JPH0445155B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for thawing frozen foods, and more specifically, the present invention relates to a method for thawing frozen foods, and more specifically, thawing frozen foods in a natural state that is almost on the verge of freezing, without using humidified air through gas-liquid contact. The present invention also relates to a method for thawing frozen foods using a high-humidity thawing chamber that can thaw frozen foods into a slightly frozen state and store them in the ideal thawed state at high humidity.

Prior Art As a means of distributing fresh meat in large quantities, it is common practice to bring the meat into contact with liquefied gas, flash-freeze it at an ultra-low temperature, and then transport this frozen meat to the place of consumption. Fish such as tuna caught in deep-sea fishing are also transported or distributed in a frozen state. For this reason, retail stores, etc. at the end of the distribution channel, must thaw these frozen meats and frozen fish (hereinafter referred to as "frozen foods") before selling them, and an increasing number of stores are equipped with dedicated thawing cabinets. There is.

Conventional methods of thawing frozen foods include:
A natural thawing method in which frozen foods are left at room temperature and an electric thawing method in which forced heating is performed using electric heat are known. However, in the natural thawing method, it is generally difficult to control the thawing state, and the disadvantage is that the thawing may be insufficient or may be thawed excessively. Furthermore, the electric thawing method has the disadvantage that thawing tends to be uneven. In addition, these thawing methods have been pointed out to have drawbacks, such as the fact that drips (gravy) are likely to come out when the meat is thawed due to a decrease in the humidity of the surrounding atmosphere, resulting in a significant decrease in the product value after thawing.

Therefore, when thawing frozen foods that tend to drip, the air inside the thawing chamber is brought into contact with spray water (gas-liquid contact) and humidified, and this humidified air is circulated inside the chamber to add moisture to the surface of the frozen foods. The use of high-humidity thawing chambers, which condense water and thaw it using the latent heat released when it condenses, is becoming widespread.

Problems to be Solved by the Invention The above-mentioned high-humidity thawing chamber that uses humidified air through gas-liquid contact has the advantage of suppressing the outflow of drips because moisture condenses on the surface of the food. The problem is derived. One of them is that during thawing of frozen food, significant frost forms on the surface of the food, and when this frost melts at the end of thawing, the surface of the food becomes wet, which has a serious impact on storage after thawing. That's true. Another one is
By bringing the air inside the refrigerator into contact with the sprayed water, bacteria, etc. are likely to be mixed into the humidifying water, and countermeasures must be taken to prevent contamination of the food after thawing.

Purpose of the Invention The present invention has been proposed in order to suitably solve the problems inherent in conventional high-humidity thawing chambers that use air humidified through gas-liquid contact. Without changing the quality of frozen food,
Frozen foods that can be hygienically thawed to a natural state on the verge of freezing or a slightly frozen state (hereinafter referred to as "slightly frozen state") in a short period of time, and furthermore, can be stored at high humidity in the ideal thawed state. The purpose is to provide a method for decompressing.

Means for Solving the Problems In order to overcome the above-mentioned problems and achieve the intended purpose, the method for thawing frozen food according to the present invention includes: arranging an evaporator connected to the refrigeration system to face a brine cooling tank; In a high humidity thawing chamber configured to circulate brine stored in this brine cooling tank to a cooler inside the chamber, after storing frozen foods in the chamber,
The brine in the brine cooling tank is circulated to the cooler, and heat exchange is performed between the frozen food and the cooler via the air inside the refrigerator, thereby humidifying the frozen food and cooling the brine. When the temperature inside the refrigerator drops to a predetermined temperature due to rapid heat absorption from the brine, a heating source connected to a part of the brine circulation system is activated, and the brine temperature and the temperature inside the refrigerator are The same first temperature is set, the frozen food is thawed by the relative temperature difference with the internal temperature, and when the time required for the center temperature of the frozen food to reach the predetermined temperature has elapsed, the refrigeration system is operated. to cool the brine in the brine cooling tank, and at the same time, the heating source is only partially activated to apply thawing heat to the brine, so that the internal temperature is approximately the same as the brine temperature and lower than the first temperature. By setting the second temperature, the surface temperature of frozen food is brought close to the temperature inside the refrigerator, and the inside of the refrigerator is kept at high humidity. After the food has been thawed, the refrigeration system continues to operate, all of the heating sources are stopped, and the interior of the refrigerator is kept at a constant temperature and high humidity to keep the thawed food in a slightly frozen state. It is characterized by being stored in

