Step 1: Understanding the Concept:
Freeze drying (Lyophilization) is a dehydration process used to preserve heat-sensitive materials. It involves freezing the product and then removing the solvent under vacuum.
Step 2: Detailed Explanation:
1. Process: The water in the product is first frozen into ice.
2. Phase Change: Under reduced pressure (vacuum), the ice is converted directly into water vapor without passing through the liquid phase. This physical change (Solid \(\rightarrow\) Gas) is called sublimation.
3. Advantages: Since the product is dried at very low temperatures, there is minimal degradation of thermolabile drugs (e.g., vaccines, antibiotics).
Step 3: Final Answer:
Because the drying mechanism relies on the sublimation of ice, freeze drying is frequently referred to as sublimation drying.