JP2017009272A - Freezing method and freezing device of food product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a freezing method and a freezing device of an unheated food product, capable of reducing drips after thawing, and easily and surely obtaining a frozen food excellent in the repeatability of a quality before freezing.SOLUTION: There are included: a step of seal packaging a food product; a cooling step of soaking the food product in a liquid refrigerant formed with flow and cooling and holding the food product at a temperature of 0°C or lower, preventing freezing; and a freezing step of soaking the food product in an antifreeze liquid at -20°C or lower followed by freezing from a super cooling state. A freezing device includes: a refrigeration tank for storing a liquid refrigerant at 0°C or lower; a cooling tank for storing an antifreeze liquid at -20°C or lower; a cooling mechanism included in the outside of the cooling tank and cooling the antifreeze liquid; and a circulation mechanism circulating the antifreeze liquid between the cooling tank and the cooling mechanism and forming air jet of the antifreeze liquid in the cooling tank.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for freezing cooked or semi-cooked food and a freezing apparatus therefor, and in particular, a method for freezing food that suppresses the occurrence of drip at the time of thawing and has excellent reproducibility of quality before freezing. The present invention relates to a refrigeration apparatus.

  In order to preserve food for a long period of time, it is frozen and the quality of the food after thawing is often a problem. In particular, in a cooked or semi-cooked food, since the ingredients are greatly changed locally, the process of freezing and thawing is very complicated and it is difficult to maintain the quality. For example, when freezing is performed at a slow cooling rate, the passage time of the maximum ice crystal formation zone, which is a temperature range in which ice crystals are generated, becomes long. At this time, ice crystals grow large starting from the most freezing portion in the food, the cell membrane of the food breaks down, and moisture containing umami components and the like flows out as a drip when defrosting and deteriorates the texture. On the other hand, a technique for rapidly freezing food is also known. That is, the ice crystal growth is suppressed by rapidly passing through the maximum ice crystal formation zone.

  For example, Patent Document 1 discloses a freezing method in which an uncooked food such as meat or fresh fish is rapidly frozen using an ethyl alcohol antifreeze. Here, a refrigeration apparatus comprising a freezing tank having a refrigerant pipe on the side wall for containing antifreeze liquid and having an opening in the upper part, and a basket-like liquid-permeable container provided in the upper part thereof so as to be movable up and down and containing food inside. Is used. The food contained in the liquid-permeable container is immersed in the antifreeze liquid in the freezing tank and frozen, but when brought into contact with the antifreeze liquid having a larger heat capacity than air, it can be cooled more rapidly than air cooling. In other words, since the maximum ice crystal formation zone is passed in a short time, the ice crystals to be generated do not grow greatly, and drip at the time of thawing food can be reduced.

  Similarly, in Patent Document 2, in the rapid freezing of food using an antifreeze, a crack in the outside of the food is caused by expansion of the food that freezes with time delay by increasing the temperature gradient in the thickness direction of the food. It describes the so-called cracking problem that causes For example, when a food having a thickness of 18 mm or more and having a temperature difference of 60 ° C. or more with respect to the antifreeze liquid is likely to be cracked. On the other hand, the freezing method which freezes the uncooked or cooked food by being immersed in the antifreeze liquid (frozen liquid) of the range which makes the temperature difference with the food before freezing (before immersion) 20-40 degreeC is disclosed. ing. For example, the temperature of food after freezing is −20 ° C. using an antifreeze solution of −35 ° C., but the temperature difference from the antifreeze solution can be reduced to 40 ° C. or less by pre-cooling the food to about 0 to 3 ° C. In addition, the temperature gradient in the thickness direction of food immersed in antifreeze can be reduced, and the food can be prevented from cracking.

