Freeze Drying 101

Published: 3/9/2023
Updated: 12/19/2024

Welcome to my FAQ page for Freeze Drying in your own home that I have learned through researching and processing my own food! This is a LIVE blog so check back often if you want updates! This blog will cover freeze drying food ONLY; however, freeze-drying has been used in biomedical research and processing too!

What is freeze drying?

Freeze drying is a process of preserving food through lyophilization or cryodesiccation, which in simpler terms is a process to remove the water from whatever it is you are trying to preserve. 

How does freeze drying work?

1) Freeze     2) Vacuum     3) Heat     4) Complete

1) The process starts with freezing the product to a sub-zero temperature (usually around -50°F), this process takes between 2-6 hours depending on the water content.

2) Then the pump attached to the machine will begin to bring the chamber pressure down to become a vacuumed space. This is measured in mTorr.

3) Once the chamber has reached an mTorr between 200-800mTorr, the trays where the product is located is then heated to above a certain temperature (depending on the product needs) and the water inside the product begins to evaporate. Since the product is inside a vacuum, the water is able to "skip" the liquid stage and jump to a gas stage and the gas will begin to "pool" inside the chamber around the edges, creating a sheet of ice. 

4) Once the freeze dryer "thinks" the food is completely dried out, it will finish the cycle and begin to cool the chamber down again. I would check the trays after it has reached below the freezing point. If something is cold to touch, giving an "ice" feeling, it may not be done yet. You can place the trays back in and add time.

5) When the freeze dryer cycle is done, you should immediately store your items in a air tight container or mylar bag (7mm minimum thickness) with an oxygen absorber and place it in a cool, dark place with a low moisture level. Periodically check your supplies to ensure nothing is soft or smells bad. If it smells or has become soft and not crunchy in texture, throw it away. 

Benefits of Freeze Dryer vs. Dehydrating

To make it simple, freeze drying food offers a longer self stable food, and contains 98% of it's nutritional value versus a dehydrated food.

During the freeze drying process, the only thing that is removed is the water. During dehydrating, the water is "cooked" out which also cooks out some of the nutritional value to the food.

Freeze dried food is thought to last up to 25 years if stored correctly (there is no study to say this is true), versus the dehydrated foods lasting 6 months to 2 years.