A soybean paste jar body type fermentation process and a control method thereof

Abstract

The present application relates to the field of fermented bean paste, to solve the problem of weakening flavor of product although the fermentation time is shortened in the prior art, and provide a fermented bean paste tank type fermentation process and a control method thereof, comprising the following steps: after the fermentation substrate is sent into a fermentation device, an alternating closed fermentation process and an aeration fermentation process are carried out; the closed fermentation process comprises: alternating stirring operation section and standing fermentation section; the standing fermentation section comprises: conventional standing section and layered standing section; after water above the fermentation substrate is led out, the aeration fermentation process is carried out; after the aeration fermentation process is completed, the led-out water is introduced into the fermentation substrate again, stirred uniformly and subjected to the closed fermentation process. Through the alternating closed fermentation process and the aeration fermentation process, not only the guarantee of product flavor is realized, but also the switching timing of the closed fermentation process and the aeration fermentation process is judged through pH value monitoring, which is beneficial to production automation.

Description

Technical Field

[0001] This invention relates to the field of fermented soybean paste, and more specifically, to a fermentation process for fermented soybean paste in tanks and its control method. Background Technology

[0002] Traditional fermentation of fermented soybean paste primarily involves open-air fermentation. To achieve standardized production, current technologies are researching and adopting closed-system tank fermentation. This allows for controlled fermentation environments, improved product consistency, shorter fermentation cycles, and reduced impacts from external bacteria, pests, and dust. Due to the reduced bacteria, high salt concentrations are no longer needed to suppress them, allowing for the use of a low-salt system. However, while the completely closed tank fermentation process isolates harmful bacteria from the external environment, it also isolates beneficial bacteria, affecting the product's flavor to some extent. To compensate for this flavor deficiency, current technologies typically employ specific complex microbial strains for fermentation, which places high demands on the strains and limits the range of suitable strains.

[0003] There is an urgent need for a fermentation process that is low in salt overall, has a short fermentation time, and can ensure the flavor of the product as much as possible. Summary of the Invention

[0004] The purpose of this invention is to provide a fermentation process and control method for fermented soybean paste in tanks, which solves the problem that although the fermentation time is shortened when the fermentation process is industrialized and standardized in the existing technology, the flavor of the product is weakened.

[0005] The embodiments of the present invention are achieved through the following technical solutions:

[0006] A fermentation process for fermented soybean paste in tanks includes the following steps:

[0007] After the fermentation substrate is fed into the fermentation device, it undergoes alternating closed fermentation and aeration fermentation processes.

[0008] The closed fermentation process includes: alternating stirring operation sections and static fermentation sections; the static fermentation sections include: conventional static fermentation sections and layered static fermentation sections;

[0009] After the water above the fermentation substrate is drained, an aeration fermentation process is carried out.

[0010] After the aeration and fermentation process is completed, the water drawn out is reintroduced into the fermentation substrate, stirred evenly, and then subjected to a closed fermentation process.

[0011] Preferably, the side wall of the fermentation device is provided with multiple water outlets arranged longitudinally; during the water extraction process, water is extracted using the water outlet located above the solid medium layer and below the upper surface of the water layer.

[0012] Preferably, during the stratified settling phase of the fermentation system, water is continuously drawn out from above the fermentation substrate.

[0013] A method for controlling the fermentation process of fermented soybean paste in tanks includes:

[0014] Obtain the acid value of the fermentation system and find the minimum time required for the acid value to be greater than or equal to the preset acid value; before the fermentation time reaches the minimum time, the fermentation system is in a closed fermentation process;

[0015] Based on the salt tolerance of the strain, the optimal concentration range of brine in the fermentation substrate was obtained;

[0016] Based on the salt tolerance of the acid-producing bacteria and the optimal concentration range, the salinity range of the fermentation system during the aeration fermentation process is obtained, and thus the amount of water drawn out is obtained.

[0017] Preferably, the fermentation substrate includes: salt-tolerant yeast; the control method includes:

[0018] During the aeration fermentation process, the relationship between the content of volatile esters in the fermentation system and the fermentation time is obtained, thereby obtaining the fermentation time required for the increase rate of volatile esters to be less than or equal to the preset rate, and finally obtaining the fermentation time of the aeration fermentation process.

[0019] Preferably, the control method includes:

[0020] To obtain the relationship between the salt concentration of the aqueous phase, the pH value of the fermentation system, and the metabolic rate of acid-producing bacteria in the aeration fermentation process;

[0021] The relationship between the metabolic rate of acid-producing bacteria, the pH value of the fermentation system and the rate of increase of volatile esters in the aeration fermentation process was obtained. The maximum metabolic rate when the pH value and the rate of increase of volatile esters conformed to a monotonically decreasing relationship was obtained, and then the salt concentration of the aqueous phase in the aeration fermentation process was obtained.

[0022] The pH value at the end of the aeration fermentation process is obtained based on the preset speed.

[0023] Preferably, the control method includes:

[0024] The initial fermentation time is determined when the amino acid and reducing sugar content reaches the preset minimum value during the fermentation process; the first aeration fermentation process begins after the initial fermentation time.

