Coffee is a climacteric sensitive crop. Factors like elevation, rainfall, and temperature can influence the crop performance considerably. It requires hot humid climate with intervals of dry weather for proper ripening of fruits. The two commercially important species of coffee are Coffea arabica and Coffea robusta. The coffee plant is a small tree which extends to the height of 5 ft. in case of Coffea arabica and 5.5 to 6 ft. in case of Coffea robusta. Coffee can be grown up to 25 ft. in wild state but is pruned for two reasons; to facilitate harvesting and to maintain optimal tree shape.
Arabica type grows well under cool weather condition and usually grown at elevation of 1000 – 1500 meter above sea level with temperature ranging from 15.6 – 23.9°C. This variety needs acidic soil with rich amount of organic manner and good water holing capacity. Robusta type coffee prefer hot humid climate with temperature ranging from 20 – 29.4°C. it is commercially grown at elevation of 500 – 1000 meter above sea level.
Propagation and planting:
Coffee is usually propagated from seeds. Although other method of vegetative propagation like cutting, grafting and layering are possible. Seeds are collected from healthy and highly productive bushes. Usually near ripe to fully ripe berries are harvested for seed purpose. The pulp of the fruit are removed by hand without injuring the parchment cover and the beans are dried under shed. Germination usually takes about 40 – 50 days when the seedlings attempt a height of about 6.7 cm, they are transplanted to secondary nursery.
For proper planting pits of about 50 x 50 cm should be enough for transplanting the seedlings. Before planting, the pits should be filled will with manures and mixed with soil thoroughly. The spacing between two plants should range from 2 – 2.5 m in Arabica variety and 2.5 – 4 m in Robusta variety. Coffee plant will yield between 3 -5 years and lasts up to 30 – 40 years.
The coffee fruit (cherry) is picked when it is ripe. A properly ripe fruit is the one which gives out seed on a gentle finger squeeze leaving pulp and skin in the hand. After flowering it usually takes 8 – 9 months for proper ripening and since all the fruits in a bush do not ripe at a time, the picking is a selective operation. The ripening time also depends on the variety, climatic condition, soil etc. only properly ripen cherries are required to be harvested as under ripe over ripe cherries results to poor quality coffee. Picking is done naturally in a few round. The first round of picking is known as ‘fly picking’ which should be done carefully after examining the stage of maturity and ripening. Second round of picking is done when the majority of cherries are ripen and the picking operation is done systematically from one side of the plantation so as the complete the entire field. Process of harvesting is completed in 2 – 3 round of picking operation. The cherries should be harvested with stalk from the tree.
The cherry of coffee tree houses coffee seed within its skin and pulp. Coffee cherries are processed to remove skin and pulp obtain green coffee beans by series of steps. The marketable green coffee beans should have moisture content of 12 – 13 %. Processing of coffee cherries can be done by using two different methods.
1. Natural process / dry process
2. Washed process/ wet process
Natural Process: This process is the simplest method consisting three basic steps. The harvested cherries may be subjected to some form of classification and dried entirely, most usually in the sun, sometimes we use an artificial drier. The drier temperature should not exceed between 50 – 60°C. The dried cherry coffee is then subjected to milling operation (dehusking / dehulling) to seperate out the green beans.
The harvested cherries are spread to thickness of 8 cm on drying floors and allowed to dry in the open sun for 2 – 3 weeks, till the cherry gives rattling sound when cherries are shaken. Usually in the evening, the spread out cherries are heaped up and covered till the next morning when they are once again spread on the floor. Coffee prepared from such dried cherries has got a typical fruit flavor and the product after curing is also known as ‘cherry coffee’.
Wet process: This process is more sophisticated than dry process and gives better quality coffee and commands a higher price. In this method, few steps like classification, pulping, demucilaging and drying are followed before curing of coffee beans. Especial care is taken that only ripe fruit is sorted out by hands during picking or immediately after picking. Ripe cherries are fed to the pulping machine for removal or skin and pulp. The pulped coffee is then treated to remove mucilages. Demucilaging can be achieved by
1. Natural fermentation
2. Treatment with alkali (lye peeling)
3. Frictional removal in specialized machines
For fermentation, pulped coffee is usually put in fermentation vats and kept covered with gunny clothes or bags for about 24 – 36 hours at a temperature of 21 – 26°C. Fermentation takes longer time in cool weather than in warm weather. Proper stage of fermentation can be detected when the beans gives gritty feel when squeezed by hand. Till the sticky mucilages remain on the parchment, the fermentation is considered incomplete. Finally fermented beans are washed with water for quick and complete removal of mucilages. The beans are agitated thoroughly and washed 3 – 4 times for complete cleaning of beans. Even if a part of mucilage substance remains on the beans, it may cause deterioration in the quality of coffee. Cleaned beans are then sun dried on floors or dried by using artificial driers.
wet processing: https://www.youtube.com/watch?v=Az0W61hotLM
Natural Processing: https://www.youtube.com/watch?v=yagagM7SlWs
Name : Pratiksha Shrestha
Ms. Shrestha holds masters degree in food engineering and bioprocess technology from Asian Institute of Technology (AIT) Thailand. She is currently working for Government of Nepal at Department of Food Technology and Quality Control (DFTQC), Kathmandu. She is also a teaching faculty in College of Applied food and Dairy Technology (CAFODAT) affiliated to Purbanchal university, Nepal.