What is the Difference Between Freeze Dried and Dehydrated

The main difference between freeze dried and dehydrated food is that freeze-dried food loses moisture up to 98-99% whereas dehydrated food loses moisture up to 95% moisture. Therefore, the shelf life of freeze-dried food can be longer up to 25 years while the shelf life of dehydrated food is longer up to 15 years. Furthermore, 97% of the original nutrients are retained in the freeze-dried food while only 5-60% of nutrients are retained in the dehydrated food.

Freeze-dried and dehydrated food are two types of food that undergo different food preservation methods for considerably a longer shelf life.

Key Areas Covered

1. What is Freeze Dried
     – Definition, Process, Importance
2. What is Dehydrated Food
     – Definition, Process, Importance
3. What are the Similarities Between Freeze Dried and Dehydrated
     – Outline of Common Features
4. What is the Difference Between Freeze Dried and Dehydrated
     – Comparison of Key Differences

Key Terms

Dehydrated, Freeze-Dried, Moisture Content, Nutrition, Processing, Shelf Life, Taste

What is Freeze Dried

Freeze-dried is a modern, industrial technique of food preservation. It is a low-temperature dehydration process, which involves freezing the product while lowering the temperature to remove ice by sublimation. Here, sublimation is the transition of a substance directly from solid to the gas phase, without passing through the intermediate liquid phase. During the process, a higher content of moisture is removed from the product, around 98-99% of moisture. Therefore, the shelf life of the product is longer, which can be up to 25 years.

Figure 1: Freeze-Dried Ice Cream

More importantly, freeze-drying results in a high-quality product due to the involvement of a lower temperature. Therefore, the quality of the rehydrated product is excellent. Also, this retains most of the nutrients of the product. Other than as a food preserving technique, freeze-drying is used to store biological samples including bacteria and yeast and biomedical samples including tissues and organs in organ transplantation.

What is Dehydrated

Dehydration or curing is a conventional method of food preservation, which uses heat to reduce the moisture content of the product. It draws out the moisture content by osmosis. Also, it decreases the water potential of the food since it increases the solute concentration of the food. Some methods of dehydration include smoking, spicing, and cooking. In addition to preservation, dehydration is a flavoring process as well. That means; some additives such as sugar, salt, nitrates, and nitrites can be added while preserving. Additives also increase the solute concentration in the food.

Figure 2: Prosciutto – An Italian Dry-Cured Ham

Though the basic principle of dehydration is to make the product inhospitable to the microbial growth, preventing the food spoilage, it can only remove water content up to 95%. Therefore, the shelf life of the food product is somewhat low when compared to freeze-drying method. Moreover, due to the use of high heat during dehydration, most nutrients are destroyed and the quality of food is decreased.

Similarities Between Freeze Dried and Dehydrated

• Freeze-dried and dehydrated food are two types of preserved food with a longer shelf life.
• The main principle of preservation in these methods is the reduction of the moisture content of the food.
• Also, both methods prevent the growth of microorganisms including mold, yeast, and bacteria on the food by removing water.
• Furthermore, storage under cold temperatures will increase the shelf life.

Difference Between Freeze Dried and Dehydrated

Definition

Freeze-dried food refers to the food preserved by rapidly freezing and then subjecting to a high vacuum which removes ice by sublimation while dehydrated food refers to the food dried in order to remove a considerable amount of moisture. Thus, these definitions explain the fundamental difference between freeze dried and dehydrated food.

Other Names

Freeze-drying is also known as lyophilization or cryodesiccation while dehydration is also known as curing.

Significance

Freeze-drying is a modern industrial technique of food preservation while dehydration is an ancient technique used since 12,000 BC.

Types of Food

Another difference between freeze dried and dehydrated food is that freeze-drying is used to preserve chocolate, ice cream, fruits, bacon, etc. while dehydration is used to preserve, meat, fish, and vegetables.

Process

One other important difference between freeze dried and dehydrated food is that while freeze-drying involves lowering the pressure, freezing the product by sublimation. In contrast, dehydration involves the evaporation of water using heat.

Temperature Used

Moreover, a low temperature is used in freeze-drying while a high temperature is used in dehydration.

Moisture Content

Moisture content is a major difference between freeze dried and dehydrated food. Freeze-drying removes a higher amount of moisture from food while dehydration removes a comparatively lesser amount of moisture from food.

Shelf Life

The shelf life of freeze-dried food is longer, like 25 years, while the shelf life of dehydrated food is somewhat shorter as 15 years. This is one other important difference between freeze dried and dehydrated food.

Preparation

Freeze-dried food is pre-cooked and needs to be kept in water for few minutes while dehydrated food needs to be boiled or cooked.

Nutritional Value

Most of the original nutrients are retained in freeze-dried food while a considerable amount of nutrients are left over from the dehydrated food. This is also an useful difference between freeze dried and dehydrated food.

Flavor Texture and Smell

The original flavor, texture, and smell remain in freeze-dried food while dehydrated food does not retain the original flavor, texture, the smell.

Weight

Weight of the food is yet another difference between freeze dried and dehydrated food. The weight of freeze-dried food is low while the weight of dehydrated food is comparatively high. 

Additives or Preservatives

Due to the removal of a higher amount of moisture, freeze-dried food does not require additives or preservatives while dehydrated food requires a small amount of additives or preservatives due to the considerably high moisture content.

Conclusion

Freeze-drying is a more recent method of food preservation, which involves the removal of 99% of the moisture from food. This gives a longer shelf life to the food, around up to 25 years. Also, this method retains most nutrients in the food while retaining the original flavor, taste, and smell of the food. In comparison, dehydration is an ancient method of food preserving, which uses heat or sun-drying to remove the moisture from food. However, some moisture will remain in the food, reducing the shelf life. Also, due to the involvement of heat, dehydrated food loses most of the nutrients, original flavor, texture, and smell. Therefore, the main difference between freeze dried and dehydrated food is the effect on the food.

References:

1. “What Is Freeze Drying? How Does It Work? Millrock Technology, Inc.” Millrock Technology, Inc, Available Here
2. “Dehydration.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 19 May 2014, Available Here

Image Courtesy:

1. “Freeze-Dried-Ice-Cream” By Evan-Amos – Own work (Public Domain) via Commons Wikimedia  
2. “ProsciuttoSeaSalt” By Deathworm at English Wikipedia – Transferred from en.wikipedia to Commons by Roberta F. using CommonsHelper. (Public Domain) via Commons Wikimedia