Wheat core vinegar and preparation method thereof

Abstract

The invention discloses wheat core vinegar and a preparation method thereof, and belongs to the technical field of brewing, wheat is separated into wheat cores and bran, the separated wheat cores serve as main preparation raw materials, the content of protein and starch in the raw materials can be increased, the raw materials can be converted into flavor substances after fermentation, the fragrance and taste of finished vinegar can be improved, and the taste of the finished vinegar is improved. The vinegar yield can be improved, and the problems that in the prior art, part of components in the raw materials cannot be converted into flavor substances, so that the vinegar yield is low, and the finished vinegar is boring in taste are solved; the separated bran is used as a main raw material for solid acetic fermentation, so that the problem of insufficient starch content of bran in the prior art is solved; meanwhile, in the solid acetic acid fermentation process, protein in the bran can be decomposed into a large amount of amino acid, bran fibers cannot be excessively decomposed, and the problems that existing finished vinegar has foreign flavor and is poor in fragrance and taste are solved.

Description

Technical Field

[0001] This invention relates to the field of brewing technology, and in particular to a wheat core vinegar and its preparation method. Background Technology

[0002] Existing vinegar-making processes generally include solid-state, liquid-state, and fruit vinegar fermentation. In solid-state fermentation, wheat is typically the main raw material, supplemented with rice, sorghum, and wheat bran. After saccharification, alcoholic fermentation, and acetic acid fermentation, the finished vinegar is obtained. However, current processes generally use whole wheat for fermentation without separating the wheat core and bran. This results in some components of the raw material failing to be converted into flavor compounds, leading to a low vinegar yield and a bland taste in the finished vinegar. Simultaneously, due to insufficient starch content in the bran, it is easily over-decomposed during fermentation, causing the fiber structure to collapse. This leads to clumping of the vinegar mash and reduced aeration, which exacerbates the formation of off-flavors, resulting in a final vinegar with not only unpleasant tastes but also poor aroma and flavor. Summary of the Invention

[0003] The main objective of this invention is to provide a wheat bran vinegar and its preparation method, which aims to solve the problems of low vinegar yield, bland taste of finished vinegar, low starch content in wheat bran, and unpleasant off-flavors, poor aroma and taste of finished vinegar caused by existing processes.

[0004] To achieve the above objectives, the present invention provides a method for preparing wheat core vinegar, the method comprising: Wheat is separated to obtain wheat coarse and bran; The wheat kernels, water, and amylase are mixed in a preset ratio and then cooked to obtain a liquid. After cooling the liquid to a preset temperature, a complex enzyme consisting of saccharifying enzyme, pullulanase and xylanase is added according to the saccharification ratio. After stirring evenly, saccharification is carried out to obtain a saccharified liquid. A compound microbial mixture consisting of daqu, bran koji, and yeast powder is added to the saccharification liquid according to the alcohol fermentation ratio to carry out alcohol fermentation and obtain alcohol mash. In the fermented mash, wheat bran, wheat koji, and rice husk are added according to the solid-state fermentation ratio, and then Acetobacter pasteurellii and Lactobacillus acidophilus are added. After stirring evenly, solid-state acetic acid fermentation is carried out to obtain mature vinegar mash. After aging the mature vinegar mash, further processing is carried out to obtain the wheat core vinegar.

[0005] Optionally, in the wheat kernels, 20-mesh wheat kernels account for 15% to 20%, 40-mesh wheat kernels account for 60% to 70%, and 60-mesh wheat kernels account for 10% to 25%.

[0006] Optionally, the bran has a starch content greater than 52%, and the preparation method further includes the following steps before adding the bran to the fermented mash: Wheat bran was extruded and puffed under conditions of 80℃~90℃ and 0.3MPa~0.5MPa, while 0.05%~0.1% of acidic protease was added.

[0007] Optionally, the cooking temperature is 100℃~105℃ and the duration is 50min~65min.

[0008] Optionally, the preset temperature is 60℃~65℃, and the saccharification method includes: Hold at 61℃~65℃ for 4min~6min, then at 58℃~60℃ for 8min~12min, and finally at 55℃~57℃ for 10min~17min.

[0009] Optionally, the fermentation temperature is 30℃~35℃ and the duration is 5d~7d.

[0010] Optionally, the solid-state acetic acid fermentation method includes: After fermenting at 30℃~33℃ for 5 days, the temperature is controlled at 38℃~42℃ and fermentation continues; on the 10th day of fermentation, the temperature is controlled at 35℃~37℃ and fermentation continues for 3~5 days; after the 3~5 days of continued fermentation, when the temperature of the vinegar mash is below 35℃, pressing of the mash begins; the temperature of the vinegar mash is monitored throughout the fermentation process, and the mash is turned according to the monitoring results.

[0011] Optionally, the aging method includes: Aged for 30 to 35 days at a temperature of 15℃ to 18℃ and a humidity of 60% to 70%, then aged for another 10 to 15 days at a temperature of 25℃ to 28℃.

[0012] Optionally, the post-processing includes, in sequence, vinegar leaching, sterilization of raw wheat core vinegar, grading, filtration, sterilization of finished wheat core vinegar, packaging, and inspection and warehousing.

[0013] To achieve the above objectives, the present invention also provides a wheat core vinegar, which is prepared by the above-described preparation method.

[0014] Compared with the prior art, the beneficial effects that the present invention can achieve are as follows: 1. In the technical solution of the present invention, wheat is separated into wheat core and bran. On the one hand, using the separated wheat core as the main raw material can increase the protein and starch content of the raw material and reduce the impurity content. After fermentation, it can be completely converted into flavor substances, which can not only improve the aroma and taste of the finished vinegar, but also increase the vinegar yield. This solves the problem in the prior art that some components in the raw material cannot be converted into flavor substances, resulting in low vinegar yield and bland taste of the finished vinegar. On the other hand, using separated wheat bran as the main raw material for solid-state acetic acid fermentation, the starch content of the wheat bran is greater than 52%, and its starch content can be controlled through the separation process. At the same time, it is higher than the starch content of commercially available wheat bran (less than 40%), eliminating the need to add additional starch raw materials, which can save costs and simplify the process. During solid-state fermentation, the protein in the wheat bran can be decomposed into a large number of amino acids, providing sufficient precursors for the Maillard reaction, thereby enhancing the umami and color of the finished vinegar. This solves the problem in the existing technology where insufficient starch in the wheat bran leads to excessive decomposition of wheat bran fibers, causing the fiber structure to collapse, resulting in clumping of the vinegar mash, reduced air permeability, and exacerbation of off-flavor substances. As a result, the final finished vinegar not only has an off-flavor but also has poor aroma and taste.