[0025] Preferably, the control method includes:

[0026] During the aeration fermentation process, the initial air humidity inside the fermentation device is obtained;

[0027] After the ambient air passes through the humidity regulating device, the ambient air humidity reaches the second air humidity; the ratio of the second air humidity to the first air humidity is within the set ratio range.

[0028] Preferably, when the closed fermentation process begins from the start of fermentation and the pH value of the fermentation system no longer continues to decrease, the fermentation process remains in a closed fermentation state.

[0029] Preferably, when the pH value of the fermentation system in the closed fermentation process drops to a stable level, the closed fermentation process is switched to the aeration fermentation process.

[0030] Methods for determining if a value is approaching stability include: within a set time period, the variance of the pH dataset is less than a set variance.

[0031] The present invention has at least the following beneficial effects:

[0032] This invention, through alternating closed fermentation and aeration fermentation processes, not only ensures product flavor but also leverages the difference in salt concentration between the two processes to allow for the alternation of dominant microbial species in the fermentation system. This minimizes fermentation time and enables pH monitoring to determine the switching point between closed and aeration fermentation processes, facilitating production automation. While ensuring the overall product remains low in salt, the solid substrate sedimentation facilitates water extraction, transforming the low-salt system into a high-salt system. During the aeration fermentation stage, it inhibits both unwanted microorganisms and acid-producing bacteria, thus maintaining a stable pH level in the fermentation system during the aeration fermentation process. The pH value exhibits a monotonically decreasing relationship with the rate of increase in volatile esters, ensuring that the pH value can characterize the rate of increase in volatile esters. This allows for the determination of the endpoint of the aeration fermentation process by monitoring the pH value, thus automating process switching. During the aeration stage, the intake air humidity is adjusted to be close to the humidity inside the tank, reducing water evaporation, stabilizing the system's moisture and salt concentrations, and ensuring a fixed amount of water is drawn each time, simplifying process operations and facilitating industrial automation. By introducing external air in stages, combined with the continuous action of salt-tolerant yeast in the high-salt stage, the generated esters and other flavor compounds are richer, and the product flavor is closer to the mellow and complex taste of traditional processes. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 Example of a product testing report Figure 1 ;

[0035] Figure 2 Example of a product testing report Figure 2 . Detailed Implementation

[0036] To make the objectives, methods, and advantages of the embodiments of the present invention clearer, the methods in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0037] Example 1: A fermentation process for fermented soybean paste in a tank, comprising the following steps: feeding the fermentation substrate into the fermentation device and then performing alternating closed fermentation and aeration fermentation processes;

[0038] The closed fermentation process includes: alternating stirring operation sections and static fermentation sections; the static fermentation sections include: conventional static fermentation sections and layered static fermentation sections;

[0039] After the water above the fermentation substrate is drained, an aeration fermentation process is carried out.

[0040] After the aeration and fermentation process is completed, the water drawn out is reintroduced into the fermentation substrate, stirred evenly, and then subjected to a closed fermentation process.

[0041] In practice, the fermentation substrate can be set according to existing processes and formulas. For example, the fermentation substrate includes pre-fermented chili peppers, pre-fermented broad beans, brine, and a compound fermentation culture. The compound fermentation culture includes Aspergillus oryzae, yeast, and lactic acid bacteria.

[0042] Existing technologies are generally divided into two categories: traditional open fermentation and closed-system fermentation. Traditional open fermentation processes expose the fermentation system directly to the external environment, thus maintaining a high salt concentration (e.g., 20%) to inhibit or kill unwanted microorganisms. Closed-system fermentation, which is more conducive to industrial standardization, is less affected by external microorganisms and can use a low-salt system (e.g., 10%). Both types of fermentation processes have their own advantages and disadvantages. Traditional fermentation produces products with better flavor, but the fermentation environment is variable, making it difficult to maintain the optimal temperature for the microorganisms, and the fermentation time is long, which is not conducive to industrialization and standardization. Closed-system fermentation allows for simple control of the fermentation environment, and the fermentation time and product quality can be standardized. However, the flavor of the product is determined solely by the initial microbial culture, without the addition of beneficial bacteria from the external environment, resulting in a weaker flavor compared to traditional fermentation processes.

[0043] This embodiment utilizes the characteristic that during the fermentation process, the solid part of the fermentation substrate gradually settles, causing water to gradually migrate to the top of the fermentation substrate, thereby achieving cyclical regulation of the salt concentration in the fermentation substrate. When the water in the fermentation substrate is drawn out, the overall salt concentration of the substrate is high. At this time, the air inside the fermentation device is exchanged with the air in the external environment and fermentation takes place. The miscellaneous bacteria entering the fermentation system from the external environment are easily inhibited or killed by the high salt concentration. After fermentation for a period of time, the water drawn out from the fermentation substrate is reintroduced into the fermentation substrate and stirred evenly, and then sealed for fermentation.