Function The thawing method according to the present invention uses a brine-type thawing chamber that circulates a large amount of brine (antifreeze) having a large specific heat, so it is possible to use the cooler that circulates the brine at a temperature close to the temperature inside the chamber. can. Therefore, even without humidifying the air being circulated,
Frost buildup on the cooler is extremely reduced, and the inside of the refrigerator can be kept at high humidity. Furthermore, by arranging the heat sources in relation to a part of the brine circulation system, the temperature inside the refrigerator can be controlled with high accuracy and an ideal thawing state can be obtained.

Examples Next, regarding the method for thawing frozen foods according to the present invention,
A description will be given below with reference to the accompanying drawings in relation to a high-humidity thawing chamber that can suitably implement this.

FIG. 1 is an explanatory diagram showing the system configuration of a high-humidity thawing chamber according to a first embodiment in which the method of the present invention can be suitably implemented. A divided thawing chamber 2 is provided, and a plurality of shelves 4 on which frozen foods 3 are placed are arranged in the thawing chamber 2. A cooler 5 having a sufficiently large heat exchange area is arranged on one side wall of the thawing chamber 1, and its cooling surface faces into the thawing chamber 2.

The cooler 5 is also provided with an electric heater 6 that functions as a heating source, and as described later, this heater 6 is divided into two systems 6a and 6b, and is controlled to be turned on and off simultaneously or selectively by an electric control circuit. It is becoming more and more common. Further, a blower fan 7 is installed on the back of the electric heater 6, and by rotating the blower fan 7, the air inside the refrigerator that has exchanged heat with the cooler 5 or the air that has been heated by the electric heater 6 is transferred to the thawing chamber. 2 and the duct 8 formed at the bottom
It is designed so that it can be forced to circulate as shown by the arrow.

The cooler 5 is connected via a liquid sending pipe 11 and a return pipe 12 to a cooling tank 10 in which brine 9 is stored.
Forced circulation is carried out by a circulation pump 13 inserted in 1. Therefore, the cooler 5, the liquid sending pipe 11, the brine cooling tank 10, and the return pipe 12 constitute a brine circulation system as a whole. The brine cooling tank 10 has an evaporation pipe 14 below the brine storage level, and the evaporation pipe 14 is connected to a refrigeration system 15 that uses a gas refrigerant such as fluorocarbon. The brine 9 in the tank 10 is cooled by controlling the operation of the refrigeration device 15 by the electric control circuit.

In addition, a temperature sensor 1 consisting of a temperature element such as a thermistor for monitoring the temperature inside the thawing chamber 2 is installed at a suitable place in the thawing chamber 2.
6 is disposed in the tank 10, and a brine temperature detector 17 made of a temperature element such as a thermistor for detecting the temperature of the brine 9 is provided in the tank 10. Note that the electrical contact Th ₁ of the internal temperature detector 16 and the electrical contact Th ₂ of the brine temperature detector 17 are respectively connected to an electrical control circuit to be described later.

FIG. 2 shows an electric control circuit that performs on/off control of the electric heater 6, the refrigeration device 15, the circulation pump 13, the blower fan 7, etc., which were mentioned earlier. 13 (the motor), the blower fan 7 (the motor), and the first timer _TM1 are connected in parallel. 1st timer
TM ₁ closes normally closed contacts c and d until a predetermined time t ₁ has elapsed from the start of energization, and switches to close normally open contacts c and e after the set time has elapsed. Note that the contact c is connected to the power supply bus X side. Furthermore, power bus lines X, Y
In between, the normally closed contacts c and d, the electric contact Th ₁ of the internal temperature detector 16, and the electric heater 6 forming the first system.
They are connected in series by a.

