How to Freeze Dry Food

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By Bryan Rucker •  10 min read

Freeze drying is one of the best known ways to preserve food for many months or years on end.  Food that is freeze dried tends to last longer than food preserved using any other method—up to decades—and once it is reconstituted the food loses very little to none of its original taste or nutritional value.  Although freeze drying is a method that has been in existence for decades, it has only recently gained new attention thanks to the Prepper movement, in which people have begun storing rations and readying for potential emergencies before they happen.

While most survival kits consist of rations like granola bars, canned foods and the like, freeze drying has the advantage of introducing nutritious foods such as meat and vegetables into your diet—foods that cannot be stored for very long in their original state.  And since nobody knows when and for how long an emergency will persist, the ability to eat a balanced meal during these times creates a definite advantage for those who have prepared ahead of time.

There are many methods for freeze drying food, some better than others—and some less expensive than others.  Here we will describe three of those freeze drying methods:  The Freezer Method, The Dry Ice Method, and the Vacuum Chamber Method.

To accomplish freeze drying using any one of these methods you will need to have a few supplies on hand.  They include:

The Freezer Method of Freeze Drying

While not everyone owns an expensive vacuum chamber or vacuum sealer (methods we will describe in the next sections), most people own or have access to a freezer.  And the Freezer Method is perhaps the easiest and most affordable way to freeze dry food.  Here is what you will need to do using this method of freeze drying:

Prepare the Food

The first thing you will want to do is slice the food you want to freeze dry into small and fairly uniform pieces—the freeze drying process works much better with smaller and evenly cut pieces of food.  Next, line up the food you have sliced and prepared on a metal tray of some type.  Make sure the food is fairly evenly spaced out, and take care that the pieces of food are not touching each other.  If you have more food than you have room for on the first tray, merely use a second metal tray for the excess.

Ready the Freezer

Before you perform the next step—putting the food into the freezer—remove all other food from the freezer you will be using, and put it into another freezer if you have one.  Then, set your freezer to the absolute lowest temperature and close the door.  Wait a few hours while the freezer gets as cold as it is going to get.  By removing all of the other food and setting the freezer to its lowest temperature, you are actually quickening the sublimation process.  When using industrial freeze drying equipment, pressure is utilized to bring the ice directly into a gaseous form, skipping the liquid state.  This will not happen in the freezer, but the faster the water leaves the food you have prepared the more successful the freeze drying process will be.

Place Food in the Freezer

The next step is to put the metal tray with the sliced food pieces into the freezer—uncovered.  Once you have put the food into the freezer, refrain from opening the freezer door while the freeze drying process is underway.  In most cases, the freeze drying process will take about a week—or a few days more—in conventional freezer.

Test the Food

After about a week, you are ready to test the food you put into the freezer.  To do this, remove one piece of the food from the freezer and place it on a clean dry surface to thaw.  If the piece of food turns black after it thaws, indicating freezer burn, the food is not ready.  Throw that piece of food away and wait another two to three days before conducting another test.

Store the Food

Once you can remove and thaw a piece of food from the freezer without it turning black, you are ready to store your food.  Naturally, the best and most efficient way to store your food is to use a vacuum sealer and the bags that typically come with this type of sealer.  However, if you do not have a vacuum sealer, you can always use Zip-Loc bags.

Place the frozen (freeze dried) pieces of food into a Zip-Loc bag, and try your best to squeeze the air out of it—just as you would do when sealing any other type of bag.  This is a good start, but you will have to go a step further to ensure all the air has left the bag.  According to freeze drying experts, the best way to accomplish this is “to use your mouth to suck the rest of the air out.”  Here is how they explain that process: “First, seal the Ziploc Bag until there’s just enough space to fit your mouth, to form a vacuum. Second, remember that your breath is moist, so the last thing you want to do is breathe out into the bag. For this reason, make sure you start breathing in before your lips make contact with the bag. Once you have sucked all of the air out, quickly seal the bag.  Now, you’re done!”