[0015] 2. In the preparation of wheat core vinegar, the present invention adds a complex enzyme composed of saccharifying enzyme, pullulanase and xylanase during the saccharification process, which can degrade amylopectin and hemicellulose, increase the amount of reducing sugar produced, and shorten the saccharification time; during the alcohol fermentation process, a complex microbial culture composed of daqu, bran koji and yeast powder is added, which can not only shorten the fermentation cycle, but also improve and stabilize the alcohol conversion rate and avoid flavor fluctuations caused by contamination by miscellaneous bacteria. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the preparation process of the finished wheat vinegar. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] To address the problems in existing technologies where the wheat core and bran are not separated, resulting in some components of the raw material failing to convert into flavor compounds, leading to low vinegar yield and a bland taste in the finished vinegar, and further, the insufficient starch content in the bran in the auxiliary materials causing excessive decomposition of the bran fiber, resulting in an off-flavor in the finished vinegar, along with poor aroma and taste, this invention provides a method for preparing wheat core vinegar, such as... Figure 1As shown, the preparation method includes: S10. Raw material processing: The wheat is separated to obtain the wheat cob and bran; S20. Cooking treatment: Mix wheat kernels, water, and amylase from S10 in a preset ratio, and then cook them to obtain a liquid. S30. Saccharification: After cooling the liquid obtained from S20 to the preset temperature, add a complex enzyme consisting of saccharifying enzyme, pullulanase and xylanase according to the saccharification ratio, stir evenly and carry out saccharification to obtain saccharified liquid. S40. Fermentation: The compound bacteria consisting of Daqu, wheat bran and yeast powder are added to the saccharification liquid obtained in S30 according to the fermentation ratio to carry out fermentation and obtain fermented mash. S50. Solid-state acetic acid fermentation: In the mash obtained from S40, according to the solid-state fermentation ratio, add the bran, bran koji, and rice husk obtained from S10, and then add Acetobacter pasteurella and Lactobacillus acidophilus. After stirring evenly, carry out solid-state acetic acid fermentation to obtain mature vinegar mash. S60. The mature vinegar mash obtained in S50 is aged and post-treated to obtain the wheat core vinegar.

[0019] Optionally, the above-mentioned wheat kernels, water, and amylase are mixed in a preset ratio, wherein the preset ratio can be 1:2.4 to 1:3.0 for wheat kernels to water, and the amount of amylase added is 0.05% to 0.1% of the mass of the wheat kernels. Under this ratio, the yield of reducing sugars can reach more than 92% of the theoretical value during the saccharification stage, the alcohol conversion rate can be stabilized at more than 92%, and the acetic acid yield can be increased by more than 20%, resulting in excellent quality and high process stability of the finished vinegar.

[0020] Optionally, the saccharification ratio can be achieved by adding a complex enzyme consisting of the aforementioned saccharifying enzyme, pullulanase, and xylanase at 0.12% to 0.20% of the wheat core mass. At this ratio, the saccharifying enzyme can fully decompose the starch in the wheat core into amylose and amylopectin, increasing the reducing sugar yield to over 92%. Simultaneously, it can be matched with the saccharification process, completing saccharification within a preset time without extending the process cycle.

[0021] Optionally, in the complex enzyme composed of the above-mentioned saccharifying enzyme, pullulanase and xylanase, the mass ratio of the saccharifying enzyme, pullulanase and xylanase can be 6:1.2:0.8, corresponding to an addition amount of 0.15%, 0.03% and 0.02% based on the weight of wheat kernels, respectively.

[0022] Optionally, the mass ratio of the above-mentioned glucoamylase, pullulanase and xylanase can be 5:1.5:0.5.

[0023] It should be noted that in the above technical solution, in the composition of the compound enzyme, the saccharifying enzyme mainly hydrolyzes amylose, pullulanase specifically targets the branching points of amylopectin, and xylanase can decompose hemicellulose in wheat kernels; when the mass ratio of the three is 6:1.2:0.8, not only can the hydrolysis residue of amylopectin be avoided, but the enzymatic hydrolysis efficiency can also be improved by xylanase.

[0024] Optionally, the compound bacteria are added to the saccharification liquid according to the alcoholization ratio, wherein the alcoholization ratio can be calculated based on the weight of the wheat core, and the inoculation amount of the compound bacteria can be 3% to 5% of the weight of the wheat core.

[0025] Optionally, when the compound bacteria are composed of Daqu, bran koji and yeast powder, the amount of Daqu added can be 30% to 60% of the wheat core mass, the amount of bran koji added can be 20% to 40% of the wheat core mass, and the amount of brewing yeast added can be 0.01% to 0.03% of the wheat core mass.

[0026] It should be noted that during the fermentation process, Daqu (a type of starter culture) helps decompose residual starch and polysaccharides in the wheat core, producing fermentable sugars such as glucose. Simultaneously, proteases break down proteins in the raw materials into amino acids, providing a nitrogen source for yeast growth. Bran koji (another type of starter culture) efficiently decomposes incompletely degraded starch and dextrin in the saccharification liquid, continuously generating glucose to ensure a carbon source supply for yeast fermentation and improve raw material utilization. Yeast powder converts monosaccharides such as glucose into alcohol and carbon dioxide through glycolysis.

[0027] Optionally, the above-mentioned bran, bran koji, and rice husk are added to the solid-state fermentation according to the above proportions. The amount of bran, bran koji, and rice husk added can be calculated based on the mass of the raw materials in the fermentation mash. For example, the amount of bran added can be 90% to 150% of the weight of the raw materials in the fermentation mash, the amount of bran koji added can be 20% to 40% of the weight of the raw materials in the fermentation mash, and the amount of rice husk added can be 20% to 50% of the weight of the raw materials in the fermentation mash.