[0044] The microbial strains were initially inoculated onto the surface of broad beans and chili peppers and pre-fermented. The pre-fermented broad beans and chili peppers are commonly referred to as sweet pods and chili pepper embryos. Since the solid substrate is the primary source of nutrients for the microbial strains and also provides them with physical support, the microbial strains tend to attach to the surface of the solid substrate and grow during fermentation. Since there are fewer microbial strains in the aqueous phase, the microbial content in the fermentation system changes little when the water above the fermentation substrate is removed.

[0045] The removal of water from the fermentation substrate can be achieved using existing concentration devices. Concentration devices used in conjunction with fermentation equipment in the food industry are existing technologies, such as those used in common soy sauce, vinegar, and beer fermentation broths.

[0046] As an example, when the fermentation system is in the stratified settling stage, the fermentation substrate stratifies, with the solid matrix settling and the water moving upwards. The liquid above the substrate is introduced into a concentration device, where a concentration membrane, such as a reverse osmosis membrane, allows water to pass through while retaining salts and other small-molecule solutes. The retained concentrate is then reintroduced into the fermentation substrate and stirred thoroughly to obtain a fermentation system with a higher salt concentration. As an example, to avoid the impact of external driving force on the lower settling portion of the fermentation substrate when drawing water, an outlet can be installed on the side wall of the fermentation device. When drawing water, the outlet is located above the settling portion and below the water surface; automatic water discharge is achieved by opening the aforementioned outlet valve.

[0047] As an example, to reduce the need for water storage devices, water drawn from fermentation unit a can be directly introduced into fermentation unit b. That is, when fermentation unit a is switching from closed fermentation to aeration fermentation, fermentation unit b is switching from aeration fermentation to closed fermentation. This reduces the impact of some microorganisms being carried out during water extraction and lacking nutrient support to survive, thus minimizing the time the extracted water spends outside the fermentation system. Alternatively, a buffer tank can be installed to store the extracted water, avoiding the risk that process fluctuations between different fermentation units might prevent the extracted water from being directly introduced into another fermentation unit.

[0048] As an example, when the fermentation system does not require switching fermentation steps, continuous stirring does not consume energy and may even reduce the fermentation effect. Therefore, the system is in a state of continuous alternation between stirring and resting. When the system needs to switch from a closed fermentation process to an aerated fermentation process, it enters a stratified resting state, that is, the time of the conventional resting period is extended to allow the system to fully stratify.

[0049] As an example, the ventilation operation during the aeration fermentation process is achieved through a ventilation system with a dust collector, and ventilation is carried out at a constant flow rate.

[0050] As an example, the total fermentation time can be determined by existing testing methods such as physicochemical indicators, sensory evaluation, and flavor compound profiles after sampling, so that the fermented product meets the conventional requirements for fermented soybean paste.

[0051] As an example, when stratification is too slow, a pressure plate can be used to press down on the solid matrix to assist stratification. For instance, after entering the stratification settling stage, if the rate of change of the water phase height above the solid matrix is ​​less than the set rate of change, it is determined that the stratification speed is too slow. The set rate of change can be set to 2 mm / day.

[0052] The common ratio of solid substrate to water is 1:(1-2). The salt concentration of low-salt systems is usually 6%-12%, while the salt concentration of high-salt systems is usually above 12%, such as 16%-20%. When the salt concentration difference between the closed fermentation process and the aeration fermentation process is too large, the amount of water drawn out is large, and the degree of stratification is required to be high. In this case, the proportion of water in the fermentation system can be increased to promote the proportion of the aqueous phase during stratification. Alternatively, rapid stratification can be achieved by pressing the solid substrate down with a pressure plate as described above.

[0053] This embodiment achieves a self-circulating salt concentration in the fermentation system, ensuring that the final salt concentration of the product remains low, while there are periods of high-salt fermentation during the process, which maintains connectivity with the outside world and thus improves the product flavor.

[0054] Example 2: To avoid the simultaneous extraction of esters in the fermentation system when extracting water above the fermentation substrate, an improvement was made based on Example 1. In this example, the side wall of the fermentation device is provided with multiple water outlets arranged longitudinally; during the water extraction process, water is extracted using the water outlet located above the solid medium layer and below the upper surface of the water layer.

[0055] In the specific implementation process, koji mold in common compound fermentation agents provides proteases and amylases, responsible for breaking down proteins into peptides and amino acids, and starch into sugars, providing basic nutrients and precursors for subsequent fermentation. Lactic acid bacteria can utilize sugars to produce organic acids, such as lactic acid and acetic acid, adjusting the pH of the fermentation system, forming a mild sour taste, and inhibiting the growth of harmful bacteria. Yeast is mainly active in the middle and late stages of fermentation, fermenting sugars to produce ethanol, higher alcohols, etc. Ethanol undergoes esterification with organic acids to generate various aromatic esters, which are the key source of the mellow and complex aroma of fermented soybean paste. As can be seen from the above, esters are produced during the fermentation of fermented soybean paste, most of which have a density less than that of water. Therefore, after the stratified settling period, the entire system may have three layers: a bottom layer of solid matrix, a middle layer of water, and an upper layer of esters. Because the ester composition is quite complex during fermentation, it is necessary to ensure that the thickening membrane can effectively retain both salt and esters. This places high demands on the performance of the thickening membrane, increasing economic costs. In addition, esters may also contaminate the thickening membrane, affecting its performance and significantly increasing the frequency of membrane cleaning. Therefore, when drawing water from above the fermentation substrate, it is necessary to ensure that no esters are drawn out.

