processing of cassava

processing of cassava takes the following stages:

  • Cassava Harvesting.

The harvesting involves the cutting stem at heights of 25cm to 35cm from the ground using a machete and removing the tubers making sure not to damage them. This can also be done using your hands if the soil is light. The dry season is the best time to harvest cassava tubers because the tubers are rich in starch at that time and contain less moisture content which makes drying easy and the products can easily be processed and preserved. The early varieties may mature 6-8 months on average after planting, whereas the late varieties require 12 and 18 months.

The age and time (or season) of harvesting suitable for the processing of fufu (powder) is 9-12 months, and there is higher yields of product from tubers harvested during the dry season. The bitter specie is mostly used by cassava processing industries.

NB: Fufu (powder) should be processed within 2 days of harvest to prevent deterioration and loss of quality.

  • Storing Cassava.

Two to three days after harvesting, there is rapid rotting of the tubers. Since cassava roots can remain in the soil for up to 18 months after reaching maturity, the simplest prservation technique is to delay the harvest until the crop is needed. However have some disadvantages such as:

  • The cassava roots begins to increasingly lose starch.
  • They become fibrous and woody.
  • They become exposed to insect, disease and rodents attacks.

Hence, fresh cassava roots can be preserved using the following technique:

  1. Cassava buried in straw-lined trenches
  2. Storage in tightly woven bags such as rice or cocoa sacks.
  3. Storage of tubers in wooden crates containing absorbent material such as dried saw-dust.
  • sorting

This stage involves the selection of healthy roots from the lot for processing, in other words entails the separation of good cassava from bad ones. Unhealthy roots are discarded. In some cases, screening (or grading) is done. This involves the placing of certain parameters for selection such as quality, time of harvest and color. In screening all freshly harvested cassava are good but certain parameters are taking into consideration for processing.

  • weighing

This stage involves the weighing of the cassava tubers with the aid of a weighing scale. The harvested tubers are packed in sacks and hanged on the scale with the respective weight recorded in kilograms (KG). The weighing of the tubers is carried out to estimate the amount of processed product that would be achieved.

  • peeling

This involves the removal of woody tips, stalk and any fibrous roots using clean stainless steel knives. Ensuring that the rind is completely removed and avoiding excessive waste of roots. Failure to peel properly result in off-color in the final product.  NB: Sorting and peeling can be done simultaneously in small-scale processing. In large scale processing a machine known as the cassava peeler is used instead of knives.

Cassava peels (after drying) can be used for animal feed- so its advisable not to waste it.

  • washing

Washing of peeled cassava roots is then carried out with clean water to remove any dirt, including sand, soil, leaves and other impurities. This is done at least twice in a large basin.

  • fermentation

This is a metabolic process that involves the breaking down of carbonhydrates into alcohol and acetic acid. While they are many fermentation techniques for cassava, they are broadly categorized into Solid-state and Submerged fermentation. Submerged fermentation involves the soaking of the whole peeled, cut and washed tubers in water for a period of 3-4 days. The washed cassava are cut to pieces ( for the tubers that are large enough) and steeped in water to ferment. This process is carried out in stainless steel fermenting tank or drums (with tightened covers).

  • pulping

This stage follows after fermentation (submerged) has taken place. Pulping process is a unit process which involves the removal of the fibres present in the cassava tubers. This can be manually, when sufficiently soft, the roots are taken out, broken by hand and the fibres are removed by sieving. It is also carried out mechanically with the aid of a PULPIER.

NB: After fermentation process the slurry has an estimate of 70% moisture content.

  • sedimentation

Due to the large amount of water added during the pulping process (for the removal of fibres), the slurry is allowed to sediment under gravity over a period of about 24 hours. This operation is carried out in large cassava processing industries using sedimentation tanks or large containers or drums (for small scale).

After sedimentation process, the water is decanted (i.e removal of the water that lies on the surface of the containers slowly).

  • Dewatering

After sedimentation and decantation process has taken place, the finer, clean filtrate (known as slurry) are then packed in certain equal proportions into sacks with pore spaces, placing them into an hydraulic press to reduce its moisture content (this process is known as dewatering process). Note that the sacks used are doubled to prevent it from bursting during the process due to the pressure applied. This is done for a period of about 4-5 hours. A manual aided machine known as the Screw Press can also be used to achieve same purpose.

NB: After de-watering process, the slurry is estimated to contain about 50% moisture content.

  • Granulating

After the reduction of moisture content of the slurry (dewatering), the slurry is removed from the hydraulic press and then granulated. Granulating stage involves the “cake” been mechanically reduced in size to produce granules. This process is carried out with the aid of a granular.

The next stage of processing involves the drying of the granulated cake (or dried slurry). This operation is done with the aid of a Flash dryer  and at a temperature of 1500C. The flash dryer is a convective or direct drying method where the substance comes in contact directly with hot air. This process reduces the moisture content to 10%. Some of the importance of this stage include:

  • Removal of water from food reduces the microbial activities, thereby servng as a preservative method.
  • It makes it extremely light weighted than when wet.
  • Increases the shelf-life.
  • Helps in remove some of the hydrogen cyanide that is still present.
  • It makes it odourless.

NB: If unwanted particles are found after drying, the product is seived to remove them. But this rarely happens when flash dryer is used.

  • Cooling.

After drying, to obtain the desired product, either using a flash dryer or cabinet dryer (using this would require milling and seiving of the product), the fufu(powder) is left to cool for about 5-10 minutes before packaging.

 

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