The specific manifestations of poor appearance of freeze-dried products are shrinkage, crystallization, unsaturated flocculation, etc. So what are the factors that affect the appearance of food freeze dryers?
1.The influence of the concentration of the solution on the surface precursor of the Y liquid during the drying process. When the solution concentration is too high: a dense surface layer is formed after drying.
The pores of the surface layer are small, the performance of the test gas is poor, and the water inside is difficult to pass through the surface layer, so it rises along the bottle wall, causing the product to shrink out of the wall;
in addition, when the concentration is too high, the Y solution is easy to agglomerate during the freeze-drying process, and the product The appearance is uneven. When the concentration is too low, the mechanical strength is low, the product structure is loose, and even becomes powder after packaging and transportation, which affects the appearance of the product.
2. The thickness of the product is too thick. Generally 10-15 mm, the case of too thick product is similar to the case of too high concentration, not only the drying time is long, but also it will collapse and agglomerate.
3. The temperature rises and falls quickly, which can easily cause the product to leave the wall and slow. Pre-freezing speed: When the temperature of the product drops by 10-15°C per minute, it is called quick freezing, and when the temperature drops by 1°C per minute per hour during the freeze-drying process, it is called slow freezing.
The temperature of the product should not exceed the safe temperature of the product, otherwise, the activity of the product will be reduced and the caking and solubility of the product will be poor.
4. Outlet speed. The air release speed in front of the cabinet should not be too fast, otherwise the vacuum degree in the cabinet will suddenly change greatly, and turbulent flow will be formed in the container, which will make the product become flocculent or powdery, which will affect the appearance.