JPS6394957A - Thawing of frozen food - Google Patents

Abstract

PURPOSE:To carry out the thawing of even a frozen food to be eaten raw, by placing a food to be thawed in a closed space in which hot air is circulated at specific temperature and flow rate and finishing the thawing operation when the surface temperature of the food reaches a prescribed standard temperature for finishing the thawing. CONSTITUTION:The temperature of hot air circulating in a thawing chamber 11 is maintained at 25-35 deg.C and the flow rate of the air is adjusted to 3-5m/sec to increase the rate of thawing and prevent the unnecessary rise of surface temperature of the object 27 to be thawed and the drying of the surface. When the surface temperature of the object reaches a prescribed temperature set within 5-15 deg.C, preferably 8-12 deg.C, the thawing operation is finished. Even a frozen food for eating in raw state can be thawed in a short time by this process.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for thawing frozen food, specifically, a method for thawing frozen food, which involves storing frozen food in a closed space and circulating warm air within the closed space. This article relates to a method for defrosting frozen foods.

(Prior Art) Conventionally, as a thawing method of blowing warm air onto frozen food to thaw it, for example, Japanese Patent Application Laid-Open No. 57-50875 and Japanese Patent Publication No. 59-33342 disclose that After the surface temperature of the frozen food reaches a predetermined temperature (usually about 30°C) by blowing hot air at 70°C, the temperature of the hot air is gradually lowered over time to maintain the surface temperature of the frozen food at the predetermined temperature. A method has been proposed to decompress the file while However, this method requires a great deal of experience to obtain the best thawing results, as the end of thawing must be set in time.Moreover, because the thawing temperature is high, drips may flow out during thawing, and the thawing Items tend to dry out or thaw unevenly,
There is a problem in that it is unsuitable for thawing frozen foods for raw consumption such as sashimi.

As a means to solve this problem, the present inventor, together with other inventors, proposed in Japanese Patent Application No. 143335/1983 that the object to be thawed is placed in a thawing chamber of an insulated container, and a warm air is blown inside the thawing chamber. is circulated to maintain the temperature in the thawing chamber at a predetermined temperature (usually 10
We have proposed a method for thawing a frozen food, which is characterized by thawing the food while maintaining the food at a temperature of 20° C. to 20° C., and thawing the food when the surface temperature of the object to be thawed reaches a predetermined temperature (usually around 10° C.). This method balances the rate of heat transfer from the surface of the food to be thawed with the rate of heat transfer due to heat conduction inside the food and thaws at a relatively low temperature. Regardless of the type of food, outside temperature, etc., optimal thawing can always be obtained with simple operations, and frozen foods for raw consumption can also be thawed.

(Problems to be Solved by the Invention) However, the method described in Japanese Patent Application No. 60-143335 has the problem that the thawing time increases as the thickness of the frozen food increases. It was inappropriate. One way to shorten the thawing time is to increase the speed of hot air while maintaining it within the above temperature range. There was a problem in that the thermal conductivity of the thawing material became a rate-limiting condition for the thawing speed, did not contribute to the heat transfer speed, and instead deteriorated the quality of the material to be thawed. In addition, in the above method, as a means for detecting the surface temperature of the object to be thawed, a contact type temperature sensor that comes into contact with the object to be thawed and detects the surface temperature is used, so the object to be thawed is placed on a plate etc. Moreover, the measured temperature is affected by the contact state between the object to be thawed and the temperature sensor, resulting in inconsistent thawing results.

Therefore, an object of the present invention is to provide a method that can further shorten the thawing time of frozen foods, can also thaw frozen foods for raw consumption with good quality, and can always thaw them in a constant state.

(Means for Solving the Problems) As a means for solving the above problems, the present invention provides a method for thawing frozen foods by storing food to be thawed in a closed space and circulating hot air within the closed space. , the hot air is heated for 25~
While maintaining the temperature within the range of 35°C and circulating at a flow rate of 3 to 5 m/s, the surface temperature of the object to be thawed is detected, and the thawing end reference temperature is determined when the surface temperature is within the range of 5 to 15°C. The decompression is terminated when the value is reached.

The thawing termination group QfA degree is preferably set at a temperature within the range of 8 to 12°C.

In addition, a contact temperature sensor such as a thermistor may be used as a means for detecting the surface temperature of the object to be thawed.
Because of the above problems, it is preferable to use a non-contact temperature sensor. Examples of the non-contact temperature sensor 5 include a thermal detector (for example, a pyroelectric infrared sensor) and a quantum detector.

