An In-Depth Look at the Freeze-Drying Process

Freeze-drying is a process that has revolutionized the food storage industry. With this process you can store any kind of food, including fruits, vegetables, meats, and dairy products. You can even freeze dry entire meals. However, the freeze-drying process can be very delicate.

What is freeze-drying?
Freeze-drying, also known as lyophilisation, is a reliable food preservation process that extends the shelf life of any food for 20-30 years while still maintaining its structure and nutritional value. This is done by carefully extracting up to 99% of the moisture in the food, making it resistant to bacteria and deterioration.

In this process, food is prepared, arranged onto drying racks, and placed inside of a freeze-drying machine. Rather than a chemical change or preservation, the machine subjects the food to a quick physical change that leaves the structure intact. The water in the food is quickly changed from a solid state to a gaseous state, skipping the liquid state.

Origins
The freeze-drying process began during WWII as a method to transport serums and other medical supplies. Doctors found that medicines requiring refrigeration were spoiling by the time they were transported to other parts of the world. The freeze-drying process was invented to allow materials to retain their chemical properties and drastically increase their shelf-life.

The process was then adopted for other uses including food preservation and even book restoration.

The Freeze-drying Process
The process can be broken down into four stages that occur within the freeze-drying machine. A machine will consist of a freeze-drying chamber, shelves attached to heating units, a freezing coil connected to a refrigerator compressor, and a vacuum pump.

  1. Pretreatment

Before the freeze-drying process begins, food is checked for bacteria and spoilage to ensure that the food will be safe to eat when reconstituted. Some food may also be concentrated or cooked and prepared before freezing. This is done to best preserve the structure of the food, as well as increase its quality and yield. This is to ensure that your food will be the same in look, taste, and nutrition after the process is completed.

  1. Freezing

In this phase of the process, the food is placed onto the shelves in mass quantities, which is then put inside of the freeze-drying machine. The chamber is then sealed and the temperature is lowered down to between -58 to -112 degrees Fahrenheit.

When the water is in a solid form, its molecules become separated from the food molecules and leave the structure of the food intact. That is why the freezing phase is so important. If any moisture is left in the food when the drying process begins, the structure may be ruined.

  1. Primary Drying

Now that the food has been frozen in the chamber, the pressure is lowered to create a vacuum. This environment allows for a process known as sublimation, or the shift of a solid directly into a gas. Once the pressure is lowered, heat is slowly added to the trays. Because water cannot exist in a liquid form in a vacuum, the ice is converted directly into water vapor.

Sublimation leaves the structure of the food perfectly intact with its same taste, texture, and nutrients. The water vapor is filtered out of the freeze-drying chamber and condenses onto the refrigeration coils so it is away from the food and won’t risk any rehydration.

  1. Secondary Drying

The drying process occurs over the course of multiple hours or even days as the water is gradually extracted from the food. This process takes so long so the food doesn't overheat and cause it to lose any nutrients or structure. In the final stages of drying, the temperature is raised higher in order to evaporate any moisture that might still be remaining in the food. This leaves the food with 1 to 4 percent of its original water content. Now it is ready to store.

Sealing
Once food has gone through the freeze-drying process, it can be stored for up to 30 years. But there are two components that will cause our food to spoil more quickly: water and oxygen. Freeze dried food will last much longer if it is sealed in a #10 can or a mylar bag. These containers will keep moisture out of the food so that it won’t reconstitute and will be ready to use when you need it. You can also add an oxygen absorber to the container to keep your food bacteria free for years to come.

The freeze-drying process is one of the best food preservation methods out there. It allows you to store all of your favorite fruits, vegetables, and complete meals for 20-30 years that have the same look and taste of fresh food. The process can be tedious, but it provides nutritious food that can be stored in your supplies and used in your everyday cooking.

Have you tried freeze dried food? How has it changed your food storage? Comment below and let others know your opinion.

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