فریز درایر غذایی

Introduction

In the past, we discussed in detail everything you need to know about the freeze dryer, including its history, functionality, types, and various features. In this article, however, we intend to talk about one of the most important types of freeze dryers, namely, the food freeze dryer.

   Since ancient times, the storage of food for future use has been one of the most significant challenges for intelligent humans. Over time, various methods have been proposed for this purpose, with the latest being food freeze-drying, also known as freeze-drying.

   The freeze-drying process with a food freeze dryer was first used after World War II in order to preserve and store food without the need for a refrigerator. Coffee was one of the first food products to be frozen using a freeze dryer, but now vegetables, fruits, various types of meat, fish, dairy products, plants, and food flavorings can be successfully dried in these devices.

How A Food Freeze Dryer Works:

   A food freeze dryer utilizes a process called lyophilization to lower the temperature of the product below the freezing point and then uses a vacuum to extract the ice in the form of vapor. Subsequently, the vapor condenses on a condenser, turns back into ice, and is removed from between the shelves. Finally, with a gradual increase in temperature, all remaining moisture is removed from the product. This process preserves the physical structure of the food product and retains its freshness for rehydration during consumption.

   In a food freeze dryer, products are stored in trays on shelves or in large boxes, or if the freeze dryer is continuously active, they are transported on a conveyor belt. Freeze-drying is a three-stage process. During the initial freezing phase, the materials inside the dryer are cooled to a specific low temperature, which is the lowest temperature at which both solid and liquid phases can coexist simultaneously.

   This temperature varies for different materials. The freezing stage is the most critical phase of the process. After freezing, the materials enter the primary drying phase. The pressure decreases, and sufficient heat is generated for sublimation to occur. Introducing a vacuum to the freeze dryer helps control and maintain pressure, and a vapor condenser allows the water vapor, after exiting the material, to freeze again and not enter the vacuum pumps. In the final stage, the frozen water molecules are removed. In the secondary drying stage, the pressure decreases again, and the temperature increases as much as possible (this temperature increase depends on the biological properties of the materials). Ultimately, any remaining water evaporates, and the final moisture    content is usually between three and five percent.

   A specific type of these devices is home freeze dryers. Home freeze dryers provide the opportunity to produce frozen foods and snacks at home. Although these products have recently entered the market, and the first home versions were released in 2013, using these machines is easy and effective, producing high-quality dried products. To familiarize yourself with some of the best home freeze dryers for food preservation, stay with us in the following section.

Is Food Freeze Drying a Safe Process?

Drying food, like any other storage process related to food, has specific regulations. If the following cases are observed, the process of freezing food products will proceed with minimal flaws:

  • Freezing the product must be complete and accurate, meaning the product must be frozen to below the eutectic point.
  • The freezing rate should be such that the ice crystals formed are neither too small nor too large. A freezing rate of about one degree Celsius per minute is suitable for most materials.
  • The vacuum pressure in the drying chamber must be proportional to the sublimation temperature of the ice.
  • The temperature increase rate in the primary drying stage should not be such that it causes the ice to melt.
  • The maximum temperature in the final drying stage must be such that the biological properties of the product are not compromised.
  • The final residual moisture content depends on the power of the device in lowering the pressure in the drying chamber. The lower the vacuum, the greater the moisture absorption power inside the tissue, resulting in a drier product.

 

Uses of Food Freeze Dryers

Some food items freeze dry well, while not all are suitable for freeze-drying. Small fruits and vegetables can be easily dried in a freeze dryer, while larger fruits and vegetables are not suitable, although if they are cut into small pieces first, they can be freeze-dried. This applies to meat as well. Small frozen meat pieces dry well, but larger fillets must be cut into small pieces. Meat and seafood can be cooked before drying in a food freeze dryer. For some foods, freeze-drying is not cost-effective.

Samples of dried food products with freeze drying process

   Coffee is a beverage that contains taste and aroma which is created due to some chemical reactions during grinding, and it can be preserved using freeze drying. Compared to other drying methods such as room temperature drying, hot air drying, and solar drying, freeze drying coffee beans, which are frozen in a freeze dryer, contain higher amounts of essential amino acids such as leucine, lysine, and phenylalanine. Additionally, a small number of non-essential amino acids that significantly contribute to the taste can be preserved using freeze drying.

   Freeze drying is widely used for insect preservation for specific purposes. Dried insects preserved using freeze drying in a freeze dryer are used as food for various pets, bird food, fish bait, and increasingly for human consumption. Dried insects in powder form are sold as a protein base in animal feed and as a nutritional supplement for human use in some markets.

   By using the freeze-drying method, the variety of meals and snacks for astronauts, mountaineers, and military personnel can be increased. Due to the light weight of the food after being taken out of the freeze dryer, a popular and convenient product will be obtained.

   Furthermore, a larger amount of dried and frozen food can be carried compared to an equivalent weight of moist food. When consumed, dried food can easily be rehydrated with water. It should be mentioned that dried products have a longer shelf life than fresh products, making them ideal for long trips.

Examples of food products obtained through freeze-drying include:

  • Instant foods such as instant noodles and ready-made soups
  • Ready-made foods such as Bolognese sauce, stroganoff, etc.
  • Seafood such as shellfish
  • Fruit in breakfast cereals
  • Fruit juice and instant coffee
  • Black grape extract and other fruit extracts
  • Ice cream
  • Herbs and cooking spices
  • Extracts present in cow’s milk

Types of Food Freeze Dryers

There are three main types of food freeze dryers: rotary freeze dryer, multi-capacity freeze dryer, and tray freeze dryer. Rotary freeze dryers are usually used when working with liquids. Multi-capacity freeze dryers freeze small quantities of materials, while tray freeze dryers produce the driest product for long-term storage.

Advantages and Disadvantages of Food Freeze Dryers

Advantages:

  • Flavor Preservation: Products from a freeze dryer have a better taste and flavor compared to food items dried using traditional methods.
  • Food freeze dryers can serve as an alternative to canning low-acidic foods.
  • Due to moisture removal, the volume and weight of food items decrease, making it convenient for transportation.
  • Easy to use: Food items dried with a freeze dryer can be easily rehydrated with water and retain their nutritional properties with minimal damage.
  • Affordable prices for products produced using freeze-drying methods, resulting in a high return on investment in these processes.

Disadvantages:

  • High initial capital investment costs.
  • These machines have low production capacity, and significant investment is required for high-capacity production.
  • Relatively long production time for the products.
  • Due to the dry nature of the products, triple-layer packaging is necessary.

   In the above note, an attempt was made to provide useful information about food freeze dryers for the audience. Food freeze dryers are interesting and practical machines that will undoubtedly be heard more about in the future.