Method for producing culture medium for mushroom substrate

Abstract

To provide a method for making a mushroom fungal bed culture medium that allows for the selection of sawdust from a variety of tree species, not limited to specific ones, and enables high yields without the need for adding larger amounts of nutrients such as rice bran.SOLUTION: A method for making a mushroom fungal bed culture medium includes a sterilization step for preparing a container filled with a medium material and sterilizing the medium material inside the container with steam and a freezing step for freezing the sterilized medium material inside the container.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing a culture medium for mushroom beds, and more particularly, to a method for producing a culture medium for mushroom beds that promotes the growth of mushroom mycelium and increases the yield of fruiting bodies.

Background Art

[0002] In recent years, for mushroom cultivation, bed cultivation is frequently used because it enables planned production and is relatively labor-saving. In general, this bed cultivation involves filling small culture containers such as bottles and bags with a culture medium raw material obtained by mixing a nutrient agent (such as rice bran) with a culture medium substrate (such as sawdust), sterilizing it, and producing a culture medium for a mushroom bed (hereinafter sometimes referred to as a "bed culture medium"). An inoculum of mushrooms is inoculated onto this bed culture medium and cultured until it becomes a mushroom bed, and this mushroom bed is cultivated under predetermined conditions to harvest mushrooms.

[0003] In the above-mentioned bed cultivation, in order to produce high-quality mushrooms in a planned and high-yield manner, various measures have been taken, such as specifying the tree species of the culture medium substrate used for the bed culture medium or adding a variety of nutrient agents to the culture medium substrate (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, due to the recent soaring prices of culture medium substrates such as sawdust, there has been an exploration of whether tree species can be selected not only from a specific tree species but also from a wide range as a culture medium substrate. In addition, there has also been a price increase for nutrient agents such as rice bran, and there has been a consideration of whether a high yield can be achieved with a small amount of addition.

[0006] Therefore, against this background, the present invention aims to provide a method for producing a mushroom substrate that allows the selection of tree species from a wide range of species, not just specific species, as the culture medium base material such as sawdust, and that can achieve high yields even with a small amount of nutrients such as rice bran used. [Means for solving the problem]

[0007] However, in view of these circumstances, the inventors diligently conducted research and, as a result, discovered that by preparing a container filled with culture medium raw materials, steam sterilizing the culture medium raw materials in the container, and then freezing the sterilized culture medium raw materials in the container, it is possible to produce a mushroom substrate that improves mycelial growth and increases the amount of fruiting bodies, thus completing the present invention.

[0008] In other words, the present invention has the following aspects. [1] A method for producing a culture medium for mushroom mycelium, comprising: preparing a container filled with culture medium raw materials inside; a sterilization step of steam sterilizing the culture medium raw materials inside the container; and a freezing step of freezing the sterilized culture medium raw materials inside the container. [2] The method for producing a mushroom substrate culture medium according to [1], wherein the temperature is controlled in the freezing step so that the internal temperature of the sterilized culture medium raw material is in the temperature range of 0 to -5°C for at least 5 hours. [3] A method for producing a mushroom substrate culture medium according to [1] or [2], wherein the culture medium raw material subjected to the above sterilization step is set to have a water content of 0.60 to 0.75 as shown in formula (1) below. Moisture content = 1-(dry mass W / mass M) ···(1) [Effects of the Invention]

[0009] The present invention is a method for producing a mushroom substrate, comprising a sterilization step of preparing a container filled with culture medium raw materials, steam sterilizing the culture medium raw materials in the container, and a freezing step of freezing the sterilized culture medium raw materials in the container. Therefore, a mushroom substrate that promotes mycelial growth and increases the amount of fruiting bodies can be efficiently produced without increasing costs.

[0010] Furthermore, in the present invention, if the temperature is controlled in the freezing process so that the internal temperature of the sterilized culture medium material is in the 0 to -5°C range for at least 5 hours, so-called slow freezing is performed on the sterilized culture medium material. As a result, water that has permeated the culture medium material such as sawdust freezes, causing larger ice crystals to develop inside the tissue. This development damages and softens the internal tissue, making it easier for the mushroom mycelium to grow. After thawing, the ice melts and flows out as water, creating voids where ice crystals were formed. This creates adequate gaps within the mushroom substrate, allowing oxygen, which is necessary for the growth of mushroom mycelium, to circulate more easily, thus promoting mycelial growth.

