Daqu acid beer and preparation method thereof

Abstract

The invention provides yeast acid beer and a preparation method thereof. The yeast acid beer is prepared by adopting yeast powder as a fermentation inoculant and carrying out saccharification by a leaching method and natural fermentation, and the yeast acid beer comprises the following organic acids: at least one of tartaric acid with the concentration of 800-1200 mg / L, malic acid with the concentration of 400-600 mg / L, lactic acid with the concentration of 2000-4000 mg / L, acetic acid with the concentration of 100-200 mg / L, citric acid with the concentration of 50-200 mg / L and succinic acid with the concentration of 3500-4500 mg / L. The method is an acid beer brewing technology which does not depend on microorganisms in a specific region and the fermentation process is easy to control, so that complex raw material treatment and a long saccharification time process are simplified, tedious brewing steps and complex equipment requirements are reduced, and the production cost is reduced and the production efficiency is improved while the requirement of the market for the unique flavor of acid beer is met.

Description

Technical Field

[0001] The invention belongs to the field of beer brewing, and particularly relates to kojic acid beer and a preparation method thereof. Background Art

[0002] As one of the oldest beverages of mankind, beer is known as "liquid bread". As the earliest form of beer, it carries the ancient wisdom of brewing. According to the report of the American magazine "Public Library of Science Comprehensive", through the analysis of ancient pottery unearthed from the Chengxi Qiaotou site in Yiwu City, it was found that as early as 9,000 years ago, Chinese ancestors had used rice, coix seeds and tubers to ferment naturally with the help of microorganisms such as mold and yeast to brew early beer with a slightly sweet and sour taste, that is, sour beer. This discovery not only provides solid evidence for the long history of sour beer, but also shows the outstanding achievements of ancient Chinese brewing technology.

[0003] With the progress made by mankind in the field of science and technology, disinfection and sterilization technology has been gradually mastered. The emergence of refrigeration equipment and the discovery of yeast have opened a new chapter for modern beer brewing. These technological innovations have made beer brewing more standardized and large-scale, and sour beer has gradually been replaced by other types of beer. At present, the three mainstream biological acidification methods include wort acidification, mixed bacteria fermentation acidification and acidifying yeast acidification. As the fastest method, wort acidification can strictly control the acidification process and stop the acidification at any time by boiling. However, the lactic acid bacteria used in the acidification process of this method are easy to contaminate normal beer production, so many breweries have to set up a special acidification workshop to isolate the acidification process; mixed bacteria fermentation acidification is a more traditional method. Although it can produce rich flavors, the fermentation process is difficult to control and the production cycle is long; acidifying yeast acidification is acidified by inoculating yeast capable of heterologous fermentation. When the acidity reaches the requirement, brewing yeast is introduced to terminate the acidification process. Since no exogenous microorganisms are introduced, this method does not require a special acidification workshop and does not occupy a boiling pot, so it is favored by many breweries.

[0004] With the rise of craft beer, sour beer has gained increasing popularity in the market due to its complex taste and unique flavor. Nowadays, there is a "sour" trend in the global craft beer circle, and craft breweries around the world have launched their own sour beer products, from Belgian lambic to German Berliner Weisse, from American wild ale to Flanders red ale, etc. These classic sour beers have won the love and pursuit of consumers with their unique brewing processes and taste characteristics. Compared with the above biological acidification methods, sour beer fermented naturally has a more complex sour taste, a richer taste hierarchy in the body, and a higher overall quality. Among them, Belgian lambic is a classic in sour beer. It has a history of more than 1,500 years and is brewed using the natural fermentation process of wild yeast. During the brewing process, the wort is exposed to the air and undergoes open fermentation by making full use of the unique wild yeast, bacteria, and other microorganisms in the local air, and then aged in oak barrels for 1 to 3 years, which makes the flavor and taste of the beer more rich. The brewing of other classic sour beers mainly relies on mixed fermentation. Although this method can produce unique flavors, the fermentation process is difficult to control and highly dependent on the microbial environment of the brewery and its surrounding areas, which also makes it difficult for other breweries to imitate.

[0005] In China, the craft beer industry is still in its infancy, and the production and consumption markets for sour beer are relatively small. At present, the strains required for natural fermentation and the mixed fermentation technology in the country are not yet mature, which to a certain extent restricts the development of sour beer. Since natural fermentation depends on the microbial community in a specific region and has significant regionality, it is difficult to replicate.

[0006] CN 114958505 A discloses a black hulless barley beer, which is prepared from the following raw materials in parts by weight: 30 - 60 parts of black hulless barley, 30 - 50 parts of malt, 6 - 12 parts of daqu, 5 - 15 parts of Potentilla anserina, 0.1 - 0.3 parts of hops, and 0.6 - 1.5 parts of brewer's dried yeast; wherein, the total ratio of material to water is 1:(4 - 5). The black hulless barley beer has a strong aroma and taste of hulless barley, can further reduce the content of free radicals in the body, prevent diseases such as cardiovascular diseases, liver diseases, and diabetes, and slow down the aging of the body. However, the solid-state saccharification time of this beer is long (more than 36 hours), which has a greater impact on the production cycle and equipment occupancy. Moreover, the process involves different treatment methods for various raw materials, such as black hulless barley, malt, Potentilla anserina, etc., and the operation is relatively complex, requiring high-precision control of the production process. If not controlled properly, it may affect the stability of product quality.

[0007] CN 118222364 A discloses a Jiangxiang-flavored beer aged in oak barrels, its preparation method and equipment. The beer is fermented from wort, brewer's yeast, Jiangxiang-flavored liquor, and oak. Among them, the Jiangxiang-flavored liquor is fermented by high-temperature Daqu; the addition amount of Jiangxiang-flavored liquor is 0.2 - 0.6 g of Jiangxiang-flavored liquor per liter of brewer's yeast, and the addition amount of oak is 2 ± 0.5 kg of oak and 1 ± 0.5 kg of oak extract per 1000 L of wort mixture. It has a mellow and delicate taste, different from the single-flavor cereal beers using highland barley or roasted buckwheat on the market. The brewing equipment includes a magnetic field water processor, an electric field generating device, etc. The equipment is complex, increasing the equipment procurement and maintenance costs. However, the technological process of this beer has many steps. The Jiangxiang-flavored liquor is added in three stages, and the oak barrel aging requires ultrasonic treatment, etc. The process is complex and prone to operation errors or control deviations. In addition, the beer brewed by this process is obtained by directly adding Jiangxiang-flavored liquor to the beer for blending, with a high cost and not suitable for industrial brewing processes.

[0008] Existing spontaneous fermentation technologies for sour beers often rely on the microbiota in specific regions, having problems such as being difficult to replicate and scale up production, and a long production cycle and cumbersome process operations. Therefore, how to fill the gap in wild yeast-fermented beers in the country is an urgent problem to be solved currently. Summary of the Invention

[0009] To solve the problems in the prior art, the present invention provides a sour beer brewing technology that does not rely on specific regional microorganisms and is easy to control during the fermentation process, thereby simplifying the complex raw material treatment and long saccharification time process, reducing cumbersome brewing steps and complex equipment requirements, and while meeting the market's demand for the unique flavor of sour beer, reducing production costs and improving production efficiency.

[0010] The technical solution of the present invention is as follows:

[0011] The present invention provides a Daqu sour beer, which is prepared by using Daqu powder as a fermentation starter and through the leaching method for saccharification and natural fermentation.

[0012] Among them, the organic acids contained in the Daqu sour beer include at least one of the following: tartaric acid at 800 - 1200 mg / L, malic acid at 400 - 600 mg / L, lactic acid at 2000 - 4000 mg / L, acetic acid at 100 - 200 mg / L, citric acid at 50 - 200 mg / L, and succinic acid at 3500 - 4500 mg / L.

[0013] Furthermore, the kojic acid beer contains flavor substances composed of at least one of ethyl 9-decenoate at 0.35 - 1.95 mg / L, 4-ethylphenol at 3.20 - 9.25 mg / L, 4-vinylguaiacol at 1.24 - 2.36 mg / L, 2-nonanol at 0.40 - 1.25 mg / L, 2,3-butanediol at 30.5 - 39.2 mg / L, methylheptenone at 0.55 - 1.75 mg / L, and 6-methyl-5-hepten-2-ol at 0.24 - 0.81 mg / L.

[0014] Furthermore, the kojic acid beer contains flavor substances composed of at least one of ethyl acetate at 30 - 50 mg / L, ethyl butyrate at 0.40 - 0.70 mg / L, ethyl octanoate at 0.80 - 1.30 mg / L, ethyl benzoate at 0.11 - 0.31 mg / L, ethyl 9-decenoate at 0.35 - 1.95 mg / L, 4-ethylphenol at 3.20 - 9.25 mg / L, 4-vinylguaiacol at 1.24 - 2.36 mg / L, 4-ethylguaiacol at 2.2 - 3.6 mg / L, n-heptanol at 0.12 - 0.66 mg / L, citronellol at 0.11 - 0.42 mg / L, 2-nonanol at 0.40 - 1.25 mg / L, 2,3-butanediol at 30.5 - 39.2 mg / L, methylheptenone at 0.55 - 1.75 mg / L, and 6-methyl-5-hepten-2-ol at 0.24 - 0.81 mg / L.