[0056] As an example, a filter screen can be installed at the outlet to prevent light solids from being drawn out.

[0057] As an example, when the amount of raw materials, such as broad beans and chili peppers, is fixed, the volume of the solid substrate will gradually decrease as fermentation progresses, thus requiring water to be drawn out through different outlets.

[0058] Example 3: In order to reduce the unevenness of fermentation effect in the fermentation system during the stratified settling stage, an improvement was made based on Example 2. In this example, water above the fermentation substrate was continuously drawn out during the stratified settling stage of the fermentation system.

[0059] In practice, if water is drawn out after the stratified settling period, the unevenness of the fermentation system during the stratified settling process will affect the fermentation effect. Therefore, water can be drawn out gradually during the stratified settling process to ensure the fermentation effect.

[0060] As an example, a viewing window can be installed on the side wall of the fermentation unit to observe the positions of the upper and lower interfaces of the aqueous phase after the fermentation system has stratified, in order to identify the outlet that needs to be opened. Alternatively, existing image recognition technology can be used to identify the upper and lower interfaces of the aqueous phase through images taken from outside the viewing window.

[0061] Example 4: A method for controlling the fermentation process of fermented broad bean paste in tanks, comprising:

[0062] Obtain the acid value of the fermentation system and find the minimum time required for the acid value to be greater than or equal to the preset acid value; before the fermentation time reaches the minimum time, the fermentation system is in a closed fermentation process;

[0063] Based on the salt tolerance of the strain, the optimal concentration range of brine in the fermentation substrate was obtained;

[0064] Based on the salt tolerance of the acid-producing bacteria and the optimal concentration range, the salinity range of the fermentation system during the aeration fermentation process is obtained, and thus the amount of water drawn out is obtained.

[0065] In practice, an acidic environment is beneficial for inhibiting harmful bacteria, while a high-salt environment inhibits the activity of acid-producing bacteria such as lactic acid bacteria. Therefore, this embodiment prioritizes ensuring the system's acid value before the aeration fermentation process to further reduce the harm from miscellaneous bacteria during the aeration fermentation process. Exemplarily, acid value refers to the number of milligrams of potassium hydroxide required to neutralize free fatty acids in 1g of aqueous sample in the fermentation system, expressed in mg KOH / g. Exemplarily, acid value can also be simply characterized by pH value. In the early stages of fermentation, microbial activity is vigorous, and lipases are produced in large quantities and act on the oil portion of the raw materials, leading to a rapid accumulation of free fatty acids and a rapid increase in acid value. Exemplarily, the preset acid value can be set based on process experience. For example, the maximum achievable acid value in the existing process is 3.4 mg KOH / g. To accommodate process fluctuations, the preset acid value can be slightly lower than the maximum acid value, for example, it can be set to 85% * the maximum acid value. Exemplarily, the maximum achievable acid value of the fermentation system in the initial closed fermentation process can be obtained through experiments. For ease of testing, pH value can also be used to characterize acidity. For example, the minimum pH value achievable by the fermentation system in the initial closed fermentation process can be obtained through experiments, and then a preset acid value can be set as needed. As an example, the minimum pH value is 4.5, and to accommodate process fluctuations, the preset acid value is set to 5.

[0066] During the closed fermentation process, a stirring device can be used to ensure uniformity of the fermentation system and promote heat dissipation.

[0067] As an example, when the pH value of the fermentation system in the closed fermentation process reaches the set threshold, the process is switched to an aeration fermentation process, i.e., the stratified settling phase begins. The set threshold can be equal to the preset acid value.

[0068] Different microbial species exhibit varying salt tolerance. Generally, *Aspergillus oryzae* plays a crucial role in the low-salt koji-making stage. Therefore, the salt-tolerant bacteria used in the fermentation of fermented soybeans are typically yeasts, lactic acid bacteria, and other distinctive microbial groups that dominate in the mid-to-late stages. These distinctive microbial groups are species other than yeasts, lactic acid bacteria, and *Aspergillus oryzae*. Different production processes utilize different distinctive microbial groups, such as halophilic tetracocci and *Bacillus amyloliquefaciens*. Because this embodiment involves aeration fermentation at a certain acid value, acid-producing bacteria can be inhibited during the high-salt aeration fermentation process, meaning the salt tolerance requirement for acid-producing bacteria is relatively low. If the production of acids and alcohols is severely inhibited during the aeration fermentation process, the production of esters will also be inhibited, causing the fermentation effect of the aeration fermentation process to depend on the external environment and the microbial system, resulting in a decrease in fermentation effect. However, the esterification reaction of alcohols and acids is a reversible reaction, and the continuous production of alcohols can promote the production of esters. Therefore, yeasts with a certain degree of salt tolerance, such as Candida cherubicin, can be used, which can tolerate a salt level of up to 240 g / L.

