We humans simply love the idea of preservation. The most common example of this is a refrigerator. Although a refrigerator does serve many other purposes, we love them because they allow us to stash all the goodies that we can get our hands on and then gobble them later. Nothing works better than a refrigerator!
However, when we are dealing with more sensitive materials, such as medicines and drugs, the presence or absence of preservation could mean life or death for people, so we need to be extra careful that materials are not spoiled before they are used. The question is, how do we make that happen?
Freeze-Drying to the Rescue!
Freeze-drying is known by many names, such as lyophilisation or cryodesiccation, so try not to get confused. Freeze-drying by any name is an interesting method used to store and preserve pharmaceutical products and simple food items. It is basically a dehydration process in which the material is frozen first, and subsequently, the surrounding temperature is reduced.
Let’s see how this essential process works.
How It Works
The whole process of freeze-drying can be broken down into 4 major parts. These are freezing, sublimation, attainment of the dried product, and rehydration.
The microorganisms that are primarily responsible for degrading food items and medicines depend on the availability of water, so what do we do to tackle these nasty things?
We simply remove ‘water’ from the equation. What could be easier?
The first stage of the process is freezing, which is self-explanatory. The second step, however, is less well known, but actually the key to the whole process. Sublimation basically means directly changing the state of a substance from solid to gas or vice-versa. Normally, ice is first converted to water, which is then heated to convert into gas, but in sublimation, there is no liquid phase.
This is achieved with the freeze-drier. After dropping the temperature to a very low level, it drops the pressure around the material, which lowers the boiling point of water. What good does that extra step do for us? Think about it this way… when the boiling point is reduced, the solid state of ice changes to a gaseous state pretty fast. This means that when even a small amount of heat is provided to the system, the ice molecules attain enough energy to break free of the inter-molecular forces that were holding them together and become water vapor.
After this, we have a dried product that now contains only 1-5% of its original moisture content. As such, it can be stored in oxygen-proof packaging for years! The subsequent process before you actually use one of these freeze-dried products involves rehydration, i.e., the addition of water to the material to bring it back to its original form. However, there are many freeze-dried materials that can be consumed as they are, even without re-hydration (apples, for example).
This technique has countless applications in many fields, including medicine, edible materials, chemical industries and many others. Understanding and mastering this technique has enabled us to enjoy food items before (or after) their natural thriving season. That’s why we don’t have to worry about finding mangoes to eat during the winter. That’s some great news!
- How Stuff Works
- A Guide To Freeze Drying For The Laboratory – UMass Amherst College of Engineering
- General Principles of Freeze Drying – Freezedrying.com