[0015] More preferably, the kojic acid beer contains organic acids composed of at least one of tartaric acid at 974.78 mg / L, malic acid at 576.53 mg / L, lactic acid at 3750.74 mg / L, acetic acid at 153.94 mg / L, citric acid at 158.78 mg / L, and succinic acid at 4055.78 mg / L.

[0016] More preferably, the kojic acid beer contains flavor substances composed of at least one of ethyl acetate at 40.710 mg / L, ethyl butyrate at 0.586 mg / L, ethyl octanoate at 1.162 mg / L, ethyl benzoate at 0.217 mg / L, ethyl 9-decenoate at 0.880 mg / L, 4-ethylphenol at 7.330 mg / L, 4-vinylguaiacol at 1.776 mg / L, 4-ethylguaiacol at 2.978 mg / L, n-heptanol at 0.422 mg / L, citronellol at 0.253 mg / L, 2-nonanol at 0.703 mg / L, 2,3-butanediol at 35.870 mg / L, methylheptenone at 1.251 mg / L, and 6-methyl-5-hepten-2-ol at 0.533 mg / L.

[0017] Furthermore, the original wort concentration of the kojic acid beer is 12.0 - 20.0 °P, and the alcohol content is 7.0 - 11.5% vol.

[0018] Furthermore, the fermentability of the kojic acid beer is 87.0 - 93.0%, the content of diacetyl (i.e., 2,3 - butanedione) is 0.069 - 0.085 mg / L, and the content of total organic acids is 3.0 - 3.5 mL / 100 mL.

[0019] Furthermore, the colority of the kojic acid beer is 6.2 - 42.5 EBC, and pH ≤ 3.9.

[0020] Furthermore, the kojic acid beer uses malt raw materials as the main raw materials and is brewed by fermenting with kojic acid powder without adding exogenous saccharifying enzymes.

[0021] Furthermore, the kojic acid beer is brewed with raw materials containing the following mass percentages: malt raw materials, kojic acid powder accounting for more than 5 wt% and less than 20 wt% of the dry weight of the malt raw materials, hops accounting for 0.5 - 7 wt‰ of the wort mass, and lactose accounting for 0 - 1.5 wt% of the wort mass. The wort is obtained by saccharifying, heating, and filtering the malt raw materials.

[0022] Furthermore, after crushing the malt raw materials, they are mixed with water at a material - to - water ratio of 1:3 - 1:4 to obtain malt mash, and saccharification is carried out by the infusion method without adding exogenous enzyme preparations.

[0023] Furthermore, the malt mash obtained after saccharifying the malt raw materials is heated at a temperature of 78 ± 1 °C and then filtered to obtain the wort.

[0024] Furthermore, when the addition amount of the kojic acid powder is more than 5 wt% and less than 20 wt% of the dry weight of the malt raw materials, the addition amount of the hops is 0.5 - 1‰ of the wort mass, and lactose is not added, the fermentability of the kojic acid beer is 87.33 - 92.67%, the content of diacetyl is 0.072 - 0.084 mg / L, and the content of total organic acids is 3.0 - 3.32 mL / 100 mL.

[0025] Furthermore, when the addition amount of the kojic acid powder is more than 5 wt% and less than 20 wt% of the dry weight of the malt raw materials, the addition amount of the hops is 5 - 9‰ of the wort mass, and lactose is not added, the fermentability of the kojic acid beer is 87.95 - 90.89%, the content of diacetyl is 0.070 - 0.075 mg / L, and the content of total organic acids is 3.08 - 3.21 mL / 100 mL.

[0026] Furthermore, when the addition amount of the Daqu powder is greater than 5wt% and less than 20wt% of the dry weight of the malt raw materials, the addition amount of the hops is 1-7‰ of the wort quality, and the addition amount of the lactose is 1-1.5% of the wort quality, the fermentation degree of the Daqu sour beer is 88.10-88.69%, the content of diacetyl is 0.0696-0.0768mg / L, and the content of total organic acids is 3.36-3.48mL / 100mL.

[0027] Furthermore, among the raw materials of the Daqu sour beer, the malt includes at least one of Pilsner malt, wheat malt, ale malt, white wheat kernels, oats, Pilsner malt, pale caramel malt, ruby caramel malt, and black malt.

[0028] Furthermore, the Daqu powder is prepared through multiple steps such as raw material crushing, moistening, pressing into shape, culturing in the koji room, and drying.

[0029] Furthermore, the preparation method of the Daqu powder is as follows:

[0030] (1) Raw material crushing:

[0031] Select wheat as the main raw material and crush it to a particle size of 60-80 mesh;

[0032] In order to better carry out a series of biochemical reactions such as the growth and fermentation of microorganisms during the subsequent koji-making process;

[0033] (2) Moistening:

[0034] Perform a moistening treatment on the crushed wheat, and control the water addition amount at 40%-45%;

[0035] The purpose of moistening is to enable the wheat to absorb a certain amount of water, adjust its water content and state, and create suitable conditions for subsequent operations such as stepping on the koji;

[0036] (3) Pressing into shape

[0037] Perform a pressing into shape operation on the moistened material to make koji blocks, providing a relatively fixed space and environment for the growth of microorganisms;

[0038] (4) Culturing in the koji room

[0039] Put the pressed koji blocks into the koji room for culturing, and the culturing time is 25-30 days;

[0040] In this specific environment of the koji room, the microorganisms on the koji blocks start to grow, reproduce, and metabolize, carrying out biochemical reactions, and gradually forming the unique flavor and quality characteristics of Daqu;

[0041] (5) Drying

[0042] After the koji blocks are cultured, a drying operation is carried out, and the temperature during drying is controlled at 40 - 50 °C;

[0043] The purpose of drying is to further dissipate the moisture in the koji blocks to reach an appropriate moisture content of 12% - 15%, and at the same time, it also helps to volatilize some bad odors in the koji blocks and further form and stabilize the flavor;

[0044] (6) Medium-temperature koji matured koji

[0045] The temperature range is controlled at 45 - 56 °C to obtain the medium-temperature koji matured koji.

[0046] Furthermore, the daqu sour beer has a rich and delicate sour taste, and at the same time exhibits fresh fruity, floral, and herbal aromas.

[0047] The present invention also provides a preparation method of the aforementioned daqu sour beer, comprising the following steps:

[0048] Step 1: Saccharification by infusion method

[0049] After crushing the malt raw materials, they are mixed with water at a material-to-water ratio of 1:3 - 1:4 to obtain a malt mash, and saccharification is carried out by the infusion method without adding exogenous enzyme preparations, using the enzymes in the malt itself to convert starch into fermentable sugars;

[0050] Step 2: Heat the saccharified malt mash to 78 ± 1 °C and filter to obtain wort;

[0051] Boil the wort, add hops during the boiling process, then cool the wort to 18 - 20 °C and oxygenate it, controlling the dissolved oxygen content of the wort to be 6 - 8 mg / L;

[0052] Step 3: Natural fermentation

[0053] Add daqu powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20 °C, and seal the tank when the wort ferments to a sugar degree of 3.2 - 5.5 °P;

[0054] After sealing the tank, enter the diacetyl reduction stage. When the diacetyl content drops below 0.10 mg / L, cool down to 0 - 2 °C to finally obtain the daqu sour beer.

[0055] Furthermore, in step 1, the malt includes at least one of pilsner malt, wheat malt, ale malt, white wheat kernels, oats, pilsner malt, pale caramel malt, ruby caramel malt, and black malt.

[0056] In step 1 of the present invention, the principle of saccharification by the infusion method is mainly based on the biocatalytic action of enzymes in malt. Through the decomposition of amylase, starch in malt is converted into fermentable sugars, providing necessary nutrients for the subsequent fermentation process. During this process, the malt mash is not boiled, avoiding the destruction of enzyme activity by high temperature, thus ensuring the smooth progress of the saccharification process.

[0057] Further, in step 1, the saccharification by the infusion method includes two-stage saccharification. The first-stage saccharification is to keep the malt mash at 65 °C for 60 min, and the second-stage saccharification is to keep the malt mash at 72 °C for 15 min.

[0058] In the present invention, through the synergistic action of two-stage saccharification, the utilization rate of starch is optimized to the greatest extent, providing an ideal sugar and flavor basis for beer fermentation. Among them, the first-stage saccharification is mainly based on β-amylase and α-amylase, generating a large amount of maltose and preliminarily decomposing starch, aiming to increase the yield of fermentable sugars. The second-stage saccharification process is mainly based on α-amylase, supplemented by limit dextrinase, further decomposing residual long-chain starch and dextrin, ensuring the complete degradation of starch, and improving the clarity and fermentability of wort.

[0059] Further, step 1 also includes keeping the malt raw materials at 44 °C for 20 min before saccharification by the infusion method, and then keeping them at 52 °C for 10 min.

