Detailed Method and Steps for Making Maltose from Sweet Potato

1. Process flow: raw material selection -- washing sweet potatoes -- starch production -- gelatinization -- saccharification -- heating and concentration -- finished product

2. Key points of process operation:

① Raw material selection: fresh sweet potatoes with no mold, rot, pests or diseases should be selected as raw material. For sweet potatoes used to produce maltose, the amount of sugar converted from the starch they contain does not affect the yield of the boiled sugar. However, if sweet potatoes are stored for too long, the resulting maltose will have a darker color, reducing the quality of the finished maltose. Fresh sweet potatoes are most suitable for processing maltose.

② Washing sweet potatoes: put the sweet potatoes into a sweet potato washing machine, filling it to about 1/3 of the machine's capacity, fasten the door latch of the machine, and then vigorously turn the washing machine by hand. At the same time, keep pouring clean water from above. Because the sweet potatoes collide with each other inside the machine, the mud and sand attached to the potato skins are washed away by the clean water. The cleaner the better; if not washed clean, sand and mud will be mixed into the finished product later, affecting quality. You must keep turning and washing until most of the sweet potato skins have been removed, then stop turning and washing, open the machine door, and take out the sweet potatoes.

③ Starch production: place the washed sweet potatoes into a stone roller trough or on a stone mill, add an appropriate amount of water and begin grinding. The parts of the roller and mill that come into contact with the sweet potatoes must not contain iron, otherwise it will affect the color, smell and appearance of the product. Grind the sweet potatoes into a slurry, the finer the better; if not ground finely, part of the starch will be lost. Take a thin bamboo or wooden stick and tie it into a cross frame, then take a piece of thin white cloth 0.8 m square, tie its four corners to the cross frame, and place a water bucket underneath. Transfer the ground slurry into this cloth bag with a ladle, and shake the bag by hand so that the starch passes through the thin cloth with the water and flows into the bucket, until it is shaken dry. After all the slurry has been shaken, add an appropriate amount of the clarified sweet potato water from the bucket to the residue and grind it ten times, making sure it becomes completely slurry. Only in this way can the starch be fully extracted and losses avoided. Then shake and filter as above; the resulting filtrate is combined with the previous filtrate, and the residue can be used as pig feed, or to make soy sauce, sweet bean paste, etc. Let the filtered sweet potato slurry stand for about 1 hour; when the liquid above has clarified, pour off the supernatant. The white slurry settled at the bottom of the bucket is starch. Filter off the water with a cloth bag to obtain crude starch. Generally, every 100 kg of sweet potatoes can yield 16-17 kg of starch.

④ Gelatinization: put the drained sweet potato starch into a double-jacketed pot, and for every 100 kg of raw sweet potatoes' worth of starch, add about 1.50 kg of clean water to make a starch slurry of about 10%. Boil for about half an hour while stirring constantly until it becomes a paste; the starch has then been cooked and gelatinization is considered complete.

⑤ Preparation of barley malt: barley malt is used as the saccharifying agent for making maltose, and the barley must be treated. First soak the barley in cold water at about 23 degrees Celsius for about 1-2 hours. If the water temperature is lower in winter, the soaking time must be extended. The barley used as raw material must have impurities removed, and after soaking the wastewater must be separated off. The barley grains must not be soaked too much, otherwise the germination capacity will be lost. The appropriate moisture content of the soaked grains is 40%-45%. After soaking, the barley is sent for germination. At the beginning of germination, the temperature rises due to respiration, and it can be turned to dissipate heat. In addition, water must be sprinkled 2-3 times a day. At a room temperature of 25-30 degrees Celsius, germination can be completed in 4 days, and it can be used when the sprouts are 2 cm long.

⑥ Saccharification: cool the gelatinized starch to 60-63 degrees Celsius, then add malt juice and stir evenly. The malt juice can be obtained by flattening the malt with a press. The amount of malt used is 8% of the fresh sweet potato raw material, and during pressing the malt juice must be made to flow out completely. The saccharification temperature should be kept at 55-60 degrees Celsius. Under the action of the malt juice, the starch gradually saccharifies and becomes maltose and dextrin; at this time the starch paste also gradually becomes thinner. After 8 hours of saccharification, take a sample and check with iodine test solution for any starch reaction. If after adding the iodine test solution and shaking it turns blue, black or purplish red, it proves that there is still starch that has not been saccharified, so the temperature should be maintained and saccharification continued. In this way, take a sample and check once every 1 hour, until the test liquid appears light red or close to the color of the iodine test solution, which means saccharification is complete and the starch has become maltose or dextrin. At the same time, take half a test tube of the saccharification liquid and heat it over an alcohol lamp, boiling for 1-2 minutes, and observe carefully: if the suspended matter in the test tube gradually gathers into larger flocs and can separate from the liquid, and after standing for 1-2 minutes the liquid in the upper part of the test tube can clarify, then saccharification has reached its endpoint. The saccharification time needed to reach this degree generally requires 2-14 hours. After saccharification reaches the endpoint, the saccharification liquid can be heated to boiling, which both kills the saccharifying enzyme preparation and coagulates the suspended matter, making filtration easier.

⑦ Heating and concentration: after the saccharification process is finished, obtain a clear dilute sugar liquid with a plate-and-frame filter press or a cloth bag, then concentrate it. Concentration is generally carried out by heating to evaporate water. The initial heating temperature can be higher, and during heating it must be stirred thoroughly and continuously. As the sugar liquid gradually thickens, a high temperature easily causes caramelization and deepens the color, affecting quality. Therefore, the thicker the sugar liquid, the more the heating temperature should be reduced. During heating and concentration, a layer of foam forms on the liquid surface, and this floating foam must be removed continuously. This foam is protein and other substances, and floating on the surface of the sugar liquid it also hinders water evaporation and easily causes the pot to boil over. The time required for the whole concentration process depends on the water content of the sugar liquid and the heating temperature. When the sugar liquid concentration is 40 Baume degrees, it is the finished maltose product.

3. Finished product specifications:

① Chemical quality: the sugar content of the finished product (calculated as reducing sugar) should be above 50%.

② Physical appearance indicators:

Specific gravity: measured at 40 degrees Celsius, a specific gravity of 1.38 (40 Baume degrees) is qualified.

Color and smell: it should be a light yellow translucent thick liquid, with no unpleasant smell or off-flavor, and a sweet fragrance.