Food freeze-drying principle
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Shape, color and taste are unchanged. In the process of sublimation, the water is gradually removed from the surface by the molecular state, without destroying the structure of the structure, without taking away the natural pigments and aromatic substances, so the shape, color and taste are almost the same as the fresh products.
Good rehydration. During the sublimation process, the ice crystals in the food form micropores like sponges, so that after the lyophilized food is immersed in water, it can quickly recover from water and water, which is like fresh food.
Easy to eat. Because it has been washed and cut, and the rehydration is extremely fast, it is extremely convenient to eat or cook directly.
â—‹ Fruits: apples, peaches, pears, apricots, red dates, strawberries, bananas, pineapples, cantaloupes, etc.
â—‹ Meat: beef, lamb, pork, chicken, snake meat, turtle, etc.
â—‹ Aquatic products: fish fillets, shrimp, crab meat, cuttlefish, silver fish, etc.
â—‹ Convenient foods: instant noodle accessories, beef noodles, meatballs, soups, pet food, etc.
â—‹ Instant beverages: coffee, milk, soy milk, juice, royal jelly, etc.
â—‹ Seasonings: Various seasonings for cooking.
â—‹ Medicines: antler, deer blood, medlar, medlar, earthworm, ginseng, Codonopsis, angelica, rhubarb, various health foods, etc.
In China, the sales of fruit and vegetable foods are generally sold directly after harvesting, and then purchased by consumers to be cleaned and eaten, and the remaining inedible parts are transported in a centralized manner. This consumption method is not only time-consuming and laborious, but also increases duplication. Transportation treatment, and polluting the environment, does not meet the food hygiene requirements, it is clear that this is increasingly incompatible with modern, fast-paced, highly civilized, developed society.
In the 1970s, developed countries have realized the processing of fruits and vegetables in factories. By the early 1980s, they had developed into large-scale production. After harvesting, the fruits and vegetables are selected, removed from the roots, washed, pre-cooled, packaged, and refrigerated and transported into the refrigerated shelves of the supermarket. The consumers buy them and put them in the refrigerator for refrigerating. They can be cooked directly when eating, without cleaning. This kind of consumption has undoubtedly many advantages compared with traditional consumption methods in China:
The centralized treatment of the factory will inevitably bring about a profound change in agriculture. The processing of agricultural and sideline products will inevitably develop towards the direction of factoryization, scale and standardization; it can provide consumers with agricultural and sideline products that fully meet the food hygiene standards, and the freshness is greatly improved; Greatly reduce urban waste, reduce environmental pollution; reduce redundant transportation; consumers save time and effort to meet fast-paced lifestyle requirements.
The Chinese government has always strongly advocated the "vegetable basket" project, especially in the period of China's economic development, the factory processing of fruits and vegetables has been highly valued by governments at all levels, and the marketing of clean vegetables has become an inevitable trend. In the next few years, there will be greater development.
In addition, as the export of fresh fruits and vegetables is restricted by pre-cooling and fresh-keeping technology, it is increasingly unable to meet the growing international trade requirements.
The concept of pre-cooling and cooling is different. The so-called pre-cooling refers to the process of rapidly decreasing the food from the initial temperature (about 30 ° C) to the required end temperature (0 to 15 ° C). The rapid cooling process before cooling and rapid freezing is called pre-cooling; while cooling is The food temperature drops to a higher temperature than the freezing temperature, and cooling is mainly applied to the following types:
Cool and store. It is used for high-temperature refrigeration (fresh storage) of fruits, vegetables and other foods in order to preserve freshness and prolong its storage time.
Pure cooling: A temperature that is completely used for certain liquids. In pure cooling, the temperature of the fluid drops without changing state, that is, it only absorbs its own latent heat, such as cooling beer, seasoning, milk, water, wine, sodium hydroxide solution, salt water, and the like.
Precipitation cooling: generally refers to a multiphase liquid, that is, one or more liquid components solidify and precipitate upon cooling. Such as treatment of oil, paraffin, zinc gangue, sulfur dioxide, pharmaceutical plants to recover acetone, frozen concentrated seawater, fruit juice, salt water, wine, etc., precipitated tartar and some chemical treatment methods.
