S05 AF Jan_Feb 2022 Coffee_Layout 1 27/01/2022 13:44 Page 20
CROPS
Image credit: Dr Terry Mabbett
Coffee processing is extremely important in determining how the final product turns out. Dr Terry Mabbett elaborates the two methods that are used in this procedure.
Ensuring the ‘kick’ in your coffee
C
UPPED COFFEE IS an infusion of many different chemicals made by mixing boiling hot water with roasted remains of coffee beans – the seeds of the coffee tree (Coffea sp). Prominent among them is caffeine, a stimulant, which gives mainstream coffee drinkers the much soughtafter ‘kick start’ or stimulus to their metabolism. Coffee contains a huge range of additional chemicals occurring in specific concentrations and combinations to give each coffee origin (type) its own distinctive taste, aroma and flavour. Some coffee chemicals like caffeine, remain unaltered from their natural state in the fresh and living coffee bean. Others develop during processing from naturally occurring precursors that undergo chemical changes, during ‘wet processing’ on the farm, or later at the factory during roasting. All of them have one thing in common – they are soluble in water. Natural coffee chemicals must be soluble in water to exist and to move in solution in the living coffee tree and its constituent parts (e.g. coffee berries and beans).
Red-ripe coffee cherries of Coffea robusta ready for harvest and on-farm processing.
Cupped coffee chemicals have to be soluble in water to contribute to taste, aroma and flavour and in case of caffeine metabolic stimulation. The final coffee product – dry roasted beans for ‘real’ or percolated coffee or coffee granules and powder to prepare soluble (instant) coffee – may well be dry, but water plays an important part in the beginning stages of processing, at least for some coffee origins. Commercially-grown coffee is generally two types – Robusta or Arabica. Robusta has a higher caffeine content, which is reckoned to afford significant protection against insect pests and diseases. Coffee Arabica, with a lower caffeine content, has less tolerance for pests and diseases, is more discerning of growing conditions. Arabica bushes tend to thrive at higher altitudes where the air and water are cleaner, temperatures are moderated, and pests and diseases less prevalent. Compared to Arabica, Robusta is considered to be inferior in taste, flavour and aroma. It is used for making soluble coffee products sold as powder or granules and for ‘instant’ mixing with water. On the other hand, Arabica is reserved for making the percolated product, and is therefore marketed as whole dry beans, which are ground before treatment with hot water. Due to a perceived higher quality and greater potential for taste, flavour and aroma, the Arabica coffee bean tends to be treated differently during its initial stages of on-farm processing. Immediately after picking, the red ripe cherries (berries containing the beans) undergo the procedure of pulping, washing
20 African Farming - January/February 2022
www.africanfarming.net
