JPS609784B2 - High frequency thawing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-frequency thawing method for defrosting frozen foods using high-frequency waves.

In the conventional high-frequency thawing method, at the start of thawing, thawing is performed with a preset distance between the electrodes, so changes in the relative ratio (go) and dielectric constant (tan6) of the thawed object as thawing progresses ( In particular, when raising the final temperature of thawing to near the freezing point (12 to 1300℃), the rate of temperature rise of the thawed object becomes extremely slow. .

This point will be explained in more detail below.

In general, the food to be thawed is composed of components with many different properties (for example, the subcutaneous fat and red meat of tuna, or the red meat and white meat of livestock meat, etc.).
Different dielectric constants. In the conventional high-frequency thawing method, the anode current of the high-frequency oscillator and the temperature rise curve of the object to be thawed are generally as shown in FIG.

As the anode current increases, more power is supplied to the object to be thawed. Therefore, the temperature of the object to be thawed increases linearly and rapidly while the anode current increases, and after the time when the anode current reaches its maximum, the supplied power decreases, and from around time t2, the temperature of the object to be thawed rises rapidly. The temperature rise is assumed to be slight. This is due to the following reasons. That is, when the temperature of the object to be thawed is low, the dielectric constant n6 is smaller than the relative permittivity of the object to be thawed;
The high frequency voltage applied to the object to be thawed is high, and the dielectric constant is tan6.
The anode current also increases with the increase in . When the temperature of the object to be thawed exceeds time t, the relative permittivity increases (some of the ice crystals gradually appear as water), the dielectric constant n6 also increases, and conversely, the temperature of the object to be thawed increases. The voltage applied to the thawing material decreases, and the power supply to the item to be thawed decreases. When the temperature of the thawed object rises around time t2, it approaches the freezing point of the thawed object, so the temperature rise curve reaches a saturated state due to the influence of the latent heat of fusion from ice to water, and the electric field conditions at the start of thawing It takes time to bring the temperature of thawed material close to the freezing point. Now, if we start thawing with a strong electric field to supply a large amount of power to the object to be thawed from the beginning, the electric field conditions at the start of thawing will vary depending on the degree of dielectric heating of each part of the object to be thawed, as described above. Because of the difference in temperature, the temperature rises in some parts, and in extreme cases, it becomes boiled (burned), which is undesirable as it appears as temperature unevenness. Furthermore, in the case of tuna and livestock meat, the size of the object to be thawed is not constant, and finding the optimal thawing conditions requires a great deal of experience and is difficult.

An object of the present invention is to provide a high-frequency thawing method that can perform uniform thawing, easily set thawing conditions, and shorten the time compared to conventional methods when increasing the final thawing temperature. .

A high-frequency thawing method characterized in that when thawing is performed while varying the high-frequency electric field intensity applied to the object to be thawed, the electric field intensity is varied by changing the spacing between opposing electrodes after the anode current reaches its maximum value. It is.

Hereinafter, specific examples of the present invention will be explained in detail with reference to FIGS. 2 and 3.

FIG. 2 shows the basic configuration of a high-frequency decompressing device that implements the method of the present invention. This device has a pair of electrodes consisting of a first electrode 2 and a third electrode 3 that are supplied with power from a high frequency oscillator 1, and an object to be thawed 4 is placed between these first and second electrodes 2 and 3. This device performs high-frequency decompression. In this case, "In this embodiment, in order to vary the high-frequency electric field strength applied to the object 4 to be thawed, one of the pair of electrodes 2 and 3 is movable, and the interval between the electrodes 2 and 3 is gradually changed. As shown in the figure, at the start of thawing, a high frequency electric field is applied to the object 4 to be thawed at an electrode interval of 4 (=dx+Q, Q is a variable distance) relative to the thickness dx of the object 4 to be thawed. As shown in Fig. 3, the anode current lp reaches the maximum lpmax at time tm.At this time, the temperature of the object to be thawed 4, which was To at the start, increases with the passage of time.
At time tm, it becomes Tm. When the time tm passes and the time t arrives, the anode current lp starts to decrease. The temperature of the object 4 to be thawed varies from time tm to t. It continues to rise even in the middle of the day, and reaches T as time passes. When the anode current drops at time t, electrode 2 is lowered while maintaining the thawed state, and the distance between electrodes 2 and 3 is reduced to d.
When narrowing from o to d, (=dX+8, 8 is a variable distance), the anode current lp rapidly increases to lp, (lp, Sipma
x) The electric power supplied to the object 4 to be thawed increases, and the electric field applied to the object 4 to be thawed becomes stronger. At this time, the temperature of the object to be thawed 4 will rise if the distance between the electrodes 2 and 3 is not narrowed (
Time t, thereafter, is indicated by a broken line. ) as shown by the solid line. Then, as time elapses from t, the anode current lp gradually decreases, and the temperature T of the object to be thawed 4 gradually increases and reaches L as time elapses. At the time point, electrode 2 is lowered and the distance between electrodes 2 and 3 is narrowed by d (= dx + y).
, y is a variable distance), the anode current lp is lp2(l
p2Sipmax), and the electric field applied to the object 4 to be thawed is changed. At this time, the temperature of the object to be thawed 4 rises faster as shown by the solid line compared to the case where the distance between the electrodes 2 and 3 is not narrowed (shown by the broken line after the time bond song 2). The important thing in this case is that the interval between electrodes 2 and 3 is changed and the electric field is changed until the anode current lp reaches ipmax.
This is what you do after you become

