Cassava starch processing

After harvesting, cassava roots are quickly sold to processing factories to prevent reduced starch yield and increased microflora content. To ensure root freshness, factories are located in areas with short transportation distances. Upon arrival at the factory, roots are sampled and tested for starch content using a simple analytical method called specific gravity. The method involves weighing 5 kilograms of roots and measuring their specific gravity in water to estimate their dry matter and starch content. Calibration of the method is necessary for cassava grown under different conditions. A direct reading balance based on specific gravity data is used to determine the percentage of starch. The method has been found to have good correlation with a specific enzymic method for determining starch content in fresh cassava roots.

Tapioca processing machinery is diverse and varies by location. Factories in Thailand and Brazil use specialized equipment to process roots and by-products, while others use equipment commonly used for potato and corn processing. Despite these differences, all machines use a similar process of screening and density separation to produce high-quality tapioca starch. Manufacturers choose their equipment based on their own needs and requirements.

To make high-quality tapioca starch, factories follow a basic process. First, the roots are cleaned of dirt and sticks using a rotating slotted drum and washed with recycled water in a washer. Stones sink in the water, while roots are lifted by the action of the washer paddles, and later, the peel is removed from the roots. Then, roots are chopped into small chunks and fed into a saw-tooth rasper for intense attrition into a pulpy slurry. This slurry is pumped through a series of coarse and fine extractors to remove fibers, sand and starch clumps. Starch slurry is concentrated to 40% and then dewatered in a horizontal centrifuge to produce high-moisture starch cake. The cake is then dried using a pneumatic conveying dryer to lower the moisture content to around 13% prior to packing.

In cassava starch processing, saving water and energy is crucial for production cost and quality. The process uses several stages of screens and washers to purify the starch and remove fiber. Water is reused to optimize usage and flows opposite to the starch. Sulfur dioxide is used to control microbes, and water is pretreated before use. By-products like fiber are used in animal feed, and peels and sludge are composted. No waste is generated from the process, and water discharge is treated before release.

To recover starch, factories need a constant supply of fresh roots, so they are built near areas where cassava is grown. In Brazil, the processing season lasts only six months. In Thailand, processing happens all year, but some producers stop working during the rainy season when there’s less starch in the roots, and it’s less profitable.

People have tried different ways to match the inconsistent supply of cassava with the regular demand for tapioca production. One idea is to use cassava chips or pellets to recover starch, but this can affect the quality. Another proposal is to store tapioca starch in large silos like those used for potatoes, but fresh roots are still the main source for now.

The quality of tapioca starch depends on the fresh root and production practices. Despite this, commercial tapioca starch always meets industrial standards, which can vary depending on the manufacturer and user.

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