What is Freeze Drying?
Freeze drying, also known as lyophilization, has been applied for many years in many different sectors, such as food, medicine, and chemistry. As the name suggests, freeze drying is a type of drying method, and the water in the product processed in this way is removed.
Food drying is one of the oldest methods of preserving food and is used extensively today to extend the shelf life of foods. Whichever drying method (sun drying, oven dryers, hot air drying, vacuum microwave dryers, spray drying, freeze drying, etc.) is used, the basis of drying is the removal of water, thus preventing the growth of microorganisms such as bacteria, mold, and yeast. Thanks to the inhibition of the development of microorganisms, the easy deterioration of foods is prevented and the shelf life of foods is extended.
Freeze drying is a drying method in which the water in the food is first frozen, the pressure is reduced, and the water in the solid phase is removed at low temperature by passing it directly to the gas phase (transition from solid to gas phase is called sublimation) without going back to the liquid phase.
Freeze drying takes place in three stages:
1. Freezing: Products are frozen under atmospheric pressure.
2. Primary drying (sublimation): In this stage, called the sublimation stage, free water is removed.
3. Secondary drying (adsorption): In the adsorption stage, which is the last step of freeze drying, ionically bound water molecules are removed.
Advantages of Freeze Drying Method
Freeze-dried foods are of superior quality compared to foods that have been dehydrated by other methods. The main reason for obtaining high quality products with freeze drying is that the drying process takes place at a much lower temperature than with other methods. Freeze drying preserves flavor, color, and appearance while minimizing thermal damage to heat-sensitive micronutrients such as water-soluble vitamins (e.g. vitamin C). It has been shown by scientific studies that processing foods at high temperatures for a long time significantly reduces the vitamin C content of the food.
Nutrition facts: Freeze drying causes little damage to the micronutrients in the food. About 95% of the nutritional value is preserved in freeze-dried products. In other methods, such as dehydration, the high heat used during the process causes some vitamins and minerals in the food to deteriorate, and the nutritional value can be preserved by around 60% at most.
Taste and appearance: The taste and appearance of freeze-dried products are similar to their fresh form. Freeze drying does not shrink or harden food, retaining its aroma, shape, and flavor. Rehydrated freeze-dried food products are similar to their fresh forms as well.
Shelf life: Freeze-dried products have a very long shelf life. When the product is properly stored, the food can last between 15 and 25 years. The shelf life of heat-dried or frozen foods is 2 years at the most.
Weight and space: After taking water from food, they become very light, easy to carry and transport.
Freeze-dried foods are preferred because they preserve their nutritional value, have a very long shelf life, are light and portable, and are easy to prepare. Although plant-based foods are mostly preferred with the freeze drying method, a wide variety of foods can be dried with this drying method. Many of the foods in the following food groups can be freeze dried:
Fruits and fruit purees: strawberry, raspberry, blueberry, blackberry, mulberry, chokeberry, apple, orange, lemon, kiwi, pear, peach, banana, plum, fig, apricot, pineapple, avocado
Vegetables: Garlic, onions, carrots, beets, broccoli, leeks, spinach, okra, peas, brussels sprouts, cauliflower, peppers, zucchini, tomatoes, corn, celery, beans
Spices: Mint, thyme, sage, basil, lavender, ginger, radish, basil
Meats: Chicken, ham, fish