[0060] In the present invention, keeping the malt mash at 44 °C for 20 min is to release ferulic acid and decompose macromolecular proteins, and keeping it at 52 °C for 10 min is to activate β-glucanase and further decompose macromolecular proteins. The synergistic action of these two stages not only optimizes the fluidity and filtration performance of wort, but also lays a solid foundation for the formation of flavor substances such as 4-ethylguaiacol, making the final beer flavor richer and more complex.

[0061] Further, in step 2, heating the saccharified malt mash to 78 ± 1 °C helps to coagulate proteins and remove impurities, improving the clarity of wort.

[0062] In step 2 of the present invention, the filtration is to transfer the saccharified malt mash from the saccharification pot to the filter tank under heated conditions to separate the clarified wort, while maximizing the recovery of soluble components.

[0063] Further, in step 2, the filtration operation uses a filter tank. The bottom of the filter tank usually has a perforated plate or sieve plate for supporting the spent grains and allowing the wort to pass through. The filter tank is equipped with a stirrer and a drain port for separating the wort.

[0064] Furthermore, in step 2, the boiling time of the wort is 60 - 70 minutes, and the evaporation rate is 5% - 10%. During the boiling process, material changes such as the isomerization of hops, the volatilization of DMS, the coagulation of proteins, and the Maillard reaction occur. These changes endow the beer with a unique bitterness, a pure aroma, rich flavor layers, and a clear and stable quality, laying a solid foundation for the flavor and components of the beer.

[0065] Furthermore, in step 2, the boiling temperature of the wort is 100 °C.

[0066] Furthermore, in step 2, during the boiling process of the wort, based on the mass of the wort as the calculation benchmark, the addition amount of hops is controlled to be 0.5 - 1 wt‰.

[0067] In step 2 of the present invention, hops are added during the boiling of the wort. The function is not only to endow the beer with a unique bitterness and aroma, but also to contribute to the clarification and preservation of the wort. The hops include bitter hops, aromatic hops, bitter and aromatic dual - type hops, etc. There are no strict limitations on the specific varieties and origins of the hops. As long as the hops or hop products can help improve the taste, aroma and other quality characteristics of the final sour beer product and meet the brewing process and product requirements, they can be applied to the brewing process of the present invention.

[0068] Furthermore, in step 2, lactose can be optionally added during the boiling process of the wort. The purpose is to increase the real extract of the sour beer and enhance its mellow feeling. Based on the mass of the wort as the calculation benchmark, the addition amount of lactose is controlled to be 0 - 1.5 wt%.

[0069] Furthermore, in step 2, the wort is boiled for 70 min. The first addition of hops is made 10 min after the boiling starts to boil over, the second addition of hops is made 10 min before the end of boiling, and lactose is added 5 min before the end of boiling.

[0070] Furthermore, in step 2, the wort is subjected to whirlpool precipitation before cooling. The whirlpool precipitation includes a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter.

[0071] Furthermore, in step 2, the temperature of the whirlpool precipitation is controlled to be 90 - 95 °C to maintain good fluidity and particle sedimentation.

[0072] In step 2 of the present invention, the precipitate obtained after the wort undergoes the whirlpool precipitation is hot coagulum (mainly hot - coagulated protein), hop residues, and other solid impurities; the main components of the filtrate are fermentable sugars, amino acids, proteins, hop components, volatile aroma compounds, and minerals.

[0073] In step 2 of the present invention, the main purpose of aerating the wort is to provide a basis for the healthy reproduction of the Daqu powder, ensuring a rapid start of fermentation and optimizing the fermentation performance.

[0074] Further, in step 3, based on the dry weight calculation of the malt raw materials, the addition amount of the Daqu powder is greater than 5wt% and less than 20wt%.

[0075] In step 3 of the present invention, during the fermentation of the Daqu powder, the fermentable sugars in the wort are converted into alcohol and carbon dioxide.

[0076] Further, in step 3, in order to increase the hop aroma, when the wort ferments to a sugar degree of 3.2 - 5.5 °P, dry-hopping can be carried out before sealing the wort tank. The addition amount of dry-hopping accounts for 5 - 7‰ of the mass of the wort, preferably 6‰.

[0077] Further, in step 3, after sealing the fermented wort in the tank, close the exhaust valve and naturally boost the pressure to 0.13 - 0.15 Mpa.

[0078] In step 3 of the present invention, diacetyl is a by-product during the beer fermentation process, and its content directly affects the flavor of beer. The national standard for premium grade is that the diacetyl content drops below 0.10 mg / L. The detection of diacetyl is analyzed and determined according to the national standard "GB / T 4928 - 2008 Beer Analysis Method".

[0079] In step 3 of the present invention, when the wort ferments to a sugar degree of 3.2 - 5.5 °P and the diacetyl content reaches the peak value, it starts to enter the diacetyl reduction stage. At this time, the yeast in the Daqu powder uses the reducing substances (such as pyruvic acid, etc.) in the fermentation broth, and under the catalytic action of enzymes, reduces diacetyl to acetoin and other substances. The flavor thresholds of these substances are relatively high, and the adverse effects on the beer flavor are relatively small.

[0080] Further, in step 3, the temperature for diacetyl reduction is 19 - 20 °C, and the reduction time is 7 to 15 days.

[0081] In step 3 of the present invention, when the wort is cooled to 0 - 2 °C, it is cold stored for 7 days. Cold storage helps the maturation and stability of beer, and further improves the taste and flavor of beer.

[0082] Further, in step 3, after the wort is reduced to below 0.10 mg / L by diacetyl reduction and then cooled to 0 - 2 °C, it is cold stored for 7 days, and then an optional sterilization operation can be carried out (fresh beer is obtained without sterilization).

[0083] The beneficial technical effects of the present invention are reflected in the following aspects:

[0084] 1. The kojic acid beer of the present invention uses cereal crops such as barley malt and wheat malt as the main raw materials. Without adding exogenous saccharifying enzymes, it utilizes the rich microbial community in the daqu for natural fermentation, endowing the sour beer with complex and delicate sourness, accompanied by citrus and tropical fruit flavors, and having a soft and balanced taste, filling the gap in the domestic wild mushroom sour beer market.

[0085] 2. Using daqu powder as the fermentation starter and combining it with traditional brewing raw materials such as wheat, a unique formula system is formed. This formula utilizes natural microbial resources and traditional brewing raw materials, reducing the dependence on artificial additives and chemical agents, making the formula of the sour beer more natural and healthy, meeting the pursuit of modern consumers for green food. As a fermentation starter, an appropriate amount of daqu powder can increase the alcohol content and acidity, playing a key role in the fermentation process of the beer and the final formation of acidity and alcohol.

[0086] 3. The kojic acid beer of the present invention adopts the infusion saccharification process without adding exogenous enzyme preparations. By controlling parameters such as saccharification temperature and time, substances such as starch in the malt are gradually decomposed into fermentable sugars, and the saccharification process is more stable and controllable. At the same time, flavor substances and nutrients in the raw materials are better retained, providing a good foundation for the subsequent fermentation process.

[0087] 4. The natural fermentation process of the present invention does not require artificial inoculation of specific yeast strains, reducing the dependence on industrialized strains, lowering production costs, and at the same time endowing the sour beer with unique flavors and tastes. By controlling parameters such as wort dissolved oxygen, fermentation temperature, and fermentation time, fine control of the fermentation process is achieved. Especially the diacetyl reduction and cold storage processes carried out after the main fermentation stage further improve the quality and stability of the beer. Compared with the biological acidification method, the sour beer fermented with daqu powder has a richer taste layer and higher overall quality. The process of the present invention can not only fill the gap in domestic wild strain fermented beer, but also enrich domestic beer varieties through product research and development, establish standards for natural fermentation beer, and bring a new taste experience to consumers.

[0088] 5. The key indicators of the Daqu sour beer brewed by the present invention, such as the original wort concentration, degree of fermentation, alcohol content, colority, and pH value, all reach a relatively high level. These characteristics make the beer more competitive and attractive in the market. At the same time, the Daqu sour beer performs excellently in terms of acidity, aroma, and taste. Due to the diversity of the microbial flora during the natural fermentation process, the sour beer will produce various organic acids, which endow the sour beer with a unique sour taste. This sour taste is gentle and rich in layers, different from the sour taste produced by single-strain fermentation. The microorganisms in the Daqu powder will also produce flavor substances such as esters, alcohols, and phenols during the fermentation process, which coordinate with the organic acids to form a sour and mellow taste. When tasting the sour beer, there is both a refreshing sour taste, a strong aroma, and a mellow taste.

[0089] 6. The detection and analysis by liquid chromatography of the present invention show that the Daqu sour beer has obvious advantages in the content of organic acids and flavor levels. Its lactic acid content is much higher than that of lager beer and wheat beer, presenting the characteristics of sour beer and enhancing the complexity of the flavor. At the same time, the succinic acid content of the Daqu sour beer is several times that of other beers, giving it a more mellow and full taste. More particularly, citric acid is detected in the Daqu sour beer, while this organic acid is not detected in other beers and unfermented wort, adding a fresh and bright citrus fruit flavor to it. In addition, the contents of organic acids such as tartaric acid and malic acid in the Daqu sour beer are also relatively high, jointly constituting a rich and harmonious flavor level with lactic acid and succinic acid. Overall, the Daqu sour beer has a unique flavor and delicate layers, and its quality is outstanding.