  In addition, Patent Document 3 states that even in quick freezing, the cooling rate at the center is slow, and it is not always easy to reduce the amount of drip at the time of thawing and to perform high-quality freezing. Uncooked food using supercooling The freezing method is described. First, a cold air having a first temperature lower than the freezing point is applied to the food to lower the temperature while keeping the food in a supercooled state. After the supercooled state is eliminated and ice crystals are generated, the food is further lower than the first temperature. Cool with cold air at the second temperature. Here, it is stated that a supercooled state can be stably maintained by slow cooling. When cold air is applied only to the top surface of the wrapped beef, the temperature and wind speed of the cold air that can be cooled more rapidly and stably reach the supercooled state are examined. For example, in the case of cold wind at −7 ° C. and a wind speed of 0.2 m / s, a supercooled state can be obtained with a probability of 95%.

JP-A-6-129747 JP-A-6-46813 JP 2009-44981 A

  Cooling to a lower temperature while stably maintaining the supercooled state of the food requires cooling at a slow cooling rate as described in Patent Document 3, depending on the flow rate and temperature conditions of the cooling medium. The supercooled state cannot be maintained with a certain probability. In particular, in the case of cooked foods and semi-cooked foods, the freezing point of water can be lowered due to seasoning or the like. This can greatly change locally within a single food, and the freezing point is also locally different along with this, and the conditions necessary for cooling while maintaining a stable supercooled state also change locally. It is. That is, it is difficult to cool to a lower temperature while stably maintaining such a supercooled state of food. In addition, if the supercooling state could not be maintained despite cooling at a slow cooling rate to maintain the supercooled state, the slow cooling rate and the generation of water solidification heat due to the formation of ice, Food can be exposed to the maximum ice crystal formation zone for extended periods of time. As a result, the quality of food is greatly reduced as in the case of freezing at a slow cooling rate without using supercooling.

  The present invention has been made in view of the situation as described above, and the object of the present invention is to provide a frozen food that can reduce drip after thawing and has excellent quality reproducibility before freezing. An object of the present invention is to provide a method and apparatus for freezing cooked or semi-cooked food that can be reliably obtained.

  The freezing method according to the present invention is a method of freezing unheated food, the step of hermetically packaging the food, and immersing the food in a liquid refrigerant in which a flow is formed so that the food is not frozen below 0 ° C. A cooling step of cooling and holding at a temperature, and a freezing step of immersing the food in an antifreeze solution of −20 ° C. or lower and freezing from a supercooled state.

  According to such an invention, even a non-heated food can be passed through the maximum ice crystal formation zone faster than a case where the food is cooled with an antifreeze liquid from room temperature by a simple method of adding a cooling step. Thus, a drip after thawing can be reduced and a frozen food excellent in reproducibility of quality before freezing can be obtained.

  In the above-described invention, the liquid refrigerant may be an aqueous phase or an aqueous phase including a solid phase. According to this invention, it is possible to easily hold the food at a temperature not to be frozen at 0 ° C. or less, reduce drip after thawing, and obtain a frozen food excellent in reproducibility of quality before freezing.

  In the above-described invention, the freezing step is a step in which the antifreeze liquid is circulated between a cooling tank and a cooling mechanism to form a jet of the antifreeze liquid in the cooling tank and the food is disposed therein. It is good. According to this invention, the cooling rate of the food in the freezing step can be further increased, the maximum ice crystal formation zone can be passed faster, the drip after thawing can be reduced, and the quality reproducibility before freezing can be reduced. Frozen food with excellent quality can be obtained.

  In the above-described invention, the antifreeze liquid may be ethanol brine containing ethanol. According to this invention, an antifreeze can be prepared easily, drip after thawing can be reduced, and a frozen food excellent in reproducibility of quality before freezing can be obtained more easily.

  Moreover, the freezing apparatus according to the present invention is a freezing apparatus for freezing unheated food, a refrigeration tank storing liquid refrigerant at 0 ° C. or lower, a cooling tank storing antifreeze liquid at −20 ° C. or lower, A cooling mechanism provided outside the cooling tank for cooling the antifreeze liquid to at least −20 ° C. or less, and circulating the antifreeze liquid between the cooling tank and the cooling mechanism to cause a jet of the antifreeze liquid to flow into the cooling tank. And a circulation mechanism to be formed.