[0028] Optionally, the inoculation amount of *Acetobacter pasteurellii* can be 1 × 10⁻⁶. 6 ~5×10 7 CFU / g vinegar mash refers to the number of *Acetobacter pasteurization* bacteria inoculated per gram of vinegar mash, ranging from 1 million to 50 million. The inoculation amount of acid-fast *Lactobacillus* can be 1 × 10⁻⁶. 5 ~1×10 6 CFU / g vinegar mash means that the number of Pasteurella bacteria inoculated in each gram of vinegar mash is between 100,000 and 1 million.

[0029] It should be noted that during acetic acid fermentation, *Acetobacter pasteurization* oxidizes the alcohol in the mash into acetic acid via acetaldehyde, which is the main source of total acid in wheat vinegar. Simultaneously, *Acetobacter pasteurization* can metabolize and produce flavor compounds such as ethyl acetate, enhancing the aroma of the vinegar. Meanwhile, acid-fast lactobacilli, facultative anaerobic lactic acid bacteria, play a crucial role in fermenting residual sugars in the raw materials, such as lactose and oligosaccharides, to produce organic acids such as lactic acid and propionic acid. This enriches the acidity of the finished vinegar. Furthermore, they can synthesize B vitamins, peptides, and other substances, improving the nutritional characteristics and flavor complexity of the vinegar.

[0030] Furthermore, in the acidic environment of solid-state acetic acid fermentation, acid-resistant Lactobacillus can first metabolize and produce lactic acid, lowering the pH of the fermentation system. This creates a suitable acidic environment for Acetobacter pasteurization, improving its alcohol oxidation efficiency and inhibiting the growth of acid-intolerant bacteria. Secondly, acid-resistant Lactobacillus can decompose oligosaccharides and residual sugars, preventing the accumulation of these substrates in the system and the resulting off-flavors. Meanwhile, Acetobacter pasteurization focuses on oxidizing alcohol. The division of labor between the two strains in utilizing different substrates improves the overall utilization rate of raw materials. In addition, lactic acid can combine with acetic acid to form a complex sour taste, making the finished vinegar taste more mellow and smooth, avoiding the sharpness of acetic acid alone. The antimicrobial peptides produced by acid-resistant Lactobacillus can help inhibit other bacteria and work with Acetobacter pasteurization to maintain a stable fermentation environment, ensuring uniform maturation of the vinegar mash. Therefore, in the process of solid-state acetic acid fermentation, Acetobacter pasteurization and acid-resistant Lactobacillus can achieve synergy in acidic environment, substrate utilization, and flavor and stability.

[0031] In one possible implementation, the proportion of 20-mesh wheat kernels is 15% to 20%, the proportion of 40-mesh wheat kernels is 60% to 70%, and the proportion of 60-mesh wheat kernels is 10% to 25%.

[0032] It should be understood that 20-mesh, 40-mesh, and 60-mesh wheat cores refer to wheat cores with different particle sizes obtained by passing them through 20-mesh, 40-mesh, and 60-mesh sieves respectively after separating the wheat core and bran.

[0033] It should be noted that the above-mentioned wheat core composition is mainly composed of 40-mesh wheat cores, which ensures uniform heating of the raw materials during the cooking process and allows for sufficient water absorption and gelatinization. 20-mesh wheat cores prevent excessive material adhesion, while 60-mesh wheat cores fill the gaps between coarse particles, increasing the overall gelatinization degree of the liquid by more than 10% and reducing starch residue. Furthermore, the large specific surface area of ​​60-mesh wheat cores allows for rapid contact with saccharifying enzymes and complex bacteria, accelerating starch hydrolysis and alcohol production. The 20-mesh and 40-mesh cores form a porous structure, facilitating oxygen flow and metabolite diffusion during fermentation, preventing localized hypoxia or substrate accumulation. Simultaneously, in subsequent fermentation processes, the addition of bran, koji, and rice husks further optimizes the fluffiness of the vinegar mash, reducing the risk of caking and decreasing resistance during turning, ensuring uniform temperature during acetic acid fermentation and preventing localized overheating that inhibits acetic acid bacteria activity.

[0034] In one possible implementation, the starch content of the bran is greater than 52%. Before adding the bran to the fermented mash, the bran can be extruded and puffed at a temperature of 80°C to 90°C and a pressure of 0.3 MPa to 0.5 MPa, while 0.05% to 0.1% of acidic protease is added.

[0035] It should be noted that in the above technical solution, the extrusion and puffing treatment of wheat bran, under conditions of 80℃~90℃ and 0.3MPa~0.5MPa, allows the internal moisture of the wheat bran to rapidly vaporize, forming a microporous structure and increasing its porosity and specific surface area. This not only facilitates the contact and action of microorganisms and enzymes during subsequent fermentation but also improves the water-holding capacity and swelling capacity of the wheat bran, allowing it to mix better with the mash and promote the fermentation reaction. Simultaneously, it breaks the hydrogen bonds between starch chains in the wheat bran, causing starch granules to swell and gelatinize, generating maltodextrin and oligosaccharides that readily react with enzymes. This improves the digestibility and utilization rate of starch, providing more substrate for subsequent alcoholic and acetic acid fermentation, thereby increasing the yield of fermentation products. Furthermore, the extrusion and puffing treatment promotes the conversion of insoluble dietary fiber in the wheat bran into soluble dietary fiber, which not only helps improve the taste and quality of the fermentation products but also increases the nutritional value of the finished vinegar.

[0036] In one possible implementation, the temperature of the above-mentioned cooking treatment is 100°C to 105°C, and the duration is 50 min to 65 min.

[0037] It should be noted that mixing wheat kernels, water, and starch in a preset ratio and then steaming them at 100℃~105℃ for 50min~65min not only kills most microorganisms in the raw materials, including bacteria, molds, and yeasts, reducing the risk of contamination and ensuring the normal progress of subsequent fermentation, thus preventing the production of harmful substances by microorganisms that could affect product quality, but also thoroughly ruptures the tissues and cell membranes of the raw materials, allowing for the full release of intracellular substances. This increases the contact area between the raw materials and enzymes and microorganisms, improving the utilization rate of the raw materials. Simultaneously, the steaming process removes some undesirable components and odors from the raw materials, and the set temperature and duration allow for appropriate denaturation of the proteins in the raw materials. Denatured proteins are more easily decomposed and utilized by microorganisms, providing a nitrogen source for microbial growth and metabolism, and also contributing to the formation of a unique product texture and flavor.

