Having a favourite process for coffee is akin to liking blues or ska music. It’s a genre that gives tone to the flavour, where the varietal and terroir give us the difference between the Bob and Ziggy Marley reggae.

Processing coffee is just getting it from a moist cherry to a bean with 11.5% moisture content. There are many different ways of doing this, depending on how much water is available, the season, the equipment available and often on what the farmer's daddy’s daddy did.

There are two major methods of processing: dry and wet. Within the wet method there are myriad different ways to skin a cherry and we’ll examine the four most common. But first we need to harvest the cherries.

Harvesting

Harvests usually take place once a year. Sometimes there is a major harvest and another minor harvest, the fly harvest, that takes place at another time of the year. Some countries have a climate which produces cherries all year round, but in most producing countries the harvest is once a year. Usually after a period of draught, rain will bring on the flowering of the coffee plant and after a bit of attention from wind and bees the plants will bear fruit.

Harvesting by hand does still take place, but mostly in very poor economies. Unless you’re paying a high price for your coffee, you’re not paying enough to get it picked by comfortably well-off people. In many countries, the increased cost of labour, limited harvesting time and the abolition of slavery has led to mechanisation of harvesting. They’re all doing it: viticulturists in France, olive growers in Australia, foresters in Canada, everyone’s getting machines to harvest. There’s a romantic idea that the best coffees are selectively picked by the elegant hands of a gorgeous large-lipped ebony goddesses whose song trills across the lush mountainsides as her bounteous baskets fill with rubied cherries. More likely is that the harvesters are itinerant workers who move with the harvest times and find earning difficult throughout the rest of the year.

Excellent estates such as La Esmeralda, Panama do insist upon selective hand picking and pay their harvesters much more than most can afford to do. Price Peterson, who heads the estate, says “Hand picking can only be done properly by workers who are prideful of their craft, who are being rewarded at a level commensurate with their dedication. This is not the place to cut costs.” La Esmeralda sells coffee direct to roasters and has fetched prices as high as $286/kg for their coffee. However, prices like these are the income for a select few estates.

It’s true that we need the ripe beans and people can do that work for us, but people take a long time with many passes and, in the main, the economic reality for both the harvester and the landowner is that it’s better to separate after harvest with a combination of manual, mechanical and electronic means.

Even in areas where they cannot afford machines, most harvesters will grab hold of the branch and strip off all the cherries in one movement. On good plantations, they will cover the ground with canvas to prevent fungal contamination.

Machine harvesting

Hand-held harvesting machines look like suped-up hedge trimmers or some look like grass-cutters with happy hands at the end. They strip cherries off the branches using vibration. Hand-held harvesters can be used on any terrain.

A tractor attached harvester can access moderately steep slopes and allow for shade trees. They can only work where the plantation has been been replanted in rows wide enough to accommodate tractor. However, these Massey-Ferguson fashion accessories are not as efficient as the self-propelled harvesters.

 Joey Mah imitating a coffee tree going through a self-propelled mechanical harvester.

Joey Mah imitating a coffee tree going through a self-propelled mechanical harvester.

Self-propelled mechanical harvesters work like mobile car-washing machines. Instead of brushes, the machines have plastic sticks, like fat drum sticks, that vibrate, beating the cherries to conveyer belts below. The operator can adjust the speed of the machine, the angle of the sticks, the frequency and strength of vibration in order to limit damage to the plants. You can also remove the bottom half of the sticks so that the machine can harvest the faster maturing, sun-facing, upper cherries on an initial pass and reinstate them for subsequent passes.

In order to use these machines the trees need to be planted in rows and be on a slope of no more than 20º (Oxbo 9200, although this is getting steeper as the machines get better).  This method of harvest is no good in mountainous areas and precludes shade trees.

Many farmers have had to take the risk of ripping up their old plantations and replanting for mechanical harvest. If the farmer can afford the investment, profits tend to increase due to the lower harvesting costs and avoiding the inherent insecurity of having to rely on a migrant workforce. Cup quality also tends to improve because the cherries are all picked rapidly increasing homogeneity and reducing fermentation issues allowing the farmers to concentrate on the other stages of processing. Some varietals fair better than others and the cherries fall off the plant easier in some climates than others.