  According to this invention, even an unheated food can increase the cooling rate of the food, can pass through the maximum ice crystal formation zone quickly, can reduce the drip after thawing, and the quality before freezing Frozen food with excellent reproducibility can be obtained.

It is a flowchart of the freezing method by this invention. It is a block diagram (partial sectional view) of a refrigeration apparatus according to the present invention. It is a figure which shows the result of a freezing test. It is a figure which shows the result of a defrost test. It is a cross-sectional photograph of the food after the thawing test.

  Hereinafter, one embodiment of the method for freezing cooked or semi-cooked food according to the present invention will be described with reference to FIG. The freezing method of the present invention is excellent in the reproducibility of the quality before freezing, particularly in a cooked or semi-cooked food, but is also excellent in the reproducibility of the quality before freezing even in a food material that is not subjected to cooking. Needless to say.

  As shown in FIG. 1, first, food is cooked (S1). The food handled here is a food containing water at the time of freezing described later. For example, it may be a cooked or semi-cooked food containing a liquid containing an umami component such as soup stock, and the freezing point may be different depending on a local salt concentration difference. The cooked food is, for example, boiled food, and the semi-cooked food is steamed with tea before being solidified by heating. Alternatively, it may be a semi-cooked food that has been washed or cut. Semi-cooked foods include foods that have been manipulated to affect the reproducibility of quality before freezing. For example, vegetables, fruits, fresh fish, etc. whose interiors are exposed by cutting. In addition, even if it is a food raw material which does not perform cooking, it has the difference of a local freezing point to some extent, However, Such a food raw material may be sufficient and is included in the half-cooked food here for convenience.

  Next, the above food is hermetically packaged (S2). For hermetic packaging, for example, a bag-like or cup-like container made of resin can be used. Here, the wall thickness of the bag or cup is preferably thin so that the inside can be efficiently cooled by cooling from the outside of the container. If the container is filled with food and sealed with gas, it may be replaced with non-oxidizing gas and sealed, but in consideration of thermal conductivity, gas should be filled as much as possible. It is preferable to exclude them.

  Subsequently, the hermetically packaged food is cooled and held at a temperature at which it is not frozen (S3). The lower the temperature at which the food is kept freezing, the lower the temperature, and the more preferable is the so-called ice temperature range that is higher than the freezing point of the food at 0 ° C. or lower. If food is partially frozen, ice crystals can grow starting from this, so it is important not to freeze even part of the food. Therefore, it is preferable to keep the food at a temperature equal to or higher than the freezing point by using a cooling medium cooled to an ice temperature range. In particular, cooked foods have locally varying water salinity levels and varying freezing points. Therefore, if ice water is used, the temperature in the ice temperature range can be obtained very easily and reliably, and the cooling rate of food can be increased by having a higher thermal conductivity and higher heat capacity than air. preferable. That is, it is preferable that the food is immersed in ice water and kept cooled. A small amount of salt may be added to the ice water to adjust the temperature of the ice water within the ice temperature range of the food.

  Referring also to FIG. 2, the refrigeration unit 20 on the left side of the refrigeration apparatus 30 can be used for such cooling and holding. The refrigeration unit 20 includes a refrigeration tank 24 in the lower body 21, stores water in the refrigeration tank 24, and includes a heat exchanger 27 as a cooling mechanism that cools the water. The lower body 21 is provided with a pump 25 for circulating water between the refrigeration tank 24 and the heat exchanger 27 to form a flow of water in the tank and stir. The refrigeration unit 20 also includes a basket 26 that is immersed in water while holding the food to be cooled and held.