[0011] Furthermore, within the present invention, if the culture medium raw material used in the sterilization process is set to have a water content of 0.60 to 0.75 as shown in formula (1) below, it is possible to produce a mushroom substrate culture in which ice crystals develop more sufficiently during the freezing process and mycelium grows more easily. Moisture content = 1-(dry mass W / mass M) ···(1) [Brief explanation of the drawing]

[0012] [Figure 1] (a) is a flowchart showing an overview of the conventional manufacturing method, and (b) is a flowchart showing an overview of the manufacturing method of the present invention. [Figure 2] This graph shows the change in internal temperature of the culture medium raw materials in the example. [Modes for carrying out the invention]

[0013] The present invention will be described below based on examples of embodiments for carrying out the present invention. However, the present invention is not limited to the embodiments described below.

[0014] In this invention, when expressed as "X~Y" (where X and Y are any numbers), unless otherwise specified, it includes the meaning of "greater than or equal to X and less than or equal to Y," as well as the meaning of "preferably greater than X" or "preferably less than Y." Furthermore, when expressed as "X or greater" (where X is any number) or "Y or less" (where Y is any number), it also implies that "it is preferable that it be greater than X" or "it is preferable that it be less than Y."

[0015] Furthermore, in the present invention, the main component refers to a component that significantly affects the properties of the raw material, and the content of this component is usually 50% by mass or more of the total raw material, preferably 60% by mass or more, and more preferably 70% by mass or more.

[0016] The mushroom substrate culture medium used in one embodiment of the present invention is, for example, used when cultivating mushrooms such as shiitake, king oyster mushrooms, enoki mushrooms, shimeji mushrooms, maitake mushrooms, and oyster mushrooms on a substrate.

[0017] To cultivate mushrooms using a substrate, typically, as shown in Figure 1(a), a culture medium mixture of sawdust or other substrate material and rice bran or other nutrients is filled into cultivation bottles or similar containers. The culture medium mixture is then sterilized along with the cultivation bottles, and mushroom spawn is inoculated into the resulting substrate. The inoculated mushroom substrate is sealed to prevent contamination by other bacteria, and then cultured in a culture room until the mycelium has spread widely, thus creating the mushroom substrate. The resulting substrate is used for cultivation in a growing chamber until the fruiting bodies (mushrooms) that grow from it reach a harvestable size.

[0018] The production of mushroom substrate and cultivation of mushrooms in this invention generally follow this process, but it differs significantly from conventional methods in that it employs steam sterilization in the sterilization process and includes a freezing process in which the sterilized culture medium raw materials are frozen. In other words, as shown in Figure 1(b), the method for producing a mushroom substrate culture of the present invention includes preparing a container filled with culture medium raw materials, sterilizing the culture medium raw materials in the container with steam in a sterilization step, and freezing the sterilized culture medium raw materials in the container in a freezing step. The following describes each step.

[0019] <Preparation step> The culture medium raw materials used in the present invention are not particularly limited as long as they are usually used for cultivating mushrooms. For example, a mixture of a culture medium substrate such as sawdust and a nutrient such as rice bran can be used. In addition, in the present invention, sawdust of tree species that are not generally used for cultivating mushrooms can be used. That is, the tree species of sawdust used for cultivating mushrooms are limited due to reasons such as its hardness and the content of inhibitory components. However, in the present invention, since removal of such inhibitory components, softening of the culture medium substrate tissue, decomposition into substances easily utilized by hyphae, etc. are carried out, even tree species that have not been actively utilized so far can be utilized (including mixed use) without affecting the culture period and the yield. As tree species of sawdust used for mushroom cultivation, cedar, cypress, oaks, konara oaks, beech, etc. are widely used. On the other hand, elm, willow, maple, cherry, etc. have not been actively utilized so far due to the above reasons, etc., but according to the production method of the present invention, these can also be utilized. Note that, for mushroom species with a long hypha culture and mushroom bed cultivation period, more decomposition of the culture medium substrate such as sawdust occurs, so it is particularly useful for the production of mushroom bed culture media for such mushroom species. Incidentally, the hypha culture and mushroom bed cultivation periods of edible mushrooms are usually: Shimeji mushroom: 45 days (1 harvest), Eringi mushroom: 56 days (1 harvest), Beech mushroom: 105 days (1 harvest), Nameko mushroom: 115 days (1 - 2 harvests), Shiitake mushroom: 110 - 200 days (1 - 4 harvests).