[0069] The optimal concentration range of brine in the fermentation substrate satisfies the acid production of lactic acid bacteria and the physiological activities of other microorganisms. For example, a common optimal concentration range is 6wt%-12wt%. The salt tolerance of the microorganisms can be determined through existing experimental tests. As an example, after inoculating the microorganisms into culture media with different salt concentrations, the growth of the microorganisms is monitored periodically. For instance, by measuring the optical density of the culture medium to plot a growth curve, the salinity range for normal growth can be obtained. The criteria for determining normal growth can be set. For example, after obtaining the maximum growth rate of the microorganisms from the plotted growth curve, a growth rate ≥ a * maximum growth rate can be defined as normal growth. 'a' can be set according to actual needs, such as a = 75%. The closer 'a' is to 100%, the higher the requirements for the suitability of the fermentation environment for the microorganisms. As an example, after inoculating the microorganisms into culture media with different salt concentrations, the content of a certain metabolite of the microorganisms can be monitored to obtain its metabolic efficiency at different salt concentrations. For example, when the microorganism is lactic acid bacteria, the salinity range that meets the acid production rate requirements can be obtained by monitoring the pH value of the fermentation broth. Whether the acid production rate meets the requirements can be set as needed. For example, after obtaining the maximum acid production rate through testing, it can be set that if the acid production rate is ≥ b * maximum acid production rate, the acid production rate requirement is met, indicating normal metabolism. b can be set according to actual needs, such as b = 75%. The closer b is to 100%, the higher the requirement for the suitability of the fermentation environment for the strain. After measuring the salt tolerance of different strains using the aforementioned method, the optimal concentration range of brine in the fermentation substrate can be obtained. The optimal concentration range satisfies the normal survival or normal metabolism of each strain. As an example, when salt-tolerant strains are used for yeast or a specific strain, the optimal concentration range of brine in the fermentation substrate satisfies the normal survival or normal metabolism of other strains besides salt-tolerant strains. However, a judgment method that distinguishes salt-tolerant strains from other strains can be set because the physiological activity of salt-tolerant strains in low-salt systems may be lower than that in high-salt systems. When it is impossible to simultaneously meet the aforementioned conditions for normal survival or normal metabolism for all bacterial species, the threshold for judging whether salt-tolerant bacterial species are living or metabolizing normally can be lowered. For example, when the growth rate of salt-tolerant bacterial species is ≥60% of the maximum growth rate, it is considered normal growth.

[0070] As an example, the minimum salt concentration required for salt-tolerant bacteria to grow at ≥75% of their maximum growth rate was used as a benchmark for selecting other bacterial strains, ensuring that these strains exhibited the highest possible physiological activity during the closed fermentation process. For instance, the growth rate of other strains at the aforementioned minimum salt concentration was ≥90% of their maximum growth rate. When the fermentation system transitioned to an aeration fermentation process, the physiological activity of the salt-tolerant bacteria increased, while the physiological activity of the other strains decreased, thus creating a system where different strains cyclically dominated the fermentation process.

[0071] As an example, in order to minimize the salt concentration in the fermentation system, the minimum concentration value in the optimal concentration range can be selected as the salt concentration of the aqueous phase in the fermentation substrate.

[0072] As an example, based on the physiological activity of salt-tolerant bacteria at different salinity levels, the salt concentration of the aqueous phase in the fermentation system is determined during the aeration fermentation process. Then, the amount of water to be extracted from the fermentation substrate can be obtained based on the salt concentration difference between the closed fermentation and aeration fermentation processes. As an example, during the aeration fermentation process, the salt concentration of the aqueous phase in the fermentation system is such that the growth rate of the salt-tolerant bacteria is ≥90% of its maximum growth rate, thus yielding the minimum amount of water to be extracted. As an example, during the aeration fermentation process, the growth rate of other bacteria besides salt-tolerant bacteria, such as acid-producing bacteria (lactic acid bacteria), is ≥30% of their maximum growth rate.

[0073] As an example, the ratio of broad beans to chili peppers, as well as the inoculation amount of each microbial strain, can be achieved using existing technologies in this embodiment. During the implementation of the control method, the aforementioned ratio and inoculation amount remain fixed.

[0074] Example 5: To better confirm the end time of the aeration fermentation process and shorten the fermentation time, an improvement was made based on Example 4. In this example, the fermentation substrate includes: salt-tolerant yeast; the control method includes:

[0075] During the aeration fermentation process, the relationship between the content of volatile esters in the fermentation system and the fermentation time is obtained, thereby obtaining the fermentation time required for the increase rate of volatile esters to be less than or equal to the preset rate, and finally obtaining the fermentation time of the aeration fermentation process.

