Most of the flavour in coffee is determined by the environmental circumstances, coffee variety, altitude and for a very big part the processing on the farm. Also the final processing in the export plant is important. Lets have a closer look at the processing at origin.

An overview of the 5 principal processing methods of coffee at the farm

Coffee is the pit of a cherry. It consists of 2 halves that look a bit like a peanut: the seeds. The seeds have a thin skin around them, the silverskin. The pit has a harder shell around them, the hull. Around the hull you find sweet fruit flesh or mucilage, also called "honey" because it is so sweet. Coffee processes differ in the number of layers that are removed before drying and the degree of fermentation of the mucilage. Different countries and sometimes different growers have different definitions of the processing methods.

The essence of the main processing methods are:

1. Natural or Dried-in-the-Fruit Process – no layers are removed till the coffee is fully dried and ready for processing for export. Sometimes.the coffee cherries are fermented in a tank with or without water to create anaerobic fermentation. 
2. Honey Process– skin is removed (depulping), but some or most of the mucilage remains. Straight after depulping the coffee is collected on drying beds or sometimes  the coffee is fermented in a tank with or without water to create anaerobic fermentation. 
3. Washed Process– skin, pulp, and mucilage are removed using water and fermentation. The coffee is depulped and then mechanically some mucilage is washed and rubbed off. Then the coffee is stored in tanks where it is let to ferment for 24-48 hrs. The coffee is then washed clean in water channels with copious amounts of water and spread out on drying beds where the coffee is easily and quickly dried. Very clean water is required and that is in many areas a problem. Luckily in the mountains of Peru there is usually enough.
4. Pulped Natural or Semi-washed It is possible to skip the fermentation step by using mechanical means to remove some or all of the mucilage without the fermentation step or using a very short (overnight soaking) fermentation.
5. Wet-hulling – this is predominantly/only done in Indonesia and is a processing variant of semi-washed where the parchment is removed when the bean still has a high moisture level, up to 50%, and the drying of the coffee seeds takes place without their protective parchment.

In the picture you can see washed and natural coffee being dried simultaneously.

The more honey is left on the coffee pit the more aromatic the coffee becomes and the deeper the flavour. However it is lot of work, it takes much more time to process coffee this way and it is harder to get consistent. Washed coffee is still most prevalent as it produces a consistent quality and "clean" tasting coffee.

Anaerobic fermentation- in addition to these principle processing steps, there are additional techniques to alter the flavour by ensuring fermentation is anaerobic and for longer. With anaerobic fermentation, like in wine making, CO2 injection can be used to alter the acidity and fermentation (CO2 maceration). Growers can add flavouring during the fermentation to tweak profiles.

After the coffee is dried to below 12% moisture on the farm or central processing plant, the coffee gets stored till it needs to be exported. At this point the husk is still on (unless wet processed).

Just prior to exporting the coffee is usually processed in large plants. The coffee goes through various cleaning methods to remove contaminants like stones and sometimes strings from the raffia bags in which it is usually stored prior to final processing. Then the coffee is dehulled. After dehulling the coffee is graded on size. You can imagine that a fairly homegenised size makes roasting more consistent. After various grading steps where also some more contaminants and broken beans are removed, the coffee is passed through a colour sorter, where for example black coffee beans are removed. Black beans have a bad impact on flavour. Other defect beans are also removed. Depending on the grade requested the colour sorting can be more strict. For extreme grading of micro-lots the coffee is often hand sorted thereafter. After this the coffee is bagged in usually 50,60,69 or 70kg bags and 20ft containers are filled to around 19T.