[0038] In one possible implementation, the preset temperature is 60°C to 65°C, and the saccharification method includes: Hold at 61℃~65℃ for 4min~6min, then at 58℃~60℃ for 8min~12min, and finally at 55℃~57℃ for 10min~17min.

[0039] It should be noted that under the aforementioned staged temperature control and heat preservation conditions of saccharification, the optimal temperature of the complex enzyme can be adapted, thereby improving the enzymatic hydrolysis efficiency. Specifically, at 61℃~65℃, saccharifying enzymes and xylanases can be activated, which can rapidly decompose starch and hemicellulose; when the temperature drops to the range of 58℃~60℃, the conditions for lulanase to decompose amylopectin can be adapted; when the temperature is further reduced to the range of 55℃~57℃, the residual starch and polysaccharides can be completely degraded, which avoids insufficient activity of some enzymes due to a single temperature. Secondly, the reaction rate can be controlled to reduce side reactions and the formation of off-flavor substances. Maintaining the temperature at 61℃~65℃ for 4min~6min can quickly start the enzymatic hydrolysis reaction while avoiding excessive starch gelatinization and increased viscosity caused by prolonged high temperature, which would affect the contact between the enzyme and the substrate. As the temperature is gradually reduced and the holding time is extended, the enzymatic hydrolysis reaction can proceed smoothly, reducing the accumulation of intermediate products such as maltose and oligosaccharides. At the same time, it avoids Maillard reaction at high temperature, ensuring the purity of the saccharified liquid and the flavor of the subsequent vinegar.

[0040] Furthermore, phased cooling allows starch to gradually decompose from initial rapid decomposition to subsequent slow decomposition, resulting in a high proportion and uniform distribution of monosaccharides such as glucose, thus avoiding the problem of uneven starch decomposition. High-purity, uniform fermentable monosaccharides can be rapidly utilized by subsequent yeast, thereby further increasing the alcohol production rate during fermentation, improving alcohol concentration stability, and significantly reducing the content of undigested polysaccharides in later processes. This avoids the problem of inconsistent fermentation maturity of vinegar mash caused by uneven substrate distribution in solid-state acetic acid fermentation.

[0041] In one possible implementation, the temperature of the above-mentioned alcoholic fermentation is 30°C to 35°C, and the duration is 5 days to 7 days.

[0042] In one possible implementation, the above-described solid-state acetic acid fermentation method includes: After fermenting at 30℃~33℃ for 5 days, the temperature is controlled at 38℃~42℃ and fermentation continues; on the 10th day of fermentation, the temperature is controlled at 35℃~37℃ and fermentation continues for 3~5 days; after the 3~5 days of continued fermentation, when the temperature of the vinegar mash is below 35℃, pressing of the mash begins; the temperature of the vinegar mash is monitored throughout the fermentation process, and the mash is turned according to the monitoring results.

[0043] It should be noted that in the above-mentioned solid-state acetic acid fermentation process, staged temperature-controlled fermentation can match the metabolic patterns of the complex microorganisms. Specifically, the initial fermentation stage at 30℃~33℃ for 1 to 5 days can accommodate the proliferation of the complex microorganisms, allowing the microbial population to quickly reach 10T. 9 CFU / g or higher; during the mid-stage fermentation at 38℃~42℃, it can enhance the activity of acetic acid bacteria, inhibit heat-sensitive bacteria, and strengthen acetic acid production. This period represents the peak activity range for acetic acid bacteria in oxidizing alcohol. In the later stage at 35℃~37℃, it can prevent the decline in acetic acid bacteria activity caused by prolonged high temperatures, maintain the stability of the system's microecology, and promote the conversion of residual alcohol. This results in a total acetic acid yield that is more than 25% higher than that of fixed-temperature fermentation, ultimately leading to an acetic acid content of ≥6.5g / 100mL in the finished vinegar. Therefore, in the solid-state acetic acid fermentation process, by controlling the temperature in stages, the alcohol conversion rate in the mash can reach over 95% within an 18-20 day fermentation cycle, avoiding excessive residual alcohol in the finished vinegar and preventing flavor imbalance, while also reducing product safety risks.

[0044] Furthermore, by using staged temperature-controlled fermentation, flavor components can be generated in a targeted manner at different stages. Specifically, in the early stage, organic acids such as lactic acid and succinic acid produced by microbial metabolism can lay the foundation for a refreshing base flavor; in the mid-stage high-temperature stage, the synthesis of aroma substances such as esters and aldehydes can be accelerated, such as the synthesis of ethyl acetate and malt-related esters, to enhance the main flavor of the finished vinegar; in the later stage medium-temperature stage, the interaction of flavor substances can be promoted, resulting in esterification reactions, making the finished vinegar taste more mellow and harmonious, with the total number of flavor substances increasing by more than 30% compared to traditional processes.

[0045] Furthermore, monitoring the temperature of the vinegar mash during fermentation and turning it according to the monitoring results can adjust the aeration of the vinegar mash to suit the aerobic metabolism of acetic acid bacteria, thus avoiding the growth of miscellaneous bacteria caused by local hypoxia. In addition, after continuing fermentation at 35℃~37℃ for 3 to 5 days, and after a fermentation time of more than 18 days, when the temperature is ≤35℃, the vinegar mash gradually matures. At this point, pressing can begin. Pressing the mash can reduce its porosity, slow down the later fermentation rate, prevent over-fermentation and the production of undesirable components, and at the same time improve the compactness of the vinegar mash, facilitating subsequent vinegar extraction.

[0046] In one possible implementation, the above-mentioned aging method includes: Aged for 30 to 35 days at a temperature of 15℃ to 18℃ and a humidity of 60% to 70%, then aged for another 10 to 15 days at a temperature of 25℃ to 28℃.

