Method for producing processed taro

Abstract

To provide a processed sweet potato production method which uses a refrigerated sweet potato having quality equal to that of a processed sweet potato which uses a raw sweet potato by contriving a refrigeration method and a heating method and which executes heating only once in order to prevent an original flavor of a sweet potato from being lost.SOLUTION: The processed sweet potato production method which produces processed sweet potatoes from raw sweet potatoes after storage includes: a raw sweet potato refrigeration step of refrigerating the raw sweet potatoes; a refrigerated raw sweet potato storage step of storing in a refrigerated manner the refrigerated raw sweet potatoes refrigerated in the raw sweet potato refrigeration step; and a refrigerated raw sweet potato heating step of heating the refrigerated raw sweet potatoes stored in a refrigerated manner in the refrigerated raw sweet potato storage step.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing processed taro that can maintain the quality of taro and can be easily processed when the taro is frozen and used as processed taro.

Background Art

[0002] Since taro has a higher water content and is more perishable than grains, the temperature must be strictly controlled for long-term storage. For example, sweet potatoes, which are widely loved among taro, are tropical crops and are vulnerable to cold. Therefore, if stored at 10°C to -1°C for a long time, cold damage will occur and they will rot. Also, since they will sprout when stored at 20°C or higher, it is considered preferable to store sweet potatoes at around 15°C. Although the suitable storage temperature varies depending on the type of taro, it is possible to suppress spoilage and sprouting and store them in an appropriate environment. However, even in an environment suitable for storage, deterioration gradually progresses. Therefore, in order to maintain the quality immediately after digging for a long time, frozen storage is often performed.

[0003] Currently, when freezing taro such as sweet potatoes, the dug taro is washed, sorted, and defective parts are removed. Then, heating is performed as a pretreatment for freezing. This heating operation is performed to inactivate the enzymes that cause the deterioration of taro and to suppress the occurrence of drip during thawing by making the starch granules contain moisture and bringing them into a gelatinized state. Also, as pretreatment methods other than heating, the taro may be shredded to shorten the freezing time, or immersed in a solution to obtain an effect of improving the breaking strength and preventing browning (see Patent Document 1).

[0004] Among the above-mentioned pretreatments, heat treatment is widely performed because the deterioration during storage is particularly small and it is a simple method. However, when the frozen taro, that is, the thawed frozen taro, is thawed naturally, it becomes mushy and the texture is impaired. Therefore, usually, when using frozen taro, reheating is performed to thaw it to prevent mushiness.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-124911 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] However, when using frozen taro, a total of two heatings are required, once before frozen storage and once at the time of use. Repeated heating causes problems such as deterioration of the original aroma and other qualities of the taro. Therefore, it has been required to perform the heat treatment only once, just as in the case of using fresh taro, even for frozen taro.

[0007] The present invention has been made in view of the above circumstances, and provides a method for producing processed taro using frozen taro, which has the same quality as processed taro using fresh taro. In the present invention, heating is performed only once so as not to impair the original aroma of the taro. [Means for Solving the Problems]

[0008] (1) One or more embodiments of the present invention are a method for producing processed taro by freezing and storing taro and performing heat cooking at the time of using the taro to obtain processed taro, wherein the taro to be frozen and stored is fresh taro, and the method includes a fresh taro freezing step of freezing the fresh taro. By this, heating before freezing the taro can be omitted.

[0009] (2) The fresh taro freezing step is characterized in that when freezing the fresh taro, the temperature change of the fresh taro from 15°C to -5°C is performed within 24 hours. By this, the fresh taro can be frozen and stored without causing low-temperature injury.

[0010] (3) In the frozen raw taro storage step of storing the raw taro frozen in the raw taro freezing step, the frozen raw taro is stored at an outside air temperature between -5°C and -50°C. By doing so, the activity of microorganisms during frozen storage can be suppressed, and the deterioration of the quality of the taro during storage can be prevented.

[0011] (4) The raw taro freezing step is characterized in that after once setting the outside air temperature to a temperature lower than the target temperature, the frozen raw taro is stored at the storage temperature. The method for manufacturing processed taro according to claims 1 to 3, wherein the time required for freezing can be shortened, and the working efficiency is improved.

[0012] (5) The frozen raw taro heating step is characterized in that the treatment of heating the frozen raw taro is carried out by heating with warm water at 60°C to 100°C or by steaming. By doing so, it is possible to prevent the deterioration of quality such as browning and drip caused by thawing.