(Function) In the method of the present invention, the thawing speed depends on the temperature and speed of the hot air, but the quality of the object to be thawed is also correlated with the temperature and speed of the hot air. It was discovered that by keeping the speed of the hot air within a certain speed range t(n), it was possible to thaw the product without deteriorating the quality of the thawed object. .

In other words, the temperature of the warm air circulating in the closed space is kept relatively high.
By maintaining a predetermined temperature within the range of 5 to 35 degrees Celsius and at the same time circulating warm air at a speed of 3 to 5 m/s, the thawing speed can be increased, and the surface temperature of the thawed object can be prevented from rising more than necessary. By preventing surface drying and terminating thawing when the surface temperature of the object to be thawed reaches a predetermined temperature within the range of 5 to 15 degrees Celsius, preferably 8 to 12 degrees Celsius, frozen foods for raw consumption can be frozen for a short time. This makes it possible to unzip it.

In the present invention, the hot air temperature is limited to a temperature within the range of 25 to 35°C, because if the temperature is less than 25°C, even if the speed of the hot air is increased, the thawing time cannot be shortened sufficiently. If the temperature exceeds 100, thawing should be completed before the surface temperature reaches a high temperature because the center is half-thawed, and if thawing is completed after the center has thawed, the quality will be impaired due to drips. The reason why the hot air speed is set to 3 to 5 m/s is that when the hot air temperature is set within the above range, if the speed is less than 3 m/s, the center of the thawed object will be in a half-thawed state at the end of thawing. This is because if the speed exceeds 5 m/s, quality deterioration occurs due to drying.

The method includes a thawing device comprising an insulated container for storing an object to be thawed, and a hot air generating means for generating warm air circulating in the insulated container, in which the temperature of the warm air circulating in the thawing device main body l is adjusted. and a signal from a temperature sensor that detects the surface temperature of the thawed object when the surface temperature of the thawed object reaches the thawing end reference temperature. This can be carried out by using a defroster equipped with a control device comprising a defrost termination control means for stopping the hot air generating means.

The following description will be made with reference to the accompanying drawings.

In the figure, 1 is a thaw main body, 2 is a fluid, 3 is a hot air generating means, 4 is a mounting table on which an object to be thawed 27 is placed, and the thaw machine main body 1 has a heat insulating material 7 attached to its inner wall surface. It has a heat insulating structure and is divided into a hot air generation chamber IO and a thawing chamber 11 by a partition wall 8 having an air intake port 12 and an air supply port 13.

The lid body 2 has a double lid structure consisting of plates 2a and 2b made of a transparent material, such as transparent glass or plastic, and ribs 2c formed or attached along the edges of the plates 2a and 2b. Both plates 2
By forming an air layer 2d between a and 2b, a heat insulating property is imparted, and one end side is hinged to the defrost body l so that it can be opened and closed, forming a closed space together with the defrost body l.

The hot air generating means 3 includes a cross flow fan 14 and a heater 1
5 and a duct 16, air from the defrosting chamber 11 is sucked in by a cross-flow fan 14 through an intake port 12 to generate an air flow, which is heated by a heater 15 and turned into warm air from the air inlet 13 to the defrosting chamber 11. The warm air is circulated within the closed space.

Note that a thermostat 19 for preventing excessive temperature rise is provided below the heater 15.

A drip tray 24 is removably arranged on the bottom wall 6 of the thawing chamber 11, and a wire-mesh-like or lattice-like mounting table 4 on which the object to be thawed 27 is placed is arranged at a predetermined distance from the drip tray 24. has been done. Furthermore, a non-contact temperature sensor 5 is embedded in the ceiling of the thawing chamber 11.

A control device 25 as shown in FIG. 2 is disposed on the back of the thawing main body 1, and this control device 25 includes a hot air temperature control means and a thawing end control means.

The hot air temperature control means includes, for example, a temperature-sensitive switch 20 such as a thermal reed switch, and this temperature-sensitive switch 20 is disposed near the air outlet 13 (see FIG. It is connected in series with the overheat prevention thermostat 19 and the heater 15, and the heater 15 is activated depending on the temperature of the hot air.
The temperature of the hot air circulating in the thawing device main body 1 is maintained at a preset temperature within the range of 25 to 35° C. by controlling on-off energization.

The thawing end control means includes a non-contact temperature sensor 5, a thawing end temperature setting means 28, a comparator 29, and a switch means 30. The temperature is detected, a voltage corresponding to the surface temperature is output from the amplifier I7, and the output voltage is compared by a comparator 29 with a reference voltage corresponding to the thawing end temperature set by the thawing end standard 'Q temperature setting means 28. When the detected voltage reaches the reference temperature, the output signal from the comparator 29 activates the switch circuit of the switch means 30 consisting of the comparator 31 and the transistor Tr, excites the relay Ryt, and temporarily closes the contact circuit. Turn it off. Therefore, the relay RY + is demagnetized and the heater 15 and cross flow fan 14 of the hot air generating means 3 are stopped.