Mechanical methods do damage the plants, but no more than strip picking and they are far more efficient than hand picking and often lead to an increase in cup quality. Careful selective hand-picking is still the best for the plant and the coffee quality, but there are few estates that monitor picking well enough or pay well enough to ensure the best quality. In the future, all farmers who have enough flat land will be converting to mechanised harvesting to compete.

Processing

 A cutaway view of a coffee cherry stripped down to the seed.

A cutaway view of a coffee cherry stripped down to the seed.

The farmers need to process the harvested cherries into the seeds that we call coffee beans. Several layers cover the seeds. The model below shows a cherry with one seed removed. The remaining seed is covered by a thin layer of silverskin, the thick paper-like parchment, the fruity mucilage and the outer layer of thin skin. Processing is stripping these layers back to the seed and drying the seed to 11.5% moisture content.

There are two main ways of processing the cherries into beans. Traditionally, the cherries were just dried under the sun. This became known as the dry or natural process, named presumably when someone invented the wet process, which is the other main method. There’s nothing unnatural about the wet method: the 'natural' refers to the customary method. Within these two branches are myriad different processing methods depending on access to resources, climate, milling equipment, culture, rumour, superstition and what her dad used to do.

Dry Process

  Dry process. Coffee cherries drying on a covered patio.

Dry process. Coffee cherries drying on a covered patio.

Traditionally in Ethiopia and Yemen coffee was dry processed. When the Dutch started the first large commercial plantations in Java they started with the dry process method. Being a Dutch colony, the processing method was called Oost Indische Bereiding, which is a bit of a mouthful, so I’ll continue to refer to it as the dry process.

The initial drying down to 35% moisture content is critical. This should take no longer than 3 days to avoid fermentation and fungal infection. During this time the cherries need to be exposed to sunshine every day. Rain at this stage could ruin the harvest. For this reason the dry process is better suited to countries with intense heat and definite seasons.

The second stage dries the beans to 11-12% moisture content and can take anywhere up to a further 15 days. While the cherries are out on the patios, they are turned using rakes to ensure even drying.

  Traditionally, dried cherries were pounded to remove the fruit from the beans.

Traditionally, dried cherries were pounded to remove the fruit from the beans.

As the beans dry with the fruit, the beans take on some of the fruity flavours. Once the beans have dried, they are hulled using some form of friction to break them apart from the dried fruit. Traditionally, this was a large pestle and mortar. Mills use large friction hulling machines.

Since the development of the wet process many farmers used water to process higher grades of coffee and the dry process for processing the rest. Because poorer grades of bean were processed using the cheaper and less water intensive dry process, the process got a bad name. However, today some of the best coffees are process using the dry method, giving more ‘natural’ flavour options for the drinking masses. If the processing is done well, the possible aromas are dried fruit, leather, blueberry, fig through to mild funk. It’s the marmite of the coffee world: some people like it and others think it’s like licking a cat’s rear end.

Wet Process

With the increased demand back in Europe and other colonial powers keen to cash in on the craze, coffee was introduced to the Carribean and Central America. Growers using the dry process in Central America found that their beans fermented because the climate in Central America is too humid for the dry process. Fermentation thrives off moisture and sugars. Drying the cherries whole means all the sugars are trapped inside the skins.

Because extended intensely hot, dry periods are less likely in Jamaica than in Java, the growers needed a new process. The solution was to remove the skins allowing the beans to dry much faster with a further option to wash off the mucilage removing the sugars. This process also had the added advantage of being much faster than the dry process. The disadvantages are the intensive use of water and the concomitant requirement to locate the mills near a water source.

There are four main versions of this process:

Pulped natural

  Semi-washed beans drying on a covered patio.

Semi-washed beans drying on a covered patio.

It’s the dry process; but with the skins off. The cherries are pulped, which removes the skins, and the seeds are put directly out on the patio to dry. This method still demands long periods of dry, sunny weather, but not as much as the dry process. With the skins off, the beans dry much faster, so there is less chance of over-fermentation and the beans still take on some extra sweetness and fruit flavours from the mucilage.