The reason for selecting the parameter after lpmax is obtained is that when the anode current lp is increasing, the electric field is strengthened (the electrode spacing is narrowed). This is because the local temperature difference increases because the n6 is partially different.While this temperature is uneven, when the electric field is changed in the second and third stages, the temperature difference becomes even more. If the temperature of the object 4 to be thawed is raised to T2 (t2) in a relatively uniform state, the distance between the electrodes 2 and 3 must be flattened and narrowed. As a result, the temperature rises faster after T2 when the latent heat of fusion becomes large, and the thawing time can be shortened compared to when thawing is performed with a constant electrode spacing.Next, the thawing temperature increase between the method of the present invention and the conventional method An experiment was conducted to clarify the difference in the time required for decompression and the difference in the time required for decompression, and the results are shown in FIG.

In this case, the high frequency decompressor used in the experiment is as follows. Oscillation output Shoe w electrode size 80 skin x 70 oscillation frequency
1 Ogawa z anode voltage
In the arc V diagram, curve A shows the experimental results according to the method of the present invention in which defrosting is performed by varying the electrode.

The sample is a 6.4k9 drumstick tuna.

The change in the inter-electrode spacing is as follows. 2 from 0 to 20 minutes
4 enemies (tuna height 14 skins 10 spaces) 20 to 30 minutes (tuna height 14 ribs 1 spaces 6 arcs) 30 to 5
The temperature was measured by inserting a sensor at 5 ribs below the surface of the sample.

Curve B shows the experimental results using the conventional method of thawing with fixed electrodes.

Sample 9.1k9 drumstick tuna.

The electrode spacing is 25 meters from 0 to 110 minutes (tuna height 1
5 Gap 10). Curve C shows experimental results using a conventional method in which the electrodes are fixed and thawing is performed.

The sample is a 4.8 kg drumstick tuna.

The electrode spacing was 2 ratio fences (4 skins with 10 gaps at the height of the tuna) from 0 to 35 minutes. As is clear from the figure, it was confirmed that according to the conventional method, even if the weight of the sample was lighter than the sample weight of the method of the present invention, the temperature rise was poor and it took a long time to thaw.

Furthermore, in the experiment shown by curve C, temperature unevenness occurred in the sample. In this embodiment, the electrode spacing is varied twice, but it may be varied an appropriate number of times as necessary.

Furthermore, if the variable distances Q, 8, y, etc. of the electrodes are programmed in advance and automated in conjunction with a timer, good thawing can be easily performed without requiring any experience in handling the thawing device.

In addition, there are other ways to vary the electric field, such as changing the anode voltage of the oscillator in stages using a timer, etc.; This is undesirable because it is significantly higher than the equipment cost when changing.

As explained above, in the high-frequency thawing method according to the present invention, the electric field strength is varied after the anode current reaches its maximum value, so thawing can be performed uniformly without causing local temperature differences. can.

That is, if the electric field is strengthened while the anode current is increasing,
Since the dielectric constant and dielectric constant n6 of the object to be thawed differ locally, there will be a large local temperature difference, and if the electric field strength is changed next time with this temperature unevenness, This is undesirable as local temperature differences become larger and uniform thawing cannot be achieved. Further, according to the present invention, even though the thawing time can be shortened, the thawing can be performed almost uniformly. Furthermore, according to the present invention, good defrosting can be easily performed without requiring any skill. The method of the present invention includes:
Among frozen products, it is effective when it is desired to control the final temperature near the water point (freezing point), such as for fresh foods (fish, meat). Furthermore, in the present invention, the electric field strength is varied by particularly changing the spacing between the electrodes, which has the advantage of reducing the equipment cost when adopting the present invention, and furthermore, changing the spacing between the electrodes reduces the amount of thawing. This is very advantageous in practice because the spacing between the fleas can be appropriately selected according to the size of the object. In addition, when the electric field strength is increased by reducing the distance between the electrodes as in the present invention, it becomes less susceptible to the disturbance of the electric field at the end of the electrode, and the electric field becomes uniform, which is very suitable for uniform heating. It is.

[Brief explanation of drawings]

Figure 1 is a diagram showing the changes in anode current and temperature of the thawed object as thawing progresses when the electrode spacing is constant, Figure 2 is a schematic diagram of the high-frequency thawing device, and Figure 3 is a diagram showing the changes in the temperature of the thawed object when the electrode spacing is changed. FIG. 4 is a diagram showing the changes in the anode current and the temperature of the object to be thawed as the thawing progresses. FIG. 1... High frequency oscillator, 2, 3... Electrode, 4... Thawing object. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. A high-frequency thawing method in which high-frequency waves are applied to an object to be thawed disposed between opposing electrodes via the opposing electrodes, and thawing is carried out while varying the electric field intensity of the high-frequency waves, wherein the electric field intensity is A high frequency defrosting method characterized in that the variable is performed by changing the spacing between the opposing electrodes after the anode current reaches its maximum value. 2. The high-frequency decompression method according to claim 1, wherein the electric field strength is varied in stages over time.