A second timer TM ₂ and a relay X 1 are connected in parallel between the terminal e of the normally open contacts c and e of the first timer TM ₁ and the bus _Y. Also, terminal e
is connected to the bus bar Y via the normally closed contacts f, g of the second timer TM ₂ , the normally open contacts X _1-2 that cooperate with the relay X ₁ , and the electric heater 6b forming the second system. The relay contact X _1-2 and the electric heater 6b and the electric contact Th ₁ and the electric heater 6a are connected by the normally closed contact X _1-1 of the relay X ₁ . Furthermore, the terminal e and the bus line Y are connected in series by an electrical contact Th ₂ of the brine temperature detector 17 and (the motor of) the refrigeration device 15.

The temperature inside the refrigerator 16 indicates that the temperature inside the refrigerator is 5°C.
When the temperature drops below, the contact Th ₁ is closed and the cooler 5
By controlling the energization of the electric heater 6 attached to the
The temperature inside the thawing chamber 2 is maintained at about 5°C. Further, the brine temperature detector 17 is set to open its contact Th ₂ when the temperature of the brine 9 in the tank 10 becomes -2°C or lower, and maintain the temperature of the brine 9 at approximately -2°C. There is. Note that the second timer
TM ₂ is used to set the required defrosting time t ₂ and, as described later, starts operating when the first timer TM ₁ closes the normally open contacts c and e after the set time t ₁ has elapsed. and the preset thawing time (type of frozen food,
(determined in advance experimentally depending on the size, etc.), the electric heater 6b is controlled to be energized.

Next, the operating conditions of the thawing warehouse according to the first embodiment configured as described above will be explained with reference to FIGS. 2 and 3. Frozen food 3 (for example, frozen meat) is placed on shelf 3, and a door (not shown) of thawing chamber 1 is closed. Next, when a power switch (not shown) is turned on, the circulation pump 13 rotates, and the brine 9 in the timer 10 is circulated and supplied to the cooler 5. Further, the blower fan 7 rotates to circulate the air in the refrigerator in the direction of the arrow, and the first timer TM ₁ starts counting the set time t ₁ . Since the internal temperature at this point is high, the electric contact Th ₁ of the internal temperature detector 16 is open, and the electric heater 6 is not energized. Furthermore, since the contacts c and e of the first timer _TM1 are open, the refrigeration system 15 is not yet in operation.

The internal air circulating in this state contacts the surface of the frozen food 3 to exchange heat and humidify the food. Further, the air whose temperature has been lowered by this comes into contact with the cooler 5 via the duct 8, and performs heat exchange to lower the temperature of the brine 9.

As a result of taking negative heat from the frozen food 3, the temperature inside the thawing chamber 2 drops, and when it drops to 5°C or less,
The electrical contact Th ₁ of the temperature detector 16 is closed, and the electric heater 6a of the first system is energized. Also relay
The electric heater 6b of the second system is also energized via the normally closed contact _X1-1 of _X1 , and both heaters 6 maintain the temperature inside the defrosting chamber 2 at 5°C. That is, a cooler 5 having a sufficiently large heat exchange area, a brine 9 that circulates inside the cooler and can bring the entire cooler to a uniform temperature with a large amount of heat, and are installed in close thermal contact with the cooler 5. By using the electric heater 6, the temperature of the brine 9 can be made substantially the same as the temperature inside the thawing chamber 2. In this way, adjust the temperature inside the refrigerator to about 5℃.
(This is referred to as the "first temperature"), as shown in FIG. 3, the surface temperature of the frozen food 3 rises due to the relative temperature difference with the internal temperature, and thawing progresses. Moreover, since the humidified air caused by the above-mentioned gas-liquid contact is not used, there is no frost on the surface of the food and no liquid wetting due to melting of the frost, and the food remains in good condition even after thawing.