Solidification cooling: Solidification cooling refers to the conversion of a substance into a liquid to solid state, such as margarine, vegetable oil, animal oil, palm oil, chocolate, stearin, gel, and the like.
After harvesting fruits and vegetables, due to the influence of ambient temperature, the surface temperature is generally high, combined with its strong respiration, while the composition is constantly changing, the amount of heat released is continuously increasing, and the temperature will continue to rise. The higher temperature causes the breathing to accelerate the continuous release of heat, the water evaporates in a large amount, the nutrients and water of the body are continuously consumed, the rapid wilting and the freshness are reduced, and the shelf life is greatly shortened.
In order to extend the shelf life of fruits and vegetables, reduce their consumption and various losses in circulation, and enable consumers to obtain high-quality and clean fruits and vegetables, a series of post-harvest processing must be carried out at the factory, such as selection, Pre-cooling process is even more essential when it comes to tigen skin leaves, cleaning pre-cooling, water filtration, packaging, etc.
Principle of vacuum precooling method
Common pre-cooling methods are air pre-cooling, water pre-cooling, ice water pre-cooling and vacuum pre-cooling.
The water was heated to 100 ° C under normal pressure to start boiling, and the temperature was frozen to 0 ° C. When the pressure is lowered, the boiling point of water is also lowered by 613.28 PA and the boiling point is 0 °C. According to the physical property that the water is lowered with pressure to lower its boiling point, the pre-cooled food is placed in a vacuum tank to evacuate, and when the pressure reaches a certain value, the moisture on the surface of the food begins to evaporate. The advantages of the vacuum pre-cooling method are:
The surface of the food contains a lot of water, and its water vapor pressure also changes due to its high temperature. The evaporation of water is relatively slow under atmospheric pressure, and the evaporation rate is accelerated by the resistance in the vacuum state, so the food cooling rate is fast. When the initial temperature of the food is 35 °C and 3 °C, it takes about 20 minutes; in the vacuum tank, the pressure is uniform at each point, so the food is pre-cooled evenly; the cooling capacity is large, including the loading and unloading time can be run twice per hour; pre-cooling is clean and hygienic, No cross contamination.
Vacuum precooling device
The vacuum pre-cooling device is divided into four types: batch type, continuous type, mobile type and spray type. Intermittent vacuum pre-cooling unit for small-scale production, continuous vacuum pre-cooling unit for large-scale processing plants, mobile vacuum presets due to its integration, flexible assembly in the car, can be used off-site, spray-type device for Fruits and roots of foods with small surface moisture are pre-cooled. The vacuum pre-cooling device is mainly composed of a vacuum tank, a water trap, a vacuum pump, a refrigeration unit, a loading and unloading mechanism, a control cabinet and the like.
Vacuum tank: The vacuum tank is generally made of Q235B steel or I-CY18M9T1 stainless steel. The small vacuum tank adopts a cylindrical shape and is reinforced with reinforcing ribs. All the welded joints are grooved and subjected to X-ray inspection. When using Q235B material, the inner side should be treated with anti-corrosion treatment, and the outer side should be sprayed with high-strength anti-rust material. The electric door or the manual door is applied to the tank door, and the sealing performance of the processing and the fine washing system is good. A rail mechanism is arranged at the bottom of the vacuum tank to facilitate loading and unloading of materials. The vacuum tank is equipped with a drain and a cleaning system to ensure a clean interior.
Water trap: The water trap, also known as the cold tank, has the same function as the water trap in the vacuum freeze-drying device, that is, it is used to concentrate the moisture in the air to prevent moisture from entering the vacuum pump and emulsifying the oil to damage the vacuum pump assembly. The water trap of the vacuum precooling device is generally designed in a cylindrical structure.
Vacuum pump. The vacuum pump is a key component of the vacuum system. It should be determined according to the vacuum pre-cooling device of different specifications and the specific conditions, such as the rotary vane vacuum pump set and the water ring booster pump set.
Refrigeration unit: For small batch or continuous vacuum pre-cooling unit, water-cooled or air-cooled Freon condensing unit should be selected, and large unit should adopt ammonia system. For the hotter climate, the Freon water-cooled unit is generally selected, and the refrigeration unit is assembled with a vacuum pump unit and a control cabinet on a common chassis.
