Under normal circumstances, it is often felt that when quick-frozen vegetables are made, they pass through the largest ice crystal formation zone within 30 minutes, so that its core temperature quickly meets the freezing requirements. This is called quick freezing, and it is completed within a few minutes. It's called super fast freezing. The temperature of the largest ice crystal formation zone is -1 to -5 degrees. In order to improve product quality, some people recently said that the lowest temperature of the largest ice crystal formation zone should be minus 15 degrees.
When vegetables are frozen, the faster the speed, the better the quality. Because the faster the freezing speed, the particles of ice crystals will become smaller, and many of them are generated in the cells of vegetables. If the speed is too slow, ice crystals will be formed in the interstices of the cells first, and the water in the cells will not freeze when the water is below 0 degrees. Some are still in a state of supercooling at minus 15 degrees. Super-cooled water has a higher vapor pressure than ice crystals that have been frozen between the cells, so the water inside the cells will flow out through the cell wall to the outside of the cells, forming larger ice crystals between the cells.