JPH0424018B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to drying of shiitake mushrooms, and particularly to a method of drying shiitake mushrooms suitable for shortening drying time.

[Conventional technology]

Harvested shiitake mushrooms generally contain 87-92% water, but in order to make dried shiitake mushrooms that can be stored, they must be dried to reduce the water content to 15-17%.

Hot air drying is a common method for artificially drying shiitake mushrooms, and the drying time is shortened by increasing the temperature of the drying air and the amount of dehumidification. However, the drying heat source uses hot air (dry air) made by heating the air with a heater, etc., so if high-temperature air is used in the early stage of drying, the temperature difference between the hot air and the surface of the shiitake mushrooms will increase, causing moisture to be removed from the surface. Evaporation (transpiration) becomes active. On the other hand, water movement (diffusion) from the inside of the shiitake mushroom to the surface cannot follow this movement, so
The temperature of the hot air cannot be made too high.

If you try to dry the mushrooms too quickly and make the hot air temperature higher than necessary, the colloidal substances, sugars, and
Acids, free amino acids, inorganic salts, etc. stick to the surface layer,
A so-called surface hardening phenomenon occurs. The hardening of the surface of the shiitake mushroom due to this phenomenon blocks the evaporation of internal moisture to the outside, further delaying subsequent drying.

Therefore, it is common to use a drying method in which the drying hot air temperature is gradually raised in stages from a low temperature of 30 to 45°C. For example, Japanese Patent Application Laid-Open No. 195642/1984 can be cited as an improvement on such a stepwise temperature raising drying method.

However, even with this drying method, since hot air is used to warm the air, the temperature of the hot air at the initial stage of drying must be set low to prevent surface hardening of the shiitake mushrooms.

According to the disclosed example, 2 at 45°C in Hiwako
It takes 2 hours at 40℃ in Ameko. Furthermore, the temperature of the hot air in the latter stages of drying is not too high at 60°C.

Therefore, even in the former case, there is a problem in that the drying time is as long as 11 hours.

[Problem to be solved by the invention]

In the conventional method of drying shiitake mushrooms, the hot air temperature at the beginning of drying is set low to prevent surface hardening of shiitake mushrooms, and the temperature at the end of the dryer is not very high, so it takes a long time to dry. There was a problem.

An object of the present invention is to provide a method for drying shiitake mushrooms that can significantly shorten the drying time by using a closed circuit drying method that circulates high-temperature hot air.

[Means to solve the problem]

In order to achieve the above object, the method for drying shiitake mushrooms according to the present invention includes storing shiitake mushrooms in a dryer and circulating hot air through the dryer, humidifying the relative humidity to 45 to 60%, and Temperature 55-65
After pretreatment and drying with hot air heated to ℃, the temperature was increased to 60℃.
The apparatus is configured to dry shiitake mushrooms using hot air heated to ~80°C in at least one stage.

[Effect]

According to the method of drying shiitake mushrooms of the present invention, the relative humidity is
By performing pre-treatment drying (pre-treatment) with hot air (dry air) that is humidified to 45-60% and heated to a temperature of 55-65℃, the surface of the shiitake mushroom becomes high temperature while being humidified, and the Moisture transpiration becomes active. Then, the internal temperature of the shiitake mushroom increases, increasing the rate of moisture diffusion to the surface, and the evaporation and diffusion of moisture are balanced, preventing surface hardening.

Next, following the pre-treatment drying, the main drying is performed using hot air heated to a temperature of 60 to 80°C, which further increases the temperature of the shiitake mushrooms due to the high temperature and the high temperature hot air, promoting the evaporation of internal water. Ru. Moreover, even without humidifying at this time, the temperature of the shiitake mushrooms is high, so the difference in temperature from the hot air does not become large.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. 1 to 3.

As shown in FIG. 1, shiitake mushrooms (raw shiitake mushrooms) 3 were placed in a batch-type ventilation dryer 1 and placed on a tray 2, and heated in the dryer 1 with a hot air generator 7 using high-temperature exhaust gas 9, etc. In the method of drying shiitake mushrooms 3 by circulating hot air (dry air), steam is supplied from the steam generator 8 to humidify the relative humidity to 45 to 65%, and hot air heated to a temperature of 55 to 65° C. The shiitake mushrooms 3 are distributed through the air pipe 4 to the dryer 1 for pretreatment drying (pretreatment), and after the pretreatment drying, the main drying is carried out using hot air heated to a humidity of 60 to 80° C. in at least one step. has been done.