[0013] Food and beverage processed products made from processed taro produced by the manufacturing method described in (1) to (5) above as raw materials.

[0014] According to the present invention, it becomes possible to freeze and store taro without performing pretreatment such as heating for freezing. In addition, since the heating is performed only once, it is possible to prevent the original aroma of the taro from being impaired. The taro obtained by the method can be used as a processing raw material for various food and beverage products including shochu. In addition, the taro obtained by the method, that is, frozen raw taro, can be used as a processing raw material for various food and beverage products including shochu.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0016] The present invention consists of three steps: freezing, storing, and heating and thawing of taro. Hereinafter, each step will be described in detail with reference to FIG. 1.

[0017] Unlike cereals such as rice and wheat, taro contains a large amount of water and is prone to spoilage, so it is necessary to control the temperature and humidity when storing for a long time. However, even when the temperature and humidity are appropriately controlled, the quality gradually changes. Therefore, as a method of preventing quality changes during storage, it is widely practiced to freeze and store taro after heating. This is because by heating once, the enzymes involved in quality changes are inactivated. In particular, in the case of taro native to the tropical regions, it also means inactivating the enzymes that cause cold damage. On the other hand, in the present invention, since the enzyme reaction can be stopped by freezing, a heat treatment before storage is not required.

[0018] First, the harvested taro (hereinafter referred to as raw taro) is washed, and both ends and damaged parts are removed. At this time, in order to prevent the generation of drip during thawing, it is desirable not to perform cutting as much as possible except for both ends and damaged parts, but cutting may be performed to make the sizes uniform so that heating can be performed uniformly in the heating step. This step is also carried out in the same manner when making conventional frozen taro.

[0019] In the raw taro freezing step ST1, which is a step of freezing raw taro in the present invention, the temperature at the center of the taro passes through the temperature range from 15°C to -5°C within 24 hours. This is because if the temperature drops below 15°C, which is the appropriate temperature for storage, and the taro is not completely frozen for a long time, its storage stability will be impaired. In particular, the range from 10°C to -5°C should be passed through within 9 hours. The range from 10°C to -1°C is the temperature range in which the taro is susceptible to low-temperature damage. In addition, the range from 0°C to -5°C is the temperature range in which the water inside the cells freezes. If the taro passes through this temperature range slowly, ice crystals will grow and the cells will be destroyed, making it easier for drip to occur during thawing. Therefore, it is important to lower the temperature within the above-mentioned time to prevent low-temperature damage and the growth of ice crystals.

[0020] As freezing methods, there are rapid freezing and slow freezing, and either can be used. A freezing method in which the temperature range from -1°C to -5°C is passed through within 30 minutes is generally called rapid freezing. For this rapid freezing, there are methods using refrigerants such as liquid nitrogen and brine solution, and methods using a freezer with high freezing capacity. Considering the actual case of rapidly freezing taro, the use of liquid nitrogen is not suitable for industrial use because of its high cost. In addition, brine solution is salt water, and there is a problem that the salt adhering to or penetrating into the taro affects the taste after thawing. Therefore, when performing rapid freezing in the present invention, it is preferable to use a freezer with high cooling capacity.

[0021] Also, the case of freezing over 30 minutes is generally called slow freezing. When taro is slowly frozen, if the temperature is lowered over too long a time, damage will occur due to changes in the cell membrane structure, leading to a decrease in quality. To minimize the quality degradation caused by slow freezing and obtain good workability, it is desirable to lower the internal temperature of the taro to -5°C or lower within 8 hours. Even if it exceeds 8 hours, if it is frozen within 24 hours, it will have little impact on the cell membrane structure, but if it exceeds 24 hours, there is a risk of quality degradation. In particular, freezing over 48 hours is likely to cause significant quality degradation and should be avoided if possible.

[0022] In the frozen raw taro storage process of ST2, the frozen raw taro produced in the frozen raw taro process is stored with the outside air temperature set from -5°C to -50°C. The set temperature of a household freezer is generally -18°C. Also, many industrial freezers have a set temperature ranging from -20°C to -30°C, but some can be set to -50°C. From these facts, in the utilization of the present invention, an outside air temperature in the freezer from -18°C to -50°C is assumed. Also, during freezing, after once cooling to below the target storage temperature, it may be transferred to an appropriate storage temperature. The storage temperature in this case is also preferably from -5°C to -50°C, and more preferably in the range of -18°C to -50°C.

