Guide To Coffee Processing: The Wet And Dry Method


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The good quality of coffee comes from a perfectly executed processing technique. The process and preparation is the key, to which a special coffee is developed. It influences flavor and mouthfeel that affects the way a coffee tastes. 

Knowing what these processing methods gives you a better understanding of what you like best when it comes to coffee. So, let’s delve in!

What Is Coffee Processing?

Coffee processing refers to every single stage of the coffee-making process. Starting from the harvesting of coffee cherries to the time when the coffee beans are finished off and ready for consumption. 

The coffee processing we typically know is the preparation of raw material such as the raw coffee plant or coffee cherry to transform it into the kind of beans that we recognize as green bean. This process involves the act of removing all the layers that surround the coffee cherry as well as the bean.

Furthermore, it may refer to a process where these raw green coffee beans are transform into a finished product such as “cup of coffee” – from bean to cup.

Types Of Coffee Processing

The only thing we need to make a great “cup of coffee” at home is the coffee bean itself, which is actually a seed inside the coffee cherry.

So, once the harvested ripe coffee cherries are ready to process, the coffee beans can be extracted from it using either the Dry or Wet Method.

To give you an overview, the Dry and Wet method is a primary process where coffee berries in the form of dried berries (dry method) or parchment coffee (wet method) are produced as a partially processed coffee. 

If you will use these two methods, you will notice that there’s no big difference in processing the coffee beans as both methods involve the same basic fundamental processing steps.

However, a big difference in the results as their finished products produces different qualities. For example, dry method will produce a more sweeter coffee flavor than wet method.

Both methods require:

  • The bean to be cleaned and to be sorted for further processing
  • The use of machinery for the hulling process
  • The use of the sun for the drying process

Literally, the dry method involves drying and the wet method involves fermentation or any wet process in most of the time.

Dry Method

As mentioned, this method literally involves drying the whole cherry. The coffee cherries with the fruit and mucilage that surround the bean is left intact. 

It is also known as the traditional method as this process is recognized to be the oldest and simplest process that requires a little help of machinery. Sometimes refers to as the riskiest process as there are variations on how it may be carried out.

There are things to consider such as the facilities available, the final quality desired, as well as the size of the plantation.

In this method, the coffee may be dried by the sun (which is what most coffee growers do, especially small-time coffee farmers), mechanical means by a machine dryer (which is common to larger plantations), or by both if having the capability.

In areas where water resources are limited, this method takes place and more recommended.

Moreover, basically, there are three basic steps involved in this method such as cleaning, drying, and hulling

I. Cleaning

Firstly, the harvested cherries are usually sorted and cleaned. This step involves the separation of the unripe, overripe, and damaged cherries as well as the removing of dirt, soil, twigs, and leaves. 

  • Floatation – In line with cleaning, a technique where ripe cherries are separated by floatation in washing channels, which are installed close to the drying areas. When cherries are placed on a washing channel, the rejected cherries tend to float and are needed to be removed from the rest.
  • Winnowing – Another technique to be done is by winnowing. This means to separate the coffee beans from all the bits of pulp and skin which are commonly done by hand using a large sieve. The result is any unwanted cherries or other material not winnowed away can be picked out from the top of the sieve.

II. Drying

Secondly, after cleaning, the coffee cherries are then normally dried under the sun, or by mechanical means such as hot air-drying machines. As the cherries dry, they turned by hand to ensure even drying is continuously maintained. 

Approximately, it may take up to 4 weeks before the cherries are dried to the optimum for ideal moisture content. But most of the time, the drying takes more time depending on the weather conditions.

According to the International Trade Center, the finding is that there is no exact standard for ideal moisture content for dried coffee as not all coffee is the same. It is said that circumstances differ from country to country.

Sun Drying

Going back to the drying step, there are some cases where coffee beans are of poor quality because the cherries have not been dried well by the sun.

Therefore, it is recommended that the cherries are spread out in a dry place, either on the very clean ground or on planks. Placing it on large concrete or brick patios or on matting raised to waist height wire mesh tables to dry.

What Makes Sun Drying Effective?

  • The sun drying should be done on extensive flat concrete or brick areas, known as patios, or on tables made of fine-mesh wire netting.
  • Sun-drying should be preferably done on elevated tables made of fine mesh netting to encourage proper air circulation and ventilation.
  • Sun-drying normally takes 8 to 10 days prior to the required moisture content, considering high temperature and humidity.
  • Coffee dries more quickly if raised on tables because of the upward draught of warm air.
  • The use of hot air-drying machines or mechanical dryers along with sun drying becomes necessary to speed up the process, especially in large plantations.

Machine Drying

If you have the access to machinery such as a mechanical dryer, it’s best to use it to speed up the drying process. The use of a drying machine is common to larger plantations after the coffee has been pre-dried in the sun for a few days.

III. Hulling/Dehulling

And lastly, after drying the cherry, it is then hulled to produce a dry green bean. In a dry method, coffee hulling is a mechanical process that entails removing the coffee skin and husk from the cherry once it is dried, it means all the outer layers of the dried cherry are all removed in one step by the use of a hulling machine. 

There Are Things You Need To Consider When Using The Dry Method Such As:

  • Avoid drying coffee directly on soil or dirty surfaces. It can lead to dirty or earthy flavors in the finished product. 
  • When it comes to sun-dried coffee, avoid storage of partially dried coffee due to rain as well as the rewetting of it. 
  • Avoid drying coffee too slowly by spreading it too thick on drying areas. You may find it also as a major problem. 
  • Don’t let the dried coffee to be stocked anywhere as it may lead to fermented or fruity flavors along with mold-growth producing moldy or musty flavors.
  • Ensure that the coffee is not over-dried by properly controlling the drying process. Over-dried coffee can be easily damaged during hulling and may also result in a bland flavor.

