Process for preparing crafted sour beer by fermenting wort at low temperature by compounding multiple strains and lagger yeast

Abstract

The invention provides a process for preparing craft sour beer through multi-strain and lagger yeast composite low-temperature fermented wort, and relates to the technical field of beer brewage, the process comprises the following steps: mixing and saccharifying malt and brewing water to form original wort, the mixing and saccharifying treatment comprises the steps of crushing, saccharifying, filtering and boiling, and performing compound bacterium inoculation treatment on the original wort to form acid-producing wort, wherein the compound bacterium inoculation treatment comprises the step of adding lactic acid compound fermentation flora to perform synergistic fermentation. According to the crafted sour beer preparation process for fermenting wort at low temperature by compounding multiple strains and lagger yeast, by adopting a multi-strain and lagger yeast compound low-temperature fermentation process, the problems of poor flavor coordination and unbalanced strain metabolism in the traditional sour beer fermentation are solved. By utilizing scientific strain proportion and temperature control management, the sour taste, the milk fragrance and the fruit fragrance are effectively balanced, the layering sense of the beer is improved, and the flavor of the beer is richer and more stable.

Description

Technical Field

[0001] This invention relates to the field of beer brewing technology, specifically to a process for preparing craft sour beer using a low-temperature fermentation wort incorporating multiple microbial strains and lager yeast. Background Technology

[0002] Current craft sour beer brewing methods employ single-strain or dual-strain fermentation, primarily using *Lactobacillus plantarum* or *Streptococcus thermophilus*. Lactic acid fermentation first develops the sour flavor before inoculation with lager yeast to complete alcoholic fermentation. This process is simple and produces stable acidity, but its flavor profile is limited, often requiring the addition of fruit juice, whey, or aroma extracts to enhance the taste. Another type of natural mixed-strain fermentation relies on environmentally present lactic acid bacteria and yeast communities. This method has a longer fermentation cycle, resulting in unstable flavor profiles and significant batch-to-batch variations. Current sour beer fermentation methods remain largely empirical in terms of flavor development mechanisms, strain synergy, and low-temperature control.

[0003] Traditional brewing processes suffer from poor flavor harmony. When the strain ratio is unbalanced, sourness is prominent while milk and fruit aromas are insufficient, resulting in unclear beer body. Some processes prematurely terminate lactic acid fermentation to shorten the cycle, leading to insufficient flavor development; others extend the cycle to pursue flavor, but this increases inventory and energy consumption, making it difficult to adapt to the production pace of small and medium-sized craft breweries. A more prominent problem is that residual bacteria compete for nutrients during the yeast fermentation stage, producing off-flavors and affecting subsequent stability. Under multi-strain co-fermentation conditions, the lack of scientific control over the metabolic pathways and temperature stages of the strains makes it difficult to achieve a balance between sourness, milk aroma, and fruit aroma, hindering the unification of high-quality flavor and stable production in craft sour beer. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a process for preparing craft sour beer using a low-temperature fermentation of wort with multiple strains of bacteria and lager yeast. The technical problem this invention aims to solve is: how to achieve high-quality flavor and stable production of craft sour beer through low-temperature fermentation with multiple strains of bacteria and lager yeast, combined with synergistic fermentation and temperature control.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution: a craft sour beer preparation process of low-temperature fermented wort with multiple strains of bacteria and lager yeast, comprising: S1. mixing and saccharifying malt and brewing water to form original wort, wherein the mixing and saccharifying process includes crushing, saccharification, filtration and boiling; S2. The original wort is subjected to compound microbial inoculation treatment to form acid-producing wort, wherein the compound microbial inoculation treatment includes adding lactic acid complex fermentation bacteria for synergistic fermentation; S3. The acid-producing wort is boiled and inactivated to form flavored wort; S4. The flavored wort is subjected to low-temperature fermentation to form a low-temperature fermented wine, wherein the low-temperature fermentation includes inoculation with Lager yeast, segmented temperature control, and segmented pressure control. S5. The low-temperature fermented beer is filtered and bottled to form a finished craft sour beer, wherein the filtration and bottling process removes residual yeast and impurities without sterilization.