[0023] For example, by rapidly freezing the taro in a freezer with an outside air temperature of -80°C, the time until freezing can be shortened, and after it is completely frozen, it can be transferred to a storage freezer with an outside air temperature of -20°C. At this time, it is desirable to avoid continuously storing at -80°C because the cost becomes high. In addition, long-term storage below -50°C is not preferable because it affects not only the cost but also the physical properties of the taro after heat thawing. Furthermore, it may be stored at -5°C where most of the water in the cells becomes ice, but for long-term storage at a temperature higher than -18°C, there is a risk of causing quality degradation because the activity of miscellaneous bacteria cannot be sufficiently suppressed. Therefore, storage in the temperature range of -5°C to -18°C is desirably carried out as a temporary measure to reduce the cost during heating. Thus, it is desirable to store at -5°C to -50°C after once lowering to below -50°C, and more desirably store at -18°C to -50°C for long-term storage.

[0024] The storage period of frozen raw taro is preferably about 6 months at the longest. Performing long-term frozen storage causes the frozen raw taro to dry out, which is the cause of the toughness when processed into processed taro.

[0025] In the frozen raw taro heating process of ST3, the frozen raw taro is heated by warm water at 60°C to 100°C or by steaming. At this time, it is desirable that the frozen raw taro is not naturally thawed or thawed with running water, but is heated and thawed immediately after being taken out of the freezing equipment. If heating is carried out after natural thawing or thawing with running water, browning and off-odor of the taro will occur. This is because when the taro passes through the temperature range of 10°C to -1°C during thawing, the activities of enzymes related to browning and degrading enzymes increase, but when thawed over time, these enzymes are given time to act. By rapidly heating to inactivate these enzymes before they act, it is possible to prevent deterioration such as the occurrence of browning and off-odor.

[0026] To prevent the deterioration of frozen stored taro, specifically, it is desirable to perform heat thawing so that the temperature inside the taro is raised in the range of -5°C to 85°C over 30 minutes to 120 minutes during thawing. In particular, when the temperature range from -5°C to 60°C is raised over 20 minutes to 80 minutes, the enzymes can be inactivated before deterioration occurs due to the action of the enzymes. Also, when the temperature is raised to 60°C, the starch in the taro gelatinizes and can retain moisture inside the cells, so dripping can be suppressed and the taro can be prevented from becoming mushy. Although it is desirable to continuously raise the temperature from -5°C to 85°C, after raising the temperature from -5°C to 60°C, the taro can be taken out once and heated by another method or the same method to raise the temperature to 85°C.

[0027] There are various heating methods. Generally, steaming, boiling, baking, grilling, frying, and using a microwave oven are used. Industrially, there are also electric heating and light heating. In electric heating, there are methods such as resistance heating, dielectric heating, and arc heating, and in light heating, there are methods using an infrared heater and a halogen heater. As another heating method, there is also a method of blowing hot air.

[0028] In the present invention, among the heating methods described above, those that can be easily implemented and are considered for use with food, steaming, boiling, baking, grilling, frying, or using a microwave oven are preferable, similar to cooking, and heating with hot air may also be used. However, the frying method in oil limits the processing method of the potatoes after heating. Also, methods such as baking, grilling, and applying hot air do not greatly limit the processing method after heating, but there is a problem that the temperature rise rate is slow except at the locations in contact with the heat source. From the above, steaming, boiling, or using a microwave oven, which enables uniform heating and does not limit the processing method after heating, is desirable. Also, the type of thawing device is not particularly limited, and batch thawing or continuous thawing using a thawing tank can be used.

[0029] The potatoes after heating according to the present invention can be used as raw materials for processed foods such as shochu, confectionery, and potato paste. For example, in the production of shochu, the steaming process before freezing the potatoes can be omitted. Of course, the potatoes after heating can be eaten as they are without processing.

[0030] The method for producing frozen raw potatoes according to the present invention omits the pretreatment steps such as heat treatment and shredding before freezing from the current frozen potato production process. The pretreatment mentioned here refers to heating, shredding, immersion in a solution, etc. performed for the purpose of preventing deterioration during freezing, and does not include washing, sorting, and excision of defective parts of the potatoes.

[0031] The potatoes that can be stored in the present invention are not particularly limited. Examples of potato varieties include sweet potatoes, as well as potatoes, taro, yam, yam bean, taro, cassava, etc. Among them, sweet potatoes, which contain a large amount of starch and are likely to retain moisture due to gelatinization, are preferable. In the embodiments described below, sweet potatoes are used for the description, but the present invention is not limited to the scope of the examples.

