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Cassava Milling

"Milling is energy intensive, so choosing the right equipment is paramount"

Milling is usually done to improve the product’s edible quality or to make it more suitable for further processing. For cassava value addition, the dried grits are milled into flour with a hammermill. It is an energy-intensive operation and therefore choosing the correct equipment is paramount.

1. Hammermills

Hammermills are one of the most commonly used equipment for food size reduction.

Hammermills are composed of a hopper, housing, rotor, rods, hammers, sieve, blower and cyclone.

The hopper feeds the product into the housing. Inside the housing the rotor and the rods spins at high speeds. At their periphery, the hammers are attached and swing in a circular path. The hammers hit the product entering the housing, reducing its size by impact. The product leaves the housing when is small enough to pass through the sieve at the bottom. The sieve is replaceable and available with different apertures. However, the particle size is not controlled by the sieve apertures alone; there is a complex interrelationship between aperture size, shape, rotor speed, sieve thickness and total open surface area of the sieve. The blower generates the forced air needed to convey the product, and the cyclone, in the end, separates the milled material from the conveying air.

2. How to measure performance

Hammermills can be powered by electric motors or internal combustion engines. The amount of energy used depends on the initial particle size of the product being fed, its moisture content and the final particle size. Therefore, while comparing performance indices of different equipment, it is important to assure that measurements are made with similar products at alike initial and final conditions.

Grindability is defined as the mass rate of product at a certain specification (e.g., a kilogram of product passing through a sieve of certain mesh per hour).

Specific energy consumption is the amount of energy needed to reduce 1 kilogram of product into a certain particle size. Benchmarks and ranges for those energy performance indices have not yet been determined.

3. Quality and safety

  • Hammers should be made of manganese-steel or any other hard-wearing food-safe material.
  • All parts that come in direct contact with the cassava dried grits should be built with a material that does not exchange components with the food, does not react with detergents, and can be easily cleaned.
  • All belt drive components should be enclosed under a safety guard.
  • During equipment operation, a dust mask should be worn.

4. Before buying a hammermill answer these questions

  • Are the equipment grindability and specific energy consumption suitable to the process centre operation?
  • Are the hammers made of hard-wearing material (e.g. manganese-steel)?
  • Are all the parts that come in direct contact with the cassava made of food-safe material?
  • Are all the belt drive components enclosed under a safety guard?

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