Detailed method for making glutinous rice paper from sweet potato

Starch film, commonly known as glutinous rice paper, is an edible film made from starch as a raw material. In the food industry, it is used as a laminated packaging material for candy and pastry foods.

The process for making glutinous rice paper: starch emulsification, sieving -- batter preparation (adding phospholipid emulsion) -- steam insulation -- film casting -- finished product

1. Starch emulsification and sieving: Screen sweet potato starch through a 100-mesh sieve, add water at 50-55 degrees Celsius to emulsify it. The amount of water used is 2.5-3 times that of the starch. After preparation, the concentration is 15-17 Baume. Stir continuously so that the starch is completely and evenly dispersed in the water. Then pass it through a 100-mesh copper sieve and pump it into the gelatinization pot.

2. Batter preparation: After the starch emulsion enters the gelatinization pot, turn on the stirrer and add phospholipid to prepare a phospholipid emulsion. Phospholipid is an indispensable raw material for producing glutinous rice paper. During the film casting process, it helps the film separate from the copper belt, and at the same time it can also prevent adhesion between films. Phospholipid must first be dissolved in hot alkaline solution. The method is: heat a 1%-2% caustic soda solution to 85-100 degrees Celsius, add phospholipid while stirring, and heat it so that it is completely dissolved in the alkaline solution. Cool to 30-40 degrees Celsius, pass through a 100-mesh sieve, and prepare a phospholipid solution with a concentration of 1%-2%. The amount of caustic soda used is 0.8%-1.8% of the phospholipid. The pH value of the phospholipid solution is 8-9, showing weak alkalinity.

3. Steam insulation: This is the starch gelatinization process. In the gelatinization pot, heat the starch solution to 50 degrees Celsius and begin stirring. Add hot water at 85-90 degrees Celsius, control the starch concentration at 7%-8%, and keep it at 90 degrees Celsius for 1-2 hours. The stirring speed is preferably 40 revolutions per minute.

4. Film casting: The film casting machine is an integrated unit made of two aluminum drying cylinders with a diameter of 600 mm connected by a copper strip 13 m long, 400 mm wide, and 0.7 mm thick. The drying cylinders are heated by steam, and at the same time the copper strip is driven forward at a speed of 1 revolution per minute. The starch batter flows through a narrow slit 0.14-0.15 mm wide onto the copper strip and is scraped into a uniform film. The film thickness is 2-3 silk meters. After drying, it is wound onto a paper roll. The film casting machine itself forms a sealed system, controlling a certain temperature and humidity. The steam pressure in the drying cylinders is controlled at 0.15-0.25 gauge pressure. The pressure must not be too high, otherwise the film will produce many pores; if the pressure is too low, the film will not dry. Steam must be sprayed into the machine to adjust humidity. If there is too much steam, operation becomes difficult; if there is too little steam, the film becomes brittle. The moisture content of the finished glutinous rice paper is not less than 10%. To improve the strength of glutinous rice paper, 1% algin can be added before starch gelatinization, and the tensile strength can be increased by about 10%.