Vacuum quick cooling technology and its application

　　Vacuum quick cooling technology and its application

　　Vacuum quick cooling is a new technology developed in the last decade, which can be used for rapid cooling of various bakery products, cooked food products, fresh products, etc., as shown in Figure 1.

　　Figure 1: Application Scenario of Vacuum Quick Cooling Technology

　　The temperature of bread, pastry, prepared dishes and other cooked food products is generally 95-98℃, and the traditional method is natural cooling, which usually takes 3-5 hours to reduce to about 30℃, with a long process flow, large occupied space, easy breeding of bacteria, and not easy to guarantee the hygiene.

　　Large bakery enterprises use special cooling workshop, configured with extra-long stainless steel conveyor belt, although it realizes the flow operation, but the investment is large, energy consumption is high, and the process is still very long. As shown in Figure 2 below:

　　Figure 2: Belt-type baked goods cooling equipment

　　For this reason, enterprises with good conditions commonly use cold air room or chiller cooling, as shown in Fig. 3 and Fig. 4 below, and the cooling time can be shortened to more than 1 hour, but the cold air room and bakery workshop shall be constructed adjacent to each other and isolated, with large investment, and the contradiction between the processing capacity and the volume of the cold air room is also very prominent.

　　Figure 3: Baked food cooling in the cold air room

　　Figure 4: Cooked food cooling in chiller room

　　For high-value fresh products that need to be transported in the cold chain, such as flowers and vegetables, they need to be processed and packaged after harvesting, and then put into the air-conditioned warehouse to cool down to 3℃ and keep them for transportation. Due to the barrier of the outer packaging, the cooling time is generally more than 10 hours.

　　I. Principle of vacuum quick cooling

　　Vacuum quick cooling technology uses the physical property of low temperature evaporation and absorption of evaporation heat under negative pressure to realize the rapid cooling of goods, which is applicable to all foods and fresh products with high water content.

　　An atmospheric pressure is 1000 mbar, at this time the vaporization temperature of water is 100 ℃. If the air pressure drops, the vaporization temperature will gradually decrease. When the air pressure drops to 6 mbar, water will vaporize at 0°C, which means that water ice can be vaporized directly. This is shown in Figure 5 below:

　　Figure 5: Boiling point of water as a function of air pressure

　　The vaporization of water is physically known as a phase change and requires the absorption of a large amount of heat, the so-called heat of evaporation or phase change, which results in a rapid decrease in the temperature of the item to be cooled, as shown in Figure 6 below:

　　Figure 6: Relationship between pressure, boiling point and latent heat of vaporization of water

　　Based on this physical property of water, the cold items to be put into the special equipment, the use of vacuum pump pumping pressure, the cold items to be part of the water will be rapidly vaporized and absorb a large amount of heat, thus achieving rapid cooling.

　　According to different application scenarios, it can be divided into two cases. Cooked food from 100 ℃ down to room temperature, known as quick cooling. Fresh products from room temperature down to 2-3 ℃, known as pre-cooling.

　　Second, the basic structure of the vacuum speed cooler

　　According to the above principle, the basic structure of the vacuum speed chiller includes vacuum chamber (box), vacuum pump, condenser, control system and auxiliary equipment.

　　Vacuum chamber for the box structure, for bread and other bakery products, need to use stainless steel manufacturing, and the size of the box must match the size of the oven, a processing capacity of about 100kg. For fresh goods, generally use carbon steel manufacturing, specification size is usually larger, once can handle several tons of goods.

　　Vacuum pumps generally use rotary vane pumps or double screw pumps, according to the box volume size to calculate the specifications and number of vacuum pumps.

　　Condenser is also known as water trap. Water vapor flows through the condenser and condenses into water under the action of refrigerant, which can reduce the burden of vacuum pump and improve the working efficiency.

　　C. VC Compact Series Vacuum Speed Cooler for Baking

　　VC Compact series vacuum speed cooler is a new generation of products jointly developed by Yantai Equation Machinery Technology Co., Ltd. and Holland Weber Company. Designed according to the EU food machinery standard, it is specially used for the rapid cooling of all kinds of bakery products, cooked food, pre-prepared dishes, etc. It is suitable for large and medium-sized bakery food enterprises, cooked food chain enterprises and central kitchens.

　　In accordance with the EU food hygiene standards, the speed cooler is made of stainless steel, of which the vacuum chamber is made of 316L medical grade stainless steel. The interior of the box adopts the whole rounded structure, which is convenient for cleaning and leaves no hygienic dead corner. The vacuum pump adopts double screw pump of international first-line brand, with zero emission of dust and oil, and the equipment can be directly placed in the bakery.

　　The fully automatic control system adopts the technology of Dutch Weber Company, Siemens PLC and touch screen, which can easily set the cold parameters, control the cooling temperature and speed, and preset the cooling program.

　　Taking the VC10 Compact model as an example, it can process 100kg of bread at one time, and the whole cooling process is about 5 minutes, and it can work 6 times per hour with a processing capacity of 600kg.

　　Figure 7: VC Compact series food

Author：Yantai Equation Machinery Technology Co.