Introduction to freeze drying:
Freeze drying, or lyphilization, is a process that removes the solvent from a material. This process has application in the preservation of many different types of materials, from small molecules, foodstuffs, artifacts and whole organisms.
Typical application include:
1. Fine chemicals, drugs and laboratory reagents.
2. Therapeutic and industrial enzymes and biological agents, such as proteins and DNA.
3. Preservation of cells.
4. Tissues for research and medical use such as blood and bone.
5. Food stuffs.
6. Rare, sentimental and valuable artifacts, for example waterlogged books, bridal bouquets and archaeological finds.
7. As a concentration step, used to recover material from dilute samples for further investigation.
Benefits of freeze drying:
1. Dried material can be stored at warmer temperatures without suffering degradation.
2. Freeze drying can be operated in a more controlled environment than some other forms of drying, which means less chance of contamination.
3. Drying may be extended until the specified moisture level is achieved, whether that be 5% or 0.1%.
4. As the product is dried without excessive heating, proteins and other products that would be thermally denatured can be successfully preserved.
5. Freeze dried products have a very high surface area which enables them to be reconstituted very quickly. This is advantageous in products such as vaccines and emergency medications as well as instant soups and coffees.
6. Vials can be sealed under vacuum or inert gas, which helps preserve products sensitive to oxygen.
7. Dried products are much lighter than wet, offering the benefit of reducing transportation costs.
How it works?
There are 4-Step process:
First step: Fresh or cooked foods are placed in the dryer where they are frozen to -40 degrees Fahrenheit or colder.
Second step: Once the food is frozen, the freeze dryer creates a powerful vacuum around the food. Then, as the food is slightly warmed, the ice transitions into vapor and evaporates.
Third step: The freeze-dried food is then sealed in moisture and oxygen-proof packaging (Mylar bags, mason jars, or cans) along with an oxygen absorber to ensure freshness until opened.
Finally: When water is added to the food it regains its original fresh flavor, aroma, and appearance!
The freeze drying process
The first stage in the freeze drying process is for the product to be frozen. The manner of freezing will determine the crystalline structure, which in turn determines how the product will dry.
Once frozen, the material is dried first by a process known as sublimation. The product temperature is kept below its critical(glass or eutectic) temperature while a vacuum is pulled until the pressure / temperature balance is such that the ice sublimes directly into a vapor without melting.
3. Secondary drying
Simplistically, primary drying is when ice is present in the product and secondary drying takes place in the absence of resident ice. Secondary drying is a desorption process when water which is chemically bound is removed, and occurs when the product is unlikely to melt and is therefore relatively stable.
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