How Freeze Drying Works

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Ever wonder how freeze drying works to preserve your food? It seems like magic right? In a way, it is, and it works through three stages: pre-freezing, primary drying, and secondary drying.

What Is Freeze Drying?

Freeze drying or lyophilization is a complex process that involves freezing and drying food. It was first invented in the College de France in Paris by Jacques-Arsene d’Arsonval in 1906. But it wasn’t during the 1950s that people used freeze-drying for industrial food preservation. To date, the pharmaceutical and food industries use freeze drying to preserve their products.

Previously, freeze drying was available only for large food plants. But as technology evolved, homes can now get their own freeze dryer and preserve food. To fully understand and appreciate the process, here’s how freeze drying works.


The first stage is the most important phase. Here, you cool the material below its triple point. If you don’t freeze the food, only evaporation can occur, and you won’t get satisfying preservation properties.

Sometimes, this is the most neglected one, especially regarding meat. It should not be because how your food freezes affect the size of ice crystals. Why does the size of ice crystals matter?

This is because of two things: One is the larger the ice crystals, the faster the primary drying. But the problem is the second one. When large ice crystals form, they destroy cell walls and create hollow structures. This explains why freeze dried fruits and vegetables have that crunchy, airy texture to them.

mixed frozen food

Slow pre-freezing

There are two ways to freeze food. One is through your freezer/deep freezer or in your freeze dryer. This method is known as the slow freezing method, where the lowest temperature is 0°F (-18 °C). This process produces large ice crystals to form, especially when you open and close the freezer door. Opening and closing the door causes a sudden drop in temperature, leading to larger ice crystal formation.

Harvest Right eliminates this by adding a pre-freeze cycle with a freezing temperature of -30 °F to -50°F (-34 °C to -45°C). When you use the freeze-dryer to pre-freeze, you eliminate the possibility of fluctuating temperatures. The only downside is your freeze drying cycle will take longer to complete.

Flash freezing

The second one is using liquid nitrogen, which has a temperature of -320°F (-90°C). Understandably, you can’t use liquid nitrogen because it needs expert handling. The next viable option is dry ice, which has a temperature of -109°F (-78°C).

These two freezes food faster than any freezer could. In addition, they produce smaller ice crystals, which helps prevent unnecessary cellular destruction. This kind of freezing is highly advisable for meat to keep its texture and protein structure. Unfortunately, this can also increase the drying time, which is the second phase.

If you plan to use liquid nitrogen or dry ice always:

  • Wear PPE – they can cause skin irritation and burning
  • Circulate air in the room

freeze dried fruit mixed with cereal

How Freeze Drying works: Primary Drying (Sublimation)

The basic principle behind freeze drying is sublimation. This is the shift of water from solid (ice) directly to gas (vapor). This happens when ice evaporates without having to pass the liquid state.

What happens here is that the machine runs the compressor to lower the temperature in the chamber. Then the pressure goes down, causing the ice to change state to water vapor. Afterward, the vapor goes out of the machine, passing through the freezing coil to condense into frost. Condensing prevents water vapor from returning to the food, completing the separation process.

This is why you often see water or frost forming at your freeze dryer door. At this stage, roughly 93% of water sublimates, leaving your food almost bone dry. Primary drying can take several hours to a couple of days, depending on the following:

  • Food thickness
  • Moisture content
  • Sugar content
  • Outside temperature
  • Food’s frozen state

Secondary Drying

This stage eliminates any residual water molecules bound to the food. This stage is the key to preparing your food for long-term preservation and storage.

It’s a slow process that removes an extra 1%-2% moisture content and adds hours to freeze-drying time. Do note, though that prolonging this phase isn’t advisable. Some extended the secondary drying only to have an inedible final product.

Benefits Of Freeze Drying

There are many advantages to freeze drying.

Prolonged shelf life

Storing food has been a common practice and also a struggle for decades. But as of now, nothing can beat the shelf life of freeze-dried food. Removing almost all moisture from food removes the potential for bacterial growth. Depending on how you store freeze-dried food, it can last you for 25 years or more.

Nutritional value

Freeze drying food is also the best way to keep the nutrient value of food. The process keeps as much as 90% of the nutrients in food. Some say even 97% of nutrients stay because the process doesn’t involve heat.


You can only do so much with dehydrated food. But with freeze-dried food, your imagination is your limit. Freeze dried herbs can bring spark and flavor to any meal. The crunch of the fruit adds a level of fun to salads, cereals, and oatmeal. You can also grind the freeze dried fruits or vegetables into powder to make satisfying, nutritious family meals.

Now that you got an idea of how freeze drying works, did it change how you view your freeze dryer? Or did it spark your interest in owning a freeze dryer? Let us know in the comment section.

Also, do take a look at our YouTube Channel and watch out for more freeze-drying guides!

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