Rapid freezing refers to a method in which the food quickly passes through the maximum ice crystal formation zone of -1 to -5 degrees Celsius, and the average temperature reaches minus 18 degrees Celsius or lower. The rapid freezing must ensure that the various physical or The chemical change can achieve maximum reversibility. When the temperature of vegetables is lowered until the juice forms ice crystals, if the freezing speed is too slow, the surrounding free water will converge with the water in the film with high vapor pressure to transfer to the ice crystal nuclei due to the appearance of ice crystal nuclei to form large ice crystal nuclei. Crystal. The cell membranes of vegetable tissues are mostly composed of cellulose, and the ability to withstand pressure is much worse than that of animal food cell membranes (myocytes). Therefore, when the pressure generated by large ice crystals exceeds the capacity of the membrane, the membrane ruptures At the same time, the cell wall is also destroyed, and the nutrients in the cell overflow during thawing, causing the quality of the vegetable to drop sharply; on the contrary, if the freezing temperature is very low (below -30 degrees Celsius), the free water inside and outside the vegetable cell will be partially bound The water precipitates a large number of ice crystal nuclei at the same time, and finally uniform and fine ice crystals are evenly divided into the inside and outside of the cell, so that the internal and external pressure of the cell is balanced. When thawing, most of the water is absorbed by the cell tissue, and the juice loss is significantly less than slow freezing.