[0090] 7. The gas chromatography-mass spectrometry analysis results of the present invention show that the Daqu sour beer has more than 8 kinds of flavor substances compared with lager beer and has 11 unique compounds, showing excellent complexity and richness in flavor, making its quality more prominent. Through research, it is found that the detection reports of methylheptenone, 6-methyl-5-hepten-2-ol, 2-nonyl alcohol, and ethyl 9-decenoate in beer are reported for the first time. These unique compounds endow the Daqu sour beer with rich fruity, floral, and gentle fatty flavors, making its flavor performance more complex and elegant.

[0091] 8. The fermentation starter used in the present invention includes but is not limited to Daqu used in the brewing process of various types of Chinese white spirits, such as light-aroma Daqu, sauce-aroma Daqu, strong-aroma Daqu, and rice-aroma Daqu. At the same time, the present invention covers the application of all Chinese white spirit starters in the beer brewing process. Regardless of their specific fragrance types, production processes, and raw material compositions, as long as they are used as fermentation starters in the beer brewing process, they are within the protection scope of the present invention. Detailed implementation manners

[0092] Preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0093] The dry-hopped hops used in the following examples are Cascade hops (brand number HBC438) produced by Yakima Hops Company in the United States. These hops are known for their complex fruit aromas, mainly with mango, coconut, and grapefruit aromas, and also with some woody and minty flavors.

[0094] Example 1

[0095] A koji acid beer has an original wort concentration of 17.64 °P, an alcohol content of 10.84% vol, a degree of fermentation of 92.67%, a diacetyl content of 0.072 mg / L, a total organic acid content of 3.0 mL / 100 mL, a colority of 16.34 EBC, and a pH ≤ 3.9. Among them, the koji acid beer is brewed from raw materials including the following mass percentages: malt raw materials, koji powder accounting for 10 wt% of the dry weight of the malt raw materials, and hops accounting for 0.5‰ of the wort mass.

[0096] The preparation method is as follows:

[0097] Step 1: Mash by infusion method

[0098] The malt raw materials containing 60 wt% ale malt, 15 wt% wheat malt, 15 wt% oats, and 10 wt% pale caramel malt are crushed and mixed with water at a material-to-water ratio of 1:3 - 1:4 to obtain a malt mash. Infusion mashing is carried out without adding exogenous enzyme preparations, and the starch is converted into fermentable sugars using the enzymes in the malt itself.

[0099] Among them, before the infusion mashing, the malt raw materials are kept at a temperature of 44 °C for 20 min, and then at a temperature of 52 °C for 10 min; then the infusion mashing of the malt raw materials is carried out, which includes two mashing processes. The first mashing process is to keep the malt mash at a temperature of 65 °C for 60 min; the second mashing process is to keep the malt mash at a temperature of 72 °C for 15 min.

[0100] Step 2: Heat the mashed malt mash to 78 ± 1 °C and filter to obtain wort;

[0101] Boil the wort, add hops during the boiling process, then carry out whirlpool precipitation on the wort, and after precipitation, cool it to 18 - 20 °C and then oxygenate it, controlling the dissolved oxygen content of the wort to be 6 - 8 mg / L;

[0102] Among them, the boiling time of the wort is 70 minutes, the boiling temperature is 100 °C, and the addition amount of hops during the boiling process is controlled at 0.5 wt‰; the temperature for whirlpool sedimentation is controlled at 90 - 95 °C, including a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter;

[0103] Step 3: Natural fermentation

[0104] Add Daqu powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20 °C, seal the tank when the sugar content of the wort drops to 3.2 - 5.5 °P, close the exhaust valve after sealing the tank, and naturally increase the pressure to 0.13 - 0.15 Mpa. When the diacetyl content of the wort drops below 0.10 mg / L, then cool it down to 0 - 2 °C, cold store for 7 days, and then optionally perform a sterilization operation to finally obtain Daqu sour beer;

[0105] Among them, based on the dry weight of the malt raw materials, the addition amount of Daqu powder is 10 wt%.

[0106] Example 2

[0107] A Daqu sour beer with an original wort concentration of 17.1 °P, an alcohol content of 9.82 % vol, a fermentation degree of 87.33 %, a diacetyl content of 0.075 mg / L, a total organic acid content of 3.32 mL / 100 mL, a colority of 42.5 EBC, and a pH ≤ 3.9. Among them, the Daqu sour beer is brewed from raw materials including the following mass percentages: malt raw materials, 10 wt% of Daqu powder based on the dry weight of the malt raw materials, and 1 ‰ of hops based on the mass of the wort.

[0108] The preparation method is as follows:

[0109] Step 1: Mash by infusion method

[0110] Crush the malt raw materials containing 70 wt% Pilsner malt, 25 wt% Ruby caramel malt, and 5 wt% Black malt, and mix them with water at a material - to - water ratio of 1:3 - 1:4 to obtain a malt mash. Perform mash by infusion method without adding exogenous enzyme preparations, and use the enzymes in the malt itself to convert starch into fermentable sugars;

[0111] Among them, before the mash by infusion method, keep the malt raw materials at a temperature of 44 °C for 20 min, and then at a temperature of 52 °C for 10 min; then perform the mash by infusion method for the malt raw materials, which includes two - stage mashing processes. The first - stage mashing process is to keep the malt mash at a temperature of 65 °C for 60 min; the second - stage mashing process is to keep the malt mash at a temperature of 72 °C for 15 min;

[0112] Step 2: Heat the mashed malt mash to 78 ± 1 °C and filter to obtain wort;

[0113] Boil the wort, add hops during the boiling process, then perform whirlpool sedimentation on the wort, cool it to 18 - 20 °C after sedimentation, and then oxygenate it, controlling the dissolved oxygen content of the wort to be 6 - 10 mg / L;

[0114] Among them, the boiling time of the wort is 70 minutes, the boiling temperature is 100 °C, and the addition amount of hops during the boiling process is controlled to be 1 wt‰; the temperature for whirlpool sedimentation is controlled to be 90 - 95 °C, including a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter;

[0115] Step 3: Natural fermentation

[0116] Add Daqu powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20 °C, seal the tank when the sugar content of the wort drops to 3.2 - 5.5 °P, close the exhaust valve after sealing the tank, and let the pressure rise naturally to 0.13 - 0.15 Mpa. When the diacetyl content of the wort drops below 0.10 mg / L, then cool it to 0 - 2 °C and cold store it for 7 days, and then optionally perform a sterilization operation to finally obtain Daqu sour beer;

[0117] Among them, based on the dry weight of the malt raw materials, the addition amount of Daqu powder is 10 wt%.

[0118] Example 3

[0119] A Daqu sour beer with an original wort concentration of 12.96 °P, an alcohol content of 7.44 %vol, a degree of fermentation of 89.10 %, a diacetyl content of 0.0744 mg / L, a total organic acid content of 3.0 mL / 100 mL, a colority of 6.26 EBC, and a pH ≤ 3.9. Among them, the Daqu sour beer is brewed from raw materials including the following mass percentages: malt raw materials, 10 wt% of Daqu powder based on the dry weight of the malt raw materials, and 0.5 ‰ of hops based on the mass of the wort.

[0120] The preparation method is as follows:

[0121] Step 1: Mash by infusion method

[0122] Crush the malt raw materials containing 51 wt% Pilsner malt, 40 wt% wheat malt, 6 wt% white wheat kernels, and 3 wt% oats, and mix them with water at a material - to - water ratio of 1:3 - 1:4 to obtain a malt mash. Perform mash by infusion method without adding exogenous enzyme preparations, and use the enzymes in the malt itself to convert starch into fermentable sugars;

[0123] Among them, before saccharification by the infusion method, the malt raw materials are maintained at a temperature of 44 °C for 20 min, and then at a temperature of 52 °C for 10 min; then saccharification of the malt raw materials by the infusion method is carried out, which includes two-stage saccharification processes. The first-stage saccharification process is to maintain the mash at a temperature of 65 °C for 60 min; the second-stage saccharification process is to maintain the mash at a temperature of 72 °C for 15 min;

[0124] Step 2: Heat the saccharified mash to 78 ± 1 °C, and obtain wort by filtration;

[0125] Boil the wort, add hops during the boiling process, then perform whirlpool precipitation on the wort, cool it to 18 - 20 °C after precipitation and then oxygenate it, and control the dissolved oxygen content of the wort to be 6 - 10 mg / L;

[0126] Among them, the boiling time of the wort is 70 minutes, the boiling temperature is 100 °C, the addition amount of hops during the boiling process is controlled to be 0.5 wt‰; the temperature of whirlpool precipitation is controlled to be 90 - 95 °C, including a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter;

[0127] Step 3: Natural fermentation

[0128] Add Daqu powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20 °C, seal the tank when the sugar content of the wort drops to 3.2 - 5.5 °P, close the exhaust valve after sealing the tank, and naturally increase the pressure to 0.13 - 0.15 Mpa. When the diacetyl content of the wort drops below 0.10 mg / L, then cool it to 0 - 2 °C and cold store it for 7 days, and then optionally perform a sterilization operation to finally obtain Daqu sour beer;

[0129] Among them, based on the dry weight of the malt raw materials, the addition amount of Daqu powder is 10 wt%.