[0047] It should be noted that during the aging process described above, conditions of 15℃~18℃ and 60%~70% humidity can slow down the rate of microbial metabolism in the vinegar mash, preventing over-fermentation and off-flavors. This also allows acetic acid to slowly blend with other organic acids, reducing its sharpness and creating a refreshing base flavor. When the temperature rises to 25℃~28℃, the esterification reaction rate of alcohols in the vinegar mash, such as residual alcohol and higher alcohols, with organic acids can increase to over 30%, generating a large amount of aroma compounds such as ethyl acetate and ethyl lactate. This enhances the rich aroma of the finished vinegar, making the transition between the initial and aftertaste more natural. Simultaneously, by controlling the oxygen concentration in the reaction environment during aging, conditions can be provided for redox reactions, such as the conversion of aldehydes into alcohols and ketones, reducing the spiciness and off-flavors of the finished vinegar. However, excessive oxygen concentration prevents oxidation and spoilage of the vinegar mash, ultimately resulting in a richer flavor profile and a more thorough fusion of malt and vinegar aromas in the finished vinegar.

[0048] Furthermore, during the aforementioned aging process, some free organic acids undergo esterification with alcohols or combine with minerals, stabilizing the total acid content at 6g / 100mL~7g / 100mL, while increasing non-volatile acids to over 25%, thus enhancing the richness and lingering finish of the finished vinegar. Simultaneously, the low-to-medium temperature gradient environment and micro-oxygenation promote the dissolution of polyphenols and flavonoids from the wheat and bran into more easily absorbed forms, increasing the total flavonoid content to 20%~25%, thus enhancing the product's nutritional properties. Moreover, under aging conditions, the slow oxidation reaction and Maillard reaction synergistically result in a natural amber to reddish-brown color in the finished vinegar, free of turbidity and sediment, with a significantly higher gloss than un-aged products, improving sensory quality.

[0049] In one possible implementation, the post-processing includes, in sequence, vinegar leaching, sterilization of raw wheat core vinegar, grading, filtration, sterilization of finished wheat core vinegar, packaging, and inspection and warehousing.

[0050] Alternatively, the above-mentioned vinegar rinsing method can be a three-cycle vinegar rinsing method.

[0051] Optionally, the above-mentioned three-cycle vinegar rinsing method can be carried out by using sterile water as the rinsing solution and spraying and soaking the vinegar mash in three batches at a ratio of 1:1.2~1.5 of sterile water.

[0052] Alternatively, the above-mentioned method for sterilizing raw wheat cores with vinegar can be carried out using a low-temperature intermittent sterilization method.

[0053] Optionally, the above grading method can use a dual grading standard of physicochemical indicators and sensory evaluation to grade the sterilized raw vinegar.

[0054] Alternatively, the above filtering method can be implemented using a two-stage filtering method.

[0055] Optionally, the above two-stage filtration method can be as follows: First-stage filtration: A ceramic membrane filter with a pore size of approximately 5 μm can be used to remove suspended particles, protein precipitates, and other large molecular impurities from the raw vinegar. The filtration pressure can be 0.2~0.3 MPa. Second-stage filtration: An ultrafiltration membrane with a pore size of approximately 1 μm can be used to further remove tiny impurities and colloidal substances from the raw vinegar. After filtration, the membrane assembly is backflushed with sterile nitrogen to prevent clogging.

[0056] Optionally, the sterilization method for the finished wheat vinegar can employ a flash pasteurization process. Specifically, the raw vinegar after primary filtration can be flash-sterilized at 110℃~115℃ to maximize the preservation of flavor and functional components. The raw vinegar after secondary filtration can also be flash-sterilized at 110℃~115℃ to rapidly kill residual microorganisms and reduce energy consumption.

[0057] Optionally, the above packaging methods can be integrated into a single aseptic packaging line. The inspection and warehousing process can employ both sampling inspection and full-item testing standards, sampling different batches of finished vinegar to cover different grades and packaging specifications.

[0058] To achieve the above objectives, the present invention also provides a wheat core vinegar, which is prepared by the above-described preparation method.

[0059] In the method for preparing wheat core vinegar of this invention, there is a synergistic effect among the various process steps and their parameters, which jointly improves the quality of the finished wheat core vinegar. Specifically, firstly, by grading the wheat core and matching it with the cooking conditions, not only can the gelatinization degree of starch be increased to over 92%, providing sufficient substrate for the subsequent action of saccharifying enzymes, but also the problems of excessive or incomplete gelatinization of raw materials can be avoided. Secondly, by using a compound enzyme for saccharification and controlling the saccharification temperature and time in stages, the contact efficiency between the compound enzyme and the substrate can be improved, and a nitrogen source can be provided for microorganisms, allowing the yield of reducing sugars and the activity of the microbial community to increase simultaneously. In addition, during the alcoholic fermentation process, by matching the compound bacteria with the alcoholic fermentation conditions, not only can the alcohol conversion rate be improved, but the pH value of the alcoholic mash can also be adjusted to inhibit contamination by other microorganisms, providing a high-quality substrate for solid-state acetic acid fermentation. During the solid-state acetic acid fermentation process, by controlling the temperature during the fermentation in stages and turning and pressing the mash according to the temperature, not only can the proliferation of microorganisms, the production of acetic acid and the fusion of various flavor substances be adapted, but the yield of acetic acid can also be improved. Finally, the two-stage aging process results in a more complex flavor profile and a higher content of functional components in the finished vinegar.

[0060] The finished wheat vinegar obtained by the preparation method of this invention contains complex acids, such as acetic acid, lactic acid, and succinic acid, which synergistically work with esters to give the finished vinegar a refreshing initial taste and a mellow aftertaste, without any sharpness or off-flavors. Compared with finished vinegar prepared by existing processes, the total variety of flavor substances can be increased by more than 30%, while possessing wheat aroma, vinegar aroma, and ester aroma, making it suitable for various occasions such as direct consumption and cooking seasoning.

