Coffee processing - Post harvest processing methods

Coffee processing - Post harvest processing methods

Coffee processing at origin

The way in which coffee is processed following the harvest has a significant effect on the flavour. Coffee processing methods tend to vary quite considerbly from region to region. Certain origins are associated with certain types of processing but even within these general categories, there are variations in the methods used. This is one of the most exciting aspects of speciality coffee and we are currently working with two washing stations in Rwanda on some processing experiments. Essentially the coffee processing method can be described as the means used to remove the fruit from the seed and includes the process of drying the bean in its parchment to a moisture content of around 9-11%.

Washed processing

Nova coffee washing station Rwanda

Nova washing station, north of Kigali, Rwanda

This method is considered to produce the cleanest-tasting coffees with excellent clarity of flavour. Unfortunately, it requires a large amount of water so it is only possible in areas with good water supply. The waste water from this method can cause extensive environmental damage so it is important that water is treated before it is allowed back into rivers or streams. The type of coffee processing equipment needed for this method tends to be costly and a significant investement for a coffee producer. 

The first stage in the washed process is cherry flotation. Not all producers will do this but it’s highly recommended. The coffee cherry is put into a large container which is then filled with water. Underripe and defective cherry will float to the top and can be skimmed off. This will then be processed separately as low-grade coffee.

After the flotation process, the coffee cherry will be de-pulped using a mechanical device that strips the fruit, leaving the coffee bean encased in parchment. Some machines will leave some of the sticky fruit (mucilage) still on the bean while others are able to remove almost all of the fruit.

After the fruit is removed the coffee is fermented, usually in large tanks or drums. Depending on the origin or the intended outcome the fermentation stage can be executed using a variety of methods. Gishyita washing station in Rwanda will ferment the coffee in water for about 10 hours with some mucilage still intact. Some producers might rather use a dry ferment and some a combination of both using various timings. More and more producers are experimenting with less widely used fermentation techniques like anaerobic or carbonic maceration to produce unique cup profiles.

After the fermentation stage grading channels are often used to help separate heavy, dense, better quality beans from the lighter beans. After this stage, the coffee might be rinsed or even left to soak in water again.

The final stage in this process is the drying phase. At Gishyita washing station the coffee will be moved to raised drying tables under shade for 1 to 2 days to allow the drying process to start slowly. During this time the coffee is hand sorted to remove defects. After a period of time under the shade, the coffee will be moved to drying table in the sun and left to dry until the moisture content is around 10-11%. The coffee will usually be shaded during the hottest time of day and covered during periods of rain. In some origins washed coffees might be dried on concrete patios but raised beds are preferred for better air circulation.

Washed coffees are produced in almost all coffee-growing countries and make up the majority of what we purchase. There are so many different variations of the method used by different producers around the world. 

Flavour characteristics: Bright clean, juicy flavours. The best washed coffees are floral with complex acidity.

Pulped natural or honey processing

coffee processing in Nicaragua

Honey processed coffee drying in Nicaragua

This processing method is very common in Brazil where it is known as the pulped natural method. In other origins, it’s often referred to as the honey process due to the enhanced sweetness and sticky, honey-like feel of the coffee during the drying stage.

After harvest, the coffee is hand sorted before it is pulped using the same type of machine used for the washed process. The idea is to leave some of the mucilage attached to the coffee during the drying stage which bypasses the need for large amounts of water. Once some of the fruit is removed the coffee will be dried either in the sun or the shade and the exact method very much depends on the origin. In Brazil, it would usually be dried on concrete patios but in origins like Costa Rica and Nicaragua, the coffee might be dried in the shade or sun on raised beds or parabolic dryers for better air circulation. Some coffees are referred to as ‘red honey’ or ‘yellow honey’ (and various other terms) and this naming system can mean different things in different origins. To some, it refers to the amount of mucilage left on the bean. Red or Black honey might mean more fruit than White or Yellow. However, some producers use it as a way to determine how often the coffee is turned during the drying process. Less movement can result in fruitier flavours with more ferment and more movement can give a cleaner, brighter flavour.

The benefit to this method is that very little water is required so it’s great for the environment and a close water source isn’t needed. It can also enhance body and sweetness and when done well can contribute outstanding fruit notes to the final cup. This year we had Gishyita washing station in Rwanda prepare a small honey processed lot to our specific requirements. The total volume was just 30kg.

Flavour characteristics: Great balance between the bright flavours of a washed coffee and the fruity character of a natural. The best honey processed coffees are clean, bright and juicy with lots of fruit and body.

Natural processing

Natural process coffee Nicaragua

Natural processed coffee drying in Nicaragua

The natural method is the traditional way to process post-harvest in countries with wild-grown coffee. It’s a very simple process but if not done correctly the results can be very poor.

After harvest, the coffee will be carefully hand-sorted before it is laid to dry either on the ground or on raised beds. The best results from this method come from coffee dried on raised beds in countries like Ethiopia, Costa Rica and Nicaragua (although many other countries are also producing very good natural coffees). Brazil also produces a large volume of natural coffee. During the drying stage, it is important to ensure the coffee is turned regularly to avoid mould and over fermentation. It also doesn’t work particularly well in damp conditions so is best suited to origins with low rainfall. We had a small lot prepared by a co-operative in Rwanda and this was processed for us in the final half of the harvest season when rainfall is low.

Natural processed coffees when done well can be filled with amazing fruit and floral notes like strawberry, apricot, peach, and other intense berry flavours. We tend to purchase natural processed coffees from producers in Ethiopia, Costa Rica, Nicaragua and Rwanda.

Flavour characteristics: Big body with lots of fruit. The best natural processed coffees are clean with distinctive fruity flavours and lots of character.

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