[0020] The container filled with the above culture medium raw materials is not particularly limited, and usually, containers used for cultivating mushrooms can be used. However, as described later, in order to pass through steam sterilization, it is preferable that the container can maintain a predetermined shape even by heat of 100°C or higher. Furthermore, when performing steam sterilization, it is preferable to control the temperature inside the culture medium material to a predetermined level. Therefore, a container that is small enough to be carried by hand, even when filled with culture medium material, such as a mushroom cultivation bag, is preferable to a large container such as a planter.

[0021] In the present invention, considering the frozen state of the culture medium raw materials in the freezing process described later, it is preferable that the moisture content of the culture medium raw materials subjected to the next sterilization process is set to 0.60 to 0.75, more preferably 0.62 to 0.73, and even more preferably 0.65 to 0.70, as shown in the following formula (1). In other words, in the present invention, it is preferable to set the moisture content higher than usual in order to further enhance the effect in the freezing process described later. The mass M below is the mass of the culture medium raw materials (total of culture medium base material and nutrients, etc.), and the dry mass W below is the mass of the above culture medium raw materials after drying (moisture content of 5% by mass or less). Moisture content = 1-(dry mass W / mass M) ···(1)

[0022] <Sterilization process> The sterilization process is performed to kill harmful bacteria surviving in the culture medium raw materials. Various sterilization methods are known, but in the present invention, it is important to use steam sterilization. In other words, steam sterilization can remove harmful substances that inhibit mycelial growth contained in sawdust. These harmful substances include tannins, phenolic substances such as ferruginol, flavonoid compounds such as taxifolin, and resinous components such as terpenoids, which are present in the wood that is the raw material for sawdust to protect against diseases and pests.

[0023] Furthermore, steam sterilization promotes the decomposition of wood tissue by fungal hyphae using wood-degrading enzymes such as cellulase and laccase, making it easier for the mushroom mycelium to decompose the sawdust. Furthermore, high molecular weight sugars such as starch tend to become smaller in molecular weight and their assimilation ability increases when heated, while proteins tend to become more susceptible to microbial degradation when denatured by heat. Furthermore, steam sterilization ensures that the culture medium material filled in the container is firmly solidified, making it easier to maintain the shape of the pores provided for inoculation.

[0024] The above-mentioned steam sterilization includes atmospheric pressure sterilization, which is performed without applying pressure to the sterilization vessel, and high-pressure sterilization, which is performed by applying pressure to the sterilization vessel. In the present invention, either method can be used. However, atmospheric pressure sterilization is preferred because it does not require special equipment such as a pressure-resistant sterilization vessel, while high-pressure sterilization is preferred because it allows for efficient production in a short time. In the above atmospheric pressure sterilization, for example, it is preferable to set the internal temperature of the sterilization vessel to 90°C or higher, more preferably to 95°C or higher, and even more preferably to 98°C or higher. Furthermore, atmospheric pressure sterilization is preferably carried out for at least 4 hours after the internal temperature of the culture medium material reaches 98°C, and more preferably for 5 to 8 hours. In this invention, the internal temperature of the culture medium raw material is defined as the temperature measured at the point where heat from outside the container is least likely to be transferred (usually the center of the culture medium raw material).

[0025] In the above high-pressure sterilization, for example, it is preferable to raise the internal temperature of the sterilization chamber to 100°C or higher, more preferably to 115°C or higher, even more preferably to 118°C or higher, and even more preferably to 121°C or higher. Furthermore, it is preferable to perform high-pressure sterilization for a time set by the F-value correlation after the internal temperature of the culture medium material reaches the set temperature. For example, if the temperature is set to 121°C, the time is usually set to about one hour after reaching 121°C.

[0026] <Freezing process> The freezing process involves placing the container, which has undergone the sterilization process described above, into a freezer (freezer) set to a predetermined temperature, thereby freezing the culture medium raw materials inside the container. By freezing the culture medium raw materials, the water contained within them is converted into ice crystals, which can damage the structure of each ingredient contained in the culture medium raw materials. In other words, when water turns into ice, its volume expands by approximately 9%, and this change in state is utilized to damage the tissue.

