Making starch from sweet potatoes is a simple, practical, and highly scalable technology that can be easily learned and widely promoted. It offers numerous benefits, including easy access to raw materials, on-site processing, versatile usage, and significant economic returns. This process not only reduces waste but also provides an eco-friendly way to utilize sweet potato byproducts.
The basic principle behind sweet potato starch extraction lies in the physical separation of starch from other components. Sweet potatoes contain water, starch, protein, fat, fiber, and minerals. Starch is insoluble in cold water and has a higher specific gravity than most other substances, which makes it possible to separate it through sedimentation and filtration.
Here’s a detailed breakdown of the key steps involved:
1. **Raw Material Selection and Cleaning**
Start by selecting high-quality sweet potato chips that are free from pests and damage. Remove any fibrous roots and wash the pieces thoroughly with clean water to eliminate dirt and impurities.
2. **Crushing**
Cut the sweet potato into small pieces, approximately 2 cm in size, then grind them into a fine paste. The finer the grinding, the better the starch yield. This step produces a thick, porridge-like mash.
3. **Filtration**
Pour the mashed mixture into a 60-mesh sieve and filter it while adding water. Then pass it through a 120-mesh sieve for secondary filtration. The resulting starch slurry goes into a sedimentation tank, while the remaining residue can be used as animal feed.
4. **Sedimentation**
Allow the starch slurry to settle in a tank at a temperature between 15°C and 20°C for about 8–10 hours. Higher temperatures may reduce the settling time. After sedimentation, carefully pour off the upper layer of liquid (which contains impurities), and rinse the starch surface 2–3 times with clean water.
5. **Fermentation**
Add 25–30 kg of water per 50 kg of fresh sweet potato to the fermented slurry. Mix well and let it ferment at 15–20°C for around 24 hours. Fermentation is complete when a sour smell develops, the surface turns blue-green, and some foam appears.
6. **Separation and Washing**
Once fermentation is done, the top liquid (called acid slurry) can be reused for further fermentation, reducing time and improving quality. Carefully remove the brown residue on the starch surface, then collect the pure starch. Be sure to remove any sediment at the bottom of the tank.
7. **Drying and Finishing**
After removing the starch, press out excess moisture using a cloth or centrifuge. Dry the starch until its moisture content reaches around 14%. Finally, sieve and crush the dried starch to ensure a fine, uniform texture. This results in high-quality, ready-to-use sweet potato starch.
This method not only maximizes the value of sweet potatoes but also supports sustainable agricultural practices. With proper execution, it can be implemented in small-scale rural settings or larger industrial operations, offering both economic and environmental benefits.
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