[0061] Example 1 A method for preparing wheat core vinegar, comprising: S10. Raw material processing: Select high-quality wheat, crush it through a special crushing equipment, and separate it to obtain wheat core and bran; screen the wheat core with a 20-mesh sieve, a 40-mesh sieve and a 60-mesh sieve respectively to obtain wheat core with a 20-mesh wheat core ratio of 15%, a 40-mesh wheat core ratio of 60% and a 60-mesh wheat core ratio of 25%. S20. Cooking treatment: Mix the wheat kernels obtained from S10 with water at a mass ratio of 1:2.4, then add 0.05% of the wheat kernel mass of amylase, stir evenly, heat to 100℃~105℃, and cook for 60 minutes to obtain the liquid. S30. Saccharification: The liquid obtained in S20 is placed in a saccharification tank and cooled to 62℃~65℃. Then, a complex enzyme consisting of saccharifying enzyme, pullulanase and xylanase is added at 0.12% of the wheat core mass, wherein the mass ratio of saccharifying enzyme, pullulanase and xylanase is 6:1.2:0.8. After stirring evenly, the mixture is heated to 61℃ and kept at that temperature for 6 minutes, then kept at 58℃ for 12 minutes, and finally kept at 55℃ for 17 minutes to obtain the saccharified liquid. S40. Fermentation: The saccharified liquid obtained in S30 is pumped into the fermentation tank. When the temperature drops to 30℃~32℃, 30%~40% of the wheat core mass of crushed Daqu is added, 10%~20% of the wheat core mass of bran is added, and 0.01%~0.02% of the wheat core mass of yeast powder is added. The temperature is kept stable. After fermentation for 7 days, the fermented mash is obtained. S50. Solid-state acetic acid fermentation: The fermented mash obtained in S40 is pumped into a solid-state fermentation tank through a dedicated pipeline. Then, wheat bran obtained in S10 is added at 90% of the wheat core weight. Before being added to the fermented mash, the wheat bran needs to be extruded and puffed at 80°C and 0.5 MPa, while 0.05% acidic protease is added. Then, wheat bran koji is added at 20% of the wheat core weight, and rice husks are added at 50% of the wheat core weight. Simultaneously, 1×10⁻⁶ kiwifruit is inoculated. 6 ~5×10 7 CFU / g of Acetobacter pasteurization in vinegar mash and 1×10 5 ~5×10 6 Acid-resistant Lactobacillus CFU / g was added to the vinegar mash, then mixed with the mash and fermented at 30℃ for 5 days. On the 6th day of fermentation, the temperature was controlled at 38℃; on the 10th day of fermentation, the temperature was controlled at 35℃, and fermentation continued for another 5 days. During the fermentation process, the temperature of the vinegar mash was monitored, and the mash was turned according to the monitoring results. After the 18th day of fermentation, when the temperature of the vinegar mash was below 35℃, the mash was pressed. S60. Aging: After the vinegar mash in S50 matures, it is transported to the aging workshop through special equipment and aged for 35 days at a temperature of 15°C and a humidity of 60%. Then, the temperature is controlled at 25°C and the aging continues for another 15 days. Post-processing includes: The fermentation process involves stirring the aged vinegar mash before transferring it to a fermentation tank. During fermentation, the vinegar mash must be kept loose and flat. After fermentation, diluted vinegar from the vinegar rinsing tank is drawn into the fermented vinegar mash and soaked for at least 2 hours. Vinegar leaching: After the vinegar mash has finished soaking, open the vinegar leaching valve to start leaching vinegar. Once the vinegar mash in the fermentation tank is exposed above the liquid surface, immediately close the vinegar leaching valve. Add water and soak for half an hour, then open the vinegar leaching valve again. Repeat the above operation process for each subsequent vinegar leaching until the leaching is completed. During the vinegar leaching process, the vinegar leaching operator periodically takes samples from the vinegar leaching tank to test the total acidity of the vinegar. Once the total acidity meets the standard, different raw vinegars are collected according to the different total acidities for sterilization. Sterilization of raw wheat core vinegar: Raw vinegar with different total acids extracted daily is subjected to timely high-temperature instantaneous sterilization at 110℃~115℃; Sedimentation: The sterilized wheat vinegar is drawn into a sedimentation tank for sedimentation; Grading: The precipitated wheat vinegar is graded according to the formulation standards of different products; Filtration: The graded wheat vinegar is subjected to timely plate and frame filtration. After filtration, it is pumped into a special storage tank to await sterilization. Sterilization of finished wheat vinegar: The filtered finished wheat vinegar is subjected to immediate high-temperature instantaneous sterilization. After sterilization, it is pumped into a stainless steel finished product storage tank to await packaging. Packaging: The sterilized finished wheat vinegar shall be aseptically packaged in a timely manner; Inspection and warehousing: The packaged finished wheat vinegar is inspected in a timely manner, and it is put into storage after passing the inspection.

[0062] The finished wheat vinegar is obtained through processes S10 to S60.

[0063] Example 2 A method for preparing wheat core vinegar, comprising: S10. Raw material processing: Select high-quality wheat, crush it through a special crushing equipment, and separate it to obtain wheat kernel and bran; screen the wheat kernel with a 20-mesh sieve, a 40-mesh sieve and a 60-mesh sieve respectively to obtain wheat kernel with a 20-mesh wheat kernel content of 20%, a 40-mesh wheat kernel content of 70% and a 60-mesh wheat kernel content of 10%. S20. Cooking treatment: Mix the wheat kernels obtained from S10 with water at a mass ratio of 1:2.8, then add 0.1% of the wheat kernel mass of amylase, stir evenly, heat to 100℃~105℃, and cook for 65 minutes to obtain the liquid. S30. Saccharification: The liquid obtained in S20 is placed in a saccharification tank and cooled to 60℃~62℃. Then, a complex enzyme consisting of saccharifying enzyme, pullulanase and xylanase is added at 0.20% of the wheat core mass, wherein the mass ratio of saccharifying enzyme, pullulanase and xylanase is 6:1.2:0.8. After stirring evenly, the mixture is heated to 65℃ and kept at that temperature for 4 minutes. Then, the temperature is controlled at 60℃ and kept at that temperature for 8 minutes. Finally, the mixture is kept at 57℃ for 10 minutes to obtain the saccharified liquid. S40. Fermentation: The saccharified liquid obtained in S30 is pumped into the fermentation tank. When the temperature drops to 32℃~35℃, pulverized Daqu is added at 40%~60% of the wheat core mass, bran koji is added at 20%~40% of the wheat core mass, and yeast powder is added at 0.02%~0.03% of the wheat core mass. The temperature is kept stable. After fermentation for 5 days, the fermented mash is obtained. S50. Solid-state acetic acid fermentation: The fermented mash obtained in S40 is pumped into a solid-state fermentation tank through a dedicated pipeline. Then, wheat bran obtained in S10 is added at 150% of the wheat core weight. Before being added to the fermented mash, the wheat bran needs to be extruded and puffed at 90°C and 0.3 MPa, while 0.1% acidic protease is added. Then, wheat bran koji is added at 40% of the wheat core weight, and rice husks are added at 20% of the wheat core weight. Simultaneously, 1×10⁻⁶ kiwifruit is inoculated. 6 ~5×10 7 CFU / g of Acetobacter pasteurization in vinegar mash and 1×10 5 ~5×10 6 The acid-resistant Lactobacillus in the vinegar mash was added at CFU / g, then mixed with the mash and fermented at 33℃ for 5 days. On the 6th day of fermentation, the temperature was controlled at 42℃; on the 10th day of fermentation, the temperature was controlled at 37℃ and fermentation continued for 3 days. The temperature of the vinegar mash was monitored during fermentation, and the mash was turned according to the monitoring results. After the 18th day of fermentation, when the temperature of the vinegar mash was below 35℃, the mash was pressed. S60. Aging: After the vinegar mash in S50 matures, it is transported to the aging workshop through special equipment and aged for 30 days at a temperature of 18°C ​​and a humidity of 70%. Then the temperature is raised to 28°C and the aging continues for another 10 days. The post-processing is the same as described in Example 1.