Place the food you have sealed in a cool dry place for storage.

The Dry Ice Method

Another way to freeze dry food is to use dry ice.  Of course, this method tends to be a bit more expensive and extensive than the freezer-drying method, but it is also much faster.  Thus, if you are in a hurry, this is a good method to use.

The dry ice method is very similar to the freezer method.  Essentially, dry ice (CO2) is a medium that allows all the moisture in the food to evaporate quickly, which leaves it freeze dried.  The colder an environment is, the less moisture it typically has—which is why places like Antarctica have some of the driest conditions on earth.

To employ the dry ice method of freeze drying food, you will need a large container—about two to three times as large as the food you will be freezing.  The first step is to take your cut pieces of food and put them into large—sealed—plastic bags.  It’s important that the bags are completely sealed, because you do not want the dry ice to come into contact with the food at all.  Place the plastic bags into the large container, and cover the food with a thick layer of dry ice.  Reseal the container, and place it into your conventional freezer to dry.

It’s important that the container you use to freeze dry the food with dry ice has a couple of small holes on the top. This will let the gases from the dry ice—and the moisture from the food—escape the container.  It is also crucial that you wear protective gear whenever handling dry ice, such as gloves, goggles and protective clothing.

Typically, food that is freeze dried in this manner takes about 24 to 36 hours to complete.  Once the process is completed, merely follow the “storing” steps explained in Method #1 and your freeze dried food will be ready when the next big emergency strikes.

Vacuum Chamber Method

The most efficient, yet most expensive method for freeze drying food is with a special vacuum chamber.  These can be purchased at most survivalist stores and big box centers, and they are specially designed to speed up the freeze drying process.  Here’s how this method works:

Freeze the Food

Just as you did with the freezer method of freeze drying, cut your food into small pieces and place them on a metal tray.  When all the pieces have been laid out and evenly spaced, place the metal tray into the freezer with the food uncovered.  Unlike the “Freezer Method,” where you would typically wait a week to remove from the food, in this method you will merely have to wait until the food is completely frozen, which should happen in less than 6-12 hours.  Avoid opening the door at all while the food is freezing, as this can cause ice crystals to form on the food—crystals that form when warm air meets the cold environment of the freezer.

Seal the Food

Once the food pieces have been completely frozen, remove them from the freezer and immediately place them into the vacuum chamber.  Follow the temperature and pressure settings in the instruction manual for freeze drying food.  Once the machine has been set and the food has been placed in the chamber, the process should take about a week to complete—maybe a few days more.  It all depends on the level of moisture in the food and the strength of the vacuum sealer.

Store the Food

Once the sublimation process has been completed in the vacuum chamber, remove the food and follow the same directions for storing the food listed in the first method.  Make sure all the bags are completely sealed, and that every bit of air/moisture has been removed.

Reconstitute the Food

When it comes time to eat the food you have freeze dried using the Freezer, Dry Ice or Vacuum chamber method, the process for reconstituting the food is fairly easy.  Simply boil one to two cups of boiling water and add it to the food you have stored.  Once the water is added, you will notice that it will quickly return to its fresh form, as it recollects all the moisture it lost from the freeze drying process.

Whether you elect to go with the Freezer method, the Dry Ice Method, or spend a little more for the Vacuum Chamber method, becoming skilled at freeze drying may take some trial and error.  However, if it doesn’t go well the first time, try to examine what you might have done wrong—and then try again.  Freeze drying is not only one of the best ways to preserve food over the long term, it is also crucial to a good balanced diet during a prolonged emergency of any kind.

Additional resources:

image by bhofack2/Deposit Photos

Bryan Rucker

Brian Rucker has spent his entire life participating in essentially all things wildlife. His concern grew astronomically during the previous tensions between the United States and other nations. He also has grown a substantial interest in survival and sustainability due to the current shape of the world over the years. He believes that preparation triumphs all things.