The most common complaint about freeze-drying is vacuum pressure loss. Such losses are usually due to one of the following two reasons:
1. Leakage of freeze-drying system.
2. Problems with vacuum pumps.
What is freeze-drying?
Freeze drying is based on the physical process of sublimation: in vacuum, water changes directly from solid to vapor-ice evaporation. The products to be dried are first frozen deeply at atmospheric pressure, usually using low-temperature liquefied gas. It is then sublimated into a vacuum to remove the frozen water from the product as a vapor. In this way, water can be extracted from food without heating or prolonged drying, leading to loss of nutrients, flavors and vitamins.
These basic ingredients are basically not affected by freeze-drying. Extracting water in this way will only cause slight changes in the internal structure of food. The dried cells form a spongy structure. When the product is put into water, a cavity will absorb water quickly. Ideally, rehydrated freeze-dried foods are difficult to distinguish from fresh foods.
Is there a suitable vacuum pump for freeze drying?
Because freeze-drying requires oil-based rotary vane pumps to maintain vacuum, it is important to select the right pump. Standard rotary vane pump works well in water-based solution. For solvents and acids, it is recommended to use more robust mixing or combination pumps. If the solvent bypasses the collector, or if the collector is not cold enough, the steam will migrate to the pump… This will shorten the oil change interval and shorten the effective life of the pump.
Is there a suitable freeze dryer?
If you notice that the oil in the freeze dryer gets dirty quickly, make sure that your freeze dryer is suitable for your application.