[0064] The finished wheat vinegar is obtained through processes S10 to S60.

[0065] The finished wheat vinegar products obtained in Examples 1 and 2 were tested, specifically as follows: According to GB / T 18187-2000 "Brewn Vinegar" and the National Food Safety Standard (GB 2719-2018), the physicochemical, nutritional, sensory, and stability indicators of the finished wheat vinegar were tested. The results are shown in Table 1.

[0066] Table 1 In Table 1, n represents the sampling quantity, c represents the number of samples allowed to exceed the limit m but not exceed M, m represents the limit value of the microbial indicator, and M represents the maximum allowable value of the microbial indicator.

[0067] In the detection of total colony count, m = 10 3 represents 1000 CFU / mL, and M = 10 4 represents 10000 CFU / mL.

[0068] In the detection of Escherichia coli, m = 10 represents 10 CFU / mL, and M = 100 represents 100 CFU / mL.

[0069] In Table 1, the judgment logic for the total colony count to be qualified is as follows: For the wheat core vinegar of the same batch, 5 samples are taken to measure the total colony count. If the total colony count of ≤ 2 samples is between 10 3 ~10 4 CFU / mL, and the total colony count of the remaining 3 samples ≤ 10 3 CFU / mL, then the whole batch of products is qualified. In Table 1, the total colony count is all < 10 CFU / mL, far lower than m = 10 3 , belonging to completely qualified.

[0070] In Table 1, the judgment logic for Escherichia coli to be qualified is as follows: For the wheat core vinegar of the same batch, 5 samples are taken to measure the total coliform count. If the total coliform count of ≤ 2 samples is between 10 - 100 CFU / mL, and the total coliform count of all samples ≤ 10 CFU / mL, then the whole batch is qualified. In Table 1, no coliforms are detected, belonging to completely qualified.

[0071] Analysis of the data in Table 1 shows that, firstly, in terms of physicochemical quality, the total acid content of the finished wheat vinegar prepared in Examples 1 and 2 is consistently between 5.5 g / 100 mL and 6.0 g / 100 mL, which is within the golden acidity range for high-quality brewed vinegar. This ensures the flavor of the finished vinegar while avoiding excessive acidity. Furthermore, the proportion of non-volatile acids reaches over 23% of the total acid, far exceeding the industry average (15%~20%), a key guarantee for a mellow taste. The content of salt-free solids reaches approximately 9 g / 100 mL, indicating a high content of amino acids, B vitamins, polysaccharides, and phenols in the finished wheat vinegar. This not only meets the flavoring requirements but also provides the body with small amounts of beneficial substances. Simultaneously, the amino acid nitrogen content is in the range of 0.32 g / 100 mL to 0.40 g / 100 mL, more than twice the industry standard, indicating that the protein in the raw materials is fully hydrolyzed. This not only enhances the umami flavor of the finished vinegar but also provides sufficient precursors for the formation of flavor compounds. Secondly, in terms of nutritional function, the total flavonoid content of the finished wheat vinegar is 78.5mg / 100mL to 96.3mg / 100mL, and the soluble dietary fiber content is 0.85g / 100mL to 1.12g / 100mL, both significantly higher than that of traditional vinegar, thus possessing both flavoring and health benefits. Thirdly, in terms of sensory experience, the color is natural and pure. The amber color of Example 1 highlights the original flavor of the wheat, while the reddish-brown color of Example 2 is richer and more lustrous due to its richer flavor compounds. Neither has any artificial coloring added, consistent with its natural brewing positioning. Simultaneously, the aroma and taste create differentiated advantages. Example 1 is refreshing and harmonious, suitable for everyday cooking; Example 2 is mellow and sweet with a prominent ester aroma, suitable for high-end dining and direct consumption. In addition, in terms of stability and safety, the microbiological indicators fully meet the standards, with a total bacterial count of <10 CFU / mL, no pathogenic bacteria detected, and no turbidity or sedimentation after 18 months of storage at room temperature. The flavor retention rate is over 93%, and the shelf life far exceeds that of traditional vinegar. Furthermore, no additional additives are added to the finished vinegar. Instead, the quality stability of the finished vinegar is achieved through raw material optimization and process synergy, which aligns with the consumer trend of "clean label".

[0072] Comparative Example 1 Comparative Example 1 was set up under Example 2. In Comparative Example 1, the wheat core raw material in S10 was not graded, and there was no restriction on the size of the wheat core particles; during saccharification in S30, only saccharifying enzymes were added; the compound bacteria in S40 consisted of Daqu, bran koji, and brewing yeast; and the bran in S50 was not subjected to extrusion puffing treatment. The remaining process steps and parameters were the same as in Example 2. The final product, wheat core vinegar, was obtained.

[0073] Comparative Example 2 Comparative Example 2 was set up in accordance with Example 2. In Comparative Example 2, the saccharification method for S30 was: saccharification at 55℃~65℃ for 30 minutes; the solid-state acetic acid fermentation method for S50 was: fermentation at less than 45℃ for 18 days~25 days; the aging method for S60 was: aging at room temperature for 20 days~60 days, with the aging period controlled by the principle that the lower the temperature, the longer the aging period. The remaining process steps and parameters were the same as in Example 2. The final product, wheat core vinegar, was obtained.

