how to freeze dry

Question

Freeze drying, also known as lyophilization, is a preservation technique for removing water content from items by sublimation. There are two main approaches to freeze drying, depending on your resources: using a freeze dryer or using a regular freezer with dry ice.

Answer 1

Freeze Drying with a Freeze Dryer

1. Freezing: The first step is freezing the product well below its triple point (the temperature at which solid, liquid and gas phases coexist). This typically involves a specialized chamber that can reach temperatures as low as -80°C.
2. Primary Drying (Sublimation): Under a vacuum, the pressure is lowered allowing the frozen water in the product to sublimate directly from ice to vapor, bypassing the liquid stage.
3. Secondary Drying (Desorption): Once most of the ice is gone, the temperature is slightly raised to remove any remaining adsorbed water molecules.

Freeze Drying with a Freezer and Dry Ice

1. Preparation: Pre-freeze your food items in your freezer set to the lowest temperature possible (ideally below -30°C).
2. Dry Ice Chamber: Place the pre-frozen items in a cooler and cover them completely with dry ice. Dry ice sublimates at a much lower temperature than regular ice, accelerating the drying process.
3. Drying Time: Depending on the amount of food and the size of the cooler, freeze drying with dry ice can take 24 hours or more. Check on the dry ice periodically. When all the dry ice has disappeared, the food should be freeze-dried.

Here are some additional things to keep in mind:

• Freeze drying is best suited for certain foods like fruits, vegetables, and meats.
• Not all foods are ideal for freeze drying.
• Freeze-dried food should be stored in airtight containers with minimal oxygen exposure to maintain quality.