Lesson 3: How Coffee is Processed‏

Lesson one touched briefly on how coffee grows. To recap, thecoffee tree produces fleshy red fruit called a drupe, which iscommonly referred to as the 'berry' or 'cherry'. The coffee 'bean'is actually a seed which is encased within the cherry.

Raw coffee beans are light brown in colour with a distinct greenhue which varies in depth. Consequently, unroasted beans areusually referred to as 'greens'.

Speciality coffee picking tends to be undertaken by hand and goodquality harvesting takes place when the cherry is at its ripest.This can mean many re-picks as only fruit that is fully ripe isselected in order to get the very best cup of coffee possible. Incontrast, lesser quality commercial grade commodity coffees areoften strip picked, having everything taken from the plant at oncefor reasons of speed and labour economy. This can have asignificant effect on the cup quality.

After the ripe fruit is harvested, the beans need to be removedfrom the cherry fruit and mucilage, then 'hulled', cleaned andsorted. This can be achieved in a number of ways.

Wet process

The fruit of the cherry is removed from the beans before they aredried. This is referred to either as the washed process or the wetprocess, and the resulting production is known as washed coffee.

The wet method lends itself to the efficient sorting and removal ofpoor quality beans. After harvest, the fruit is immersed in waterand sorted. Whilst good ripe coffee sinks to the bottom of thetank, bad or unripe fruit, the 'floaters and stinkers' as they arecalled, rise to the top and can be removed.

The whole cherry is then pushed in water through a milling screenthat removes the flesh from the seed of the fruit, but this doesnot completely get rid of the slimy layer of mucilage, some ofwhich remains on the beans.

The mucilage can be removed either by fermenting the beans in tanksbefore washing them in plenty of fresh water to remove any residue,or by the use of machinery employing a process of mechanicalscrubbing.

The fermentation process is a very difficult thing to get right; ifleft too long the beans could have a nasty ferment taste to them,or not long enough and too much of the mucilage might remain on thebean, which would have an equally negative impact on the coffee.Conversely, fermentation that is carried out correctly can havesome very positive effects on the quality of the resulting coffeeby virtue of the process itself.

Mechanical scrubbing has a far more predictable end result, thoughremoving the fermentation stage and prematurely separating thefruit residue from the bean does take away a valuable way ofinfluencing flavour in the cup.

Once separated from the rest of the fruit and washed, the beansneed to be dried out to a water content of about 10% to achievestability. To achieve this, they are laid out to dry in the sun onpatios or drying tables until they contain around 12-13% moisture,and typically then brought down to around 10% by machine. The wholeprocess can be carried out in the machine but this generally onlyhappens when there are space or humidity issues.

Once dried the coffee is in the parchment stage with a thin paperlike outer skin on the bean which can be easily removed by 'hulling'.

Dry Process

The dry process is the oldest way of processing beans and is themost commonly used method in Asia and Ethiopia. It is sometimesalso referred to as the natural process.

After harvest, the entire cherries are cleaned and sorted to removeunripe, over-ripe or damaged fruit, before being allowed to drywhole in the sun on patios or drying tables. It can take up to 6weeks for the cherries to dry. There is a significant risk of moulddeveloping, so the cherries have to be turned regularly. Rain isanother potential issue as the whole crop could be ruined ifsubjected to a downpour.

Once dry, the complete cherry is hulled to remove the entire driedouter fruit covering all at once.

Pulped Natural

This is a mixture of the wet and dry processes. It is very popularin Brazil and is also being tried in many other countries as well.

The cherry is passed through a milling screen to remove the skinand some of the pulp like in the wet process, but fermentation ormachine scrubbing does not follow. Instead, the resulting bean isthen dried in the sun retaining many of the sugars of the cherryand creating a very interesting coffee.

Hulling and Grading

The parchment that is left coating the beans after they have beenprocessed using any of the three methods is then removed or'hulled' mechanically by a process ranging from gentle whacking bya bespoke machine to the use of a very basic millstone.

The coffee is then sorted to remove defective beans, graded forsize and quality, bagged and prepared for shipping in its greenunroasted state.