An In-Depth Look at the Freeze-Drying Process

Written by The Ready Store

Freeze-drying has been around for decades as a reliable source of food preservation. In a nut shell, the material is subjected to very low pressures that extract up to 98 percent of the water from the food. This allows for very long shelf-life – many times 30 years or more.

What is it?
Freeze-drying, also known as lyophilisation, is a dehydration process that extracts the majority of water out of a meal or food. The items are prepared and then placed on racks and placed inside the freeze-drying machine.

The machine subjects the food to a quick physical change – it is not a chemical process. The water in the food is quickly changed from a solid state to a gaseous state, skipping the liquid state.

Origins
Most consider Clarence Frank Birdseye II to be the father of the freeze-drying process (Sounds like a fake name, I know, but it’s true!). He started creating the freeze-drying process in the early 1900s.

The freeze-drying process really took off during WWII as a way to transport serums and other medical supplies. Doctors found that medicines that required refrigeration were spoiling by the time they were transported to other parts of the world. The freeze-dried process was invented and allowed for materials to retain their chemical properties and drastically increasing the shelf-life.

In a short matter of time, the process was adopted for other areas including food preservation.

Freeze-drying process
The process is typically broken down into four stages:

1. Pretreatment. Sometimes items need to be prepared before the process. There are professionals that spend days and hours making sure that the physical and chemical components of the food will be the same after the process.

Sometimes the pretreatment process can include making the food more concentrated, increasing the surface area or adding components to increase the food’s stability during the process.

This stage of the process is not always used. However, this stage is in place to ensure that your food will return to its original taste, texture, and physical state.

2. Freezing. This is probably the most important step in the process. If this is not done correctly, the food will spoil.

In mass quantities, the food is typically placed on sheets and put inside the freeze-drying machine. The food is then quickly cooled to freezing temperatures between -58 to -112 degrees Fahrenheit.

If the process is done too slowly, crystals will form on the food and destroy the food’s texture and nutritional value.

3. Primary drying. Now that the food has been brought to a very cold temperature, and heat is added to bring the frozen moisture to a gaseous state. This is typically done in a partial vacuum to speed up the process.

Sometimes this process can take a few days. If too much heat is added to quickly, it could ruin the structure of the food.

4. Secondary drying. Sometimes, even after the primary drying stage, the food can still have moisture in it. The secondary drying stage tries to remove the unfrozen water molecules. Even thought this stage isn’t always necessary, the food is brought to a higher temperature (sometimes above 32 F).

This ensures that by the end of the four stages the food typically has 1 – 4 percent of its original water levels.

Sealing
The freeze-dried food is typically stored in #10 cans or pouches to ensure that moisture doesn’t enter back in to the food. There are a lot of factors to help freeze-dried food maintain a 20-30 year shelf-life. Read our article about some of those factors.

Conclusion
Freeze-drying is a great way to preserve food that has been tested and proven. The freeze-drying process causes less damage to foods then other dehyrdration methods that use higher temperatures.

Freeze-drying is a great, reliable method to create food storage that lasts for 30 years or more.

Updated February 10, 2012

12 Comments

  1. Tom wrote:

    I’d love to see a film on the actual process.

    February 13th, 2012 at 7:35 am
  2. Mike wrote:

    I’m with Tom I would like to see the whole process

    February 13th, 2012 at 8:12 am
  3. Pete wrote:

    Sounds like a fine balancing act. Like Tom and Mike, it would be nice to see a film on the process.

    February 13th, 2012 at 8:21 am
  4. R David Paine III wrote:

    A very cool article. Thanks for posting this!

    February 13th, 2012 at 8:56 am
  5. Bobby Garmon wrote:

    Inspiring to the rest of the prepper sites to get such detailed articles.

    February 13th, 2012 at 10:20 am
  6. admin wrote:

    We couldn’t really find a good video online of the whole process. There are some videos online that show other items being freeze-dried. For example we found a video of a library using freeze-drying on their books to keep them preserved…

    February 13th, 2012 at 10:32 am
  7. Mo wrote:

    Fascinating! Thanks Mr. Birdseye! Awesome and amazing!

    February 13th, 2012 at 12:31 pm
  8. Bill wrote:

    Interesting. I am happy that it works so well.

    February 13th, 2012 at 7:41 pm
  9. Cathy wrote:

    As usual, very enlightening. Thank you!

    February 14th, 2012 at 8:44 pm
  10. The Diagnosis wrote:

    Very interesting article and very informative but to reitterate the common sentiment video of the process would be quite interesting. I’m actually surprised a show such as ‘Modern Marvels’ hasn’t shown this.

    February 16th, 2012 at 6:49 am
  11. Freeze Dried Foods wrote:

    Quiet interesting article, Yes it Sounds like a fine balancing act.

    November 29th, 2012 at 11:34 pm
  12. Joni wrote:

    This “pre treatment” process concerns me a bit. What are these “added components” used in pre treatment? It sounds a bit vague to me. I need long term food and organic is hard to find, so I have to buy what I can get. I just hope that it’s not chemically or gas treated.

    October 11th, 2014 at 5:36 pm

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