What is freeze-drying?

It’s simple, and that’s part of what makes it so special. It just takes the moisture out of food. The main objective in drying foods is preservation. But how does it differ from other dehydration methods such as air-, drum- or sun-drying? Dehydration removes about 90-95% of moisture content and yields a withered, arid appearance. Freeze-drying removes 98-99% of moisture while retaining the shape and structure of the product. Other drying methods can also result in lost nutrients and added ingredients.

Freeze-dried table

Moisture in food products enables decomposition and mold growth, thus impacting shelf life and rates of spoilage. Freeze-dried products offer the least moisture and the longest shelf life of all dehydration methods. As you can see, freeze-drying also creates the most appetizing appearance in the finished product!

Dried banana slices

Dried banana slices

Freeze-dried banana slices

Freeze-dried banana slices

The scientific name for freeze-drying is lyophilization, a low-temperature dehydration process that contrasts with most conventional dehydration methods that evaporate water using heat. This results in a product that has a longer shelf life and significantly lower weight than fresh or frozen.

Freeze Dry Process

1. Fresh produce is harvested at prime ripeness.

2. Fruits or vegetables are washed, peeled/cut and frozen.

3. Fruits or vegetables are placed on drying racks in vacuum drying chambers.

4. The moisture is evaporated at extremely low temperatures.

The lyophilization process begins with quick-freezing to preserve the physical form of the fruit or vegetable. The products are then washed and placed in a vacuum chamber and the pressure is slowly decreased and heat is introduced so that sublimation occurs. Sublimation is the transfer of water molecules from the solid (ice) phase to the gas (vapor) phase. During this slow process, which takes between 18 and 36 hours, as much as 95% of the water is removed from the product. Heat is then slowly introduced to the product so that adsorption occurs. This is when the bond between the fruit or vegetable and the remaining water molecules is broken for a completely dried product.

The water content of fruits and vegetables can be over 90%, so what begins as 1 pound of undried material nets less than an ounce of freeze-dried product that is packed with the same nutritional and flavor properties as fresh or frozen.

Fresh apple slices

Fresh apple slices

Freeze-dried apple slices

Freeze-dried apple slices

Mercer’s freeze-dried fruits remain all natural, and retain the shape, color, flavor and nutritional profile of their fresh and frozen counterparts. However, freeze-dried products can be stored ambient and provide an extended shelf life. Freeze-dried products need no sorting, cleaning or cutting prior to use, which eliminates labor and waste. Because Mercer starts with specified individually quick-frozen (IQF) raw materials, our freeze-dried products are consistent in size and cut.

At Mercer Foods, we have been providing freeze-dried solutions to our customers for over 40 years. Our commitment to high-quality, cutting-edge innovation and best-in-class customer service positions us as the top freeze-dried solutions provider to the ingredients, foodservice and retail sales channels. If you’re curious about how freeze-dried ingredients can benefit you, contact us here.