One does not require rehydration, such as freeze-dried fruit slices, fresh milk, or yogurt sugar. The other is for rehydration, such as freeze-dried powder, rice, porridge, vegetable bags, etc.
Compared with food that does not require rehydration, processing food that requires rehydration is more complicated. To avoid internal ice piercing the tissue, some accessories such as salt, sugar, milk powder, etc., are often added to protect the cell tissue.
Rehydration type freeze-dried food has the characteristics of lightweight, fast rehydration, excellent color, aroma, and taste. Compared with traditional dried and puffed food, freeze-dried food's nutritional and physical properties are better. Compared with canned food, freeze-dried food is easier to preserve, less prone to qualitative change, and has much lower costs in terms of transportation and storage, which has become the focus of many enterprises.
However, the disadvantages of the high cost of freeze-drying equipment, long freeze-drying cycle, and small relative output have always been the difficulties that this technology cannot be widely promoted. In short, freeze-dried food retains the nutrients and physiologically active ingredients of food raw materials to the greatest extent, maintains the freshness, shape, color, and taste of the food, and greatly prolongs the shelf life.