40 lbs of coffee beans.   At the end of the day the worker takes his harvest to get weighed and the picker is paid on the quality of his/her work. All of the days harvest are then combined and transported to the processing plant.

drying 3

Dry Processing

 Processing

Wet/Washed –  For the wet method of processing the pulp of the coffee cherry is removed from the beans within 24 hours of harvesting. A pulping machine washes away the skin and pulp. The beans are then put into fermentation tanks for 12-48 hours. The beans are then dried by sun or mechanical driers.

Dry/Natural – The simplest and cheapest method of processing is spreading the harvested cherries out in the sun and periodically rake and turn for 7-10 days.  The cherries are dried when the moisture content has dropped to ~11 %.  The outer shell will turn brown and the beans will rattle inside the cherry.

Pulped Natural / Semi – Washed – The pulped natural process is similar to washed in that the coffee cherry is removed before drying. In pulped natural processing the bean is dried in the sun with the mucilage still clinging to the outside of the parchment.  During drying the mucilage dries onto the bean changing the flavor profile.

Wet Processing

Wet Processing

For more detailed information on processing see our article on “Coffee Processing – What Is It?”.

Milling/Grading/Sorting

After the coffee has been processed and before it is exported it needs to be milled.  Machines are used to remove the parchment from wet processed coffee.  If it has been dry processed then the entire husk needs to be removed.   If the silver skin is to be removed from the the bean it is done by a polishing machine.

Before being packaged for export the beans will be sorted by size, weighed and evaluated for imperfections.  In many countries removing the defective beans is done by hand although it can be done with machine or both.   Beans are sized by passing through screens of different size or pneumatically by air to separate the heavy and light beans.    The milled beans are now classified as green coffee and ready to be stored in jute or sisal sacks ready for transport to importers across the world.

In the mean time your local coffee roaster has placed an order for these beans and waits for it to arrive to begin the roasting process.

Information for this article came from the following sources.

http://www.coffeeresearch.org/

http://www.rombouts.com/uk/coffee/culture.html

http://www.ncausa.org/i4a/pages/index.cfm?pageID=69

http://science.howstuffworks.com/innovation/edible-innovations/coffee5.htm