Processing Methods and Technical Key Points for Sweet Potato Vermicelli

Vermicelli is mainly processed from starches such as mung bean, pea, broad bean, and sweet potato, among which mung bean is the best. However, sweet potato is a major starch crop, with widely available raw materials, low price, and high starch content; the vermicelli has a good taste after cooking, and the production process for vermicelli is simple, so it has always been popular among people.

1. Process flow

Raw material handling -> crushing -> filtering -> sun-drying -> making paste -> extruding noodles -> cooling -> sun-drying -> finished product.

2. Production method

(1) Selecting tubers. Select sweet potatoes with smooth surfaces, no pest or disease damage, no green heads, and moderate size; remove the small ones and keep the large ones.

(2) Cleaning. Put the selected sweet potatoes into baskets and place them in water. Wash off soil and impurities. Cut off both ends and the fibrous roots on the surface.

(3) Crushing. The cleaned sweet potatoes should be promptly cut into pieces with a grinder, then ground into a slurry. When making the slurry, add water while grinding; the finer the grind, the better, so that the starch granules in the cells are released as much as possible to increase the starch yield.

(4) Filtering. The purpose is to separate the peel residue from the starch. Generally, a 2-5 chi hanging slurry cloth is used as a filter bag for filtering, for a total of two filtrations. For the first filtration, make the slurry thinner; for the second, make it thicker. Then send the filtrate into a settling tank (the peel residue can be used as feed). After standing in the tank for two days, release the upper clear liquid. Add clean water equal to 1/3 of the original water volume, stir, and filter once more. This time the filtrate enters a small tank and is left to settle.

(5) Sun-drying the starch. When the water in the tank is no longer turbid, that is, after it has all clarified, drain off the upper clear liquid. Discard the oily starch on the surface of the starch sediment layer, take out the lower starch and hang it into starch lumps (that is, starch masses), and move them to the drying yard for sun exposure. When half of the water in the starch lumps has evaporated, cut the starch lumps into several portions and sun-dry them. The drying yard should be set in a wind-sheltered, sunny place to prevent dust contamination.

(6) Making paste. This process is the key to determining the quality of the vermicelli. For every 500 grams of starch, add 25 grams of alum, mix with 2.5-3 kg of cold water, then put it into a large pot and boil, stirring continuously, until it is 80-90% cooked (forming gelatinized starch). The paste made can be mixed with other starch and stirred into a moderately soft dough.

(7) Extruding noodles and cooling. Before extruding noodles, prepare two pots (model 8), two cold water vats, and a medium-sized 48-hole noodle extruder ladle. Because sweet potato vermicelli is relatively thick, the holes of the ladle should be slightly larger than those of ladles for other vermicelli. When extruding noodles, the paste must be fully and evenly stirred, adding warm water while stirring, with the water temperature at about 50°C. Pick up a lump of paste with your hand and let it naturally stretch and hang down; if it does not break, it means the consistency is moderate and noodle extrusion can begin. Prepare a pot of boiling water and keep adding it to the extruding pot. When the water in the pot is nearly boiling (97-98°C), begin extruding the noodles, letting the paste flow down through the holes of the ladle, gradually lengthening and thinning into vermicelli (if conditions permit, it is best to use a vermicelli machine). After the vermicelli sinks to the bottom of the pot and gelatinizes, when it floats back to the surface, immediately scoop it out, put it into a cold water vat to cool, arrange it into bundles by hand, thread it onto a wooden rack, then cool it again through another cold water vat, shaking it continuously until the vermicelli becomes loose and separated into strands, then place it indoors; after it is completely cold, take it outside to dry.

(8) Drying the vermicelli. Take the vermicelli to a wind-sheltered, sunny site and hang it up to dry. After drying, it can be sorted and packaged into finished products.

3. Finished product quality requirements

The vermicelli should be uniform in thickness, consistent in color, dry and transparent, with good toughness and not easily broken.