What happens to coffee beans once they’re picked?
Processing removes the fruit from the seed inside. The seed is the part that is roasted. The pulp is discarded. Processing may be done at a local co-op, private facility (often funded by a roaster or green bean broker) or on the estate, in the case of large farms. Processing styles vary according to regional traditions. The style of and the care taken during processing has a great impact on the flavour and the quality of the bean. If processing is not carried out correctly then defects can occur, or the coffee will simply be of poor quality.
Whatever the method, processing always involves:
- Cleaning the coffee cherries to remove sticks, dirt and leaves
- Removing the flesh of the berry surrounding the seed (called ‘pulping’, as in, to remove the pulp)
- Removing the mucilaginous (gooey) layer surrounding the seed
- Drying the seed
- Removing the parchment and silver-skin on the seed
- Sorting by quality
- Grading by size
- Bagging in hessian sacks (either lined with a plastic inner or not)
There are two primary methods of coffee processing: wet and dry.
Natural process (dry processing)
To naturally process coffee, the cherries are laid out in the sun on concrete patios or raised mesh ‘beds’. The coffee beans are raked or turned by hand to ensure they dry evenly and to prevent spoilage. The coffee beans may take up to four weeks to dry to the required moisture level. Once this is reached, the shrivelled dry fruit around the outside of the seed is mechanically hulled and the seed is ready for the next stage.
The extended drying phase of natural processing concentrates the sugars and flavours in the fruit, giving the coffee powerful and strong flavours, with lower acidity and more body than washed coffees.
Washed process (wet processing)
In wet processing, the sorted coffee cherry is broken and the skin is removed. Some of the mucilage is still clinging to the bean. The sticky beans go into fermentation tanks for between twenty-four and thirty-eight hours, where a natural enzyme breaks down and removes the mucilage. This fermentation is monitored closely to ensure the beans do not take on any undesirable flavours. Once the mucilage has come off, the beans are dried to a moisture level of 10 – 15%, either in the sun or by machine. The coffee is hulled to remove the parchment and silver skin before it moves to the next stage.
Wet processed coffee tends to have brighter, cleaner flavours in the cup, with a lighter body than natural processed coffees.
There are also variations on each of these processing techniques, such as the honey process, where beans are dried in the sun still surrounded by mucilage but not their skin. Sumatra is renowned for its Giling Basa processing method, which gives coffees distinctive flavours of leather, peat moss, fir, cedar, humus and tannins.
Once the processed coffee is dry, it is cleaned again to remove any sticks, dirt or dust that accumulated during the drying phase. The coffee must then be sorted by both density and size. The beans are first graded by size, then by density. A series of sieves with different size holes separate the beans by size while a vibrating table shakes the heaviest beans to one side.
The final sorting is by colour or appearance. This is to eliminate any beans that have physical defects, such as insect damage, broken beans or unripe beans. More affluent coffee producing countries, such as Brazil and Hawaii, will have computer controlled conveyors and air jets to do this final sorting, but in many growing regions it will be done by hand.
Packing and transport
After the grading and sorting, the coffee beans are packed for transport from origin, most commonly in 60 kg or 70 kg natural fibre bags, made from jute, sisal or burlap. These bags have the advantage of being cheap and very durable. While green coffee is more stable and less perishable than roasted coffee, it does benefit from being used fresh. As it ages, coffee looses it’s flavour and brightness and the profile becomes more flat. Many roasters (including Karvan) will create seasonal blends and/or only offer single origin coffees that are from the most recent harvest so they can use the green beans when they are ate their best.
Higher grade or very fragile coffees are often vacuum packed in a laminated multilayer polythene ‘GrainPro’ bag. This preserves their flavours better, for longer.