How Does a Freeze Dryer Work?

How Does a Freeze Dryer Work?

When it comes to long-term food preservation, the best method remains the freeze-drying method. Also called cryodesiccation or lyophilization, freeze-drying is a dehydration process that uses sublimation to remove water from a material. This happens under low pressure. Without further ado, let’s find out what a freeze dryer is and how it works.

What Is a Freeze Dryer?

To preserve a perishable material, a freeze-dryer extracts water from it. This extends the life of such material and makes it suitable for transportation. In other words, a freeze dryer is a machine that preserves perishables by freezing and using low pressure and heat to remove the frozen water from them. The frozen water is turned into vapor. The freeze dryer comprises the Heaters, the Trays, the Condenser, and the Vacuum Pump.

How Does a Freeze Dryer Machine Work

There are three phases in which a freeze dryer works. These phases include freezing, sublimation, and adsorption. Let’s look into each one of them.

Freezing Phase

This is the initial and the most critical stage of the freeze-drying process. This phrase must be done under careful consideration. The process starts by freezing the material at a specific, suitable temperature. Note that the temperature differs according to the material. The machine cools the material to a specific point to ensure that instead of melting, sublimation occurs. This process maintains the material’s original form.

This phrase turns water into little ice crystals that can easily be removed through sublimation. This stage can occur in two ways, either through slow cooling, where temperature gradually drops over some time, or through a fast cooling rate, where temperature instantly drops.

Primary Drying Phase (Sublimation)

This is the primary process whereby the machine uses heat and low pressure to sublimate water from the material. It is a slow process, as too much heat can ruin the material’s physical structure. Also known as sublimation, the process occurs chiefly in the machine’s vacuum compartment. The condenser also plays a significant role, acting as a shield that covers the vacuum pump from the water vapor. After a steady and successful sublimation, the material loses 95% of its moisture content before moving to the next phase.

Secondary Drying Phase (Absorption)

The secondary phase doubles as the final stage of the process. Here, the temperature is raised higher than in the primary, and most of the water molecules are eliminated. About 1% of the moisture is retained at the end of this stage, after which the material is successfully freeze-dried.

How Is the Freeze Drying Process Initiated?

Once the button is turned on, the system releases a low-temperature gas into the chamber where the food item is stored. The gas then covers the product and cools it to a temperature below freezing. The injection of this gas is essential to reaching the sublimation temperature.

Once this temperature is reached, a unique form of dehydration occurs. This form of dehydration is considered unique because water transitions from solid to gas, skipping the liquid stage completely.

Environmental Conditions for Freeze-Drying

While most of the work happens inside the machine, the environment is integral to its success. The humidity of the environment contributes to either the spoilage or the preservation of the produce. Low humidity between 40° and 0°C is advised to retain the quality of the product.

Higher temperatures might ensure a shorter drying time but could also lead to a shortened shelf-life and reduced product quality. However, a lot of emphasis goes on the type and quality of the freeze-dryer. High-quality freeze dryers will perform well in various environments. Nonetheless, strive to operate them at room temperature or less.

Application of Freeze Dryers

There are various uses for freeze dryers. The uses range from food products to pharmaceuticals.  As we all know, freeze-drying is mainly used to preserve the lifespan and quality of any perishable consumable.

However, in the pharmaceutical area, it is used to prepare or produce vitamins and medicines. Here is a list of some materials that are better off freeze-dried to retain their quality.

  • Pharmaceuticals: Freeze drying can also be used to preserve medications at a temperature where they cannot lose their quality. Freeze drying is an effective way to prolong the shelf life of a pharmaceutical product by ensuring that moisture does not damage the medication.
  • Fruits: This may be a shocker, but you can rehydrate fruits like strawberries by freeze-drying them. Freeze-drying fruits makes them more durable and convenient for transportation. You no longer have to worry about spoilage.

  • Food and deserts: Since the purpose of freeze-drying is to ensure durability without compromising quality, freeze-drying deserts is not a good idea. At this point, you should understand that pretty much everything can be freeze-dried. To the question: how does a food freeze dryer work? Here’s a detailed answer.
      • First of all, the food is placed in the dryer, where it would be frozen to 40°F or even colder. You can freeze both uncooked and cooked food.
      • Once it is frozen, the machine vaporizes the ice around the food, causing it to evaporate.
      • At this point, the freeze-drying process is complete, and you can store your food item in an airtight bag until you are ready to use it.
  • Animal feed: You can also freeze dry grains, meat, and other foods that you feed birds and other animals.

Problems to Avoid During Freeze Drying

The freeze-drying process may be easy to complete; however, you can sabotage it with one mistake. Whether you have vast experience or you are a newbie to freeze drying, you can reduce problems by avoiding the following actions:

  • Avoid Overheating: Do not attempt to use high heat levels to speed up the freezing process. Freeze drying has a step-by-step procedure that you should follow for the best results. High temperatures can also damage your food items and specific parts of your freezing machine.
  • Avoid Freeze-drying in Big Chunks: Freeze-drying can be stressful, especially when you have a large quantity of food to dry. However, you should resist the urge to dry your food in big chunks. Bigger food chunks mean that your food will take a longer time to dry. Instead, cut your food into small, uniform chunks to enhance faster and even drying.
  • Avoid Combinations of Different Foods: Combining different foods is a no-no when it comes to freeze-drying. Each food has a unique flavor, and when you combine different foods with strong flavors, it spoils the taste of each food.
  • Mixing Fruits or Other Plant Foods With Meat is a No-go. Imagine freeze-drying raw beef and strawberries; the strawberries could get contaminated and lose their original taste. Freeze-drying does not kill bacteria in food; it only inhibits their growth, so contamination is possible.
  • Not Cleaning Your Machine After Usage: Proper hygiene is important when handling food and different edible items. Cleaning your freeze-dryer will reduce the growth and spread of germs in it. Proper cleaning also eliminates buildup and reduces the chances of malfunctioning.
  • Not Storing Properly: Beyond the preparation for drying, pay attention to your post-drying activities. Keep your food away from moisture, light, and strong odors that can affect its taste and reduce its shelf-life.
  • Food High in Fat and Sugar: You can indeed freeze-dry any food, but you should avoid drying foods with high fat and sugar content. For one, the fat in the food will start to give off an unpleasant and repugnant smell, making it unfit for consumption.

On the other hand, sugary foods remain sticky no matter how long you dry them. So to avoid the mess and unpleasant smell, avoid drying these kinds of foods. If you must dry any of them, reduce the fat content so you can enjoy them after drying.

  • Condenser Overload: Every machine has a maximum capacity to ensure it remains in optimal working condition. When you overload the machine trays with different foods at once, it puts pressure on the machine and increases its chances of malfunctioning.

Are Freeze-Dried Foods Healthy?

Yes, freeze-dried foods are healthy and fit for consumption. The dried food still maintains its vitamin and fiber quality and remains highly nutritious. The only difference is that drying reduces the fluid content of the food; however, everything else stays the same.


Freeze-drying has successfully increased the shelf-life of different food types across several industries. If you deal in perishable food items, you should try freeze-drying to reduce spoilage and waste in your business.

To get quality freeze-dryers and other food-related machines at affordable rates, contact Saintytec. We are the one-stop shop for the best quality products anytime, any day. Contact us to get started!

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