[0027] For example, when freezing food, the temperature of the food usually drops rapidly until it reaches its freezing point below 0°C. However, the temperature then plateaus in the -1 to -5°C range, and it is known that the temperature will not drop below this level until about 80% of the water in the food has crystallized into ice. This is because most of the cooling energy is used to remove the latent heat of freezing, and the above-mentioned -1 to -5°C temperature range is called the maximum ice crystal formation zone.

[0028] When freezing food, it is generally considered preferable to freeze it as quickly as possible to avoid compromising the flavor after thawing, and to quickly pass through the maximum ice crystal formation zone and maintain a temperature below it. Rapid freezing of food results in smaller ice crystals forming inside the tissue, leading to less tissue damage and a tendency for less drip loss after thawing. Rapid freezing typically refers to a freezing process that ensures the product temperature (internal temperature) passes through the maximum ice crystal formation zone within 30 minutes.

[0029] In this invention, the temperature control method is not required as long as freezing can be achieved, and rapid freezing is not essential. Rather, it is preferable to perform slow freezing so that the internal temperature of the sterilized culture medium raw material is in the 0 to -5°C temperature range for at least 5 hours, more preferably 6 hours or more, and the majority of the freezing process may be spent in this temperature range. By performing slow freezing, ice crystals develop more significantly during freezing, making the tissue more susceptible to damage. Therefore, even if there is a lot of drip after thawing, the water can be reabsorbed and retained within the tissue, reducing the amount of water that is seen as syneresis (water loss) on the surface (outside).

[0030] The mushroom substrate culture medium produced in this manner is usually stored frozen and thawed before use (inoculation). Furthermore, because it can be stored frozen for extended periods, it allows for production adjustments through storage in preparation for periods of high demand (high prices), and enables the use of refrigerated containers during transportation.

[0031] The above thawing method is not particularly limited and may include natural thawing (thawing at room temperature) or intentional thawing. Examples of intentional thawing include low-temperature thawing, high-temperature thawing, thawing under running water, thawing in warm water, heating thawing, and microwave thawing.

[0032] Then, inoculation of the thawed mushroom substrate can be carried out in the same way as in normal processes, for example, using an inoculation machine (inoculation process). The inoculated mushroom substrate can be cultured in a culture room set to predetermined conditions to produce a mushroom bed (cultivation process). The obtained mushroom bed can be cultivated in a cultivation room set to predetermined conditions to produce fruiting bodies (mushrooms), and those that reach a predetermined size can be harvested (cultivation process).

[0033] According to the above manufacturing method of the present invention, when the container is filled, the water that was abundant around the culture medium material without penetrating it penetrates deeply into the culture medium material through the sterilization process. Then, through the freezing process, the water that has penetrated into the culture medium material changes into ice crystals, damaging the structure of the culture medium material. As a result, the culture medium material becomes more flexible, making it easier for mushroom mycelium to grow. Furthermore, as the culture medium material thaws and the ice turns into water and flows out, gaps are formed, allowing for smoother oxygen supply and further facilitating mycelial growth.

[0034] Therefore, sawdust from tree species that were previously deemed unsuitable for mushroom cultivation because it inhibited mycelial growth can now be used in mushroom cultivation media. On the other hand, in some mushroom cultivation media, various shapes of sawdust are used to create volume (without making it dense) for the purpose of long-term cultivation. For example, in the case of small cube-shaped materials, fibrous materials, chip dust, wood shavings, chips, and wood fragments, it is generally observed that as the size of the material increases, it becomes more difficult for mycelium to penetrate the interior. However, even with these shapes, the growth of mycelium is not inhibited. [Examples]

[0035] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. In the examples, "parts" and "%" refer to mass.

[0036] [Examples 1-4, Comparative Example 1] As the culture medium material, sawdust (Quercus serrata), rice bran, and wheat bran were mixed in a ratio of 8:1:1 (dry mass ratio). 1.2 kg of the above culture medium material was filled into the container shown below, and a hole for inoculation was formed in the center of the surface of the culture medium material. The moisture content of the culture medium material at this time was 62%. The culture medium material in the container was steam sterilized at 120°C for 70 minutes and allowed to cool to room temperature. Subsequently, for Examples 1 to 4, a freezing process was carried out under the conditions shown in Table 1 to prepare the mushroom substrate. The freezing process was carried out for 12 hours for each example. Figure 2 shows the change in the internal temperature of the culture medium material at this time. (container) A cylindrical mushroom culture bag with a diameter of 12 cm, made of 50 μm thick high-density polyethylene (HDPE), and fitted with a ventilation filter.