  The cooling unit 20 further includes an elevating device 28 that elevates and lowers the car 26 with a wire or the like in the upper main body 22, and an operation panel 29 for controlling operations of the elevating device 28, the pump 25, and the heat exchanger 27. The upper body 22 is further provided with a door 32 into which the car 26 can be taken in and out. That is, the food that is hermetically packaged is held in the basket 26, and is inserted into the upper body 22 from the 32 doors and attached to the lifting device 28. The operation panel 29 is operated to lower the car 26 by the elevating device 28 and immerse it in water from the upper part of the cooling bath 24. As a result, the food can be kept cooled.

  At this time, if the water is iced water and cooled by the heat exchanger 27 so that both the water phase and the solid phase can be maintained, the temperature can be easily set to the ice temperature range. Further, salt or ethanol may be added to water to lower the freezing point below 0 ° C., and the temperature may be controlled to be in the ice temperature range according to the food to be cooled and held.

  In the cooling holding, it is preferable that the core temperature of the food is also cooled to near the ice temperature range to reduce the temperature gradient inside the food. Therefore, it is advisable to determine the holding time in advance depending on the type and size of the food.

  Subsequently, the hermetically sealed food is immersed in an antifreeze solution of −20 ° C. or lower and frozen under supercooling (S4). The refrigeration unit 10 of the refrigeration apparatus 30 described above can be used for such freezing.

  Referring to FIG. 2 again, the refrigeration apparatus 30 includes the refrigeration unit 10 on the right side in the figure. The refrigeration unit 10 includes a freezing tank 4 formed of a heat insulating wall 3 in the lower body 1, stores an antifreeze liquid 11 in the freezing tank 4, and includes a heat exchanger 7 as a cooling mechanism that cools the antifreeze liquid 11. The lower body 1 is provided with a pump 5 for circulating the antifreeze liquid 11 between the freezing tank 4 and the heat exchanger 7 to form a flow of the antifreeze liquid 11 in the tank and stirring it. In particular, the pump 5 is capable of ejecting the high-pressure antifreeze 11 from a nozzle or the like so that the flow rate of the antifreeze 11 to be circulated becomes high. The pump 5 may include a conduit that guides the antifreeze liquid 11 cooled from the heat exchanger 7. The freezing unit 10 also includes a car 6 that is immersed in the antifreeze liquid 11 while holding the food to be frozen. In addition, although a cooling tank is good also as a structure which equips a side surface with a heat exchanger, when it is the cooling tank 4 provided with said heat exchanger 7 and the pump 5, the cooling rate of a foodstuff can be made high and it is preferable.

  The refrigeration unit 10 further includes an elevating device 8 that elevates and lowers the car 6 with a wire or the like in the upper body 2, and an operation panel 9 for controlling the operations of the elevating device 8, the pump 5, and the heat exchanger 7. The upper body 2 is further provided with a door 12 into which the car 6 can be taken in and out.

  As the antifreeze 11, for example, ethanol brine using an aqueous solution of about 50% by volume of ethyl alcohol can be used. Depending on the temperature of the food held in the cooling holding (S3), the amount of food, the speed of the jet of the antifreeze 11 and the like, the antifreeze 11 can freeze the food exposed to the jet under supercooling. Preferably, it is a liquid that can be cooled at once to a temperature of about -20 to -30 ° C, for example, and is controlled to a temperature of at least -20 ° C or less as described above. That is, when the antifreeze liquid 11 comes into contact with the surface of the container in which the food is hermetically packaged while maintaining the liquid phase, the heat of the container is efficiently absorbed, and the food in the container is reliably cooled, preferably at a stretch under supercooling. It can be frozen.

  In the freezing of the food (S4), the hermetically packaged food is held in the car 6, inserted into the upper body 2 from the door, and attached to the lifting device 8. The operation panel 9 is operated to lower the car 6 by the elevating device 8 and immerse it in the antifreeze 11 from the upper part of the freezing tank 4. At this time, the antifreeze 11 given as a jet efficiently removes heat from the surface of the food container, and the food inside the container can be surely brought into a supercooled state and can be quickly frozen. In particular, since the food is cooled in the cooling hold (S3), it is frozen at a stretch from the supercooled state.