Loading and unloading mechanism. The loading and unloading mechanism shall be determined according to the user's loading and unloading mode. The single package loading and unloading shall be carried out by conveyor belt or rail, and the overall loading and unloading shall be carried out by battery forklift or hydraulic propeller. The control system is equipped with manual and automatic system engineering, and when any one system fails, it is operated by another system.
Freeze-dried vegetables are vegetables that are quickly frozen and then sent to a vacuum vessel for dehydration. The vegetables made by the freeze-drying process not only maintain the color, aroma, taste and shape of the vegetables, but also preserve the vitamins, proteins and other nutrients in the vegetables to the utmost extent. Just add the water to the vegetables and return to fresh vegetables within a few minutes. Freeze-dried foods should not be refrigerated. As long as they are packed in a sealed package, they can be stored, transported and sold at room temperature for a long time. Since this food has only 5% water content, it is of good quality and light weight, which can greatly reduce its operating expenses.
Vacuum freeze-dried food production started late in China. The large-scale freeze-dried food production line did not appear until the late 1980s, and the equipment was imported. From the perspective of domestic and international market demand, the development prospects of China's freeze-dried food industry are extremely broad.
In the early stage of the development of freeze-dried food, due to low yield and high price, it was limited to special staff such as aerospace, ocean sailing, polar expedition, and mountainous work. After entering the 1990s, the variety and quantity of freeze-dried foods have grown rapidly, not only for most vegetables, but also for fruits, meat, soy milk, juice, honey, etc. Nowadays, in the food industry raw materials, cooking materials, native products, condiments, supplements, beverages, snack foods, etc., there are increasing lyophilized products.
Nowadays, freeze-dried foods have developed to a higher level, such as freeze-dried instant noodles, not only seasonings are lyophilized, but also noodles are lyophilized, and a sufficient amount of freeze-dried vegetables are combined with nutrition. Freeze-dried soup, with lyophilized seasonings, vegetables, eggs and other reasonable mix, ready to eat, convenient and delicious. Powder vegetables, freeze-drying technology combined with ultra-fine pulverization technology, making various vegetables into ultra-fine powder that is easily digested and absorbed, adding noodles, biscuits, cakes, sweets, beverages, etc., to make a new generation of health food, suitable for young children. And the elderly. Granulated vegetables, Japanese people mix lyophilized rapeseed, spinach, radish leaves, celery, peas, carrots, pumpkin, snow stalks, etc. into granules. This vegetable granule is rich in natural nutrients such as chlorophyll, carotene, various vitamins and minerals, and has a delicious taste. It is suitable for patients or malnourished people.
According to the statistics of the State General Administration of Customs and the State Administration of Commodity Inspection, in the 1990s, the export volume of dehydrated vegetables in China increased by 30% every year. The export volume of dehydrated vegetables in China accounted for about 2/3 of the world's total output. The price of freeze-dried vegetables in the international market is 4 to 6 times that of hot-dried and dehydrated vegetables, and is becoming a staple food for international trade. The international market freeze-dried food is in short supply, but the domestic freeze-dried food industry is still in the early stage of development, and the output is still very low. Therefore, China should speed up the development of freeze-dried foods, and carry out deep processing and value-added of rich agricultural products, and earn foreign exchange through export. At present, the freeze-dried foods produced in China mainly include: soup, shrimp, semi-finished products (such as egg powder), health products (such as freeze-dried ginseng) and instant noodles (such as dehydrated vegetables in diced noodles, diced meat, etc.), and the annual output is insufficient. 3000 tons. According to experts' prediction, by 2010, only one of China's high-grade instant noodle accessories will require about 40,000 tons of freeze-dried food, plus various fast-food ingredients, soups, beverages, etc., and the annual consumption of freeze-dried food will exceed 100,000 tons. . The huge demand for freeze-dried food at home and abroad provides an opportunity for China to develop the freeze-dried food industry.
