D-class cold storage is mainly used to store meat, aquatic products and products suitable for this temperature range;
J-class low-temperature cold storage is mainly used to store ice cream, ice cream, low-temperature food and medical supplies;
The quick-frozen warehouse is mainly used for special purposes such as quick-frozen food and industry. The temperature of fresh-keeping warehouse is generally (+2℃ ~+5℃).
Mainly used for the preservation of fruits and vegetables, dairy products, fresh eggs and fresh meat. Keep food at a low temperature, and the temperature is generally not lower than 0℃. Cryopreservation of food does not mean that the lower the temperature, the better, and not all foods can achieve good preservation effect at any low temperature. General food stored in fresh-keeping warehouse does not affect its internal organization. Preservation can keep the original flavor and freshness of food. At the same time, customers should not pursue too low storage temperature. The decrease of temperature will directly increase the initial investment and operation cost of equipment.
Fresh-keeping storage is a way to inhibit the activity of microorganisms and enzymes and prolong the long-term storage of fruits and vegetables. Fresh-keeping is the main way to keep modern fruits and vegetables fresh at low temperature. The fresh-keeping temperature range of fruits and vegetables is 0℃ ~ 65438 05℃. Fresh-keeping storage can reduce the incidence of pathogenic bacteria and the decay rate of fruits, and also slow down the respiratory and metabolic processes of fruits, thus achieving the purpose of preventing rot and prolonging storage period.
Features of fresh-keeping warehouse:
1, perfect original refrigeration unit, high efficiency and energy saving, excellent quality;
2. High-efficiency ceiling evaporator;
3. Advanced microcomputer control system and advanced control method (negative pressure parking);
4. High-quality double-sided color steel polystyrene cold storage plate with small floor space and good thermal insulation performance;
5. More than 20 years of cold storage design and installation experience, and a large and efficient technical team; 6. Advanced construction machinery and advanced installation technology;
7, professional construction team, each construction personnel have long-term experience in refrigeration engineering construction. The temperature of cold storage is generally (-15℃ ~- 18℃).
Cold storage refers to short-term or long-term storage of cold food and frozen food at different temperatures in cold storage. Mainly suitable for the storage of meat, aquatic products and other foods.
Generally speaking, the cold storage is to store the food with this demand in order to maintain its required temperature and quality. Because when the temperature drops below-15℃, the freezing rate of food is high, microorganisms and enzymes basically stop moving and growing, and oxidation is also very slow. Therefore, food can be preserved for a long time and has good cold storage quality.
In addition, refrigerated food also requires the temperature in the warehouse to be relatively stable, and excessive temperature fluctuation will cause food spoilage.
Polystyrene silo: The silo body is made of polystyrene foam plastic (EPS) as the interlayer and metal materials such as plastic-coated steel plate as the surface layer, which combines the superior thermal insulation performance and good mechanical strength of the materials. It has the characteristics of simple and quick assembly, long insulation life, simple maintenance, low cost, high strength and light weight, and is one of the best materials for cold storage.
Refrigeration function:
1, perfect original refrigeration unit, high efficiency and energy saving, excellent quality;
2. High-efficiency ceiling evaporator;
3. Advanced microcomputer control system and advanced control method (negative pressure parking);
4. High-quality double-sided color steel polystyrene cold storage plate with small floor space and good thermal insulation performance;
5. More than 20 years of cold storage design and installation experience, and a large and efficient technical team;
6. Advanced construction machinery and advanced installation technology;
7, professional construction team, each construction personnel have long-term experience in refrigeration engineering construction, after strict job training, show certificates. The so-called quick freezing refers to the method that when the average temperature reaches-18℃, food quickly passes through its maximum ice crystal formation area and freezes. Food will undergo various changes during freezing, such as physical changes (volume, thermal conductivity, specific heat, dry consumption, etc. ), chemical changes (protein denaturation, discoloration, etc. ), changes in cell tissue, biological and microbial changes, etc. The characteristic of quick-frozen food is to keep the original nutritional value, color and flavor of food to the maximum extent. In other words, in the process of freezing, it is necessary to ensure the maximum reversibility of the above changes in food.
