What Are The Merits of Different Green Coffee Processing Methods?

Question

I've noticed that there's a distinct lack of Q&A's on green coffee processing methods. As this is one of the earliest steps on the journey from seed to cup, I was curious:

What are the merits of different green coffee processing methods? (i.e., impact on characteristics of coffee, labor, time, etc.)

In other words: Why does Farmer A prefer to use the dry process method while Farmer B favors the wet process?

Processing Methods:

• Dry Process
• Wet Process
• Semi-Dry Process/Pulped Natural

Answer 1

• Dry Process | This is the oldest method of modern processing. It requires very little equipment. It is basically a manual process of letting the coffee cherries raisin up, then peeling them. It is a labor intensive process. Dry processing tends to produce body heavy, smooth coffees with complex notes. Dry processing is used extensively in Brazil and accounts for the distinct different flavor profiles from other South American coffees. Dry processing is not practical in humid, wet, or temperate areas, as dry heat is necessary to dry the fruit in a short enough amount of time and to assure that mold or fungus does not set in.
• Wet Process | This method start with running the cherries through machinery to remove the skin and outer layers of the fruit. The beans with remaining inner layers of fruit are soaked in water and allowed to ferment. Additional processing is done to remove the final inner layers surrounding the bean. The result is left to dry (usually with additional machine assistance). Wet processing requires a comparatively large investment in equipment, access to enough water for the process and creates waste water that must also be dealt with. The process does allow for multiple areas to sort beans (floating during fermentation, in channel after fruit strip, etc) that potentially allow for a more uniform product. Wet processed coffees tend to be missing the overt fruit notes of a dry process, but this is debatable and can vary based on fermentation methods (additional additives are sometimes used in the fermenting process).
• Semi-Dry / Pulped Natural / Wet Hulled / Semi-Washed | This process is similar to the wet process except the fermentation step is skipped and specialized machines are used to strip the final layers from around the bean. This method can produce beans with the best of both processing methods, but the machines used to strip the inner layers away are also prone to damaging beans. This is a faster method of processing but again requires machine investment and resource use.

There are many other factors influencing coffee processing that should be kept in mind. Individual farmers may not have a choice of processing method. In many places the processing centers for coffee are quite separate from farms and only one processing center may be available. Local conditions will also largely dictate what methods are appropriate or available. There are also a myriad of variations on these methods that may produce different results and weather can play a factor as well (think about an area hit by a monsoon while large batches are trying to dry). At some level, all farmers are trying to get paid for what they produce. That being the case, most will prefer some combination of whatever local processing method is available and/or cheapest and produces the highest pricing for their product.

Answer 2

Disclaimer: After I have met with the world espresso champion who is also a local coffee producer in El Salvador today, I decided to improve this answer.

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I think, one should know the diversity of these three main techniques to distinguish the differences. There will be other minor techniques, as well.

All these techniques are in essence used to protect the bean from bacteria, mold and fungi right after the harvest. The coffee fruit is full of sugar and fermentation starts rapidly after the fruit leaves the tree. Thus, peeling of the fruit from the bean rapidly may help to get rid of the mold risk. If you choose to get the fruity tastes affect your bean and leave the fruit around your bean, then you should take proper care about mold and fungi. This may be especially difficult in big plantations as you need around 20 days and huge flat areas.

1. Wet process can be said the industry standard. The fruit is totally peeled off to the bean, then the beans are dried.

   1.a. Double-washed process is a process that the fruits are first washed to the bean. After the fermentation starts, it is washed for a second (or several) times. This technique is also known as Kenyan process. The result is a very clean flavor.

2. In dry process, the fruits are left intact to dry themselves. During this process, they should be moved regularly to protect them from mold and fungus. When the humidity is around 13%, they are peeled of, washed and dried for the second round.

3. In Semi-dry/semi-washed/pulped-natural/honey, just the skin of the fruit is peeled of, but the meaty part is left on the bean. Then, the fruit is dried, peeled of to the bean, washed and dried for the second round.

   3.a. In 50% washed processing method is the method where the processing is akin to honey method, but the meaty part of the fruit is peeled of halfway to the bean. This peeling of may be done in the beginning or sometime during the fermentation. As mentioned, the aim is balancing the sugar level and protecting the beans from mold, etc.

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It is clear that pulp-natural or dry processing are costlier than wet processing -whatever the metric is; monetary, labor or time.

Another factor is flavor. Dry or pulp-natural processed beans include more fruity notes as the fruit fermented together with the bean during the first drying phase.

(It is said that pulp-natural beans are less acidic than dry beans, but I have not experience that myself.)

Note that, dry or pulp-natural processing is not available everywhere. E.g. if you see a bag of Guatemala dry processed beans*, just run away. As Guatemalan weather is so humid, you can hardly dry process the fruit without mold.

(*) Probably, it doesn't even exist.

Further reading that matches origins and processing techniques.