"A smooth paste is created by consistently small output particle size"
After being peeled and washed, cassava roots need to be reduced to a smooth mash, with particles of uniform size. Grating is widely used in several industries and many types of equipment are available.
For cassava, grating is done mainly with a rotating drum grater or with a hammer mill.
1. How to measure performance
When selecting equipment to turn cassava into a smooth mash, the main performance indices are throughput, specific energy consumption and particle size coefficient of variation.
Throughput measures how many kilograms of peeled cassava roots the machine can grate per hour of operation.
Specific energy consumption (electric or fuel) is the amount of energy needed per kilogram of cassava grated into a mash.
Particle size variation is a measure of relative variability on size distribution of the particles. Preference should be given to an equipment that produce grits with a low particle size distribution as this indicates a smoother output.
2. Types of cassava graters
Different machines for cassava grating are compared below.
Rotating drum graters
Rotating drum graters are generally made up of a drum with a grating surface that rotates inside a housing with a feeding hopper on top. The grating surface can be made of a nail-punctured stainless-steel sheet, bent into a cylindrical shape, with the protrusions facing outwards. The grating surface can also be made of longitudinally arranged saw-tooth blades.
Roots are fed at the hopper on the top of the housing and size reduction is done by grinding. The size of the particle is determined by the space between the drum and the housing walls. Some models allow changing this space, and thus permit controlling the size of the particles. Depending on the adjustment made, particle size can range from 0.5 mm to 1.0 mm.
Hammer mills are made up of a high-speed rotor, hammers, a cylindrical housing with a feeding hopper on top, and a sieve on bottom. The hammers are attached to the outside of the rotor and swing through a circular path inside the housing.
The roots are fed into the hopper and are hit by the quickly rotating hammers, crushing the roots with their impact. The product leaves the housing when it can pass through the sieve on the bottom. Particle size is, therefore, controlled by the speed of the hammers and the size of the sieve. Sieve aperture should be larger than the desired particle size because particles that pass through it are usually considerable smaller than the aperture. Depending on the adjustment, particle size can range from 0.05 mm to 10.00 mm.
3. Quality and safety
- All parts that come directly in contact with the roots should be made of food-grade stainless-steel
- The hammers from the hammer mill can be made of manganese-steel. Manganese-steel has the advantage of being vert hard-wearing, while having all the other necessary characteristics from stainless-steel
- Do not purchase equipment where food contact materials have been painted
- Do not purchase an equipment that has exposed belts.
- Parts that does not come in direct contact with food must be made of a material resistant against corrosion
4. Before buying a grater answer these questions
- Is the equipment throughput suitable to the factory operation?
- Is the specific energy consumption of the equipment adequate?
- Is the particle size coefficient of variation suitable?
- If opting for a rotating drum grater, can the grating surface be easily replaced? Has this cost been accounted?
- If opting for a hammer mill, is the hammers made of manganese-steel?
- Are all the parts that come in direct contact with the food made of stainless-steel (or manganese-steel for the hammers)?
- Are all the parts of the equipment resistant against corrosion?
- Are all the belt drive components enclosed under a safety guard?