Discussion on storage and fresh-keeping packaging

Discussion on storage and fresh-keeping packaging technology of grapes (V)

"7.2 mechanical refrigeration

mechanical refrigeration is carried out in a permanent storage building under good heat insulation conditions. There is a mechanical refrigeration device inside, which can create suitable storage conditions for fruits through manual adjustment and control

1. Disinfect the warehouse and packaging and disinfect the warehouse and packaging first before collecting and packaging precooled fruits. Refer to section 5.1.2 of this book for specific methods

2. After storage and stacking of berries, they can be stored after strict classification and precooling. The storage volume should not be too large at a time. Generally, the storage volume at the end of February this year should be less than 10% of the total storage volume. For example, for a cold storage with a storage capacity of 150 tons, the one-time storage capacity should be controlled below 12 tons

the storage of fruits in the warehouse should be reasonably arranged, so as not to waste space, but also conducive to management and ventilation. Therefore, in order to maintain the smoothness and circulation of air flow in the storehouse, the reserved channel or clamp should not be perpendicular to the direction of air flow. A gap of 10---15cm should be left between the fruit basket and the storehouse wall, a ventilation gap of 5---10cm should be left between the stack and the ground, and an appropriate gap should also be maintained between the fruit box (basket) and the fruit box

3. The management of grape cold storage the management of cold storage is mainly the regulation of temperature, humidity and ventilation

(1) temperature control. The suitable temperature for storage of grape berries is -1---0 ℃. During storage, the storage temperature should be kept relatively constant to avoid fluctuations, and should not be high or low, otherwise it will stimulate the increase of fruit respiratory intensity, accelerate fruit aging and browning of fruit stems and ear stems. In addition, large temperature fluctuations will also cause condensation and aggravate decay. If the temperature is too high, a large number of berries will be hot rotten, and if the temperature is too low, it is easy to form chilling injury and freezing injury of berries. When the temperature is lower than -1 ℃, the fruit stalk and ear will cause different degrees of freezing damage (the freezing point of the fruit stalk is -1.1 ℃, and the freezing point of the ear stalk is -1.1---1.3 ℃). Therefore, during storage, the temperature in the warehouse should be detected at multiple points every day to master the temperature changes and regulate them

at the end of storage, when the berries are taken out of the warehouse, due to the high external temperature, the method of directly calculating the impact strength of the film pendulum impact tester is taken out of the warehouse, or placed in the greenhouse, the berries are easy to sweat, and the surface condensation causes decay. Therefore, the berries must be heated slowly when leaving the warehouse, so as to ensure the storage quality

(2) humidity regulation. The suitable relative humidity for grape berry storage is 90% - 95%. Too high or too low humidity is not conducive to Berry storage. Too low humidity will cause rapid water loss, atrophy and browning of fruit stems and panicle stems. High humidity and low temperature are the main reasons for the chilling injury of fruit stems, ear stems and fruit grains; Excessive humidity and high temperature are easy to cause fruit stems and ear stems to mildew and rot. Fresh keeping bags are packed for storage, and the humidity in the bags is more than 95%, which is generally not controlled. In mechanical refrigeration, the evaporator and pipes often absorb water vapor in the air and frost, while manual defrosting further consumes water in the air. The reservoir with cement structure also has great hygroscopicity to gas, all of which may reduce the air humidity in the reservoir and affect the storage quality of berries. Therefore, it is necessary to moisturize regularly. The specific measures are: when designing the cold storage, increase the evaporation area (evaporation pipeline and evaporator surface area), reduce the difference between evaporation temperature and storage temperature, and control frosting. Secondly, spray water on the ground and walls of the warehouse or hang wet straw curtains, and install automatic spray at the air blast port of the cooling system to directly increase the air humidity. When the humidity in the warehouse is too high, ventilation can be used to reduce the opening times of the warehouse door. 2. The influence of the selection of resin on the mechanical properties of products. Measures such as spreading hydrated lime, calcium chloride or charcoal on the ground can be taken to reduce it

(3) ventilation. During grape storage, special attention should be paid to ventilation, and carbon dioxide and other irritant gases released by respiration during berry storage, such as ethylene, acetaldehyde, ethanol, etc., should be eliminated in time to prevent accumulation and promote fruit ripening and aging. In the early stage of storage, berries have high respiratory intensity, and ventilation is required once a day or every two days. Ventilation should be carried out in the morning or evening when the temperature is low, and attention should be paid to avoiding rain and fog weather and refrigeration. In the middle and late stage of storage, the ventilation frequency can be appropriately reduced, generally once every 10-15 days, or combined with cooling

(4) frosting and defrosting. The surface of the evaporator in the cold storage is frosted, which reduces the humidity in the cold storage, hinders the heat conduction of the pipeline, and affects the refrigeration effect. The main defrosting measures are:

① direct the hot gaseous condensate into and flow through the evaporator. When the storage temperature rises to 1 ℃, turn off the compressor. The temperature of the evaporator rises, causing the frost layer on the surface to dissolve or peel off

② spray water regularly to cool the evaporator to prevent the formation of frost layer

③ constantly spray the evaporator with solutions with high freezing temperature, such as 5% - 8% concentrated brine, to prevent the formation of frost

④ electric heater heating defrosting

(5) grapes have strong tolerance to sulfur dioxide, and sulfur fumigation in the storehouse is an important means to kill grape storage diseases. The practice of sulfur fumigation in refrigerated grape whole storehouse is basically the same as that in ventilated storehouse, but because the temperature of refrigerated storehouse is suitable and constant, the time and dose of sulfur fumigation each time should be reduced. When partially fumigating sulfur, cover the stack with a certain thickness of plastic film, fumigate at a dose of 2-3g/m3, ventilate after 20-30min, repeat once every 10-15 days, and then fumigate every 1-2 months. In this way, it can be stored for a long time at a temperature of about 0 ℃ and a relative humidity of more than 90%

(to be continued)