[0076] In the specific implementation process, since the aeration fermentation process is an open fermentation, the amount of esters in the fermentation system can be sampled and tested at any time. The detection method is existing technology and will not be described in detail in this embodiment. The fermentation time is the fermentation time of the aeration fermentation process. A curve showing the relationship between the content of volatile esters and the fermentation time can be plotted, and a fitting function can be obtained. The increase rate of volatile esters at different fermentation time points can be obtained through the first derivative of the fitting function. Usually, the increase rate is the fastest in the early stage of fermentation. As organic acids are continuously consumed, the increase rate gradually slows down. A preset rate can be set as needed. For example, after obtaining the average increase rate of the first 5 days as M, the preset rate can be set to 50%M. Thus, the fermentation time required for the increase rate of volatile esters to be ≤ the preset rate can be obtained. The aeration fermentation process can be stopped when the increase rate equals the preset rate, and the fermentation system can be transferred to the closed fermentation process.

[0077] Example 6: To facilitate real-time monitoring during production and to confirm the endpoint of each fermentation step, an improvement was made based on Example 5. In this example, the control method includes:

[0078] To obtain the relationship between the salt concentration of the aqueous phase, the pH value of the fermentation system, and the metabolic rate of acid-producing bacteria in the aeration fermentation process;

[0079] The relationship between the metabolic rate of acid-producing bacteria, the pH value of the fermentation system and the rate of increase of volatile esters in the aeration fermentation process was obtained. The maximum metabolic rate when the pH value and the rate of increase of volatile esters conformed to a monotonically decreasing relationship was obtained, and then the salt concentration of the aqueous phase in the aeration fermentation process was obtained.

[0080] The pH value at the end of the aeration fermentation process is obtained based on the preset speed.

[0081] In the specific implementation process, the pH value and the rate of increase of volatile esters can be obtained by continuous sampling. If the end point of the aeration fermentation process is determined by the rate of increase of volatile esters, the time needs to be determined in the laboratory stage. However, the raw materials of fermented soybean paste are from natural sources rather than industrial sources, and the raw materials inevitably have certain fluctuations. Therefore, the fermentation time determined in advance in the laboratory stage may not be suitable for all industrial production lines. In order to improve the intelligence of the production line and realize the automatic and simple determination of the fermentation end point of the closed fermentation process and the aeration fermentation process, the applicant hopes to indirectly characterize the rate of increase of volatile esters by using other characteristics of the system that are easy to monitor during the fermentation process.

[0082] During the aeration fermentation process, acid-producing bacteria, such as lactic acid bacteria, are inhibited, resulting in limited acid production. Other microorganisms are also suppressed or even killed due to the high salinity and acidity. In the fermentation system, acid is continuously consumed as a nutrient for microorganisms and constantly reacts with alcohols to form esters. However, the rate of acid production affects the pH level of the system, making it difficult to directly characterize the rate of increase in volatile esters using the system's pH value.

[0083] To better characterize the rate of increase of volatile esters using the system pH value, this embodiment obtained the metabolic rate range where the pH value and the rate of increase of volatile esters exhibit a monotonically decreasing relationship. In order to convert alcohols into esters more quickly, the maximum proxy rate within the metabolic rate range was selected. Then, the salt concentration of the aqueous phase in the aeration fermentation process was obtained based on the maximum metabolic rate, and the amount of water drawn out during the conversion from the closed fermentation process to the aeration fermentation process was also obtained.

[0084] When the acid-producing bacteria produce acid at a sufficiently slow rate, the amount of acid produced is less than the amount of organic acid consumed, and the pH value of the fermentation system gradually increases. As the acid is continuously consumed, the rate of increase of volatile esters gradually slows down. That is, the less acid there is, the slower the rate of increase of volatile esters. Therefore, the pH value can be used to characterize the rate of increase of volatile esters.

[0085] The metabolic rate can be detected by referring to Example 4.

[0086] The endpoint of the aeration fermentation process is determined by the change in the pH value of the system. This allows the equipment to monitor the pH value in real time and automatically control the time to switch to the closed fermentation process. After switching to the closed fermentation process, acid-producing bacteria can produce a large amount of acid again until the system reaches the acid value required for switching to the aeration fermentation process. This simplifies the automatic cyclic switching between the two processes.

[0087] As an example, when the rate of increase in pH and volatile esters does not conform to a monotonically decreasing relationship, acid-producing bacteria can be screened and replaced.

[0088] Example 7: To better determine the timing of the first aeration fermentation process, improvements were made based on Examples 4-6. In this example, the control method includes:

[0089] The initial fermentation time is determined when the amino acid and reducing sugar content reaches the preset minimum value during the fermentation process; the first aeration fermentation process begins after the initial fermentation time.

[0090] In the specific implementation process, since the endpoint confirmation of the aeration fermentation step in this embodiment is related to the esterification reaction, the enzymatic hydrolysis reaction involved in the substrate needs to be fully completed before entering the first aeration fermentation step, and a certain amount of acid and alcohol needs to be present. Acids are usually obtained by fermentation of glucose and ethanol. Ethanol is usually obtained by fermentation of glucose and some amino acids. As can be seen from the foregoing, to enter the full esterification reaction stage, sufficient sugar and amino acid substrates need to be obtained through enzymatic hydrolysis in the early stage of fermentation.