When the set time _t1 of the first timer TM1 has elapsed, the normally closed contacts c and d are opened to turn off _the power to the electric heater 6a of the first system, and at the same time the normally open contacts c and e are closed. do. At this time, since the contact Th ₂ of the brine temperature sensor 17 is already closed, the operation of the refrigeration device 15 is started, and the brine 9 in the tank 10 is cooled by the evaporator 14 and maintained at -2°C. . By closing the timer contacts c and e, relay _X1 is energized, opening its normally closed contact _X1-1 and closing its normally open contact _X1-2 .

Furthermore, since the contacts f and g of the second timer TM ₂ are closed, energization to the electric heater 6b constituting the second system continues. The reason why the electric heater 6b of the second system continues to be energized is explained as follows. When the set time _t1 of the first timer _TM1 has elapsed, the center temperature of the frozen food 3 is approximately -
Since the temperature is kept at 7°C, which is sufficiently low, the inside of the refrigerator will gradually cool down.
Therefore, the temperature inside the refrigerator is corrected by heating with the electric heater 6b of the second system. That is, the electric heater 6b is used to provide thawing heat to the brine 9, and is set to such an extent that it does not interfere with the cooling capacity of the refrigeration device 15.

Further, by closing the contacts c and e of the first timer TM ₁ , the second timer TM ₂ starts a time-limiting operation for a preset defrosting time t ₂ . At this time, frozen food 3
As shown in Figure 3, the center temperature has risen to about -7°C, approaching the temperature zone of the "maximum ice crystal melting zone," which takes the longest time to pass through. Therefore, the set time t ₁ of the first timer TM ₁
is experimentally determined in advance according to the type, size, etc. of the frozen food 3, so that the center temperature of the frozen food 3 will be approximately -7° C. when time _t1 has elapsed. Note that the refrigeration device 15 continues to operate, and when the temperature of the brine 9 in the tank 10 becomes -2°C or lower, the contact Th ₂ of the brine temperature detector 17 is activated.
is opened to stop the operation of the refrigeration device 15, and this on-off control lowers the temperature of the brine 9 to about -2
Keep at ℃.

In this way, the temperature of the brine 9 is maintained at about -2° C., and the brine 9 having a large heat capacity is circulated through the cooler 5 having a sufficiently large heat exchange area, so that the entire cooler is kept at a uniform temperature. As a result, there is almost no temperature difference between the temperature in the thawing chamber 2, which is partitioned by panels with excellent heat insulation, and the surface temperature (-2° C.) of the cooler 5. Furthermore, since the surface temperature of the frozen food 3 approaches the temperature inside the refrigerator, the temperature inside the refrigerator becomes a high humidity state as shown in FIG. That is, in this example,
The interior of the refrigerator can be kept in a high humidity state without a humidifier. When the internal temperature rises, the specific heat of the internal air itself that exchanges heat with the frozen food 3 increases, and therefore thawing is promoted more effectively. In this way, the center temperature of the frozen food 3 gradually rises from -7°C to -2°C, which is a natural state almost on the verge of freezing or a slightly frozen state, and approaches the end of thawing.

When the defrosting is completed, the _second timer TM2 times up, opens the normally closed contacts f and g, and turns off the electricity to the electric heater 6b forming the second system. As a result, thawing heat is no longer applied, and the freezing device 15
Only the operation of the vehicle will continue. Further, when the temperature of the brine 9 in the tank 10 becomes -2°C or lower, the contact Th ₂ of the brine temperature detector 17 opens, and the refrigeration equipment 1
5 is stopped and the temperature of the brine 9 is reduced to about -2
Keep at ℃. That is, the inside of the refrigerator is maintained at a constant temperature of around -2°C and high humidity, and in this atmosphere, the frozen food 3 does not dry out, and both the surface temperature and the center temperature are maintained at about -2°C.

When the aforementioned thawing is completed and all the foods stored in a slightly frozen state are taken out, new frozen foods are stored in the thawing chamber and the next thawing operation begins. In this case, the first timer TM ₁ and the second timer TM ₂
The counting time is reset according to the thawing state of the food, and the first timer _TM1 starts counting the set time _t1 . The brine 9 is therefore circulated and the thawing process described above is repeated. By the time the previous stage of thawing is completed, the internal temperature is -2
The temperature inside the refrigerator was maintained at a constant temperature of around 5°C and high humidity, but when the door was opened to store new frozen food and the brine circulation resumed, the internal temperature quickly rose to about 5°C. .