  When the supercooled state is cancelled, freezing of water locally starts in the food and heat of solidification is generated. With normal slow cooling, this increases the temperature of the food and makes it difficult for freezing to proceed, resulting in a longer stay in the maximum ice crystal formation zone. On the other hand, according to the present embodiment, the amount of heat held by the food is reduced by cooling and holding (S3), and the amount of heat obtained by totaling the heat of solidification accompanying freezing of moisture is also reduced. Therefore, the temperature of the food can be rapidly lowered even after the supercooled state is released in the process of rapid freezing. This speeds up at least the maximum ice crystal formation zone and reduces quality degradation after thawing, compared to conventional quick freezing, where food stored at room temperature is rapidly frozen with antifreeze. .

  In particular, if the core temperature of the food is cooled to near the ice temperature range in the cooling hold (S3), the thermal gradient in the thickness direction of the food is small even when rapidly cooled in the freezing (S4). Almost the entire region can be supercooled. That is, the food can be frozen from the supercooled state at once without performing difficult control such as cooling the whole area of the food to a low temperature below the freezing point while stably maintaining the supercooled state at a slow cooling rate. . Therefore, even a cooked or semi-cooked food having locally different components such as salt concentration and different freezing points can be frozen at a stretch from a supercooled state.

  Moreover, according to the freezing part 10, as mentioned above, the jet of the antifreeze liquid 11 can be formed in the freezing tank 4, and the cooling rate of a foodstuff can be maintained high. This also makes it possible to increase the speed of passing through the maximum ice crystal formation zone, and to reduce deterioration in quality after thawing.

  The food frozen in this way is stored, thawed, cooked as appropriate, etc., and used for food. Even if it is cooked or semi-cooked, It can be made into a food with little production, little deterioration of quality, that is, excellent reproducibility of quality before freezing.

[Freezing test]
Next, a refrigeration test comparing the refrigeration method according to the present embodiment with other refrigeration methods will be described with reference to FIG.

  In the freezing test, it is generally considered that the quality after thawing is likely to deteriorate due to freezing, which is boiled cotton tofu (boiled cotton tofu), boiled konjac (boiled konnyaku) , Raw strawberries and konjac jelly were used. First, these foods were hermetically packaged approximately 100 g each in a bag-like container made of resin. In addition, about the konjac jelly, about 25g was used for the commercial item enclosed with the airtight container as it was. The method of the present invention is excellent in the reproducibility of the quality before freezing even for foods that are not particularly cooked. For this confirmation, a freezing test is also performed on raw strawberries.

  As shown in FIG. 3, the food was frozen by the cooling methods of Comparative Example 1, Comparative Example 2, and Example. In Comparative Example 1, slow freezing was performed. Specifically, the hermetically sealed food was kept at 20 ° C. and cooled by air at −20 ° C. In Comparative Example 2, quick freezing was performed. Specifically, the hermetically packaged food was held at 20 ° C. and cooled by immersing in ethanol brine at −30 ° C. using the freezing unit 10 of the above-described freezing device 30. In the examples, quick freezing was performed after cooling. That is, in the method of the above-described embodiment, specifically, the hermetically packaged food is immersed in ice water using the refrigeration unit 20 of the refrigeration apparatus 30 described above, and 1 ° C. in order to bring the core temperature close to 0 ° C. It hold | maintained until it became below, and it immersed in -30 degreeC ethanol brine using the freezing part 10, and cooled. The core temperature can be measured, for example, by separately preparing a food for core temperature measurement in which a thermometer is inserted up to the core and simultaneously cooling the food.

  FIG. 3A shows the time required for the food to freeze. That is, in Comparative Example 1, the time from the start of cooling with air at −20 ° C., and in Comparative Example 2 and Examples, the time after immersion in ethanol brine. In addition, freezing was confirmed by measuring the core temperature of the food and becoming −10 ° C. or lower. Moreover, in FIG.3 (b), the time required until freezing by quick freezing after the cooling by an Example was set to 1, and the ratio with respect to this was shown. In the figure, “x” indicates that the product was not frozen even after cooling for 180 minutes.