Quick-freezing food has the following advantages:
(1) Avoid the formation of large ice crystals between cells.
(2) reduce the extravasation of intracellular water and reduce the loss of juice during thawing.
(3) The contact time of concentrated solute in cell tissue with food tissue, colloid and various components is obviously shortened, and the harm of concentration is minimized.
(4) The rapid lowering of food below the temperature of microbial growth activities is beneficial to resist the growth of microorganisms and their biochemical reactions.
(5) The food stays in the freezing equipment for a short time, which is conducive to improving the utilization rate of the equipment and continuous production.
Most foods begin to freeze when the temperature drops to-1℃, and most ice crystals form between-1℃ and -5℃. This stage is called the highest ice crystallization stage. Quick freezing can greatly shorten the freezing time at this stage and remove this part of heat as quickly as possible, which is of great significance to improve the quality of quick-frozen food.
Modified atmosphere storage at -35℃(+2℃/-2℃) in quick-freezing warehouse is an advanced new method for fruit and vegetable preservation. In essence, modified atmosphere storage is to increase the adjustment of gas composition on the basis of preservation. By controlling the temperature, humidity, carbon dioxide, oxygen concentration and ethylene concentration in the storage environment, the respiration of fruits and vegetables is inhibited and the metabolic process is delayed. Compared with ordinary cold storage, modified atmosphere storage can better maintain the freshness and commodity of fruits and vegetables, and prolong the storage period and sales shelf life.
Modified atmosphere storage can achieve the most suitable conditions for fruit and vegetable storage, and its effects are as follows:
1 Inhibit respiration, reduce the consumption of organic substances, and maintain the excellent flavor and aroma of fruits and vegetables.
2. Restrain water evaporation and keep fruits and vegetables fresh.
3. Inhibit the propagation of pathogenic bacteria, control the occurrence of some physiological diseases, and reduce the rate of fruit decay.
4. Inhibit the activity of some after-ripening enzymes, inhibit the production of ethylene, delay the aging process of after-ripening, keep the fruit hardness for a long time, and have a long shelf life.
Storage of fruits and vegetables in low oxygen environment can inhibit the growth of mold and the generation of diseases and pests, and avoid the generation of substances harmful to human body.
Compared with ordinary cold storage, modified atmosphere storage has higher requirements on building structure and equipment installation. In addition to good thermal insulation performance, it is also required to strictly control the gas exchange inside and outside the warehouse, add airtight layers and doors, and a series of controlled atmosphere equipment. In terms of storage and preservation technology, it is also higher than ordinary cold storage.
Problems needing attention in modified atmosphere storage and application of fruits and vegetables;
1. controllable atmosphere storage building
Modified atmosphere storage is developed on the basis of cold storage of fruits and vegetables. On the one hand, it has many similarities with fruit and vegetable cold storage, on the other hand, it is very different from fruit and vegetable cold storage, mainly in the following aspects:
(1) The volume of controlled atmosphere storage. Take 30 ~ 100 t as a bay.
(2) Modified atmosphere storage must have good air tightness. Because the required gas components should be formed in modified atmosphere storage, and the set indexes should be maintained for a long time during the storage of fruits and vegetables to reduce the gas exchange inside and outside storage, modified atmosphere storage must have good air tightness.
(3) The safety of modified atmosphere storage. Because the controlled atmosphere storage is a closed cold storage, when the temperature in the storage rises and falls, its gas pressure also changes, which often leads to pressure difference inside and outside the storage. For this reason, a balance bag and a safety valve are usually installed on the controlled atmosphere storage to limit the pressure within the designed safety range.