Semi-washed

Most of the mucilage is removed from the bean leaving very little fruit to give flavour to the bean. There are many methods to remove the mucilage ranging from metal brushes, to rollers or manual agitation over a wire mesh. The idea is to take most, but not all of the mucilage off. These beans are less fruity than the pulped natural, but sweeter than the fully washed.

Giling Basah

 The ubiquitous hand mill that gives the 'giling' to giling basah.

The ubiquitous hand mill that gives the 'giling' to giling basah.

Literally “turned, wet” this method is peculiar to Indonesia with two stages of drying: with parchment (the hard, paper-like casing sound each bean) to 40% moisture content and without the parchment down to 11.5%. The removal of the parchment was probably to speed things up, but it also creates a distinct rich flavour to the coffee, like dark teak that can sometimes head towards musty.
The giling basah method also creates coffee that emits more CO₂ after roasting and has increased crema in espresso.

Fully washed

All the mucilage is removed from the bean using fermentation or chemical stripping followed by washing. This method is generally reserved for high quality coffees, but the complete removal of the fruit can wash out a lot of the sweetness and fruity flavours from the bean.

 Overview of processing.

Overview of processing.

Defaecation process

A word about Kopi Luwak: it’s cat shit. It commands high prices, not because it’s good, but because it’s rare. Because it gets the high prices, it’s also a great boon for Indonesians and an execration for the excreting civets. The myth of happy peasant Indonesians traipsing through the jungle and stumbling upon organic cat poo needs only a jiffy’s reflection to slip on. The reality is amassed caged cats being force-fed coffee cherries. It is the foie gras of the coffee world, but without the enhanced flavours to recommend it. I’ve tried it: give it a wipe.

Moisture content

The beans are all dried to 11-12% moisture content for shipping. Dry the beans too much and they lose their individual characteristics and just produce flat and woody brews. If the beans have too much moisture, they may ferment or the beans may start to rot during transit and storage.

Once the cherries have been picked they need to be processed rapidly to prevent fermentation or contamination. If the weather is unsuitable for outside drying, the beans can be dried in large drying machines. Indeed, these machines, decried by some in the industry, not only give producers guaranteed processing independent of the weather, but also more even drying than patio drying.

 Big industrial driers at Ponto Alegre, Brazil.

Big industrial driers at Ponto Alegre, Brazil.

Putting down

Many producers will store the beans in their parchment for a few weeks. At Ponto Alegre they dry the beans to 15% moisture content on the patios then move them to wooden stores where they are dried a further 1% before going into the driers for the final drying to 11.5%.

At La Esmeralda they pack the beans in plastic for four to eight weeks, periodically testing the coffee and sending it only once they’ve decided that it has ‘matured’ enough. And at Caxambú & Aracaçu, Usha will play classical or new age music to the beans as they rest.

Dehulling

With the exception of giling basah, once the beans have dried, we need to remove the parchment. This is known as dehulling and is either done by hand, pestle and mortar and a few squabbling aunties or by big industrial machines.

Decaffeination

There are several different ways to decaffeinate coffee. Despite the Swiss Water® marketing department claiming to the contrary, all of them involve chemicals (besides, Swiss Water® is based in Canada, so they’re off to a bad start with their fact telling). The methylene chloride (MC) process is the cheapest and most common. Scaremongers would have you believe that it’s carcinogenic. Cancer is bad, but it’s unlikely to come from decaf coffee.

I’ve found the Swiss Water® Process to be good, and the CO₂ filtration method the best for roasting. Although I have a personal preference for drinking CO₂ processed coffee, I can’t definitively say that one method tastes the best because I have never processed one coffee by all decaffeination methods and done a side-by-side comparison.

To get a good tasting coffee, it’s important to start off with good beans. Unfortunately, there aren’t many Cup of Excellence decaf beans out there. The reasons for this are twofold: the process is cost-effective only when done in bulk (minimum of 3,000 kg) and consumers don’t value decaf. Decaf can taste excellent, it just doesn’t often get the chance.

Polishing

Polishing removes the silverskin layer on the bean. It’s not always done and is only aesthetic.

 

The beans are now in the right state for shipping, but they’re still a very mixed bag. There’s one more important step needed before they are bagged and sold and that is grading.