[0032] Previously, when storing tubers, heating was required twice, before storage and before use. However, by implementing the present invention, it becomes possible to perform heating only once before use. In addition, this method can suppress the loss of the aroma of tubers and can be used as a raw material for various foods and beverages.

Example

[0033] 〈Example 1〉 The temperature when freezing raw tubers was examined. Sweet potatoes immediately after harvest, washed and with defective parts cut off, were left standing in freezers at an outside air temperature of -20°C and -80°C to produce frozen raw sweet potatoes. The variety of sweet potato was Koganesengan, and the weight was approximately 200 g to 250 g. The freezers used and the storage temperatures were freezing at -20°C using Hosokazaki HF-63ST3 and at -80°C using Kanou Refrigeration LAB21.

[0034] The time required for the temperature inside the sweet potato to reach from 15°C to -5°C was approximately 25 minutes at an outside air temperature of -80°C and approximately 330 minutes at an outside air temperature of -20°C. When the temperature drop inside the sweet potato stopped, the lowest temperature inside the sweet potato stored at an outside air temperature of -20°C was -18°C, and the lowest temperature inside the sweet potato stored at an outside air temperature of -80°C was -67°C.

[0035] The frozen raw sweet potatoes stored at an outside air temperature of -20°C and -80°C were taken out of the freezer, put into a household steamer without thawing, and steamed at an outside air temperature of 100°C for 1 hour. Table 1 shows the results of a sensory test comparing the aroma, taste, and appearance of these sweet potatoes after steaming.

[0036]

Table 1

[0037] When storing at both cold storage temperatures of -20°C and -80°C, the quality of the steamed sweet potatoes did not deteriorate, and they showed almost the same aroma and taste as when fresh sweet potatoes were steamed. However, for the sweet potatoes stored at -80°C, a slight change was observed where the center part became slightly white and hard. Therefore, it was determined that a cold storage temperature of -20°C was more suitable for the production of frozen raw sweet potatoes.

[0038] <Example 2> It was considered to carry out the freezing process at a temperature lower than the storage temperature and store it at the target temperature after it was sufficiently frozen. Fresh sweet potatoes were frozen at an outside air temperature of -40°C, and frozen raw sweet potatoes obtained were prepared by transferring them to a freezer at an outside air temperature of -20°C for storage. After storing for one week, a steaming test was carried out to compare with the frozen raw sweet potatoes that were frozen and stored at an outside air temperature of -20°C. At this time, almost no difference in quality was observed for either of the frozen raw sweet potatoes. Carrying out the freezing process at a temperature lower than the storage temperature is effective as a method to shorten the time required for producing frozen raw sweet potatoes and improve work efficiency.

[0039] <Example 3> The thawing conditions of frozen raw sweet potatoes were investigated. Frozen raw sweet potatoes were produced from freshly harvested sweet potatoes that were washed and had defective parts cut off. The variety of sweet potatoes used was Koganesengan, the weight was 200 g to 250 g, and the set temperature of the freezer was -20°C. A Hosokazaki HF-63ST3 freezer was used. These frozen raw sweet potatoes were taken out after one month and put into a household steamer while still frozen, and steamed at an outside air temperature of 100°C for 1 hour. Also, to compare the effects of different thawing times, the frozen raw sweet potatoes were thawed naturally, by running water, and in warm water. Whether they were completely thawed was judged by the feel when touching the sweet potatoes. For these thawed sweet potatoes, steaming was also carried out at an outside air temperature of 100°C for 1 hour after thawing. Table 2 shows the results of a sensory test comparing the aroma and appearance of the steamed sweet potatoes.

[0040] [Table 2]

[0041] As shown in Table 2, when frozen raw sweet potatoes were thawed naturally, thawed in running water, and then steamed after thawing in 50°C warm water, significant browning was observed in the sweet potatoes, and the aroma of the sweet potatoes became extremely bad. When performing warm water thawing, by heating at 60°C or higher, the starch gelatinizes and can retain moisture inside the cells, so the generation of drip can be prevented. When thawed in 80°C warm water, it had a sweet aroma and had almost no effect on the texture. Also, when steamed after thawing in boiling water at 100°C, although it had a sweet aroma, the pulp became hard. When directly steamed, it had a sweet aroma and the texture was the same as when steaming raw sweet potatoes. From this, the aroma and physical properties of the sweet potatoes were most favorable when directly steamed without going through the thawing process.