(Second Embodiment) FIG. 4 shows another high-humidity thawing chamber in which the method of thawing frozen food according to the present invention can be suitably carried out, in which the above-mentioned heat source 6 is connected to the brine cooling tank 1.
It is located in 0. The heat source 6 includes, for example, an electric heater 6a as a first system provided at a substantially intermediate position of the tank 10, and an electric heater 6b as a second system disposed close to the connection opening of the liquid sending pipe 11 of the tank 10. Both of them are arranged to be immersed in brine 9. Therefore, both electric heaters 6a and 6b are provided with an insulating coating enclosed in an insulating sheath or the like. A brine temperature sensor 17 is also provided, the probe of which is immersed in the brine 9 in the tank.

An example of the electric control circuit in this case is shown in FIG. In addition, when the detected temperature exceeds 5°C, the brine temperature detector 17 opens the contact Th-a and the temperature reaches 5°C.
When it becomes below, the contact Th-a is closed. The other contact Th-b is connected to the detected temperature of the brine 9 by -2.
It is set to close when the temperature is higher than ℃, and to open when the temperature falls below -2℃.

Therefore, the operation of the thawing warehouse according to this embodiment is started,
As described above, when the temperature of the brine 9 is lowered to 5° C. or lower by circulating the air inside the refrigerator, the contact Th-a of the brine temperature detector 17 is closed and the electric heater 6a of the first system is energized. Let's do it. As a result, the temperature of the brine 9 in the tank 10 is maintained at 5°C, and the air inside the refrigerator which exchanges heat with the brine 9 via the cooler 5 is also maintained at 5°C. Due to the temperature difference between this internal air and the frozen food 3, the food thaws. At this time, similarly to the first embodiment, the air inside the refrigerator is not humidified, so no frost is formed on the surface of the frozen food 3.

When the set time t ₁ of the first timer TM ₁ has elapsed in this state, the center temperature of the frozen food 3 has risen to about -7° C., as shown in FIG. 3.
When the set time _t1 has elapsed, contacts c and d are opened to turn off the electric heater 6a of the first system, and the other contacts c and e are closed. At this time, since the temperature of the brine 9 is already maintained at 5° C., the contact Th-b of the temperature sensor 17 is closed. Therefore, the operation of the refrigeration system 15 is started, and the brine 9 in the tank 10 is cooled by the evaporator 14. This cooling occurs when the temperature of the brine 9 becomes -2°C or less and the contact Th of the temperature sensor 16
-b is released, and thereafter brine 9
The temperature is maintained at approximately -2°C.

By closing the contacts c and e of the first timer _M1 , the second timer _TM2 starts a time-limited operation for the preset defrosting time _t2 , and until the set time _t2 has elapsed, the normally closed Electricity is applied to the electric heater 6b forming the second system through the contacts f and g. This electric heater 6b
As described above, is for applying thawing heat to the brine 9, and is set to an extent that does not interfere with the cooling capacity of the refrigeration device 15.

When the temperature of the brine 9 is maintained at about -2°C in this way, the cooler 5 with a sufficiently large heat exchange area
There is almost no difference between the surface temperature (-2° C.) and the temperature inside the refrigerator, and the surface temperature of the frozen food 3 also approaches the temperature inside the refrigerator, so the temperature inside the refrigerator becomes a high humidity state. As mentioned above, when the internal temperature rises, the specific heat of the internal air itself that exchanges heat with the frozen food 3 increases, and thawing is promoted more effectively, thus the center temperature of the frozen food 3 gradually decreases to -7. ℃ to almost frozen natural state or slightly frozen state -2
The temperature will rise to near the end of thawing.

