Most coffee farmers in Vietnam remain passive when it comes to the drying stage. Some invest in drying yards but still depend on the weather. With the exception of a few farmers in regions growing Arabica (which are processed by the wet method), the majority follow the dry processing method.
Current Dry Processing Methods
Table of Contents
1. Drying whole cherries on the yard
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Advantages:
– No need to pulp the cherries before drying.
– If it rains unexpectedly, the cherries are less likely to turn black than when pulped (although they still cannot withstand prolonged rainy periods).
– When dried on yards with good drainage, the risk of blackening from rain is lower than if the cherries had been pulped first. -
Disadvantages:
– Drying time is long and requires a lot of labor for guarding and raking.
– The longer the cherries stay on the yard, the higher the chance of being caught in rain. Each time they are soaked, several extra days of raking and drying are needed.
– High risk of loss due to theft or runoff on sloped ground.
– If prices rise suddenly, the coffee may not be dry enough to sell; by the time it dries, the market may be flooded and prices drop.
2. Pulping before drying
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Advantages:
– Much faster drying—only about three sunny days with good sunlight—so it overcomes the disadvantages of drying whole cherries. -
Disadvantages:
– If rain occurs even once during drying, there is a very high risk that the coffee will turn black.
– After pulping, continuous sunshine is required. Without it, the beans quickly become moldy.
Proposed Method: Drying Whole Fresh Cherries
To overcome the drawbacks and leverage the benefits of both methods, two techniques for drying whole cherries are recommended. When choosing between building a drying yard or investing in a dryer, it is better to invest in a dryer because it does not depend on the weather. Drying a batch of coffee cherries takes only 18–20 hours, using coffee husks or coal as the main fuel.
1. Static Dryer (recommended for most farmers)
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Capacity: 150–200 kg of fresh cherries per square meter.
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Fuel: Coffee husks; the amount of husk from milling the cherries is enough to dry an equivalent amount of fresh cherries.
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Airflow: Use a special centrifugal fan capable of blowing hot air at 100–120 °C through the mesh of the static dryer. Do not use an axial fan, as its low compression ratio will not achieve the desired result.
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Power Source: The fan can be driven by an electric motor or a small engine.
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Operation: The only drawback is the need to manually turn the coffee every 2–3 hours. However, after 18–20 hours the coffee will be dry enough that it will not spoil or blacken.
Note:
– The drying mesh frame can be fabricated wherever basic metalwork is available, but the correct mesh size and a sturdy frame are crucial for long-term use.
– Since this is a direct-firing dryer, only use coffee husks to dry whole cherries. Do not use coffee husks to dry parchment coffee (coffee beans with husk removed), as it will leave a smoky odor. For parchment coffee, burn coal instead.
Farmers should select the size of the drying mesh and furnace according to their own circumstances to save costs and suit their needs.
2. Drum Dryer
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Main drawback: Higher initial investment than a static dryer.
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Advantages:
– No need to turn the coffee manually.
– Can dry whole cherries, parchment coffee, or green beans.
– Produces even drying quality, independent of workers’ skill in turning.
– For whole-cherry drying, simply load the cherries, fire up the furnace, and run the drum dryer. Drying time is similar to the static dryer.
Currently, Viết Hiền Company is developing three drum dryer sizes to meet different scales of production:
– 5 m³, 15 m³, and 20 m³ units, capable of holding 2.5, 7.5, and 10 tons of fresh cherries per batch, respectively.
The larger 7.5–10 ton models are more suitable for buyers of fresh coffee cherries who process them, rather than for individual farmers.