Freezing: The food is rapidly frozen under low temperature conditions, causing the water inside to form ice crystals.
Reduced pressure: The frozen food is placed in a vacuum chamber, and the surrounding pressure is reduced, causing the ice crystals to convert into water vapor at a lower temperature.
Water removal: The water vapor is drawn out by a vacuum pump, causing the water inside the food to change directly from a solid to a gas state, thus avoiding the loss of nutrients caused by water.
Solidification: After pressure reduction and water removal, the water inside the food has been completely removed, resulting in a dry state.