[0037] The above-mentioned mushroom substrate was inoculated with 8g of shiitake mushroom spawn, and cultured under the following conditions. The number of days until mycelial spread was measured. The spread state refers to a state where 95% or more of the substrate is covered with mycelium (the same applies below). The results are shown in Table 1 below. The mushroom substrate, which had undergone a freezing process, was thawed naturally at room temperature (around 23°C) before inoculation. (Culture conditions) Temperature 20~23℃, humidity 60~80%, CO2 concentration 3000ppm or less.

[0038] [Table 1]

[0039] In all of Examples 1-4, the number of days required for mycelial spread was reduced compared to the conventional method (Comparative Example 1), demonstrating an effect of promoting the growth of shiitake mushroom mycelium. In particular, Examples 1 and 2, in which the freezing process involved passing through the 0 to -5°C temperature range for 5 hours or more, showed an even shorter number of days required for mycelial spread, indicating an even greater effect.

[0040] [Examples 5-6, Comparative Example 2] As the culture medium ingredients, sawdust (cedar), wheat bran, rice bran, and corn cob were mixed in a ratio of 6:3:2:1 (dry mass ratio). 1.2 kg of the above culture medium ingredients were filled into the container shown below, and a hole for inoculation was formed in the center of the surface of the culture medium ingredients. The moisture content of the culture medium ingredients at this time was 66%. The culture medium ingredients in the container were steam sterilized at 98°C for 450 minutes and allowed to cool to room temperature. Subsequently, in Examples 5 and 6, the culture media were prepared by going through a freezing process under the conditions shown in Table 2. The culture media that went through the freezing process were thawed at room temperature (around 23°C) before inoculation. (container) A cylindrical mushroom culture bag with a diameter of 12 cm, made of 50 μm thick high-density polyethylene (HDPE), and fitted with a ventilation filter.

[0041] Eight g of king oyster mushroom spawn was inoculated into the above-mentioned substrate, and the number of days until mycelial spread was measured under the following conditions. The results are shown in Table 2 below. (Culture conditions) Temperature 20~23℃, humidity 70~80%, CO2 concentration 3000ppm or less.

[0042] [Table 2]

[0043] The results in Table 2 show that the same excellent effect of promoting mycelial growth was observed not only in shiitake mushrooms but also in king oyster mushrooms.

[0044] [Examples 7-8, Comparative Examples 3-4] As the culture medium material, sawdust (Quercus serrata), rice bran, and wheat bran were mixed in a ratio of 8:1:1 (dry mass ratio). 1.2 kg of the above culture medium material was filled into the container shown below, and a hole for inoculation was formed in the center of the surface of the culture medium material. At this time, the moisture content of the culture medium material was adjusted to the moisture content shown in Table 3 below. Next, the culture medium material in the container was steam sterilized at 120°C for 90 minutes and allowed to cool to room temperature. After that, Examples 7 and 8 were each subjected to a freezing process under the conditions shown in Table 3 to prepare the mushroom substrate. (container) A cylindrical mushroom culture bag with a diameter of 12 cm, made of 50 μm thick high-density polyethylene (HDPE), and fitted with a ventilation filter.

[0045] The prepared mushroom substrate cultures were observed from the side of the container and evaluated based on the following indicators. The cultures that underwent the freezing process were evaluated after thawing at room temperature (around 23°C). ◎ (Excellent): No water separation at all. ○ (Good): Separation was observed in the lower 1 / 5. △ (Slightly poor): Separation was observed in the lower 1 / 3. × (bad): Separation of water was observed in the lower half.

[0046] [Table 3]

[0047] The results in Table 3 show that in Examples 7 and 8, which underwent a freezing process, water was able to penetrate sufficiently into the interior of the mushroom substrate, reducing the amount of water observed as syneresis. Since excessive syneresis of water in the mushroom substrate tends to inhibit the growth of mushroom mycelium, it is presumed that comparative examples 3 and 4 would experience slower mushroom mycelial growth.