When the defrosting is completed, the _second timer TM2 times up, opens the normally closed contacts f and g, and turns off the electricity to the electric heater 6b forming the second system. As a result, thawing heat is no longer applied, and the freezing device 15
Only the operation of the vehicle will continue. The temperature of brine 9 is -
When the temperature drops below 2°C, the contact Th- of the temperature detector 17
b is opened, the operation of the refrigeration device 15 is stopped, and the temperature of the brine 9 is maintained at about -2°C. That is, the inside of the refrigerator is maintained at a constant temperature of around -2°C and high humidity, and in this atmosphere, the frozen food 3 does not dry out, and both the surface temperature and the center temperature are maintained at about -2°C.

Effects of the Invention As explained above, according to the method for thawing frozen food according to the present invention, frozen food can be thawed to a natural state almost frozen or to an ideal slightly frozen state without making it wet. Moreover, it can be stored in this ideal thawed state without drying. Further, according to the present invention, frozen foods can be thawed hygienically without dripping.

[Brief explanation of drawings]

Figure 1 shows the method for thawing frozen food according to the present invention.
A system configuration diagram of a high humidity thawing warehouse according to an embodiment that can be suitably implemented, FIG. 2 is an electrical control circuit diagram of the embodiment shown in FIG. 1, and FIG. 3 is experimental data of the embodiment shown in FIG. 1. The graph shown in FIG.
FIG. 5 is a schematic vertical cross-sectional view of a brine cooling tank in a high-humidity thawing chamber according to an embodiment, and is an electrical control circuit diagram of a high-humidity thawing chamber according to a second embodiment. 1... Thawing chamber, 2... Thawing chamber, 3... Frozen food, 4...
Placing shelf, 5...Cooler, 6...Heat source, 6a...Electric heater forming the first system, 6b...Electric heater forming the second system, 7...Blower fan, 8...Duct, 9...Brine, 10...Brine Cooling tank, 11...Liquid sending pipe, 12...Return pipe, 13...Circulation pump, 1
4...Evaporator, 15...Freezer, 16...Interior temperature detector, 17...Brine temperature detector.

Claims (1)

[Scope of Claims] 1. A high-humidity thawing warehouse configured such that an evaporator connected to a refrigeration system faces a brine cooling tank and brine stored in the brine cooling tank is circulated to a cooler inside the warehouse, After storing the food in the refrigerator, the brine in the brine cooling tank is circulated through the cooler, and heat is exchanged between the frozen food and the cooler via the air inside the refrigerator, thereby heating and cooling the frozen food. When the brine is cooled and the temperature inside the refrigerator drops to a predetermined temperature due to the removal of negative heat from the frozen food, a heating source disposed in relation to the brine circulation system is activated;
The brine temperature and the temperature inside the refrigerator are set to the same first temperature, and the frozen food is thawed by the relative temperature difference with the temperature inside the refrigerator, and the time required for the center temperature of the frozen food to reach the predetermined temperature elapses. At that point, the refrigeration system is operated to cool the brine in the brine cooling tank, and the heating source is only partially activated to provide thawing heat to the brine, bringing the temperature inside the refrigerator to the brine temperature. A second temperature that is the same and lower than the first temperature is set, and the surface temperature of the frozen food is brought close to the temperature inside the refrigerator, and the inside of the refrigerator is kept at high humidity, thereby increasing the specific heat of the air inside the refrigerator and increasing the temperature of the frozen food. After the frozen food has been thawed, the refrigeration system continues to operate, all the heating sources are stopped, and the inside of the refrigerator is maintained at a constant temperature and high humidity to finish the thawing. A method for thawing frozen foods characterized by preserving the frozen foods in a slightly frozen state. 2. The patent provides that the cooler disposed inside the thawing warehouse has a heat exchange area large enough to sufficiently cool the brine circulating in the cooler using negative heat from the frozen food. A method for thawing a frozen food according to claim 1. 3. According to claim 1 or 2, the heating source is an electric heater, and the electric heater is attached to a cooler that forms part of a brine circulation system disposed in a thawing warehouse. How to thaw frozen foods as described. 4. Claim 1, wherein the heating source is an electric heater coated with an insulation coating, and the electric heater is disposed so as to be immersed in the brine in a brine cooling tank that forms part of a brine circulation system. ~The method for thawing a frozen food according to any one of Item 3.