[0130] Example 4

[0131] A Daqu sour beer has an original wort concentration of 17.77 °P, an alcohol content of 10.64 % vol, a degree of fermentation of 90.46 %, a diacetyl content of 0.084 mg / L, a total organic acid content of 3.12 mL / 100 mL, a colority of 17.61 EBC, and a pH ≤ 3.9. Among them, the Daqu sour beer is brewed with raw materials including the following mass percentages: malt raw materials, 10 wt% of Daqu powder based on the dry weight of the malt raw materials, and 1 ‰ of hops based on the mass of the wort.

[0132] The preparation method is as follows:

[0133] Step 1: Saccharification by the infusion method

[0134] The malt raw materials containing 60 wt% ale malt, 15 wt% wheat malt, 15 wt% oats, and 10 wt% pale caramel malt are crushed and mixed with water at a material-to-water ratio of 1:3 - 1:4 to obtain a malt mash. Saccharification is carried out by the infusion method without adding exogenous enzyme preparations, and the starch is converted into fermentable sugars by the enzymes in the malt itself.

[0135] Among them, before the infusion method saccharification, the malt raw materials are maintained at a temperature of 44 °C for 20 min, and then at a temperature of 52 °C for 10 min; then the infusion method saccharification of the malt raw materials is carried out, which includes two-stage saccharification processes. The first-stage saccharification process is to maintain the malt mash at a temperature of 65 °C for 60 min; the second-stage saccharification process is to maintain the malt mash at a temperature of 72 °C for 15 min.

[0136] Step 2: Heat the saccharified malt mash to 78 ± 1 °C and filter to obtain wort.

[0137] Boil the wort, add hops during the boiling process, then carry out whirlpool precipitation on the wort. After precipitation, cool it to 18 - 20 °C and then oxygenate it, controlling the dissolved oxygen content of the wort to be 6 - 10 mg / L.

[0138] Among them, the boiling time of the wort is 70 minutes, the boiling temperature is 100 °C, and the addition amount of hops during the boiling process is controlled to be 1 wt‰; the temperature of the whirlpool precipitation is controlled to be 90 - 95 °C, including a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter.

[0139] Step 3: Natural fermentation

[0140] Add Daqu powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20 °C, and seal the tank when the sugar content of the wort drops to 3.2 - 5.5 °P. After sealing the tank, close the exhaust valve and let the pressure rise naturally to 0.13 - 0.15 Mpa. When the diacetyl content of the wort drops below 0.10 mg / L, then cool it to 0 - 2 °C and cold store it for 7 days, and then optionally carry out a sterilization operation to finally obtain Daqu sour beer.

[0141] Among them, based on the dry weight of the malt raw materials, the addition amount of Daqu powder is 10 wt%.

[0142] Example 5

[0143] A kojic acid beer has an original wort concentration of 18.07°P, an alcohol content of 10.85% vol, a fermentation degree of 90.89%, a diacetyl content of 0.075 mg / L, a total organic acid content of 3.08 mL / 100 mL, a colority of 17.92 EBC, and a pH ≤ 3.9. Among them, the kojic acid beer is brewed from raw materials including the following mass percentages: malt raw materials, kojic acid powder accounting for 10 wt% of the dry weight of the malt raw materials, and hops accounting for 7‰ of the wort mass.

[0144] The preparation method is as follows:

[0145] Step 1: Saccharification by infusion method

[0146] The malt raw materials containing 60 wt% ale malt, 15 wt% wheat malt, 15 wt% oats, and 10 wt% pale caramel malt are crushed and mixed with water at a material-to-water ratio of 1:3 - 1:4 to obtain a malt mash. Saccharification by infusion method is carried out without adding exogenous enzyme preparations, and the starch is converted into fermentable sugars by the enzymes in the malt itself.

[0147] Among them, before saccharification by infusion method, the malt raw materials are kept at a temperature of 44 °C for 20 min, and then at a temperature of 52 °C for 10 min; then saccharification by infusion method of the malt raw materials is carried out, which includes two-stage saccharification processes. The first-stage saccharification process is to keep the malt mash at a temperature of 65 °C for 60 min; the second-stage saccharification process is to keep the malt mash at a temperature of 72 °C for 15 min.

[0148] Step 2: Heat the saccharified malt mash to 78 ± 1 °C and obtain wort through filtration.

[0149] Boil the wort, add hops during the boiling process, then carry out whirlpool precipitation on the wort, and after precipitation, cool it to 18 - 20 °C and then aerate it, controlling the dissolved oxygen content of the wort to be 6 - 10 mg / L.

[0150] Among them, the boiling time of the wort is 70 minutes, the boiling temperature is 100 °C, the addition amount of hops during the boiling process is controlled to be 1 wt‰; the temperature of the whirlpool precipitation is controlled to be 90 - 95 °C, including a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter.

[0151] Step 3: Natural fermentation

[0152] Add Daqu powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20 °C, and seal the tank when the sugar content of the wort drops to 3.2 - 5.5 °P. Before sealing the tank, dry-hop with hops accounting for 6‰ of the wort mass. After sealing the tank, close the exhaust valve and let the pressure rise naturally to 0.13 - 0.15 Mpa. When the diacetyl content of the wort drops below 0.10 mg / L, then cool it down to 0 - 2 °C and cold store for 7 days, and then optionally perform a sterilization operation to finally obtain Daqu sour beer;

[0153] Among them, based on the dry weight of the malt raw materials, the addition amount of Daqu powder is 10 wt%.

[0154] Example 6

[0155] A kind of Daqu sour beer, with an original wort concentration of 18.48 °P, an alcohol content of 10.8% vol, a fermentation degree of 88.10%, a diacetyl content of 0.0768 mg / L, a total organic acid content of 3.48 mL / 100 mL, a colority of 18.23 EBC, and pH ≤ 3.9. Among them, the Daqu sour beer is brewed with raw materials including the following mass percentages: malt raw materials, 10 wt% of Daqu powder based on the dry weight of the malt raw materials, 1‰ of hops based on the wort mass, and 1.25 wt% of lactose based on the wort mass.

[0156] The preparation method is as follows:

[0157] Step 1: Saccharification by infusion method

[0158] Crush the malt raw materials containing 60 wt% ale malt, 15 wt% wheat malt, 15 wt% oats, and 10 wt% pale caramel malt, and mix them with water at a material-to-water ratio of 1:3 - 1:4 to obtain a malt mash. Perform saccharification by infusion method without adding exogenous enzyme preparations, and use the enzymes in the malt itself to convert starch into fermentable sugars;

[0159] Among them, before saccharification by infusion method, keep the malt raw materials at a temperature of 44 °C for 20 min, and then at a temperature of 52 °C for 10 min; then perform saccharification by infusion method on the malt raw materials, which includes two saccharification processes. The first saccharification process is to keep the malt mash at a temperature of 65 °C for 60 min; the second saccharification process is to keep the malt mash at a temperature of 72 °C for 15 min;

[0160] Step 2: Heat the saccharified malt mash to 78 ± 1 °C and filter to obtain wort;

[0161] Boil the wort, add hops and lactose during the boiling process, then perform whirlpool precipitation on the wort, and cool it to 18 - 20 °C after precipitation and oxygenate it, controlling the dissolved oxygen content of the wort to be 6 - 10 mg / L;

[0162] Among them, the boiling time of the wort is 70 minutes, the boiling temperature is 100 °C, the addition amount of hops during the boiling process is controlled at 1 wt‰, and the addition amount of lactose is controlled at 1.25 wt%; the temperature of whirlpool precipitation is controlled at 90 - 95 °C, including a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter;

[0163] Step 3: Natural fermentation

[0164] Add Daqu powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20 °C, seal the tank when the sugar content of the wort drops to 3.2 - 5.5 °P, close the exhaust valve after sealing the tank, naturally increase the pressure to 0.13 - 0.15 Mpa, when the diacetyl content of the wort drops below 0.10 mg / L, then cool down to 0 - 2 °C and cold store for 7 days, and then optionally perform a sterilization operation to finally obtain Daqu sour beer;

[0165] Among them, based on the dry weight of the malt raw materials, the addition amount of Daqu powder is 10 wt%.

[0166] Example 7

[0167] A Daqu sour beer with an original wort concentration of 18.78 °P, an alcohol content of 11.08 %vol, a fermentation degree of 88.69 %, a diacetyl content of 0.0696 mg / L, a total organic acid content of 3.36 mL / 100 mL, a colority of 19.04 EBC, and a pH ≤ 3.9. Among them, the Daqu sour beer is brewed with raw materials including the following mass percentages: malt raw materials, 10 wt% of Daqu powder based on the dry weight of the malt raw materials, 7 ‰ of hops based on the mass of the wort, and 1.25 wt% of lactose based on the mass of the wort.