[0091] As an example, with the fermentation substrate unchanged, the peak values ​​of sugars and amino acids in the conventional process are obtained. A preset minimum value is set based on these peak values. For example, the preset minimum value = 60% of the peak value, to ensure that sufficient substrate is generated from the enzymatic hydrolysis reaction before proceeding to the aeration fermentation step. The detection of reducing sugar and amino acid content is a routine detection technique in the field of soybean fermentation and is one of the necessary detection indicators; the specific detection steps will not be elaborated in this embodiment.

[0092] As an example, when the amino acid and reducing sugar contents both reach the preset minimum values, the pH value of the system is used to determine whether the gasification fermentation process needs to be entered.

[0093] As an example, in the early stages of fermentation, the primary process relies on enzymes to break down polysaccharides and proteins. At this point, the system temperature can be controlled at 30-40℃ to ensure enzyme activity. In the middle and later stages of fermentation, to promote esterification and Maillard reactions, the fermentation system temperature can be increased to 50-60℃. That is, after the first transition to the aeration fermentation step, the system temperature can be maintained at 50-60℃. Of course, the temperature in the middle and later stages of fermentation needs to be set according to the thermotolerance of the microbial strain. If the thermotolerance is insufficient to meet 50-60℃, the temperature of the later stages of fermentation needs to be appropriately reduced.

[0094] Example 8: To facilitate simple control of the salt concentration in the fermentation system during the aeration fermentation process, an improvement was made based on Example 7. In this example, the control method further includes:

[0095] During the aeration fermentation process, the initial air humidity inside the fermentation device is obtained;

[0096] After the ambient air passes through the humidity regulating device, the ambient air humidity reaches the second air humidity; the ratio of the second air humidity to the first air humidity is within the set ratio range.

[0097] In practice, during the aeration fermentation process, water in the fermentation system will evaporate to some extent. If the water content in the fermentation system is constantly changing, the amount of water that needs to be removed each time the process transitions from closed fermentation to aeration fermentation will vary, increasing the complexity of the process. Therefore, this embodiment uses an additional humidity control device to ensure that the humidity of the air introduced from the external environment is consistent with the humidity of the air inside the fermentation device. The closer the set ratio is to 1, the higher the stability of the water content in the system. The exemplary set ratio range is (0.95, 1.05). The humidity control device is existing technology, and the air humidity inside the fermentation device can also be monitored using existing humidity sensors.

[0098] Since the fermentation system in this embodiment is similar to that of a sealed fermentation system, there is almost no evaporation of water. Therefore, if the water content of the product needs to be lower, the aqueous phase can be concentrated using a matching concentration device to retain the effective ingredients. This not only reduces the water content in the product but also further enhances the umami and flavor of the fermented bean paste.

[0099] Example 9: In order to better determine the endpoint of the closed fermentation process, an improvement was made based on Example 7. When the pH value of the fermentation system no longer continues to decrease from the start of the closed fermentation process, the fermentation process is always in the closed fermentation process.

[0100] In practice, during the aeration fermentation process, the organic acids in the fermentation system gradually decrease. When the system transitions to a closed fermentation process, the physiological activity of acid-producing bacteria increases, and the amount of acid produced increases significantly. However, with the large-scale reproduction of yeast, its consumption of organic acids also increases. Coupled with the consumption from esterification reactions, the pH value in the closed fermentation process may change with fermentation time. In the later stages of fermentation, the pH value in the closed fermentation process may slowly rise until it stabilizes. That is, in the later stages of fermentation, it is difficult to use the degree of pH decrease to guide the end point of the closed fermentation process. Moreover, the overall microbial activity weakens in the later stages of fermentation, entering a post-ripening stage dominated by biochemical reactions. At this time, esterification and Maillard reactions are the main reactions, and the impact of no aeration on the product flavor is also relatively weak.

[0101] As an example, a specific decrease value can be set to determine when the pH value stops decreasing. For example, if the pH value decreases by less than 1, it can be determined that the pH value has stopped decreasing.

[0102] Example 10: In order to better determine the end point of the closed fermentation process, an improvement was made based on Example 7. When the pH value of the fermentation system in the closed fermentation process drops to a stable level, the closed fermentation process is switched to the aeration fermentation process.

[0103] Methods for determining if a value is approaching stability include: within a set time period, the variance of the pH dataset is less than a set variance.

[0104] In practice, once the pH value at the end of the aeration fermentation process is fixed, it means that the pH value at the beginning of the closed fermentation process is fixed. However, as the fermentation time increases, the rate at which the pH value of the fermentation system decreases and the minimum achievable pH value in the closed fermentation process vary. Therefore, in this embodiment, the end point of the closed fermentation process is no longer guided by a fixed pH value. Instead, when the pH value of the fermentation system in the closed fermentation process decreases to a stable level, the closed fermentation process is switched to the aeration fermentation process to ensure that the system has sufficient acid for the esterification reaction in the aeration fermentation process and to inhibit miscellaneous bacteria.