To develop China's freeze-dried food industry, we must develop food freeze-drying equipment in China. China is a large agricultural country with abundant edible resources of vegetables and meat. It processes such food resources into freeze-dried foods. For example, domestically produced freeze-drying processing equipment is only 1/4 of the imported equipment. At the same time, we will seize the opportunity of the development of the western region and develop large-scale food exports such as freeze-dried vegetables and freeze-dried beef jerky. This is an export-oriented foreign exchange project with promising prospects, high profits and low risks. For a long time, China's agricultural and animal husbandry products have been lingering in the stage of exporting raw materials or primary processing, giving people a general feeling of low technical content. Through the development of freeze-dried foods, China will increase the grade of food exports and obtain higher added value. Although the production cost of freeze-dried food is high, the sales price is higher and the benefits are very good.
Do you know that food is freeze-dried?
In the European, American and Japanese markets, you can see a wide range of freeze-dried foods. These are made by vacuum freeze-drying technology. Vacuum freeze-drying technology is a high-tech dehydration technology that protects food, food, and quality. Freeze-dried vegetables, fruits, meat, aquatic products, spices, etc., in addition to applications in aerospace, military, mountaineering, tourism, exploration, mining and other industries, have now entered restaurants and families. From the overall development trend, equipment energy consumption is getting lower and lower, and the production cycle is getting shorter and shorter. The price of freeze-dried food in the international market is 4-6 times that of hot air-dried and dehydrated food, and it is becoming a hot commodity in international trade.
The lyophilized food is obtained by rapidly freezing the fresh food and then feeding it into a vacuum vessel for dehydration. Under vacuum conditions, the moisture is raised from the solid ice to the gas, thereby dehydrating and drying the material. The food made by the freeze-drying process not only has color, aroma, taste and shape, but also preserves vitamins, proteins and other nutrients in the food. Before eating, it will be processed slightly and will be restored to fresh food within a few minutes.
Freeze-dried foods should not be refrigerated. After being sealed and packaged, they can be stored, transported and sold at room temperature for a long time. Since lyophilized food has 5% water content, good quality and light weight can greatly reduce its operating expenses. For example, after the tomato sauce is processed by lyophilization, 1000 g of fresh tomato sauce can be processed into 320 g of lyophilized ketchup powder, which is restored to ketchup with the addition of water. Loved by people. Today, freeze-dried tomato sauce has become a replacement for ketchup.
In the production of vacuum freeze-dried food, there are generally processes such as material selection, cleaning, cutting, blanching, and sterilization. It should remove the insects and eggs attached to the roots and leaves and the sediment, use magnetic fields to remove metal debris, use static electricity to remove foreign matter such as hair and scales, and avoid excessive heating. No matter whether it is cooking or impregnating, it must be done according to the process requirements. It is possible to produce high quality freeze-dried foods after good treatment. The pre-treated items are quickly frozen, and the faster the freezing, the smaller the crystals in the articles, and the less damage to the structure of the articles. The freezing time is short, and the protein does not undergo a qualitative change under the action of aggregation and concentration.
The food after quick freezing must be vacuum sublimated and dried quickly, and the vacuum is required to quickly reach the sublimation pressure, and the sublimation heat energy is supplied in time to maintain the sublimation temperature, and radiant heating is generally used.
The freeze-dried food is porous, and the surface of the tissue is enlarged by 100 to 150 times. Therefore, the chance of contact with oxygen increases. When returning to normal pressure from low temperature and low pressure, it should be carried out in a nitrogen atmosphere. The pulverization and packaging should be carried out at a relative humidity of 30 to 40% and a temperature of 25 ° C or less. In order to keep the dry food below 5% water, desiccant should be placed in the package and a small amount of moisture should be adsorbed. Packaging materials should be selected for poor gas permeability, high strength, and good color.
Freeze-drying technology can process a variety of vegetables, fruits, fish, instant noodles, spices and coffee, tea, Chinese medicine and so on.