[0168] The preparation method is as follows:

[0169] Step 1: Mash by infusion method

[0170] Crush the malt raw materials containing 60 wt% ale malt, 15 wt% wheat malt, 15 wt% oats, and 10 wt% pale caramel malt, and mix them with water at a material - to - water ratio of 1:3 - 1:4 to obtain a malt mash. Perform mash by infusion method without adding exogenous enzyme preparations, and use the enzymes in the malt itself to convert starch into fermentable sugars;

[0171] Among them, before the mash by infusion method, keep the malt raw materials at a temperature of 44 °C for 20 min, and then at a temperature of 52 °C for 10 min; then perform the mash by infusion method for the malt raw materials, which includes two - stage mashing processes. The first - stage mashing process is to keep the malt mash at a temperature of 65 °C for 60 min; the second - stage mashing process is to keep the malt mash at a temperature of 72 °C for 15 min;

[0172] Step 2: Heat the saccharified wort to 78 ± 1 °C and filter to obtain wort;

[0173] Boil the wort, add hops and lactose during the boiling process, then perform whirlpool sedimentation on the wort. After sedimentation, cool it to 18 - 20 °C and then oxygenate it, controlling the dissolved oxygen content of the wort to be 6 - 10 mg / L;

[0174] Among them, the boiling time of the wort is 70 minutes, the boiling temperature is 100 °C, the addition amount of hops during the boiling process is controlled at 1 wt‰, and the addition amount of lactose is controlled at 1.25 wt%; the temperature of the whirlpool sedimentation is controlled at 90 - 95 °C, including a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter;

[0175] Step 3: Natural fermentation

[0176] Add Daqu powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20 °C. When the fermentation reaches the sugar content of the wort drops to 3.2 - 5.5 °P, seal the tank. Before sealing the tank, dry - add hops accounting for 6‰ of the wort mass. After sealing the tank, close the exhaust valve and naturally increase the pressure to 0.13 - 0.15 Mpa. When the diacetyl content of the wort drops below 0.10 mg / L, then cool it to 0 - 2 °C and cold - store it for 7 days, and then optionally perform a sterilization operation to finally obtain Daqu sour beer;

[0177] Among them, based on the dry weight of the malt raw materials, the addition amount of Daqu powder is 10 wt%.

[0178] Example 8

[0179] A kind of Daqu sour beer, with the original wort concentration of 17.55 °P, alcohol content of 10.1% vol, fermentation degree of 87.95%, diacetyl content of 0.070 mg / L, total organic acid content of 3.21 mL / 100 mL, colority of 42.5 EBC, pH ≤ 3.9. Among them, the Daqu sour beer is brewed with raw materials including the following mass percentages: malt raw materials, Daqu powder accounting for 10 wt% of the dry weight of the malt raw materials, and hops accounting for 7‰ of the wort mass.

[0180] The preparation method is as follows:

[0181] Step 1: Mash by infusion method

[0182] Crush the malt raw materials containing 70 wt% Pilsner malt, 25 wt% Ruby caramel malt, and 5 wt% Black malt, and mix them with water at a material - to - water ratio of 1:3 - 1:4 to obtain a wort mash. Perform infusion mashing without adding exogenous enzyme preparations, and use the enzymes in the malt itself to convert starch into fermentable sugars;

[0183] Among them, before saccharification by the infusion method, the malt raw materials are kept at a temperature of 44 °C for 20 min, and then at a temperature of 52 °C for 10 min; then saccharification of the malt raw materials by the infusion method is carried out, which includes two-stage saccharification processes. The first-stage saccharification process is to keep the mash at a temperature of 65 °C for 60 min; the second-stage saccharification process is to keep the mash at a temperature of 72 °C for 15 min;

[0184] Step 2: Heat the saccharified mash to 78 ± 1 °C and obtain wort through filtration;

[0185] Boil the wort, add hops and lactose during the boiling process, then carry out whirlpool precipitation on the wort, cool it to 18 - 20 °C after precipitation and then oxygenate it, and control the dissolved oxygen content of the wort to be 6 - 10 mg / L;

[0186] Among them, the boiling time of the wort is 70 minutes, the boiling temperature is 100 °C, the addition amount of hops during the boiling process is controlled to be 1 wt‰; the temperature of the whirlpool precipitation is controlled to be 90 - 95 °C, including a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter;

[0187] Step 3: Natural fermentation

[0188] Add Daqu powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20 °C, seal the tank when the sugar content of the wort drops to 3.2 - 5.5 °P, dry-hop with hops accounting for 6‰ of the mass of the wort before sealing the tank, close the exhaust valve after sealing the tank, naturally boost the pressure to 0.13 - 0.15 Mpa, when the diacetyl content of the wort drops below 0.10 mg / L, then cool it to 0 - 2 °C and cold-store for 7 days, and then optionally carry out a sterilization operation to finally obtain Daqu sour beer;

[0189] Among them, based on the dry weight of the malt raw materials, the addition amount of Daqu powder is 10 wt%.

[0190] Comparative Example 1

[0191] A kind of Daqu sour beer with an original wort concentration of 11.74 °P, an alcohol content of 6.66 %vol, a fermentation degree of 88.63 %, a diacetyl content of 0.0864 mg / L, a total organic acid content of 2.88 mL / 100 mL, a colority of 4.53 EBC, and pH ≤ 3.9. Among them, the Daqu sour beer is brewed with raw materials including the following mass percentages: malt raw materials, and Daqu powder accounting for 5 wt% of the dry weight of the malt raw materials.

[0192] The preparation method is as follows:

[0193] Step 1: Saccharification by the infusion method

[0194] The malt raw materials containing 51 wt% pilsner malt, 40 wt% wheat malt, 6 wt% white wheat kernels, and 3 wt% oats are crushed and then mixed with water at a material-to-water ratio of 1:3 - 1:4 to obtain a malt mash. Saccharification is carried out by the infusion method without adding exogenous enzyme preparations, and the starch is converted into fermentable sugars by the enzymes in the malt itself.

[0195] Among them, before the infusion method saccharification, the malt raw materials are kept at a temperature of 44 °C for 20 min, and then at a temperature of 52 °C for 10 min; then the infusion method saccharification of the malt raw materials is carried out, which includes two-stage saccharification processes. The first-stage saccharification process is to keep the malt mash at a temperature of 65 °C for 60 min; the second-stage saccharification process is to keep the malt mash at a temperature of 72 °C for 15 min.

[0196] Step 2: Heat the saccharified malt mash to 78 ± 1 °C and filter to obtain wort.

[0197] Boil the wort, add hops during the boiling process, then carry out whirlpool precipitation on the wort, cool it to 18 - 20 °C after precipitation and then oxygenate it, controlling the dissolved oxygen content of the wort to be 6 - 10 mg / L.

[0198] Among them, the boiling time of the wort is 70 minutes, the boiling temperature is 100 °C, and the addition amount of hops during the boiling process is controlled to be 0.5 wt‰; the temperature of the whirlpool precipitation is controlled to be 90 - 95 °C, including a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter.

[0199] Step 3: Natural fermentation

[0200] Add Daqu powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20 °C, seal the tank when the sugar content of the wort drops to 3.2 - 5.5 °P, close the exhaust valve after sealing the tank, and naturally increase the pressure to 0.13 - 0.15 Mpa. When the diacetyl content of the wort drops below 0.10 mg / L, then cool it to 0 - 2 °C and cold store it for 7 days, and then optionally carry out a sterilization operation to finally obtain Daqu sour beer.

[0201] Among them, based on the dry weight of the malt raw materials, the addition amount of Daqu powder is 5 wt%.

[0202] Comparative Example 2

[0203] A kojic acid beer has an original wort concentration of 14.49°P, an alcohol content of 8.52% vol, a degree of fermentation of 90.17%, a diacetyl content of 0.0648 mg / L, a total organic acid content of 4.32 mL / 100 mL, a colority of 9.47 EBC, and a pH ≤ 3.9. Among them, the kojic acid beer is brewed from raw materials including the following mass percentages: malt raw materials, and kojic acid powder accounting for 20 wt% of the dry weight of the malt raw materials.