Note that the blower pipe 5 is a return pipe provided below the tray 2, and the blower pipe 4 opens above the tray 2.
It is also connected to a circulation fan 6, and drying air is taken in through a damper 11. and three-way valve 1
2, 13, and 14, an on-off valve 15, an exhaust pipe 10, etc. are attached.

Next, the operation of this embodiment will be explained.

A tray 2 containing shiitake mushrooms 3 to be dried is placed in a dryer 1, and air taken in by a circulation fan 6, exhaust hot air sucked from a blower pipe 5, and steam generator 8 are supplied to the blower pipe 5. The steam is sent to a hot air generator 7 through a blow pipe 4 to make it high temperature, and the high temperature hot air obtained here is sent to a dryer 1 through a blow pipe 4, and the shiitake mushrooms are pretreated and dried by this hot air.

Then, the valve 15 of the steam generator 8 is closed to stop the supply of steam, and only high-temperature hot air is sent to the dryer 1, and the shiitake mushrooms are actually dried by this hot air. Note that during the above operation, a part of the exhaust heat air is sent to the exhaust pipe 1.
Exhaust from 0.

The relative humidity is also related to the hot air temperature, but the second
As shown in the graph of drying time and moisture content, if it is 40% or less, the movement of internal moisture due to shrinkage of shiitake mushrooms becomes slow in the latter stage of main drying, and the degree of water loss relative to drying time decreases. do. On the other hand, if it exceeds 60%, water droplets will form on the surface and the water loss at the initial stage of main drying will be slow, so it should be set at 45 to 60%.

In addition, if the hot air temperature during pre-treatment drying is less than 55℃, it will take longer to dry, while if it exceeds 65℃, the temperature difference between the mushrooms and the shiitake mushrooms will increase, causing surface hardening of the shiitake mushrooms. shall be.

Furthermore, the hot air temperature in the main drying is as shown in the graph of drying time and moisture content in Figure 3.
The higher the temperature, the shorter the drying time, but due to the temperature of the shiitake mushrooms during pre-treatment drying, the difference between the surface temperature and
It is necessary to consider that the temperature is within 20℃, and 60℃
If the temperature is below, the temperature of the shiitake mushrooms will not rise and it will take time to dry them. On the other hand, if the temperature exceeds 80℃, the surface of the shiitake mushrooms will become scorched. Therefore, the temperature of the hot air is set at 60 to 80°C based on the temperature range of shiitake mushrooms during pre-treatment drying. However, the main drying is performed at a higher temperature than the pretreatment drying temperature.

There is a close relationship between the above-mentioned relative humidity and hot air temperature, and by using humidified hot air, the surface of shiitake mushrooms can be kept appropriately moist. , and can also significantly increase the temperature of shiitake mushrooms.

Hereinafter, specific examples will be given and explained.

1st Example Using dryer 1, Shiitake mushroom 3 with humidity of 85% before drying
(12 pieces) were arranged on a tray 2, and the tray 2 was placed in the dryer 1 and processed under the conditions shown in FIG.
i.e. relative humidity 50%, hot air temperature (blow temperature)
Pretreatment at 60℃ for 30 minutes, then hot air temperature 60℃ to 70℃
℃ for 15 minutes, then pre-dry for 60 minutes while maintaining the hot air temperature of 70℃, and then increase the temperature from 70℃ to 80℃ for 15 minutes, and then reduce the temperature of the shiitake mushrooms while maintaining the hot air temperature of 80℃. The temperature difference between (physical temperature) is 5℃
It was dried in the second stage until it was within the following range. The time required for the latter stage drying was 1 hour and 36 minutes.

FIG. 5 shows the results of measuring how the temperature (physical temperature) of shiitake mushrooms actually changes under the above conditions.