Taking the J DG type as an example, the freeze-dried food production line includes pre-treatment, quick freezing, sublimation drying and packaging. In order to create normal working conditions for the quick-freezing warehouse and sublimation drying warehouse, it is necessary to support the refrigeration system, heating system, equipment monitoring system and material transportation system, as well as steam boilers and circulating water. The most critical equipment for the lyophilization line is the sublimation drying chamber, which is a large horizontal cylinder with a multi-layer heater that is inserted between the multi-layer heating frames. The skips are transported along the sky rail from the pre-treatment room (loading), through the quick-freezing (freezing) and drying bins (sublimation drying and dewatering) to packaging (unloading), and then return to the pre-treatment room along the sky track. This recycling of materials is very convenient, hygienic and safe. The water vapor trap is arranged on both sides of the heating rack (or independent of the warehouse), and the heating plate on the heating rack is subjected to special surface treatment to transfer heat energy to the material in a radiative manner (sublimation heat). The water vapor trap can quickly capture the material. The water vapor that is sublimated. It takes only 5 minutes to transport the material of a dry warehouse from the quick-freezing warehouse to ensure that the frozen material does not melt.
China is a large agricultural country with rich vegetables, meat and aquatic resources. It processes such food resources into freeze-dried foods and uses domestically produced freeze-drying processing equipment at a price of only 1/4 of imported equipment. Seizing the opportunity of the development of the western region and developing the export of frozen foods such as freeze-dried vegetables and freeze-dried beef jerky is an export-oriented foreign exchange project with promising prospects, high profits and low risks. For a long time, China's agricultural and animal husbandry products have been lingering in the stage of exporting raw materials or primary processing, giving people a general feeling of low technical content. Through the development of freeze-dried vegetables and meat, etc., we will improve the grade of China's export foods and obtain higher added value (100-300 yuan per kilogram of freeze-dried vegetables). There are some local famous and special products all over the country. After being processed by freeze-drying process, they become the famous and special products of high-grade dehydration.
The international market freeze-dried food is in short supply, and the domestic freeze-dried food industry is still in the early stage of development, and the output is still very low. However, it has attracted a large number of foreign buyers to buy in the Chinese market. This has the external cause of the shortage of freeze-dried food in the international market, and the internal cause of the low production cost of freeze-dried food in China. China should make full use of the opportunity of the large-scale development of the western region, vigorously develop freeze-dried foods, and deepen the value-added of agricultural and sideline products in the western region and earn foreign exchange through export. At present, the freeze-dried food produced in China mainly includes: soup, shrimp, semi-finished products (such as egg powder), health products (such as freeze-dried ginseng) and instant noodles (such as dehydrated vegetables and diced meat in instant noodles), etc. Less than 3,000 tons. According to experts' predictions, in 2010, only one of China's high-grade instant noodle accessories, about 40,000 tons of freeze-dried food, plus a variety of fast food ingredients, soups, beverages, etc., the annual consumption of freeze-dried food will exceed 100,000 tons. The huge demand for freeze-dried food at home and abroad provides a great opportunity for the development of China's freeze-dried food industry.
Although the production cost of freeze-dried food is high, the sales price is higher and the benefits are very good. Last year foreign purchase price (RMB·Yuan/freeze-dried product·kg): beef 130, mutton 180, carrot 130, green onion 140, 枸æž240 yuan, spinach 160, lily 200, mushroom 260, strawberry 180, onion 130, green pepper 190 , red pepper 210, garlic tablets 60-100, garlic seedlings 130. To develop China's freeze-dried food industry, China's food freeze-drying equipment must be developed. The Lanzhou Institute of Modern Physics of the Chinese Academy of Sciences has used decades of technology development for accelerators and aimed at the international advanced level. In 1993, J DG series food freeze dryers were developed, and its technical performance is leading domestically. Since 1996, more than ten production lines have been built in Shandong, Henan, Shaanxi, Gansu and other places, and 32 sets of JDG60, 90, 100F and 200F freeze dryers have been assembled. At present, freeze-dried shallots, freeze-dried yam, freeze-dried strawberries, etc., have been built and continue to receive orders from foreign companies.
The larger the scale of processing freeze-dried food, the lower the cost and the higher the benefit. It is estimated that each year, 100 pieces of garlic, carrot, and beef can be processed in 100 days. The freeze-drying area requires 200 square meters of production line, and the production cost of more than 6 million yuan. The annual output value can be more than 30 million yuan. Profits and taxes are above 30%, about 10 million yuan.