To remove most impurities and dirt clinging to the outer layer (silver skin) of coffee beans, thereby increasing acceptance during cupping and giving the beans a glossy, appealing appearance, Vietnamese exporters have been shipping polished coffee for a long time.
No matter how coffee polishing machines are designed, the basic principle has remained unchanged for decades: the beans are forced to rub against the honeycomb-like internal structure of the machine and steel blade plates on both sides. As the beans rotate and move from the intake to the outlet, the friction scrapes off the silver skin while simultaneously polishing the beans.
Limitations of Traditional Dry Polishing
This forced dry friction significantly increases the breakage rate after polishing. To meet buyers’ requirements of over 90% polish, processors often had to polish the beans twice, which raised the breakage rate to about 4–5% and overall material loss to around 2–3%.
Later, wet polishing machines were developed to address these drawbacks. However, they introduced new problems: the beans had to be soaked in water to loosen the silver skin before polishing. This process created large volumes of wastewater, leading to complaints from local communities and scrutiny from environmental authorities. It also required substantial energy and fuel to dry the coffee again.
A German-developed technology emerged around the same time as wet polishing, using a mist-spraying system before polishing. Beans were tumbled inside a mesh drum while a fine mist was sprayed for about an hour, allowing the beans to polish each other as well as the rotating paddles. While this reduced wastewater, it consumed significant energy, had a low capacity of only about 500 kg/hour, caused about 2% material loss, and increased breakage by around 2.5%. The dust chamber revealed a high proportion of broken beans mixed in.
Domestic Innovations and Challenges
In Vietnam, several equipment manufacturers attempted to adapt advances from other industries. For example, some machines combined steel-bristle brushes with mist spraying before polishing. But these solutions still suffered from high energy consumption—around 100 kW for a capacity of roughly 800 kg/hour—and frequent replacement of the steel brushes. Breakage rates remained too high.
Developing a machine that overcame all these shortcomings seemed nearly impossible. Yet, after three years of trials and improvements from 2002 to 2005, a breakthrough was achieved. The resulting machine now serves both Vietnamese coffee processors and some foreign companies operating in Vietnam, helping deliver high-quality coffee to demanding international markets.
Key Features of the New Coffee Polisher
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High-Pressure Mist & Continuous Polishing: Uses high-pressure pumps to spray a fine mist while continuously polishing, allowing the beans to polish themselves through natural friction.
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No Internal Blades or Honeycomb Structure: Eliminates metal parts inside the machine, reducing breakage.
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Eco-Friendly: No wastewater is generated and no post-polishing drying is required.
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Low Loss and Breakage: Material loss is only about 1.1–1.2% (dust and silver skin), with breakage after polishing just 0.2–0.4%.
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Efficient Energy Use: Total electricity consumption is around 30 kW/hour, with a capacity of 750–800 kg/hour.
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Preserves Bean Quality: Equipped with an instant cooling system to prevent color fading or dullness during long-term storage.
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User-Friendly Operation: Controlled via a touch-screen interface and an automated PLC system for easy start-up and shutdown by operators.
This advanced polishing technology provides a cleaner, shinier bean with minimal loss, reduced environmental impact, and operational efficiency—an important step forward for Vietnam’s coffee processing industry.