The earliest report on the vacuum frying patent literature began in U.S. Patent No. 3635722, issued to 1972, which teaches the original closed frying mode. In 1977, the Japanese patent (No. 28865) proposed a fried banana equipment and process, but the fat content of the fried product was too high and the product quality was poor.
In 1983 and 1985, the vacuum oil fryer introduced in Japanese patents (Nos. 183048/1983 and 92718/1985) was technically improved. The raw materials were fried under vacuum and de-oiled under vacuum. Due to some defects in the original vacuum frying technology, for example, the product is easily deformed, shrunk, the frying temperature is low, and the time is long. In 1989, U.S. Patent No. 4828859 discloses a method and a device for vacuum frying fruit and vegetable products using pretreatment technology. Thus, the technology has been improved.
In 1993, U.S. Patent No. 5182982 proposed a continuous vacuum frying device, which simplifies the feeding and discharging processes, prevents the deposition of products in the fryer, improves the product quality, and improves the production efficiency. Japan has developed rapidly in this technology, its technology and equipment have appeared in Southeast Asia, and gradually promoted to various regions of the world. China's food research & development institutions have absorbed a variety of low-temperature vacuum frying technology on the basis of introduction.
The ideal low-temperature vacuum frying equipment should have higher efficiency, can process a large amount of three times of steam in a short period of time and can quickly establish a vacuum condition with a vacuum of not less than 92 Kpa; The internal de-oiling device can realize de-oiling under vacuum conditions, which can effectively reduce the oil content of the product; finally, it also has an automatic control device with parameters such as temperature time to avoid the instability of product quality caused by human factors.
The automatic dual-chamber vacuum fryer produced by Qingdao Liuyi Machinery is carried out in a single chamber and operated under vacuum for the frying and de-oiling, saving one device compared to the technology that separates the two operations. This design is ideal and simpler for the operator.