[0105] As an example, once the pH value stabilizes, the process is immediately switched from closed fermentation to aeration fermentation.

[0106] As an example, a minimum time is specified for the closed fermentation process. If the time it takes for the pH value to stabilize is less than the aforementioned minimum time, the closed fermentation process is maintained until the minimum time is reached. The minimum time can be set as needed, such as 30 days.

[0107] As an example, the set time can be configured as needed, such as 5 or 10 days. pH values ​​are measured daily at set intervals, and multiple measurements can be taken daily. The pH data collected within the set time period forms a dataset, and then the variance of the dataset is calculated. The smaller the variance, the smaller the data fluctuation, and the more stable the pH values. Setting a smaller variance indicates a higher requirement for pH stability; this can be configured as needed, for example, to a variance of 0.3.

[0108] from Figure 1-2 It is evident that the product obtained through the fermentation process provided by this invention possesses excellent quality, with both flavor and umami meeting the standards. Furthermore, the control method can also be implemented... Figure 1-2 The content of amino acid nitrogen and total acid in the fermentation process is used as one of the criteria for determining the end point of the fermentation process.

[0109] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fermentation process for fermented broad bean paste in a tank, characterized in that, Includes the following steps: After the fermentation substrate is fed into the fermentation device, it undergoes alternating closed fermentation and aeration fermentation processes. The closed fermentation process includes: alternating stirring operation sections and static fermentation sections; the static fermentation sections include: conventional static fermentation sections and layered static fermentation sections; After the water above the fermentation substrate is drained, an aeration fermentation process is carried out. After the aeration and fermentation process is completed, the water drawn out is reintroduced into the fermentation substrate, stirred evenly, and then subjected to a closed fermentation process.

2. The fermentation process for fermented broad bean paste in tanks according to claim 1, characterized in that, The fermentation device has multiple water outlets arranged longitudinally on its side wall; during the water extraction process, water is extracted using the water outlet located above the solid medium layer and below the upper surface of the water layer.

3. The fermentation process for fermented broad bean paste in tanks according to claim 2, characterized in that, During the stratified settling phase of the fermentation system, water is continuously drawn out from the top of the fermentation substrate.

4. A method for controlling the fermentation process of fermented broad bean paste in tanks according to any one of claims 1-3, characterized in that, include: Obtain the acid value of the fermentation system and find the minimum time required for the acid value to be greater than or equal to the preset acid value; The fermentation system is in a closed fermentation process until the minimum fermentation time is reached; Based on the salt tolerance of the strain, the optimal concentration range of brine in the fermentation substrate was obtained; Based on the salt tolerance of the acid-producing bacteria and the optimal concentration range, the salinity range of the fermentation system during the aeration fermentation process is obtained, and thus the amount of water drawn out is obtained.

5. The control method according to claim 4, characterized in that, Fermentation substrates include: salt-tolerant yeasts; the control methods include: During the aeration fermentation process, the relationship between the content of volatile esters in the fermentation system and the fermentation time is obtained, thereby obtaining the fermentation time required for the increase rate of volatile esters to be less than or equal to the preset rate, and finally obtaining the fermentation time of the aeration fermentation process.

6. The control method according to claim 5, characterized in that, include: To obtain the relationship between the salt concentration of the aqueous phase, the pH value of the fermentation system, and the metabolic rate of acid-producing bacteria in the aeration fermentation process; The relationship between the metabolic rate of acid-producing bacteria, the pH value of the fermentation system and the rate of increase of volatile esters in the aeration fermentation process was obtained. The maximum metabolic rate when the pH value and the rate of increase of volatile esters conformed to a monotonically decreasing relationship was obtained, and then the salt concentration of the aqueous phase in the aeration fermentation process was obtained. The pH value at the end of the aeration fermentation process is obtained based on the preset speed.

7. The control method according to any one of claims 4-6, characterized in that, include: The initial fermentation time when the amino acid and reducing sugar content both reach the preset minimum value during the fermentation process is determined. The first aeration and fermentation process begins after the initial fermentation time.

8. The control method according to claim 7, characterized in that, include: During the aeration fermentation process, the initial air humidity inside the fermentation device is obtained; After the ambient air passes through the humidity regulating device, the ambient air humidity reaches the second air humidity; the ratio of the second air humidity to the first air humidity is within the set ratio range.

9. The control method according to claim 7, characterized in that, When the closed fermentation process begins from the start of fermentation and the pH value of the fermentation system no longer continues to decrease, the fermentation process remains in a closed fermentation state.

10. The control method according to claim 7, characterized in that, When the pH value of the fermentation system in the closed fermentation process drops to a stable level, the closed fermentation process is switched to the aeration fermentation process. Methods for determining if a value is approaching stability include: within a set time period, the variance of the pH dataset is less than a set variance.

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