What is freeze drying step?

General steps to successful freeze drying are as follows: 1. Product freeze Moisture is ‘locked’ into the product by freezing in a separate freezer. NB: Difficult products can be frozen inside the Freeze Dryer. Shelf freezing reduces the shelf temperature in the chamber to -18°C or lower, but this adds to the processing time. So, most of customer use separate freezer. 2. Product load Product is placed into a drying chamber by trolley, which is evacuated to low pressure. As a guide, atmospheric (sea level) pressure is 100000Pascal, and the chamber is evacuated to less than 100pascal before drying begins. 3. Product dry step Energy is then gradually applied to the product over a period of 10-24 hours, although this varies depending on the product and loading. This heat (energy) causes the ice to sublimate – that is transform from ice to vapour without passing through the liquid phase. The water vapour is then attracted to the lower temperature ice coil where it condenses as ice. 4. Unload and Pack Product is removed and packed in air tight sealed bags to prevent rehydration, so package material is very import to choose for freeze dried product.