Wet Method

On the other hand, the wet method involves fermentation or any wet process such as washing the beans once the layers of the cherries are removed.

When using this method, only the ripe cherries are recommended to be processed. The fact that it requires the use of specific equipment and a substantial amount of water to both move the cherry and to extract the beans through the entire process, ripe cherries are indeed qualified for this.

When properly done, expect that the qualities of the coffee beans are better preserved. When it comes to the wet method, it is all about boosting the natural flavors of the bean itself. Also, the coffee produced by this method is usually worth it as being of better quality and commands higher prices.

Moving on, even though you have the most careful strategy in harvesting, a certain number of partially dried and unripe cherries, as well as some stones and dirt, will always be present among the ripe cherries. 

Therefore, preliminary sorting and cleaning of the cherries is also necessary and should be done in this type of processing method as soon as possible after harvesting. 

This operation can be done by either of the following:

  • Washing the cherries in tanks filled with clean and flowing water. 
  • Screens may also be used to improve the separation between the ripe and unripe, large and small, cherries.
  • Other strategies may include manual sorting of ripe and rejected cherries.

Once the harvested coffee cherries are sorted and cleaned, the next step is to place it into a de-pulper for further processing.

De-Pulping/Pulping 

Pulping or de-pulping is the main difference between the dry and the wet method and is usually done through the aid of a machine (de-pulper) which squeezes the cherries between surfaces, leaving the flesh and the skin of the cherry on one side, giving an easy work to remove the skin and the fruit.

That is why only ripe cherries are recommended to this type of method as ripe coffee cherries are soft, and when they pass through these de-pulping machines, they break easily and only the coffee beans pass through successfully. 

And because de-pulping is done by mechanical means, it normally leaves some residual flesh as well as sticky mucilage that adhere to the parchment surrounding the beans. Some coffee farmers tend to remove these things that surrounds the beans to avoid possible contamination of coffee beans by-products resulting from the degradation of the mucilage.

Furthermore, the pulping operation should also be done immediately after harvesting to avoid any deterioration of the cherries which later on might affect the quality of the beans.

Fermentation

Fermentation is very critical in terms of final coffee quality, therefore, it’s a best practice to carefully monitor the fermentation process, else, the coffee may acquire undesirable and sour flavors.

When it comes to its process, first, the newly de-pulped beans are placed in large fermentation tanks filled with clean water for a certain period of time. 

At this point, the mucilage is broken down by its natural enzymes which can be easily washed away by the end of the fermentation process. For most coffee, mucilage removal takes between 12 and 24 hours, depending on the temperature, thickness of the mucilage layer, and concentration of the enzymes. 

Then the end of the fermentation is assessed by feel, as the parchment surrounding the beans loses its slimy texture and acquires a rougher “pebbly” feel.

Wrapping it up, once the fermentation is complete, the coffee is thoroughly washed with clean water in tanks or even in special washing machines if necessary, leaving only the beans or parchment coffee before being dried. 

Again, the ideal moisture content of a coffee is 11%, therefore, to reduce the moisture to an optimum of 11-12%, the parchment coffee is dried either in the sun, in a mechanical dryer if possible, or by a combination of the two. 

Parchment coffee is dried coffee with the hard endocarp and silver skin still attached to the beans. Therefore, when beans are dried, dehulling is also done to remove the parchment, leaving only the green coffee beans ready for roasting, and consumption.

Packaging

After the dried cherries are sent to the mill and hulled, sorting, grading, and bagging or packaging will then take place. The dried cherry and/or parchment coffee are packed in special silos or in bags. 

Green coffee beans should be packed and sealed in bags made of food-grade or non-toxic materials such as jute sacks. When using sacks or bags, give the effort to provide necessary labels and should be imprinted on it, indicating the production batch number and date, including the cooperative/farmer/area presented in codes if it’s available. 

Always be careful not to use any bags that are available. Bags that were used to store chemicals, fertilizers, and feeds must not be reused to avoid possible contaminations.

Storage

Sometimes you will store coffee beans if it’s needed and necessary, and as far as proper storing of coffee beans is concerned, the bagged green coffee beans must be placed in pallets or similar material so that it will not be in direct contact with the ground.

When Choosing a Storage Room/Place, consider the followings:

  • The storage sheds should be weather-proof.
  • The storage room should be well ventilated.
  • Storage facilities should be free from moisture and insects/pests.
  • The storage area should be located away from sources of smoke and other odors that may contaminate the coffee.
  • Storage facilities should be designed to minimize damages to the coffee, a facility that is not subject to flooding.
  • The storage area should be kept clean and hygienic to avoid possible pest infestation.

Furthermore, even it is given that regular monitoring of coffee beans should be implemented, it’s best to also choose a storage facility that will help to maintain the moisture content of the green coffee beans. That is, keep the beans in an area with humidity less than 60%, else, the beans will start to absorb moisture.

Final Thoughts

To give a summary, the ripe coffee cherries are processed under two basic systems: the dry processing system which produces what’s called dried coffee cherry or natural coffee, and the wet processing system that generates parchment coffee.

In the end, what matters is to develop processing and even trading systems that maintain the high-quality characteristics of the coffee and at the same time minimize the risks associated with physical coffee quality and mold formation.

Like this Article? You Might Also Want to Read: How Does Processing Method Affects Coffee Taste?

Reference:

Food and Agriculture Organization Postharvest handling and processing of coffee in African countries

[Note: This guide is based on the Code of Good Agricultural Practices for Coffee, Philippine National Standard for Coffee]