[0042] 〈Example 4〉 Based on the results of Examples 1 and 3, a shochu production test using frozen sweet potatoes was carried out. Sweet potatoes immediately after harvest were washed and the defective parts were cut, and then frozen at an outside air temperature of -20°C and -80°C to produce frozen raw sweet potatoes. After one month, these frozen raw sweet potatoes were taken out, put into a household steamer while still frozen, and steamed at an outside air temperature of 100°C for 1 hour. After removing the rough heat, they were crushed to be less than 2 cm square. For comparison, frozen sweet potatoes produced by the conventional method of freezing after steaming and stored at -20°C for one month, and raw sweet potatoes stored at 15°C, the optimal storage temperature for raw sweet potatoes, for one month were also steamed at 100°C for 1 hour using a household steamer, and after removing the rough heat, they were crushed to be less than 2 cm square.

[0043] 200 g of rice koji and 200 g of water added with Kagoshima No. 5 yeast were mixed to obtain a first mash, and this first mash was fermented at 30°C for 5 days. 1000 g of crushed sweet potatoes and 540 g of water were added to this first mash and mixed well to obtain a second mash. This second mash was fermented at 30°C, and distillation was carried out on the ninth day after adding the sweet potatoes to obtain sweet potato shochu. The alcohol content of the obtained sweet potato shochu was approximately 37%.

[0044] In the production of sweet potato shochu, even when using frozen raw sweet potatoes, a good fermentation process was followed. There was also no significant difference in the speed of alcohol production and the amount of alcohol obtained compared to the cases of using raw sweet potatoes or frozen sweet potatoes. From the above points, it was found that using frozen raw sweet potatoes does not affect fermentation, and conventional production is possible.

[0045] The obtained sweet potato shochu was left to stand for about one month, then filtered and watered down to adjust the alcohol content to 25%. Gas chromatographic analysis was performed on these shochus to compare the aroma components. The gas chromatographic analysis apparatus used was an Agilent 5973 MSD. The general aroma components at this time are shown in Figure 2, and the trace aroma components are shown in Figure 3.

[0046] Regarding the general aroma components shown in Figure 2, regardless of the storage conditions of the sweet potatoes, almost equivalent values were shown. It was found that even when using frozen raw sweet potatoes, there is no significant impact on the aroma, and shochu with the same aroma as before can be obtained.

[0047] The trace aroma components shown in Figure 4 are the components that characterize the aroma of sweet potato shochu. However, when the sweet potatoes deteriorated, they increased significantly, showing concentrations dozens to hundreds of times higher than those when using fresh sweet potatoes. When making shochu with such deteriorated sweet potatoes, the trace aroma components are recognized as a pungent smell. In gas chromatographic analysis, an increase in trace aroma components could not be confirmed for the shochu produced using frozen raw sweet potatoes, and it showed values similar to or lower than those of raw sweet potatoes.

[0048] When sensory evaluation was conducted by three sake-tasting experts, no abnormal odors such as pungent smell were confirmed in the shochu produced using frozen raw sweet potatoes. Regarding the difference in aroma between the shochu made with raw sweet potatoes or frozen sweet potatoes, sake-tasting experts could hardly feel any difference even when tasting the sake. From this, it was confirmed that high-quality shochu can also be produced when using frozen raw sweet potatoes.

[0049] From Example 4, it was shown that it is fully possible to produce shochu using frozen raw taro. Also, regarding the aroma and texture of sweet potatoes, since they are not inferior compared to the case of steaming raw taro, the uses are not limited to shochu production, and in addition to the aroma, they can also be used for confectionery production where color and texture are emphasized.

[0050] <Example 5> When heating frozen raw taro, since the temperature of the frozen raw taro is lower than that of raw taro, it is necessary to heat it for a longer time than raw taro. Actually, when steaming frozen raw taro for 60 minutes in the same way as when steaming raw taro, there are cases where a fishy smell is felt from the frozen raw taro even after steaming, suggesting that the heating is insufficient.

