JPS6360989B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for freezing fresh foods, and more particularly to a method for freezing meat, seafood, vegetables, and other processed foods for long-term preservation in a fresh state. [Prior Art] There is a liquid immersion method as a food freezing method. This is a method of freezing food by immersing it in brine (antifreeze), but since the food is in close contact with the brine, the degree of freezing is large. Freezing is used to prevent drip formation and protein denaturation due to deterioration during frozen storage of food.
This is intended to make the tissue less susceptible to physical damage caused by ice crystals due to component concentration. For this reason, the basic idea has been to freeze food so that the freezing rate is as high as possible, the final temperature is as low as possible, and the contact between the cooling medium and the food is as close as possible. In this respect, the liquid immersion method is an excellent freezing method, and the inventors have been improving brine based on this theory. [Problems to be solved by the invention] However, in the liquid immersion method, a phenomenon occurs in which ice crystals grow in the center of the food and one thick ice crystal extends from the center toward the surface. The tissue is destroyed and the quality deteriorates.
The mechanism of this phenomenon is unknown, but it appears that the tissue ruptures from the center toward the surface.
It is thought that the entire surface of the food was rapidly frozen, causing distortion in the center, which reached its limit and was destroyed. As described above, the liquid immersion method has the disadvantage that the entire surface of the food is rapidly frozen, resulting in destruction of the center. This drawback is even more serious in the liquefied gas method, which uses liquefied gas with an extremely low boiling point. Therefore, an object of the present invention is to make it possible to freeze the entire food in good condition without deteriorating the quality of the center of the food. [Means for Solving the Problems] The inventor discovered that while all conventional freezing methods attempt to increase the contact area with the food surface as much as possible in order to rapidly freeze meat, Considering the disadvantage that ice crystals grow in the center and destroy the tissue, the idea was to freeze the whole food by freezing it from one side so that the freezing end point would not be inside the food. The method involves contacting one side of a heat transfer means such as a container, tray, or flat plate with cooled brine or low-boiling liquefied gas, and contacting the object to be frozen with the other side of the heat transfer means. Freezing progresses only from the surface. [Operation] This invention allows freezing to progress only from one side of the food in contact with the heat transfer means without freezing the entire food, so ice crystals do not grow inside the food and destroy the tissue. Freezing progresses inward from the contact surface with the heat transfer means and ends when it reaches the food surface other than the contact surface. The quality is uniform throughout. [Example] Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a schematic diagram of an apparatus embodying the method according to the present invention, in which 1 is a tank with an open top, 2 is a pipe installed in the tank 1, 3 is a compressor, and 4 is a heat transfer The container 5 is the object to be frozen. The tank 1 is filled with an inorganic or organic brine 6. The brine 6 is stirred by a stirring blade (not shown) in the tank 1, and is repeatedly compressed, liquefied, and evaporated by a compressor 3, and cooled by a refrigerant such as ammonia or fluorocarbon that circulates in the piping 2. be done. The heat transfer means is not limited to a container as shown in FIG. 1, but may also be a tray or a flat plate that does not sink unless the object to be frozen 5 comes into direct contact with the brine 6. Further, in this embodiment, the container 4 serving as a heat transfer means is floated on the brine 6, but the brine 6 is inside the container 4.
It may be removably fixed in the tank 1 as long as it does not fit inside the tank 1. The material of the heat transfer means is metal, resin, glass, or a composite thereof. In this embodiment, since the container 4 is floated, the convection of the brine 6 by the stirring blades is not impaired, and the liquid temperature near the surface can be maintained at a low temperature. The freezing method is as follows: 1 to 1 after putting the object to be frozen 5 into the container 4
After floating in brine 6 for 2 hours, the container 4 is pulled up and the frozen object 5 is removed. When freezing, it is important to note that heat transfer efficiency will be reduced due to frost and ice adhering to the bottom of the container 4, so when placing the frozen object 5 into the container 4, be sure to lift the container 4 from the brine 6 to remove frost and ice. It is to take. Although brine is used in this embodiment, a low boiling point liquefied gas such as liquid nitrogen or liquid carbon dioxide may be used. Next, experimental examples will be shown in which the freezing method according to the present invention was applied to various foods. Experimental Example 1 Pork with a thickness of about 75 mm and a weight of 1.1 kg was placed on an aluminum tray and frozen using the above method, and the temperature at each part was measured. The pork is chilled beef that has been refrigerated at 0°C. The brine was a mixture of 40% propylene glycol, 10% calcium chloride, 50% water, and a small amount of rapeseed oil, and was maintained at -37°C. As shown in FIG. 2, temperature measurements were made at three points: 15 mm from the tray near the center of the green meat (point A), 40 mm from the tray (point B), and 75 mm from the tray (point C). FIG. 3 is a plot of the measurement results as temperature vs. time, and it can be seen that freezing progresses from the bottom to the top. After freezing for 3 hours, -27℃ at point A and -23℃ at point B.
The temperature was -8°C at point C, but reached its lowest temperature at 5 hours, at -29°C at point A, -27°C at point B, -21°C at point C, and remained constant thereafter. In this way, the product temperature is considerably lower than that of conventional methods. We examined the frozen state inside the meat, but there was no difference between the surface and the center, and no ice crystals had grown throughout. After thawing, a sensory test was conducted, and evaluation was made with chilled meat that did not freeze as 100. The results are shown in Table 1. Table 1 also shows that meat that was directly immersed in brine and frozen was also evaluated in the same way.

〔Effect of the invention〕

In this invention, freezing starts from one side of the food and progresses to the other side through the inside of the food, without freezing from the entire periphery of the food. When the remaining unfrozen portion is frozen, the entire food is frozen in good condition without expanding and bursting and destroying the tissue of the object to be frozen. Therefore, frozen items can be kept in the same condition as fresh items. Therefore, the taste, color tone, and elasticity return to their original state after thawing, and furthermore, since there is no dripping after thawing, the freshness before freezing can be maintained. Furthermore, the method of the present invention has the advantage that there is no need to package the food.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus embodying the method according to the invention. FIGS. 2 and 3 relate to Experimental Example 1, in which FIG. 2 is a cross-sectional view showing the measurement method, and FIG. 3 is a freezing curve of pork. 1...tank, 2...piping, 3...compressor, 4...container, 5...material to be frozen, 6...brine.

Claims (1)

[Claims] 1. A container,
The feature is that one surface of a heat transfer means with an open top such as a tray or flat plate is brought into contact with the object to be frozen, while the other surface of the heat transfer means is brought into contact with the object to be frozen, so that freezing progresses only from the contact surface with the heat transfer means. Freezing methods for fresh foods.