[0204] The preparation method is as follows:

[0205] Step 1: Saccharification by infusion method

[0206] Crush the malt raw materials containing 51 wt% pilsner malt, 40 wt% wheat malt, 6 wt% white wheat kernels, and 3 wt% oats, and mix them with water at a material-to-water ratio of 1:3 - 1:4 to obtain a malt mash. Perform saccharification by the infusion method without adding exogenous enzyme preparations, and use the enzymes in the malt itself to convert starch into fermentable sugars;

[0207] Among them, before saccharification by the infusion method, keep the malt raw materials at a temperature of 44°C for 20 min, and then at a temperature of 52°C for 10 min; then perform saccharification by the infusion method on the malt raw materials, which includes two saccharification processes. The first saccharification process is to keep the malt mash at a temperature of 65°C for 60 min; the second saccharification process is to keep the malt mash at a temperature of 72°C for 15 min;

[0208] Step 2: Heat the saccharified malt mash to 78 ± 1°C, and filter to obtain wort;

[0209] Boil the wort, add hops during the boiling process, then perform whirlpool precipitation on the wort, cool it to 18 - 20°C after precipitation and then oxygenate it, and control the dissolved oxygen content of the wort to be 6 - 10 mg / L;

[0210] Among them, the boiling time of the wort is 70 minutes, the boiling temperature is 100°C, and the addition amount of hops during the boiling process is controlled at 0.5 wt‰; the temperature of the whirlpool precipitation is controlled at 90 - 95°C, including a rotation time of 5 - 10 minutes to ensure the aggregation of solid substances towards the center, and a standing time of 20 - 30 minutes to fully sediment the particulate matter;

[0211] Step 3: Natural fermentation

[0212] Add kojic acid powder to the oxygenated wort for fermentation, keep the main fermentation temperature at 18 - 20°C, seal the tank when the sugar content of the wort drops to 3.2 - 5.5°P, close the exhaust valve after sealing, and naturally increase the pressure to 0.13 - 0.15 Mpa. When the diacetyl content of the wort drops below 0.10 mg / L, then cool it to 0 - 2°C, cold store it for 7 days, and then optionally perform a sterilization operation to finally obtain the kojic acid beer;

[0213] Among them, based on the dry weight of the malt raw materials, the addition amount of the daqu powder is 20 wt%.

[0214] Test example

[0215] (1) Physical and chemical property test

[0216] According to the "Beer Analysis Method GB / T 4928 - 2008", the physical and chemical properties of the daqu sour beer prepared in the above-mentioned examples and comparative examples were detected, and the results are shown in Table 1.

[0217] Table 1 Physical and chemical test results of the daqu sour beer prepared in the examples and comparative examples

[0218]

[0219]

[0220] It can be seen from the data in Table 1 that the original wort concentration of the daqu sour beer prepared in the examples of the present invention is 12.0 - 20.0 °P, the fermentation degree is 87.0 - 93.0%, the alcohol content is 7.0 - 11.5% vol, the colority is 6.2 - 42.5 EBC, and the content of total organic acids is 3.0 - 3.5 mL / 100 mL. The raw materials of Examples 1, 4, 5, 6 and 7 are the wort formulas of high-gravity ale, the raw materials of Examples 2 and 8 are the wort formulas of Flanders red ale, and the raw materials of Example 3, Comparative Example 1 and Comparative Example 2 are the wort formulas of ordinary wheat beer, aiming to brew sour beers of different styles with daqu powder.

[0221] In Example 3, Comparative Example 1 and Comparative Example 2, the wort formulas are the same, but the addition ratios of the daqu powder are different. With the increase of the addition ratio of the daqu powder, the alcohol content, original wort concentration and total organic acid content of the beer also increase. This is mainly because the daqu brings in more microorganisms and fermentable sugars. Different from traditional commercial yeasts, the daqu is a mixture containing microorganisms, enzymes and raw materials.

[0222] In Examples 1, 4 and 5, the saccharification processes are the same, but the addition amounts of hops are different. The addition amount of hops in Example 1 is 0.5‰, in Example 4 is 1.0‰, and in Example 5 is 7‰. Among them, 1‰ was added during boiling in Example 5, and 6‰ was directly dry-hopped in the fermentation tank at the end of the main fermentation to enhance the hop aroma of the beer. It can be seen from the data that the addition of hops reduces the fermentation degree by 2%, because hops have antibacterial effects, but have little impact on the fermentation performance of the daqu.

[0223] In conventional beer brewing, Saccharomyces cerevisiae cannot metabolize lactose. Therefore, adding lactose to wort can increase the real concentration of beer and enhance its mellow feeling, especially suitable for high-bitterness beers (such as IPA), to achieve a perfect taste of bitter-sweet balance. In Example 6 and Example 7, the wort formula and saccharification process were the same as those in Example 1, but 1.25% lactose (1.25 kg lactose per 100 L wort) was added during the boiling process. Compared with Example 6, an additional 6‰ of hops was dry-hopped in Example 7 when the fermentation was sealed. By comparing Example 6 with Example 4, and Example 7 with Example 5, it can be seen that the addition of lactose not only increased the real concentration of the koji acid beer, but also reduced the degree of fermentation and enriched the taste of the beer.

[0224] Compared with Example 2, in Example 8, 6‰ of hops was dry-hopped when the tank was sealed to give the beer a more intense hop aroma. From these two examples, it can be seen that with the addition of caramel malt and black malt, the color and real concentration of the koji acid beer increased, but the degree of fermentation decreased slightly. This is mainly because the content of fermentable sugars in special malts is relatively lower than that in pale malts.

[0225] (2) Flavor evaluation

[0226] The koji acid beers obtained from the above examples and comparative examples were subjected to flavor evaluation, and the results are shown in Table 2.

[0227] Table 2 Flavor evaluation results of the koji acid beer products obtained from the examples and comparative examples

[0228]

[0229]

[0230] According to the evaluation results in Table 2, the koji acid beer provided by the examples of the present invention showed a relatively high degree of fermentation, with a dry body, rich floral and fruity aromas, and a unique koji flavor. Except for Comparative Example 2, the taste of other samples was soft and balanced, and there were no bad flavors such as stable smell caused by wild yeast.

[0231] In Example 3 and Comparative Examples 1 and 2, although the wort formula was the same, the addition ratio of koji powder was different. As the addition ratio of koji powder increased, the acidity of the beer also increased. When the addition ratio of koji reached 20%, the taste of the beer was too sour and astringent, and there was a stable smell caused by wild bacteria. Sensory evaluation showed that the best effect was achieved with a 10% addition of koji.

[0232] In Examples 1, 4, and 5, although the saccharification process is the same, there are differences in the addition amount and method of hops. In Example 5, the dry-hopping process of IPA-style hops is adopted. Although the beer is slightly sour, the unique flavor of the daqu is not obvious. The overall taste is similar to that of popular sour IPAs, but more delicate and complex.

[0233] The wort formula and saccharification process of Examples 6 and 7 are the same as those of Example 1, but 1.25% lactose (1.25 kg lactose per 100 L of wort) is added during the boiling process. Experimental data and tasting results show that lactose can increase the body thickness and sweetness of daqu beer. In Example 7, dry-hopping the hops makes its taste closer to sour IPA.

[0234] Both Example 8 and Example 2 adopt the wort formula of Flanders Red Ale, but the dry-hopping process of hops is added in Example 8. Example 2 is close to Flanders Red Ale in appearance and flavor, with the wild yeast flavor of barrel-aged natural fermentation, but the acidity is slightly insufficient, and the process can be further optimized.

[0235] In the present invention, the tastes of Examples 3, Comparative Example 1, and Comparative Example 2 are close to Belgian lambic beer, and its fermentation broth can be further blended with fruit juice to make daqu fruit sour beer. The tastes of Examples 1, 4, and 5 are close to the wild yeast saison style. Subsequently, more types of grains and spices can be added during the saccharification process to enhance the complexity of its aroma and taste. Examples 5, 7, and 8 all adopt the dry-hopping process of hops. Since the addition of hops inhibits the growth of some microorganisms in the daqu, the flavors of these beers are closer to traditional beers, with a weaker sour taste but a strong hop aroma. The dry body produced by daqu fermentation makes its flavor reach a balance between sour IPA and Brut IPA. The dark daqu sour beer in Example 2 can be further aged in an oak barrel to enhance its taste and complexity.

[0236] (3) Testing of organic acid content

[0237] The organic acid contents in the daqu sour fermented beer (Example 7), lager beer, wheat beer, and the unfermented wort of the same batch were detected by liquid chromatography.

[0238] Table 3 Organic acid contents of different types of beers

[0239]

[0240] Through data analysis, it can be found that due to the synergistic effect of multiple microorganisms, kojic acid beer has obvious advantages in organic acid content and flavor levels. Its lactic acid content is as high as 3750.74 mg / L, far higher than that of lager beer (167.84 mg / L) and wheat beer (199.55 mg / L), presenting the characteristics of sour beer and enhancing the complexity of the flavor. At the same time, the succinic acid content of kojic acid beer is as high as 4055.78 mg / L, several times that of other beers, giving it a more mellow and full-bodied taste.

[0241] More particularly, kojic acid beer contains 158.78 mg / L of citric acid, which is not detected in other beers and unfermented wort, adding a fresh and bright citrus fruit flavor to it. In addition, the contents of organic acids such as tartaric acid and malic acid are also relatively high, jointly constituting a rich and harmonious flavor level with lactic acid and succinic acid. Overall, kojic acid beer has a unique flavor, delicate layers, and outstanding quality.

