Learn more about the fascinating world of freeze-drying!
Freeze drying removes water from organic material to create food products that may be stored for long periods without spoiling. The scientific name for the process is lyophilization (say that, three times fast), which involves three steps: Freezing, Primary Drying, and Secondary Drying.
Step number 1: Freezing
Although this may seem obvious, given the name, when you open that delicious bag of SkuttleBugs, it isn’t cold! So, what purpose does freezing the product have? The freezing process is the most important step to ensure the product keeps its taste, color, and shape!
Most organic material (food) is 80-95% water, and for the drying process to be at its best, that water has to go from a frozen state to a gaseous state while skipping its liquid form. Freezing must happen slowly for the best outcomes and can be done under pressure in a freeze-drying machine!
We prepare the food items by cutting them into the size and shape we want and then spreading them onto a tray that fits into the freeze dryer. Once they are in the machine, they will begin cooling to about 0F. Once that occurs, the machine will begin to increase the pressure inside.
Once we have frozen the food to the appropriate pressure and temperature, it’s time to begin step two, the drying process!
Step 2: Primary drying or sublimation
During this phase, 95% of the water is removed! Remember that we started to freeze the water in place in the first phase by slowly lowering the temperature of the product to 0F.
Next, we increase the pressure to move that frozen water into a gaseous state! We won’t go into the science behind this, but our freeze-drying machines balance temperature and pressure to remove water carefully and slowly. If either is off, the final product will still retain moisture and be mushy and unable to be stored.
During phase 2, the temperature inside the freeze-drying machine is as low as -50F! To lend some perspective, your freezer in your kitchen or garage is sitting at 0F! Once this temperature is reached, the food will become rock solid. Then, the trays the food is sitting on will begin to heat up slowly. When we say to heat up, we mean they will get to about -20F! During this heating and pressure process, the frozen water in the food moves into a gaseous state, skipping the liquid state. This is called sublimation and is the key to freeze-drying.
This process can take up to 24 hours to complete.
The final step is Secondary Drying.
In this step, the pressure in the machine is decreased, and the remainder of the moisture in the food will be released and removed. We are left with the famous crispy, crunchy, fun texture of freeze-dried food and a product that can be stored for years in your pantry!
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