Second Example Using the same dryer 1 as above, the humidity before drying was 91.6.
% shiitake mushrooms (40 pieces) were arranged on tray 2, placed in dryer 1, and treated under the conditions shown in FIG. That is, pre-drying at a relative humidity of 50% and hot air temperature of 60°C for 30 minutes, then increasing the temperature from 60°C to 70°C in 15 minutes, pre-drying at 90°C for 60 minutes, and then starting from 70°C with hot air temperature. After raising the temperature to 80°C for 15 minutes, the latter stage was dried until the temperature difference from the actual temperature was within 5°C. The time required for the latter stage drying was 2 hours and 47 minutes.

FIG. 7 shows the results of measuring changes in the temperature (physical temperature) of shiitake mushrooms under the above conditions in the same manner as above.

From the results of the first and second examples, it is clear that according to the present invention, the temperature of the shiitake mushroom is significantly raised by high-humidity, high-temperature hot air prior to main drying, and the movement of internal moisture is significantly activated, and the surface of the mushroom is As the surface heats up while being humidified, moisture evaporation from the surface becomes active, and this moisture evaporation and internal moisture diffusion become balanced and the surface is dried without hardening. Shiitake mushrooms were dried at a high temperature during the pretreatment process, so the temperature was raised further using high-temperature hot air, and the mushrooms were rapidly dried without surface hardening caused by temperature differences. And the total drying time was significantly shortened to about 3.5 hours to 5 hours.

Further, the measurement results of moisture content with respect to drying time based on each of the above-mentioned Examples are shown in FIG.

Here, the measurement results of the present invention show the average curve of the first and second embodiments, and the conventional method cited as a reference divides the hot air temperature into three stages within a range that does not cause surface hardening, namely, the initial temperature of 40°C, Mid-term temperature 50℃,
This shows a curve obtained at a late temperature of 60°C.

Note that the amount of dehumidified air was 1 m/sec in the present invention and 0.5 m/sec in the conventional method.

As a result, the drying method according to the present invention showed a sharp water reduction curve, and the average drying time was a little over 4 hours, which was extremely short, and the product was dried to a predetermined moisture content (15 to 17% dry moisture).

On the other hand, the conventional method simply uses hot air in the early stage of drying and starts drying from a low temperature.
The temperature of the shiitake mushrooms does not rise much, resulting in a very gentle curve, and since the hot air temperature is not high in the middle and late stages, the curve is similarly gentle, and in the end,
It took 3 hours in the initial stage, 3 hours in the middle stage, and 4 hours in the latter stage to reach the predetermined moisture content (dry moisture content 15-17%), and the total drying time was as long as 11 hours. However, the pretreatment drying time of the present invention is 0.5 to 1
It takes a long time, and within this range, all shiitake mushrooms can be brought to almost the same temperature regardless of their water content or size.

Further, in the above embodiment, an example was given in which the temperature was increased in two stages during main drying. In this case, the evaporation of internal moisture is more intense at the boundary between the first-stage drying and the second-stage drying, contributing to shortening the drying time, but one-stage drying may be used.

〔Effect of the invention〕

According to the present invention, since the shiitake mushrooms are pre-treated and dried with high-temperature, high-humidity hot air and then dried with high-temperature hot air, the surface hardening phenomenon of the shiitake mushrooms does not occur, and the diffusion of internal moisture is significantly activated. Drying time can be drastically shortened.

Moreover, since the drying time is short, energy consumption is significantly reduced, and high-quality dried shiitake mushrooms with little deformation due to uniform shrinkage are obtained.

Furthermore, the obtained dried shiitake mushrooms had a pink underside and had high commercial value.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure shows a graph showing changes in water content due to relative humidity.
FIG. 3 is a graph showing changes in moisture content due to hot air temperature, FIGS. 4 and 6 are graphs showing changes in relative humidity and hot air temperature according to the first and second embodiments, and FIGS. is a graph showing the change in temperature of shiitake mushrooms according to the first and second examples, and FIG. 8 is a graph showing the relationship between drying time and moisture content. 1... Dryer, 6... Circulation fan, 7... Hot air generator, 8... Steam generator.

Claims (1)

[Claims] 1. In a method of drying shiitake mushrooms in which mushrooms are placed in a dryer and hot air is circulated through the dryer, the relative humidity is set to 45 to 60.
%, and after pre-treatment drying with the hot air heated to 55 to 65°C, the shiitake mushrooms are subjected to main drying with the hot air heated to 60 to 80°C in at least one step. How to dry shiitake mushrooms.