[0242] (4) Measurement of flavor substance content

[0243] To further analyze the unique flavor of kojic acid beer, headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) was used for analysis and compared with lager beer. The specific experimental steps are as follows: Each sample (5 mL) was added to a 20 mL headspace vial containing 2.2 g of sodium chloride (NaCl) and 50 μL of 1-butanol solution (1 mg / mL, with water as the solvent) as the internal standard. A 2 cm DVB / Car / PDMS fiber (Supelco, USA) was loaded into the SPME injector. The experiment was set to stir at 250 rpm for 45 minutes at 40 °C to extract volatile compounds from the headspace. Subsequently, the SPME fiber was desorbed at 280 °C for 3 minutes, and the sample was injected into the injection port of the GC. The chromatographic column used was HP-5MS (60 m × 0.32 mm × 0.25 μm, Agilent), the carrier gas was helium with a purity of ≥99.999%, the flow rate was 1 mL / min, and separation was carried out according to a specific heating program: the initial temperature was 40 °C, held for 3 minutes, then the temperature was increased at a rate of 3 °C / min to 120 °C, held for 3 minutes, then the temperature was increased at a rate of 5 °C / min to 240 °C, and held for 5 minutes. The ion source temperature of the mass spectrometer was maintained at 240 °C, the solvent delay time was set to 2 minutes, and the mass spectrometry acquisition range was 35 - 700 amu.

[0244] The retention index (RI) was calculated using an alkane solution (C6-C25, Sigma-Aldrich). The identification of the compounds was based on matching the mass spectra with those in the standard mass spectrometry library of the National Institute of Standards and Technology (NIST, Gaithersburg, Maryland), and was confirmed by combining the RI data. The concentration of volatile compounds was calculated by the chromatographic peak area and the one-point quantification method based on an internal standard.

[0245] By performing GC-MS analysis on the flavor substances in kojic acid beer (Example 7) and lager beer, 31 flavor substances were isolated and identified from kojic acid beer, while 23 flavor substances were isolated and identified from lager beer.

[0246] Table 3 Flavor substances in lager beer analyzed by GC-MS

[0247]

[0248]

[0249] Table 4 Flavor substances in kojic acid beer (Example 7) analyzed by GC-MS

[0250]

[0251]

[0252] According to the GC-MS analysis results, kojic acid beer has 8 more flavor substances than lager beer and has 11 unique compounds, showing excellent complexity and richness in flavor, making its quality more prominent. For example, methylheptenone brings fresh fruity and herbal aromas, giving the beer an elegant refreshing feeling; n-heptanol and 6-methyl-5-hepten-2-ol provide delicate fruity and floral aromas, making the overall aroma more layered.

[0253] Koji beer is rich in ester substances. In particular, key aroma substances such as ethyl acetate, ethyl butyrate, and ethyl octanoate are much higher than those in lager beer. The acidic compounds and ester substances act synergistically to add sweet fruity and floral aromas to kojic acid beer, balancing the sense of fusion of sour and sweet. At the same time, the presence of citronellol adds a fresh lemongrass aroma, making the overall flavor more refreshing and pleasant.

[0254] In addition, phenolic compounds (such as 4-ethylphenol and 4-vinylguaiacol) impart deep spicy and slight smoky flavors, significantly enhancing the uniqueness and complexity of the beer; and alcohol compounds such as 2,3-butanediol further enhance the mouthfeel thickness of the beer, making the overall flavor more mellow and full.

[0255] It is worth noting that the detection reports of methyl heptenone, 6-methyl-5-hepten-2-ol, 2-nonyl alcohol and ethyl 9-decenoate in beer are reported for the first time. These unique compounds endow kojic acid beer with rich fruity, floral and gentle fatty aromas, making its flavor performance more complex and elegant. In addition, the study also found that the contents of 4-ethylguaiacol, 4-ethylphenol and 4-ethenylguaiacol in kojic acid beer reached 2.978 mg / L, 7.33 mg / L and 1.776 mg / L respectively, and the content of phenolic aroma substances in it was much higher than that of ordinary beer, similar to the flavor characteristics of naturally fermented beers such as Saison and Lambic.

[0256] The above are only the preferred embodiments of the present invention, and do not constitute any other form of limitation to the present invention. Any modification or equivalent change made according to the technical essence of the present invention still belongs to the scope protected by the present invention.

Claims

1. A kojic acid beer, characterized in that, The koji acid beer is prepared by using koji powder as a fermentation starter and through saccharification by the leaching method and natural fermentation. Among them, the koji acid beer contains organic acids composed of the following: at least one of tartaric acid at 800 - 1200 mg / L, malic acid at 400 - 600 mg / L, lactic acid at 2000 - 4000 mg / L, acetic acid at 100 - 200 mg / L, citric acid at 50 - 200 mg / L, and succinic acid at 3500 - 4500 mg / L.

2. The kojic acid beer according to claim 1, characterized in that, The koji acid beer contains flavor substances composed of the following: at least one of ethyl 9 - decenoate at 0.35 - 1.95 mg / L, 4 - ethylphenol at 3.20 - 9.25 mg / L, 4 - vinylguaiacol at 1.24 - 2.36 mg / L, 2 - nonanol at 0.40 - 1.25 mg / L, 2,3 - butanediol at 30.5 - 39.2 mg / L, methylheptenone at 0.55 - 1.75 mg / L, and 6 - methyl - 5 - hepten - 2 - ol at 0.24 - 0.81 mg / L.

3. The kojic acid beer according to claim 1 or 2, characterized in that, The koji acid beer contains flavor substances composed of the following: at least one of ethyl acetate at 30 - 50 mg / L, ethyl butyrate at 0.40 - 0.70 mg / L, ethyl octanoate at 0.80 - 1.30 mg / L, ethyl benzoate at 0.11 - 0.31 mg / L, ethyl 9 - decenoate at 0.35 - 1.95 mg / L, 4 - ethylphenol at 3.20 - 9.25 mg / L, 4 - vinylguaiacol at 1.24 - 2.36 mg / L, 4 - ethylguaiacol at 2.2 - 3.6 mg / L, n - heptanol at 0.12 - 0.66 mg / L, citronellol at 0.11 - 0.42 mg / L, 2 - nonanol at 0.40 - 1.25 mg / L, 2,3 - butanediol at 30.5 - 39.2 mg / L, methylheptenone at 0.55 - 1.75 mg / L, and 6 - methyl - 5 - hepten - 2 - ol at 0.24 - 0.81 mg / L.

4. The kojic acid beer according to claim 1 or 2, characterized in that, The fermentation degree of the koji acid beer is 87.0 - 93.0%, the content of diacetyl is 0.069 - 0.085 mg / L, and the content of total organic acids is 3.0 - 3.5 mL / 100 mL.

5. The kojic acid beer according to claim 1 or 2, characterized in that, The koji acid beer is brewed with raw materials containing the following mass percentages: malt raw materials, koji powder accounting for more than 5 wt% and less than 20 wt% of the dry weight of the malt raw materials, hops accounting for 0.5 - 7 wt‰ of the wort quality, and lactose accounting for 0 - 1.5 wt% of the wort quality. The wort is obtained by saccharifying, heating, and filtering the malt raw materials.

6. A method for preparing kojic acid beer according to any one of claims 1-5, characterized in that, Including the following steps: Step 1: Saccharification by the leaching method After crushing the malt raw materials, they are mixed with water at a material - to - water ratio of 1:3 - 1:4 to obtain a malt mash. Saccharification by the leaching method is carried out without adding exogenous enzyme preparations, and the starch is converted into fermentable sugars by the enzymes in the malt itself. Step 2: Heat the saccharified malt mash to 78 ± 1 °C and filter to obtain wort. Boil the wort, add hops during the boiling process, then cool the wort to 18 - 20 °C and oxygenate it, controlling the dissolved oxygen content of the wort to be 6 - 10 mg / L; Step 3: Natural fermentation Add Daqu powder to the oxygenated wort for fermentation, maintain the main fermentation temperature at 18 - 20 °C, and seal the tank when the wort ferments to a sugar degree of 3.2 - 5.5 °P; After sealing the tank, enter the diacetyl reduction stage. When the diacetyl content drops below 0.10 mg / L, cool down to 0 - 2 °C to finally obtain Daqu sour beer.

7. The preparation method according to claim 6, characterized in that, In Step 1, the infusion mashing includes two-stage mashing. The first-stage mashing process is to hold the malt mash at 65 °C for 60 min; the second-stage mashing process is to hold the malt mash at 72 °C for 15 min.

8. The preparation method according to claim 7, characterized in that, In Step 2, lactose is optionally added during the boiling process of the wort; based on the mass of the wort as the calculation basis, the addition amount of lactose is controlled to be 0 - 1.5 wt%.

9. The preparation method according to claim 8, characterized in that, In Step 3, in order to increase the hop aroma, when the wort ferments to a sugar degree of 3.2 - 5.5 °P, dry-hop is carried out before sealing the wort tank, and the addition amount of dry-hop accounts for 5 - 7‰ of the mass of the wort.

10. The preparation method according to claim 9, characterized in that, In Step 3, the temperature for diacetyl reduction is 19 - 20 °C, and the reduction time is 7 to 15 days.

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