[0048] [Example 9, Comparative Example 5] As the culture medium material, sawdust (Quercus serrata), rice bran, and wheat bran were mixed in a ratio of 8:1:1 (dry mass ratio). 1.2 kg of the above culture medium material was filled into the container shown below, and a hole for inoculation was formed in the center of the surface of the culture medium material. The moisture content of the culture medium material at this time was 60%. The culture medium material in the container was steam sterilized at 120°C for 70 minutes and allowed to cool to room temperature. Subsequently, in Example 9, the culture medium was prepared by going through a freezing process under the conditions shown in Table 4. That is, both Example 9 and Comparative Example 5 used 100% Quercus serrata sawdust as the sawdust. (container) A cylindrical mushroom culture bag with a diameter of 12 cm, made of 50 μm thick high-density polyethylene (HDPE), and fitted with a ventilation filter.

[0049] 8g of shiitake mushroom spawn was inoculated into the above-mentioned mushroom substrate, and the mycelium was allowed to spread in the culture room under the following conditions. The mushroom substrate that had undergone a freezing process was thawed at room temperature (around 23°C) before inoculation. (Culture conditions) Temperature 20~23℃, humidity 60~80%, CO2 concentration 3000ppm or less.

[0050] The mushroom beds infested with the above-mentioned mycelium were moved to a growth chamber, and fruiting bodies (shiitake mushrooms) were allowed to develop under the following conditions. Shiitake mushrooms that developed within 20 days after the bag was broken were harvested, and the yield was measured. The measurement results are shown in Table 4 below. (Conditions for occurrence) Temperature 13~17℃, humidity 80~90%, CO2 concentration 3000ppm or less, illuminance 100~500Lux.

[0051] [Table 4]

[0052] The results in Table 4 show that even when using sawdust made from Quercus serrata, a commonly used material for mushroom growing media, the example product yielded a higher shiitake mushroom harvest up to 20 days after bag breakage compared to the comparative example product. Based on the shiitake mushroom growth, it was estimated that a further difference in yield would be observed if the cultivation period were extended.

[0053] [Example 10, Comparative Example 6] The shiitake mushroom yield was measured in the same manner as in Example 9 or Comparative Example 5, except that the composition of sawdust in the culture medium was changed to 75% oak and 25% alder. The measurement results are shown in Table 5 below.

[0054] [Table 5]

[0055] As shown in Table 5, when alder, which is not commonly used as sawdust for mushroom growing media, was mixed in at 25%, the yield itself decreased compared to when 100% sawtooth oak was used. However, the difference in shiitake mushroom yield up to 20 days after bag breakage was even greater for the example product compared to the comparative example product.

[0056] [Example 11, Comparative Example 7] The shiitake mushroom yield was measured in the same manner as in Example 9 or Comparative Example 5, except that the composition of sawdust in the culture medium was changed to 50% oak and 50% alder. The measurement results are shown in Table 6 below.

[0057] [Table 6]

[0058] As shown in Table 6, when the amount of alder was further increased to 50%, although the yield itself decreased even more compared to the 100% oak blend, the difference in shiitake mushroom yield up to 20 days after bag breakage was even more pronounced in the example product compared to the comparative example product. These results suggest that even tree species not commonly used as culture medium substrates may have the potential to be used as mushroom growing media. [Industrial applicability]

[0059] The present invention's method for producing a mushroom substrate medium is suitable for producing a mushroom substrate medium that can increase the amount of fruiting bodies.

Claims

1. Prepare a container filled with culture medium ingredients. A sterilization step in which the culture medium raw materials in the above container are steam-sterilized, A freezing step in which the sterilized culture medium raw materials in the above container are frozen, A method for producing a culture medium for mushroom mycelium.

2. The method for producing a mushroom substrate culture medium according to claim 1, wherein in the freezing step described above, the temperature is controlled so that the internal temperature of the sterilized culture medium raw material is in the temperature range of 0 to -5°C for at least 5 hours.

3. A method for producing a mushroom substrate culture medium according to claim 1 or 2, wherein the culture medium raw material subjected to the above sterilization step is set to have a water content of 0.60 to 0.75 as shown in the following formula (1). Moisture content = 1-(dry mass W / mass M) ... (1)

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