What are the difficulties in processing sweet potato vermicelli?

I. Dull gray color of vermicelli

Cause: Sweet potatoes are pulped, separated, and settled to obtain starch, commonly called crude starch. Crude starch contains impurities, phenolic substances, and many pigments, and is grayish-white. The phenolic substances in it oxidize and brown very easily, so the finished vermicelli is bound to turn black.

Solution: refine the starch.

Method: add 2 to 3 times the amount of water to the crude starch, stir, add an appropriate amount of sweet potato starch decolorizing agent, and after about 20 minutes, filter through a 120-mesh nylon screen. After the filtrate settles for 4 to 6 hours, remove the upper clear water, then add water and stir, and settle again. Repeat this 3 times to achieve the purpose of decolorization and purification.

II. Vermicelli strands stick together and are difficult to separate

Cause: Dough that is too thin, too slow cooling after extrusion, and adding too much starch paste will all cause the vermicelli strands to stick together, resulting in many stuck strands and difficult separation.

Solution: When mixing the dough, the amount of water and starch paste added should be appropriate. For every 100 kg of dry starch, the total amount of water and starch paste added should preferably not exceed 90 kg. Use an electric fan or blower aimed at the extrusion port of the vermicelli machine to speed up cooling. When mixing the dough, alum and rapeseed oil can be added at 0.3% to 0.4% of the weight of the dry starch. If producing silver-thread vermicelli with a diameter of less than 1 mm, an appropriate amount of vermicelli quality improver (strand-separating agent) should be added.

III. Vermicelli clouds the cooking water and breaks into pieces (no elasticity)

Cause: This is usually caused by dough that is too thin, or by too low a temperature during gelatinization so that it is not fully cooked, but poor starch quality or excessive decolorization that damages the starch structure can also cause vermicelli to lack elasticity.

Solution: In addition to mixing the dough to an appropriate dryness and wetness and increasing the temperature during gelatinization, pea starch can be blended in at 10% of the weight of the dry starch when mixing the dough to enhance elasticity; when making the starch paste, it is best to use mung bean or pea starch. One of sodium alginate, agar, and konjac refined powder can also be added at 0.3% to 0.5% of the weight of the dry starch. The first two should be boiled until dissolved and added as starch paste, while konjac refined powder can be added directly when mixing the dough.

IV. The surface of the vermicelli beads up and is not smooth and clean

Cause: Too high a temperature during gelatinization, and uneven rapid shrinkage of the vermicelli after leaving the machine when it encounters cold, form a bead-like shape with one section large and one section small, not smooth. Dough that is too dry and has too little water aggravates this phenomenon.

Solution: Lower the temperature of the water in the jacket of the vermicelli machine to reduce the temperature difference before and after the vermicelli leaves the machine. The total moisture content of the dough should be between 45% and 50%.

V. Vermicelli is brittle and breaks easily

Cause: Not being fully cooked during extrusion, drying in the sun before it has cooled thoroughly after extrusion, adding too much alum, drying too thoroughly, and long-term stacking without packaging will all make vermicelli brittle and cause losses during storage and transport.

Solution: In addition to taking measures against the causes, sodium pyrophosphate can be added at 0.1% of the weight of the dry starch when mixing the dough to retain moisture; 0.1% to 0.5% salt can also be added to let it absorb moisture naturally.