Coffee Cherry Harvesting
What we refer to as coffee beans are in fact seeds from cherry-like fruits. Coffee trees produce cherries that begin yellow in colour they then turn orange and finally to bright red when they are ripe and ready for picking.
Coffee cherries grow along the branches of trees in clusters. The exocarp is the skin of the cherry and is bitter and thick. The mesocarp is the fruit beneath and is intensely sweet with a texture much like that of a grape. Then there is the Parenchyma, this is a sticky layer almost honey-like which protects the beans inside the coffee cherry. The beans are covered in the endocarp, a protective parchment-like envelope for the green coffee beans which also have a last membrane called the spermoderm or silver skin.
On average there is one coffee harvest per year, the time of which depends on the geographic zone of the cultivation. Countries South of the Equator tend to harvest their coffee in April and May whereas the countries North of the Equator tend to harvest later in the year from September onwards.
Coffee is usually picked by hand which is done in one of two ways. Cherries can all be stripped off the branch at once or one by one using the method of selective picking which ensures only the ripest cherries are picked.
Coffee Cherry Processing
Once they have been picked they must be processed immediately. Coffee pickers can pick between 45 and 90kg of cherries per day however a mere 20% of this weight is the actual coffee bean. The cherries can be processed by one of two methods.
This is the easiest and most inexpensive option where the harvested coffee cherries are laid out to dry in the sunlight. They are left in the sunlight for anywhere between 7-10 days and are periodically turned and raked. The aim being to reduce the moisture content of the coffee cherries to 11%, the shells will turn brown and the beans will rattle around inside the cherry.
The wet process differs to the dry method in the way that the pulp of the coffee cherry is removed from the beans within 24 hours of harvesting the coffee. A pulping machine is used to wash away the outer skin and pulp; beans are then transferred to fermentation tanks where they can stay for anywhere up to two days. Naturally occurring enzymes loosen the sticky parenchyma from the beans, which are then dried either by sunlight or by mechanical dryers.
The dried coffee beans then go through another process called hulling which removes all of the layers. Coffee beans are then transferred to a conveyor belt and graded in terms of size and density. This can either be done by hand or mechanically using an air jet to separate lighter weighing beans which are deemed inferior. Coffee harvesting countries ship coffee un-roasted; this is referred to as green coffee. Approximately 7 million tons of green coffee is shipped world wide annually.
The coffee roasting process transforms the chemical and physical properties of green coffee beans and is where the flavour of the coffee is fulfilled.
Green coffee beans are heated using large rotating drums with temperatures of around 288°C. The rotating movement of the drums prevents beans from burning. The green coffee beans turn yellow at first and are described coffee grinder machine as having the aroma an aroma similar to popcorn.
The beans ‘pop’ and double in size after around 8 minutes that indicates they have reached a temperature of 204°C, they then begin to turn brown due to coffee essence (inner oils) emerging. Pyrolysis is the name for the chemical reaction that produces the flavour and aroma of coffee as a result of the heat and coffee essence combining. Anywhere between 3 and 5 minutes later a second ‘pop’ occurs indicative of the coffee being fully roasted.
Coffee roasting is an art form within itself, coffee roasters use their senses of smell, sight and sound to ascertain when coffee beans are roasted perfectly. Timing is fundamental in the coffee roasting process as this affects the flavour and colour of the resulting roast. Darker roasted coffee beans will have been roasted for longer than lighter coffee roasts.