The most common method of Apple cold storage is to expose the containers that contain them to cold air circulating in a suitable chamber. The fruit, once cooled, remains in the same place, thus avoiding the need for double handling. In the cold room, the heat is lowered in stages, each phase presenting a lower temperature than the preceding one.
The process involved in Apple cold storage facility:
In the beginning, the heat removed by the product, the one that penetrates through the building structure and the one produced by the fan that moves the air.
These are collected by the cold air itself to release them on the surface of the refrigerator, which through the walls of the ducts will give them to the refrigerant that circulates at a lower temperature.
The volume of air in motion should be sufficient to lower the temperature of the fruit. The rate of cooling of the stored product depends on the air jet, the type of container used, the way the merchandise is stacked, and the difference in temperature between the environment and the fruit.
For the cold air to be effective, it must be gently distributed through the corridors that leave the piles of containers, which will lack gaps that facilitate the formation of eddies, taking advantage of the line of minimum resistance.
If the air is not distributed evenly throughout the chamber, the temperature of the product can vary widely from one place to another and after a certain storage time, the quality of the fruit is inconsistent.
It has been said that the rate of air renewal should be adequate but not excessive because it would overload the work of the fans.
Optimal storage conditions for apples:
For instance, to obtain a 50% increase in air circulation, the power of the fans would have to be increased by 350%, but with this measure of heat transfer, it would increase by 30%.
The increase in air circulation has an economic limit or because when it is cooled without excessive ventilation capacity, one has to settle for maintaining the fixed rate of heat extraction.
Experimentally, it has been shown that to preserve fruit it is appropriate to renew the volume of air corresponding to the empty chamber 40 times per hour, which means circulating approximately 2.3m the increase in air circulation has an economic limit or because when it is cooled without excessive ventilation capacity, one has to settle for maintaining the fixed rate of heat extraction.
Conveniently, the air moves between the stacks of containers, so the cooling unit and the fan should be placed vertically and equipped with suction at ground level with air discharge to the space between the top of the piles and the ceiling of the chamber (attached figure
If the room is large and rectangular and its capacity is greater than 100Ton, it is advisable to attach simple conical ducts drilled at intervals to the ceiling so that they distribute the air evenly throughout the Apple cold storage chamber.
The fan and its motor can be housed in the lining of the refrigerator if there is an access hatch to facilitate its maintenance, in the vault of the chamber, or in another suitable place such as the wall of the building itself.
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What happens if apples are not stored properly?
When the temperature of the fruit has dropped to the conservation level, the heat seeping through the walls decreases to about a fifth and it is no longer necessary to activate the circulation.
So, the fan can be kept at half speed. This procedure reduces the air movement by almost half and requires less power since the cooling plant has to remove less heat.
However, the electrical panel that controls the operation of the fan will allow the appliance to work at full capacity whenever the plant requires it. If these needs are forgotten, there is a risk that the fruit will be injured because the ambient temperature is too low.
Food modifications during freezing:
Freezing causes an increase in the concentration of the solutes present. Despite the decrease in temperature, the speed of the reactions increases, despite the decrease in temperature according to the law of mass action. This increase in the speed of the reactions occurs between –5ºC and –15º C.
This increase in the concentration of solutes causes changes in the viscosity, pH, the redox potential of the unfrozen liquid, ionic strength, osmotic pressure and surface tension, among others.
The action of these factors associated with the effect of the disappearance of a part of the liquid water, causes unfavorable changes in the food, an example of which is the aggregation of proteins.
These effects can be limited when the passage through the aforementioned temperature range is carried out quickly. This range is called the danger zone or critical zone.
Controlled Atmosphere Chambers as one of the best Apple cold storage:
As we have seen previously, the main environmental factors that most directly influence the respiration rate of the fruit are the Apple cold storage temperature and the richness of the Apple cold storage chamber in carbon dioxide and oxygen:
The facilities that allow these factors to be regulated are called controlled atmosphere Apple cold storage chambers (CA). Conservation under CA conditions can only be successful if all the surfaces of the premises are truly hermetic against oxygen and carbon dioxide leaks because they have been previously coated with a product that is impervious to these gases.
To preserve Bramley’s Seedling apples between 3.3 and 3.9ºC in an environment where the carbon dioxide concentration remains below 10%.
The coating must be effective enough to limit their escape to a maximum of 1.1m 3per day and per ton of stored fruit, which represents approximately half of the effective production corresponding to this variety.
To maintain good control, a manually operated Apple cold storage reservoir should be installed with the help of valves coupled to the vents.
To preserve apples under a tension of 2.0-2.5% oxygen and therefore virtual carbon dioxide, the requirements are even more stringent because the oxygen concentration between the interior and exterior atmospheres of the chamber presents a difference of 18%, almost twice that of carbon dioxide from apples.
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