Chipping or cutting sweet potato roots into thin slices should be done to facilitate efficient drying, handling and storage, and to avoid jamming the grinding machine during feed milling operations. The desired size of chips should not exceed 1.5 cm thick and 10 cm long.
There are two methods of chipping sweet potatoes
- Manual chipping or slicing by means of cutting knives or “bolo”
- Mechanical chipping by means of chopping machines operated manually or by engine.
Manual chipping is suited for small-scale operation (less than half a hectare yield). However, for huge volume of roots (more than one hectare yield), mechanical chipping is necessary.
An example of a mechanical chipper is the one developed by the Bureau of Plant Industry. The BPI rootcrop chipper has a rated capacity of 0.3 tons per hour when pedal operated and 1.5 tons per hour when operated by a 3-horse power gasoline engine.
It cutting blades are mounted on a vertical disk located opposite a feed hopper. These blades are adjustable, allowing roots to be chopped to desired thickness, from 5 mm to 20 mm thick, and from 100 mm to 180 mm long.
Dry sweet potato chips to 12-13% moisture content through sun-drying or artificial heat drying.
Sun Drying – spread chips uniformly in mat or concrete floor. Expose directly under the sun for 2-3 sunny days. Turn chips periodically to facilitate efficient drying. Drying period depends on the availability of sunlight and size and thickness of chips.
Artificial Heat Drying – This is utilized in the absence of sufficient sunlight. Recommended drying facilities:
1. Static-Bed Dryers – All commercial batch dryers, e.g. storage, bin, tray and through-circulation dryers, used for wheat, rice, corn and similar products may be used for drying sweet potato chips.
2. Moving-Bed Dryers – These are similar to static-beds except that the bed moves either continuosly or intermittently from one end to another. This allows continuous feeding of wet material from one end and continuous withdrawal of dried product from the other.
3. Natural Convection Type Dryer or Improved “Tapahan” – This utilizes a wide variety or combustible fuel, such as wood and coconut husk. Fuel is burned inside a steel tube made of three oil barrels welded together. This tube lies at the bottom of the pit covered by a perforated metal drying platform. Air entering the bottom of the pit is warmed by heat radiating from the barrel’s surface and rises up through the drying platform and layer of materials to be dried. Flue gas and other products of combustion are released above the drying platform thru a chimney coming from the end of a steel tube or combustion chamber. To increase its capacity, provide up to 10 layers of tray or drying platform above the steel tube or combustion chamber.
source: Palnt Industry Production Guide on Sweet Potato, BPI Sweet Potato Commodity Profile, DA-Eastern Visayas Integrated Agricultural research Center