(4) In general, the modified atmosphere warehouse should be built as a single-story building. When fruits and vegetables are transported, stacked and stored in the warehouse, the ground will bear a great load. The building height of large-scale controlled atmosphere storage is generally about 6 m.
2. Configuration of refrigeration equipment and temperature sensor in controlled atmosphere storage.
(1) Refrigeration system: The refrigeration equipment in the controlled atmosphere warehouse mostly adopts piston single-stage compression refrigeration system, and the refrigerant is R22, and the cooling mode in the warehouse can be direct evaporative cooling.
(2) Configuration of temperature sensor: During the operation of a well-designed controlled atmosphere warehouse, the temperature difference in the warehouse can be less than 0.5℃.
3. Main controlled atmosphere equipment and auxiliary equipment of controlled atmosphere warehouse
(1) nitrogen generator. At present, there are two main nitrogen generators for controlled atmosphere storage: adsorption and separation of carbon molecular sieve nitrogen generator and membrane separation hollow fiber membrane nitrogen generator.
(2) CO2 remover: CO2 remover can be divided into two types: intermittent (usually called single tank machine) and continuous (usually called double tank machine).
(3) ethylene remover. There are two main methods to remove ethylene: potassium permanganate oxidation and high temperature catalytic decomposition.
(4) Humidifying device. Humidity mixing humidification, ultrasonic humidification and centrifugal atomization humidification are three commonly used humidification methods in modified atmosphere storage.
4. Reasonable use and management of controlled atmosphere storage
(1) Use space reasonably and effectively.
(2) Fast forward and fast out
(3) Good air circulation
The temperature of controlled atmosphere storage (+2℃ ~+5℃) cold storage is generally -22 ~-25℃.
The temperature of the low-temperature warehouse is below -20℃, because seafood and cold drinks need to be below -20℃ to avoid deterioration. If they don't reach -20℃, the flavor of seafood will be completely different. The characteristic of low-temperature storage is that the instruments are put into the cold storage step by step from time to time. After a period of time, the temperature of the cold storage reaches -20℃. There is no special requirement during this period, but the storage temperature is strict. -18℃~-23℃ is a typical low-temperature storage, but the storage temperature of cold drinks containing dairy products should be set at -20℃~-28℃
Most professional refrigeration personnel think that the lower the temperature of the freezer, the better, and the shelf life of frozen items can be extended, but sometimes it is determined according to the required storage temperature of various items. For fruits and vegetables, low storage temperature can easily lead to frostbite, while meat products can be stored at low temperature for a long time. However, from the point of view of economy and energy, the choice of storage temperature should be based on longer storage time. For example, meat can be stored at-18 C for 4-6 months and at-23 C for 8- 12 months. Since meat will reach consumers within 5 months, it is sometimes considered whether to choose the storage temperature of-23 C.
Precooling method
Air precooling: air precooling method has the advantages of easy adjustment of air temperature and humidity and low equipment cost.
Vacuum precooling: according to the physical property that the boiling point of water decreases with the decrease of pressure, the precooled food is put into a vacuum tank for vacuum pumping. When the pressure drops to a certain value, the water on the food surface begins to evaporate, absorbing the latent heat of vaporization, and the food itself is cooled by vacuum precooling.
Water precooling: the method of lowering the cooled food from the initial temperature to the required final temperature with water is called water precooling.
Characteristics of low temperature storage:
1, perfect original refrigeration unit, high efficiency and energy saving, excellent quality.
2. High-efficiency ceiling evaporator;
3. Advanced microcomputer control system and advanced control method (negative pressure parking);
4. High-quality double-sided color steel polystyrene cold storage plate with small floor space and good thermal insulation performance;
5. More than 20 years of cold storage design and installation experience, and a large and efficient technical team;
6. Advanced construction machinery and advanced installation technology;
7, professional construction team, each construction personnel have long-term experience in refrigeration engineering construction, after strict job training, show certificates.