[0051] To sufficiently heat the frozen raw taro, the temperature of the frozen raw taro stored at -20°C in the warehouse during steaming was measured over time and compared with the case of steaming raw taro. Steaming was carried out using a household steamer, and immediately after the steam passed through, the raw taro and the frozen raw taro taken out from the freezer were put in. The internal temperature of the frozen raw taro at the start of steaming was -17°C, and the temperature of the raw taro was 18°C. The temperature change at this time is shown in Figure 4. The raw taro was taken out 60 minutes after being put into the steamer.

[0052] At this time, in order to steam the frozen raw taro to the same extent as steaming the raw taro for 60 minutes, approximately 80 minutes of steaming was required. After sufficient steaming, no fishy smell was felt from the frozen raw taro, and the quality as a shochu raw material improved in terms of aroma.

[0053] <Example 6> When producing shochu with frozen taro, another problem is that the sweet potato is easily crushed by the steaming performed before charging, and clogging of the production line is likely to occur, resulting in a decrease in workability. In order to obtain good workability, it is desirable that the hardness of the sweet potato after steaming is the same as that after steaming raw taro. Therefore, the hardness of the sweet potato was measured.

[0054] Raw sweet potatoes were cut and 2-cm cubes were prepared. These cubes were stored frozen at -20°C to obtain frozen raw sweet potato cubes. Also, cubes that were steamed for 15 minutes were used as standard raw sweet potato cubes. After the rough heat was removed, they were immediately subjected to measurement. A part of the steamed cubes was stored frozen at -20°C to obtain frozen sweet potato cubes. For the frozen raw sweet potato cubes and the frozen sweet potato cubes, on the day after freezing, they were thawed by steaming, and after the rough heat was removed, they were immediately subjected to measurement. Table 3 shows the steaming times of each sweet potato cube. For the measurement, a texture meter CR-500DX and COMPAC-100 manufactured by Sun Scientific were used. A cylindrical acrylic plunger with a diameter of 10 mm was attached, and the measurement was carried out at a compression speed of 1 mm / second and a maximum load of 20 N.

[0055]

Table 3

[0056] When based on raw sweet potatoes steamed for 15 minutes (raw sweet potato A), the maximum breaking stress load of the frozen steamed sweet potatoes was reduced to less than half. On the other hand, when the frozen raw sweet potatoes were steamed for the same time as the raw sweet potatoes, they were slightly hard (frozen raw sweet potato A), but by extending the steaming time, they became as hard as the raw sweet potatoes (frozen raw sweet potato B). The results at this time are shown in Figure 5. From these results, it was found that the frozen raw sweet potatoes are harder than the frozen sweet potatoes and are less likely to be crushed.

Claims

1. A method for manufacturing processed taro, which involves processing raw taro into processed taro after preservation, the method comprising: a raw taro freezing step of freezing raw taro; a frozen raw taro preservation step of preserving the frozen raw taro frozen in the raw taro freezing step; and a frozen raw taro heating step of heating the frozen raw taro frozen and preserved in the frozen raw taro preservation step by steaming. The method for manufacturing processed taro is characterized by including these steps.

2. The method for manufacturing processed taro according to Claim 1, wherein in the raw taro freezing step, when setting the outside air temperature for freezing the raw taro, the temperature change of the raw taro from 15°C to -5°C is carried out within 24 hours.

3. The method for manufacturing processed taro according to Claim 1 or 2, wherein in the frozen raw taro preservation step, the frozen raw taro is preserved at a predetermined temperature between -5°C and -50°C for the outside air temperature setting.

4. The method for manufacturing processed taro according to any one of Claims 1 to 3, wherein in the raw taro freezing step, the outside air temperature is set to a temperature lower than the target preservation temperature once, and then the frozen raw taro is preserved at the preservation temperature.

5. The method for manufacturing processed taro according to any one of Claims 1 to 4, wherein the taro is sweet potato.

6. A method for manufacturing shochu using processed taro, which involves freezing and preserving taro and heating and cooking the taro when it is used to make processed taro. The method for manufacturing shochu is characterized by including: a raw taro freezing step of freezing the raw taro, which is the taro to be frozen and preserved; a frozen raw taro preservation step of preserving the raw taro frozen in the raw taro freezing step; a frozen raw taro heating step of heating the frozen raw taro preserved in the frozen raw taro preservation step with warm water at 60°C to 100°C or by steaming to obtain the processed taro; a shochu manufacturing step of making a primary mash by adding water and yeast to koji, adding the crushed processed taro and water to the primary mash to make a secondary mash when alcohol fermentation progresses, and performing distillation to obtain shochu when alcohol fermentation has sufficiently progressed.

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