Fruit and Vegetable Vacuum Freeze Dryer

The fruit and vegetable vacuum freeze dryer consists of two main parts: the main unit and auxiliary units. These components work together to ensure a stable and efficient freeze-drying process. The core structure is divided into six modules, all made of food-grade 304 stainless steel or aluminum, meeting food hygiene standards. Some high-end models use 316L stainless steel for parts in contact with food, meeting pharmaceutical-grade cleanliness requirements:

1. Freeze-drying chamber: The core working area, divided into a material compartment and a condensation compartment. It adopts a space-efficient rectangular sealed design, capable of withstanding positive and negative pressure. The seal uses high-temperature and low-temperature resistant silicone rubber, and the insulation layer uses closed-cell elastic thermal insulation material. The chamber is equipped with shelves (special hollow plywood, high strength, and good sealing) for placing fruits and vegetables. The top layer has a heat radiation compensation plate to ensure uniform temperature inside the chamber. An aviation-grade acrylic observation window is located on the side for real-time monitoring of the freeze-drying process. A drain outlet is located at the bottom. The chamber also includes auxiliary components such as a pressure gauge, temperature measuring resistor, and safety valve to ensure operational safety and process control.

2. Refrigeration Unit: The "cooling core" of the equipment. Mainstream models employ a cascade two-stage compressor, capable of achieving ultra-low temperatures of -70℃ in the cold trap, with a water capture capacity of 4-15 kg/batch. It rapidly captures water vapor generated during sublimation, preventing disruption of the vacuum environment, reducing defrosting frequency, and improving production continuity. It is suitable for processing high-moisture fruits and vegetables (such as cucumbers and watermelons). Some models can optimize pre-freezing temperatures based on food characteristics, addressing issues such as color preservation and odor control in heat-sensitive fruits and vegetables.

3. Vacuum Unit: Crucial for maintaining a high vacuum environment. Equipped with a corrosion-resistant vacuum pump, it can stably maintain an ultimate vacuum of ≤5Pa. A differential pressure valve (gas ballast valve) prevents oil backflow, avoiding contamination of raw fruit and vegetable materials. It also features rapid vacuuming capabilities, shortening the drying cycle and improving production efficiency. Suitable for processing high-end fruits and vegetables, medicinal herbs, and other materials requiring high purity. The vacuum pump exhaust port is equipped with an oil mist collector to prevent exhaust gas pollution.

4. Heating Unit: Responsible for precise temperature control, employing a silicone oil circulating heating medium. Compared to traditional electric heating, this improves temperature control accuracy by 50%, ensuring a shelf temperature difference of ≤1℃. Some high-end models utilize zoned temperature control technology, controlling the temperature difference within 0.5℃. It can precisely adjust the heating curve according to the characteristics of different fruits and vegetables (leafy vegetables, berries, root vegetables), avoiding nutrient loss or morphological damage caused by localized overheating. Simultaneously, heat recovery technology can be used to recover and reuse heat from the sublimation stage, reducing energy consumption.

5. Circulation and Pneumatic System: The circulation system is responsible for the circulation and delivery of silicone oil and refrigerant, ensuring uniform and stable temperature and vacuum levels. The pneumatic system controls the automatic locking of the chamber door cylinders, ensuring the chamber's airtightness and preventing vacuum leakage during freeze-drying, thus improving equipment operational stability.

6. Intelligent Control System: The "brain" of the equipment, equipped with an industrial-grade PLC and touch screen, supports the storage of 40 sets of process recipes, and can monitor and record temperature and vacuum curves in real time, meeting GMP audit traceability requirements; some models support remote monitoring via mobile APP and export of freeze-drying curves via USB flash drive, eliminating the need for 24-hour on-site personnel, reducing labor costs, and can also optimize freeze-drying curves through AI algorithms to achieve automatic adjustment of process parameters, improving product stability and production efficiency.

Production Process Flow

The core technology of fruit and vegetable freeze dryers is based on the three-phase equilibrium principle of water. When the pressure is below the triple point pressure of water (approximately 611 Pa), ice can directly sublimate into water vapor without passing through a liquid state.
The complete freeze-drying process consists of three stages:

1. Pre-freezing stage

Fresh fruits and vegetables are rapidly frozen at temperatures ranging from -30°C to -50°C. This converts free and bound water within the cells into solid ice crystals, preventing ice crystal growth and damage to cell structure.

Impact of freezing rate: Rapid freezing (10-50°C/min): Forms fine microcrystals, causing minimal cell damage and resulting in high-quality products. Slow freezing (1°C/min): Forms coarse ice crystals, which is beneficial for sublimation drying but may damage cell structure.

2. Primary Drying (Sublimation Stage)

In a high vacuum environment of ≤5 Pa, solid ice crystals sublimate directly into water vapor without passing through a liquid state. This stage requires precise control of the partition temperature (typically -40℃ to +30℃) to allow the ice crystals to sublimate slowly, preserving the porous structure of the fruits and vegetables.

3. Desorption and Drying (Desorption Stage)

Heating to +20℃ to +60℃ removes bound water tightly connected to the solid material, reducing the final moisture content to 1%-4%.

Drying endpoint determination criteria:

Material temperature and heating plate temperature tend to match and remain consistent for a period of time.

Vacuum degree in the drying chamber becomes basically stable.

Cold trap temperature returns to its no-load value.