Note that in order to prevent malfunction of the switch means 30 at the start of defrosting, a programmable unijunction transistor PUT that turns on after a predetermined time is connected to one input terminal of the comparator 31. In the figure, R4 and R5 are resistors, C1 is a capacitor, and D is a diode.

The method of the present invention is carried out in the following manner using the decompressor configured as described above. That is, first, open the lid 2, place the frozen food 27 as the object to be thawed on the mounting table 4, and press the defroster switch SW.The self-holding circuit maintains the relay RY+ in the ON state, and the cross flow Power supply to the fan 14 and heater 15 is started. The airflow generated by the crossflow fan 14 is heated by the heater 15 and
Warm air with a temperature of 5 to 35°C is sent from the hot air generation chamber 10 to the air outlet 1.
3 to the lower part of the thawing chamber 11, flows around the frozen food 27 on the mounting table 4 from bottom to top at a speed of 3 to 5 m/sec, removes cold heat from the frozen food 27 and becomes cold, and the intake air The air enters the hot air generation chamber 10 again through the opening 12 and is reheated, repeating the cycle and circulating within the closed space of the defroster.

During thawing, the surface temperature of the frozen food is constantly detected by the non-contact temperature sensor 5, and when the detected temperature reaches the thawing end reference temperature, the output voltage of the amplifier 17 becomes equal to the reference voltage, and the output from the comparator 29 The switch means 30 is activated to stop energizing the heater 15 and the fan drive motor M, and thawing is completed. Note that when the frozen food 27 is thawed and drips, etc. flow out, the drips fall onto the drip tray 24.

(Example) Using the thawing machine shown in the figure, the thawing end base yarn temperature Ts was set at +9°C or +10°C. 600g of the fish was thawed in different thicknesses, the time until the thawing was completed was measured, and after the thawing was completed, the sashimi was made into sashimi and a taste test was conducted. The results are shown in Table 1 together with the results of the conventional example.

Table 1 No. Thickness Hot air temperature Flow rate Thawing time Taste (mm
) ('C) (m/s) (min) Test 1
8030439 ◎ 2*80 30 2 72 x3*80
30 6 32 x44030435
◎ 5*80 15 2 135 ◎6*80
15 4 108 X7*40 15
2 115 ◎In Table 1, numbers 5 to 7 are the results for the conventional example, and number 2.3 is the result for the comparative example. Note that the thawing end reference temperature Ts is +10°C for sample numbers 1 and 4, and 9°C for the others. Number 2.3
The reason why each sample was given an X in the taste test was because the center of the former was half-thawed, and the surface of the latter was dry, similar to sample No. 6.

As is clear from the results in Table 1, according to the method of the present invention, the thawing time can be significantly shortened compared to the conventional method, and since thawing is completed when the surface temperature of the object to be thawed reaches 10°C, There was no deterioration in quality and the taste was sufficiently satisfying even when eaten raw.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, the thawing time can be significantly shortened without impairing the quality, regardless of the thickness of the object to be thawed, and even raw foods such as sashimi can be thawed. Can be thawed.

In addition, by detecting the surface temperature of the object to be thawed with a non-contact temperature sensor, the end of thawing can be accurately detected, and excellent effects such as consistently good thawing can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view of the thawing device according to the present invention, and Fig. 2 is a circuit diagram of the thawing control device. Temperature sensor, lO ~ warm air generation room (closed space),
ll ~ Thawing chamber (closed space), 14 ~ Fan, 15 ~ Heater, 25 ~ Control device, 27 ~ Item to be thawed (frozen food), 2
8-Defrosting end reference temperature setting means, 29-Comparing means, 30
~Switch means.

Claims (3)

[Claims] (1) In a method of thawing frozen food by storing an item to be thawed in a closed space and circulating warm air within the closed space,
3 while maintaining the temperature of the warm air within the range of 25 to 35°C.
It is characterized by circulating at a speed of ~5 m/s, detecting the surface temperature of the object to be thawed, and terminating the thawing when the surface temperature reaches a thawing end reference temperature within the range of 5 to 15°C. How to thaw frozen foods. (2) The method according to claim 1, wherein the thawing end reference temperature is within a range of 8 to 12°C. (3) The method according to claim 1 or 2, in which a non-contact temperature sensor is used as means for detecting the surface temperature of the object to be thawed.