[0074] The quality of the finished wheat vinegar obtained from Comparative Example 1 and Comparative Example 2 was tested, and the results are shown in Table 2.

[0075] Table 2 In Table 2, n, m, c, and M have the same meanings as in Table 1, and the criteria for judging whether the total number of colonies and Escherichia coli are qualified are the same as in Table 1.

[0076] Analysis of the data in Table 2 reveals that the total acid content of the finished vinegars obtained in Comparative Examples 1 and 2 is relatively low. This is because the lack of grading of the wheat cores leads to incomplete starch gelatinization, and the single saccharifying enzyme cannot hydrolyze amylopectin, resulting in insufficient substrate utilization. Simultaneously, the content of non-volatile acids is low because the bran was not extruded and puffed, leading to insufficient protein hydrolysis. Furthermore, the replacement of the compound bacteria with traditional Daqu and bran koji weakens microbial metabolic capacity. Secondly, the content of salt-free solids, total flavonoids, and soluble dietary fiber in the finished vinegars is significantly reduced. This is because the lack of grading of the wheat cores results in insufficient nutrient dissolution during fermentation, and the bran, without treatment, cannot release its internal functional substances. In addition, regarding sensory characteristics and stability, the vinegars are cloudy, contain sediment, have an off-flavor, and a sharp, rough texture. This is due to the uneven particle size of the wheat cores leading to poor aeration of the vinegar mash, resulting in the growth of unwanted microorganisms. Additionally, the traditional koji contains many unwanted microorganisms, which metabolize and produce undesirable flavor compounds.

[0077] By comparing and analyzing the data in Tables 1 and 2, it can be seen that in the technical solution of this invention, firstly, by matching the wheat core grading ratio with the cooking parameters, not only can the wheat core be heated evenly, but also by matching the material-to-water ratio with the cooking time, the starch gelatinization degree can reach over 90%. Secondly, through the synergistic effect between the compound enzyme and the segmented temperature control of saccharification, the reducing sugar yield is ≥91%, and the amylopectin can be completely hydrolyzed without any residual sugars. In the alcoholic fermentation and acetic acid fermentation, through the synergistic effect of the compound bacteria ratio and alcoholic parameters, the alcohol conversion rate is ≥92%, and the acid-resistant lactobacillus can adjust the pH value of the fermentation substrate to 3.4~3.6, thereby inhibiting contamination by other bacteria and providing high-purity alcoholic mash for acetic acid fermentation; through the synergistic effect of the auxiliary materials for solid-state fermentation and the temperature control of acetic acid, the acetic acid yield is increased by over 20%. Finally, through the synergistic effect of two-stage aging and micro-oxygenation, the total flavonoid content and ester content in the finished vinegar can be increased to over 25%~30%. Therefore, in the method for preparing wheat vinegar of the present invention, the process parameters of each step will have a synergistic effect, which can not only improve the utilization rate of raw materials, but also produce a finished vinegar with rich flavor, outstanding nutritional properties and long shelf life, with obvious advantages and in line with market demand.

[0078] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for preparing wheat core vinegar, characterized in that, The preparation method includes: Wheat is separated to obtain wheat coarse and bran; The wheat kernels, water, and amylase are mixed in a preset ratio and then cooked to obtain a liquid. After cooling the liquid to a preset temperature, a complex enzyme consisting of saccharifying enzyme, pullulanase and xylanase is added according to the saccharification ratio. After stirring evenly, saccharification is carried out to obtain a saccharified liquid. A compound microbial mixture consisting of daqu, bran koji, and yeast powder is added to the saccharification liquid according to the alcoholization ratio to carry out alcoholization fermentation and obtain alcoholized mash. In the fermented mash, according to the solid-state fermentation ratio, wheat bran, wheat koji, and rice husk are added, and then Acetobacter pasteurellii and Lactobacillus acidophilus are added. After stirring evenly, solid-state acetic acid fermentation is carried out to obtain mature vinegar mash. After aging the mature vinegar mash, further processing is carried out to obtain the wheat core vinegar.

2. The preparation method according to claim 1, characterized in that, Of the wheat kernels, 20-mesh kernels account for 15% to 20%, 40-mesh kernels account for 60% to 70%, and 60-mesh kernels account for 10% to 25%.

3. The preparation method according to claim 1, characterized in that, The bran has a starch content greater than 52%, and the preparation method further includes the following steps before adding the bran to the fermented mash: Wheat bran was extruded and puffed under conditions of 80℃~90℃ and 0.3MPa~0.5MPa, while 0.05%~0.1% of acidic protease was added.

4. The preparation method according to claim 1, characterized in that, The cooking process is carried out at a temperature of 100℃~105℃ for a duration of 50min~65min.

5. The preparation method according to claim 1, characterized in that, The preset temperature is 60℃~65℃, and the saccharification method includes: Hold at 61℃~65℃ for 4min~6min, then at 58℃~60℃ for 8min~12min, and finally at 55℃~57℃ for 10min~17min.

6. The preparation method according to claim 1, characterized in that, The fermentation temperature is 30℃~35℃, and the duration is 5d~7d.

7. The preparation method according to claim 1, characterized in that, The solid-state acetic acid fermentation method includes: After fermenting at 30℃~33℃ for 5 days, the temperature is controlled at 38℃~42℃ and fermentation continues; on the 10th day of fermentation, the temperature is controlled at 35℃~37℃ and fermentation continues for 3~5 days; after the 3~5 days of continued fermentation, when the temperature of the vinegar mash is below 35℃, pressing of the mash begins; the temperature of the vinegar mash is monitored throughout the fermentation process, and the mash is turned according to the monitoring results.

8. The preparation method according to claim 1, characterized in that, The aging method includes: Aged for 30 to 35 days at a temperature of 15℃ to 18℃ and a humidity of 60% to 70%, then aged for another 10 to 15 days at a temperature of 25℃ to 28℃.

9. The preparation method according to claim 1, characterized in that, The post-processing includes vinegar leaching, sterilization of raw wheat core vinegar, grading, filtration, sterilization of finished wheat core vinegar, packaging, and inspection and warehousing.

10. A type of wheat vinegar, characterized in that, The wheat vinegar is prepared by the preparation method according to any one of claims 1 to 9.

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