Processing of sweet potato chips

1. Technological process: raw material selection-cleaning-slicing-color protection-dehydration-vacuum frying-deoiling-cooling-packaging

2. Operation points:

① raw material selection: choose oval sweet potatoes which are fresh and full, compact meat, no mildew, no diseases and insect pests and mechanical injuries.

② cleaning: first soak the sweet potato in clean water for 1-2 hours, then remove the sediment and inclusions from the potato by hand or washing machine, then remove the epidermis of the sweet potato with a stainless steel knife and soak it in clean water quickly.

③ slice color protection: because sweet potato is rich in starch and high solids content, its slice thickness should not exceed 2 mm. The sliced sweet potato chips will soon have starch overflow on the surface, and browning can occur when placed in the air for a long time, so they should be immediately treated in boiling water for 2-3 minutes, then removed and cooled in water. Heat treatment mainly has the following functions: destroying enzyme activity and stabilizing color; removing starch exposed on the surface after tissue slices are removed to prevent part of starch from being immersed in cooking oil in the process of frying and affecting the quality of oil; preventing the adhesion of slices during frying. Heat treatment is the α-ripening process of starch, which can prevent starch gelatinization to form a colloid isolation layer due to the gradual heating of oil temperature during frying, which affects the dehydration of internal tissue and reduces the dehydration rate. The fried sweet potato chips without this process have high hardness and poor taste.

④ dehydration: sweet potato chips need to be dehydrated before frying to remove surface moisture. The equipment that can be used are punching rotary drum, rubber sponge extrusion roller, vibrating mesh conveyor belt and centrifuge.

⑤ vacuum frying: vacuum frying technology overcomes the shortcomings of high temperature frying, can better maintain the nutrition and color of sweet potato chips, and make them taste crisp, crisp and not greasy. The vacuum frying system includes a working part and an auxiliary part. The main part of the work is to complete the vacuum frying process, including frying tank, storage tank, vacuum system, heating part and so on. The subsidiary part mainly completes the process of adding oil, discharging waste oil, cleaning containers and pipes (including oil storage tank, lye tank) and so on. The vacuum system can use a water ring vacuum pump to produce a vacuum of more than 93.3 KPA (700 mm Hg) in the vacuum tank. The vacuum can lift the oil from the storage tank to a maximum height of more than 10 meters. However, if it is used as a vacuum suction device, the factors such as flow resistance, flow velocity and vacuum fluctuation should also be taken into account. When frying in vacuum, fill the storage tank with 1x3 volume of cooking oil and heat it to 95 degrees Celsius; put the basket with sweet potato chip screen in the frying tank and lock the lid of the tank. After closing the vacuum valve of the oil storage tank, vacuum the frying tank, open the oil circuit connecting valve between the two tanks, and the oil is pressed into the frying tank from the storage tank; close the oil circuit connecting valve and heat it to keep the oil temperature at 90 degrees Celsius, raise the vacuum to 86.7 KPA in 5 minutes and 93.3 KPA in 10 minutes. In this process, it can be seen that a large number of bubbles are produced and potato chips float up, and the vacuum can be controlled to the limit of no sudden boiling according to the actual situation. When the foam basically disappears and the oil temperature begins to rise, the heating can be stopped. Then, under the condition of maintaining the deep-frying vacuum, the oil circuit connecting valve is opened, and all the oil in the frying tank flows back to the storage tank under the action of gravity. Then close the vacuum valve of each tank, turn off the vacuum pump, and finally slowly open the valve connecting the frying tank to the atmosphere, so that the pressure in the tank is consistent with the atmospheric pressure.

⑥ deoiling cooling: place sweet potato chips in a centrifuge while hot, centrifuge at a speed of 1200 rpm for 6 minutes, then spread them out to cool.

⑦ graded packaging: the products are bagged and sealed according to shape and color conditions. It is best to use vacuum nitrogen-filled packaging to keep the water content of the finished product at about 3%, which seems to ensure the quality of the finished product.