  In any food, the time required for freezing was the shortest in the example. It can be estimated that the speed of passing through the maximum ice crystal formation zone was also the fastest in the case of the example.

[Thawing test]
Furthermore, the thawing test performed on the food frozen in each of Comparative Example 1, Comparative Example 2, and Example described above will be described with reference to FIGS.

  As shown in FIG. 4, the amount of drip produced by further natural thawing of the foods frozen by the methods of Comparative Example 1, Comparative Example 2, and Example other than konjac jelly was measured. The method is as described above for the refrigeration test. However, the food that was not frozen by slow freezing for 180 minutes in Comparative Example 1 was further cooled, and the whole food was frozen before being subjected to a thawing test. The weight (drip amount) of the drip produced was expressed as a percentage of the drip rate relative to the weight of the food (sample amount).

  It is considered that the drip rate is the smallest in the case of Examples in any food, and the quality deterioration after thawing is the least.

  Furthermore, the cross-sectional photograph is shown in FIG. In Comparative Example 1, nests are apparently generated, and it is considered that the ice crystals grew greatly by staying in the maximum ice crystal formation zone for a long time. On the other hand, in the comparative example 2 and the example, no nest was generated, and it is considered that there was little quality deterioration. The same tendency was observed in konjac boiled and strawberry.

  As a result of tasting after thawing and observing the texture and taste of each of the tofu boiled cotton, konnyaku boiled and strawberries, the taste of the comparative example 1 is clearly deteriorated. The texture was like a lump and had a difficult texture for use as a food. There was a clear difference in taste and texture between Comparative Example 2 and the Examples, and the Examples had a taste and texture close to those before freezing. This is supported by the difference in drip amount described above.

  As described above, according to the above-described embodiment, as can be seen from the fact that the amount of drip after thawing is smaller than that of Comparative Example 1 and Comparative Example 2, freezing that suppresses the deterioration of the quality of the food after thawing is achieved. Make it possible. In particular, the quality after thawing, even for cooked or semi-cooked foods that are difficult to cool to a low temperature below the freezing point while stably maintaining a supercooled state at a slow cooling rate Deterioration can be suppressed, drip after thawing can be reduced, and a frozen food excellent in reproducibility of quality before freezing can be obtained easily and reliably.

  As mentioned above, although the Example by this invention and the modification based on this were demonstrated, this invention is not necessarily limited to this, A person skilled in the art will deviate from the main point of this invention, or the attached claim. Various alternative embodiments and modifications could be found without doing so.

5 Pump 6 Basket 10 Refrigeration unit 11 Antifreeze 20 Refrigeration unit 30 Refrigeration equipment

Claims (5)

A method for freezing unheated food,
Sealing and packaging the food;
A cooling step of immersing the food in a liquid refrigerant in which a flow is formed and cooling and holding the food at a temperature of 0 ° C. or less and not freezing;
A freezing step comprising immersing the food in an antifreeze at −20 ° C. or lower and freezing it from a supercooled state.   The refrigeration method according to claim 1, wherein the liquid refrigerant is an aqueous phase or an aqueous phase including a solid phase.   2. The freezing step is a step of circulating the antifreeze liquid between a cooling tank and a cooling mechanism to form a jet of the antifreeze liquid in the cooling tank and disposing the food product therein. Or the freezing method of 2.   The freezing method according to any one of claims 1 to 3, wherein the antifreeze is ethanol brine containing ethanol. A freezing device for freezing unheated food,
A refrigerated tank storing liquid refrigerant at 0 ° C. or lower;
A cooling tank for storing an antifreeze at −20 ° C. or lower;
A cooling mechanism provided outside the cooling tank to cool the antifreeze liquid to at least −20 ° C. or less;
A refrigeration apparatus comprising: a circulation mechanism that circulates the antifreeze liquid between the cooling tank and the cooling mechanism to form a jet of the antifreeze liquid in the cooling tank.