Chemical and thermal methods of purifying potatoes and vegetables
Chemical and thermal methods of purifying potatoes and vegetables. The continuous lye method is based on softening the surface of the cleaned potatoes with hot soda ash (NaOH), which facilitates the removal of the epidermis and eyelets. There are three variants of this method:
• high temperature lye treatment (90-100°C), by 2-6 minutes,
• lye cleaning at a temperature of 50-70 ° C, by 5-15 minutes,
• dry lye treatment, consisting in drying potatoes, after treatment with lye, infrared heaters.
Drawing. Diagram of the technological line for cleaning potatoes with the lye method: 1 - feeding conveyor, 2 lift, 3—Coil scrubber, 4 – lye purification device, 5 - high pressure scrubber, 6 ~ brush device for removing the cuticle, 7 - inertization tank, 8 - conveyor, 9 - sulfurization device, 10 - finished product hopper with scales.
Temperature, lye concentration (5-25%) and the leaching time is selected according to the quality of the potatoes processed and the type of product produced. After treatment with lye, the potatoes are transferred to the washer, where the epidermis is removed with a stream of water. The lye residues are washed off in a neutralizing bath (1-2% citric acid solution). Potato losses during cleaning, including cleaning, amount to 17-21 %. The disadvantage of this method is the production of a large amount of wastewater. When cleaning potatoes by the dry method, the skin is removed with brushes, which makes it possible to reduce water consumption and the amount of wastewater several times. Potato losses are lower by 15-20%.
In the leach-steam method, potatoes are first blanched, as a result, starch is glued in the subcutaneous layer of the tuber, which is an effective barrier to prevent lye from penetrating deeper into the tuber. This starch is removed mechanically along with the epidermis.
In Poland, only a few food industry plants use lye purification of potatoes, while maintaining strict control of this process, there is always a possibility of the toxic liquor penetrating into the tubers. The lye methods are characterized by high efficiency (12-16 tons per shift).