Coffee Processing Methods – From Cherry to Green Bean
Updated: Jul 9, 2018
Dried Coffee Cherries
Coffee must be processed from fruit to green bean before roasting. There are a number of ways of achieving this and each method produces a bean with quite different characteristics. For example, there is one type of coffee from one lot on a single farm, but the beans are divided and processed differently. Depending on the processing, one coffee may end up tasting sweeter and with more floral flavours after roasting, the other with greater acidity and fruity flavours. Workshop Coffee in London have offered these origins as a great example.
The particular processing method is not always chosen for flavour though. Other factors include resource availability, climate and tradition. From this, four basic methods for processing coffee can be identified. In more recent years, these methods have been varied and tweaked by different farmers/millers to produce new results, showing the endless variety of ways to process coffee. However, here we shall only focus on the four main methods and the general characteristics they impart on the bean.
Before any processing though, ripe coffee cherries must be collected and taken to a processing mill, sometimes called wet mills. The fruit’s skin, mucilage (flesh) and various other layers must be removed through a series of pulping, fermentation and hulling. The beans are then dried to moisture content of around 12%, and must remain at a short range of 1-2% of this for roasting to be effective. Here is how each processing method differs.
1. Centre Cut 2. Bean 3. Silver Skin 4. Parchment/Hull 5. Pectin 6. Pulp 7. Outer Skin
The Natural/Dry Process
A method that carries substantial risk for defects and uneven drying to occur. The natural, or dry process, involves drying coffee cherries in the sun by either being left on the tree, on patios or on raised beds. Raised beds typically allow for greater air flow, reducing the risk of mould. It is a very labour intensive process which requires workers to constantly turn the cherries and be vigilant for mould. This can last 3-4 weeks.
After drying, coffee is rested and aged inside its parchment for one to two months. This helps extend the longevity of the green bean, meaning it can be stored longer whilst waiting for roasting without losing quality of flavour. Finally the beans are hulled, removing the parchment. All that is left is for grading and shipment.
Taste Characteristics – More sugars are deposited into the bean with this method and the long drying time results in reduced acidity but also, sweet and fermented fruit flavours. These can be truly delicious with flavours of nectarine, blueberry, strawberry and mango. They can also be a disaster and be described as farmyard-like or compost.
Some professionals are strongly averse to dry processed coffees because of the higher rate of defects. For some, flavours reminiscent of fermentation are a defect and the clarity of well washed coffees should be the standard. My feeling is this opinion narrows the possibilities of what coffee can be, in the same way others dismiss very dark roasts. Ultimately it is a case of high standards during processing which produces exceptionally beautiful and flavoursome, dry processed coffees.
Notable countries using this method – Ethiopia, Brazil
Honey/Pulped Natural Process
Much like the dry method, the coffee is dried with some of the fruit flesh still attached. It differs in that the skin is removed and so to a certain percentage of the mucilage. Removing the skin allows for a reduced risk of defect, but in leaving some flesh on the bean, sweetness can be increased. After drying, the coffee is hulled and rested.
There are many variations of this method with names such as eco-pulping, which is less water intensive way of pulping, and also a range of colours to describe the amount of mucilage left on the drying bean. In China, a whole host of terms are used to denote slight variations, such as mango or red wine.
Taste Characteristics – Expect sweet flavours with fewer of the fermented fruit notes tasted in the dry process. Also a fuller body than washed coffees. The sweetness is reminiscent of honey (surprise, although the honey name comes from the Spanish word for the mucilage), raw sugar, molasses and red wine.
Notable countries using this method – Costa Rica, El Salvador, Brazil
Credit - Britannica - Costa Rica drying on patios
The wet process requires a lot of water to strip the bean of skin and mucilage, then breakdown the stickiest part of the flesh with fermentation. The coffee is placed in water baths for up to 48 hours in this fermentation process, with longer times starting to affect the coffee’s flavour negatively. The rest of the flesh is scrubbed off and the beans are then dried, outdoors or mechanically, to reduce the moisture content to the desired 12%. As with the other methods, the coffee is then rested and hulled. This processing method is not usually used in dry areas with little rainfall.
Taste Characteristics – Washed coffees are the most acidic and their cleanliness (absence of defects and unpleasant flavours) is much sought after. Clarity is the aim here, with many washed coffee from Kenya exhibiting exciting and sharp flavours of blackcurrant and plum whilst Colombian coffees are frequently described as having dark cherry flavours. Many believe it is the bean’s true qualities that are tasted when enjoying a washed coffee. I prefer to think of it as another process that adds diversity to the flavour of coffee.
Notable countries using this method – Kenya, Rwanda, Colombia
Water baths for the washed process - Off-season in Pu'er, China
Semi-Washed/Wet-Hulled/Giling Basah Process
A common processing method used in Indonesia, particularly in Sumatra. The coffee is pulped and then dried to about 30% moisture. The drying process is then stopped and the parchment removed in hulling. This typically happens after the resting phase in the other methods. The coffee is then dried again to the desired level.
Taste Characteristics – Coffee processed in this way has a very unique and distinct flavour, which some consider to be a defect. There is very little acidity and a full and heavy body. Flavours are earthier, like leather, wood, resin, spice and tobacco. I find these coffees quite difficult to enjoy but they are well liked in Asia and often used in espresso blends to add to body. Better examples have slight, high fruity notes blending well with the traditional heavy flavours, which can be umami and sweet.
Notable countries using this method – Indonesia
All these methods are labour intensive, requiring great numbers for the harvesting, sorting and processing of coffee cherries. In addition to the work involved in the methods above, sticks and stones must be sorted out, defective beans removed and the beans graded, shipped and well looked-after. Coffee goes through many hands before even reaching the roaster and it is here we begin to understand the price of the coffee we drink.
Credit - Collaborative Coffee Source
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