The processing flow of strawberry freeze-drying: fresh strawberry cleaning, handle removal draining slicing loading, weighing food freeze-dryer part (warehousing pre-freezing cold trap refrigeration vacuum exhaust vacuum sublimation drying leaving warehouse) weighing vacuum packaging.
Main operating points:
1. Material selection
Choose mature, spotless, decay-free fresh strawberries, remove petioles and leaves, wash them 3-4 times with clean water, then drain them, cut each strawberry into 3-4 pieces, so that the thickness of each piece is 6-8 mm.
2. pre freezing
The strawberries were put into the freeze-dried tray rack and put into the freezer for freezing. The temperature was - 35 C and the freezing time was 1 - 2 h. The center temperature of strawberries was below the eutectic point temperature.
freezing in freezer
3. Vacuum sublimation drying
(1) Under constant pressure
First, the cold trap temperature of food freeze dryer is pre-cooled to - 45 C. When the cold trap temperature drops to - 45 C, the vacuum pump is opened to make the vacuum reach 20 PA and maintain this pressure. Then the shelf is heated and the frozen strawberries are sublimated and dried. In the sublimation drying stage, the constant cold trap temperature is strictly maintained, while in the heating process, the central temperature of strawberry is not higher than its eutectic point temperature, and the surface temperature of strawberry is not higher than its allowable temperature. When the surface and center temperatures of strawberries are close to each other, sublimation drying ends. The sublimation drying of strawberries generally lasts for 4-5 hours.
(2) Under variable pressure conditions
Firstly, the cold trap temperature of food freeze dryer is pre-cooled to - 45 C. When the cold trap temperature drops to - 45 C, the vacuum pump is opened to make the vacuum reach 80 pa, and the shelf is heated at the same time. When the temperature of heating shelf rises to 30 C, the pressure is adjusted to 40 PA and kept for a period of time; when the shelf temperature rises to 45 C, the pressure is reduced to 20 PA and maintained until the end of sublimation drying for about 3-4 hours.
5. Analytical drying
The pressure of the analytic drying stage is maintained at 20 pa, the shelf temperature is 48 C, and the time is generally 1 - 2 h.
6. Out-of-warehouse packaging
When the analytic drying is over, the heating of the shelf is stopped, the vacuum pump, the refrigerator and the cooling water system are closed, and the venting valve is opened to restore the pressure in the freeze-drying box to normal pressure, and then the warehouse is released. Strawberries that have been lyophilized should be packaged aseptically immediately after they leave the warehouse.