[0006] Preferably, the brewing water has a hardness of 75 mg / L and a pH of 6.2, and the mixed saccharification treatment step is as follows: S11. The malt is pulverized to form broken malt material, wherein the husk breakage rate of the pulverized material is ≥90% and the endosperm is 14 mesh.

[0007] S12. The broken wheat material and the brewing water are mixed in a certain proportion to form a saccharification mixture, wherein the mass ratio of the mixture is 1:2.0-1:2.1.

[0008] S13. The saccharification mixture is subjected to constant temperature saccharification treatment to form a fermentable sugar solution, wherein the constant temperature saccharification treatment includes holding at 50°C for 20 minutes and holding at 68-69°C for 70 minutes.

[0009] S14. The fermentable sugar solution is filtered and boiled to form the original wort, and the boiling time is 15 minutes.

[0010] Preferably, the lactic acid complex fermentation microbial community includes Lactobacillus plantarum, Lactobacillus casei, Streptococcus thermophilus, and Bifidobacterium, and the mass ratio of Lactobacillus plantarum, Lactobacillus casei, Streptococcus thermophilus, and Bifidobacterium is 4:5:2:3.

[0011] Preferably, the *Lactobacillus casei* produces lactic acid esters to enhance the milky aroma, the *Lactobacillus plantarum* produces malic acid and isoamyl acetate to enhance the fruity aroma, the *Streptococcus thermophilus* promotes the metabolism of the *Lactobacillus casei* and the *Lactobacillus plantarum*, and the *Bifidobacterium* regulates the acidity of the wort to maintain flavor balance.

[0012] Preferably, the co-fermentation is carried out in an anaerobic environment, with a fermentation temperature of 36℃-38℃, a fermentation time of 6-7 days, and an internal pressure of 0.02MPa-0.04MPa.

[0013] Preferably, the boiling inactivation treatment is performed at a temperature of 98℃-100℃ for 60 minutes ± 5 minutes. Qingdao daphne is added at the 5th minute of the boiling inactivation treatment, and Cascatel is added at the 50th minute of the boiling inactivation treatment. After the boiling inactivation treatment is completed, the wort is cooled to 18℃ to form the flavor-fixing wort. The proportion of Qingdao daphne added is 0.010%–0.015% of the total mass of the acid-producing wort, and the proportion of Cascatel added is 0.040%–0.050% of the total mass of the acid-producing wort.

[0014] Preferably, the dosage of the Lager yeast is 1 g / L. The low-temperature fermentation treatment includes a main fermentation stage, a heated fermentation stage, a sealed fermentation stage, and a post-fermentation stage. The temperature of the main fermentation stage is 10℃±0.5℃, the fermentation time is 4 days, and the internal pressure is 0 MPa. The temperature of the heated fermentation stage is 12℃±0.5℃, the internal pressure is 0 MPa, and the fermentation time is 5 days. The fermentation time of the sealed fermentation stage is 7 days, and the internal pressure is 0.18 MPa. The post-fermentation stage includes a first stage and a second stage. The temperature of the first stage is 4℃±0.5℃, the internal pressure is 0.18 MPa, and the fermentation time is 1 day. The temperature of the second stage is 0℃, the internal pressure is 0.18 MPa, and the fermentation time is 6 days.

[0015] Preferably, the filtration and filling process uses a microporous membrane with a pore size of 0.55 μm.

[0016] This invention provides a process for preparing craft sour beer using a low-temperature fermentation wort incorporating multiple microbial strains and lager yeast. It offers the following advantages: This invention addresses the problems of poor flavor harmony and metabolic imbalance in traditional sour beer fermentation by employing a low-temperature fermentation process combining multiple strains of bacteria and lager yeast. Through scientifically controlled bacterial ratios and temperature management, it effectively balances sourness, milkiness, and fruitiness, enhancing the beer's complexity and resulting in a richer and more stable flavor profile.

[0017] This craft sour beer brewing process, which combines multi-strain and lager yeast in low-temperature fermentation of wort, ensures the natural flavor of the craft sour beer. The low-temperature fermentation and sterilization process avoids interference from residual microorganisms, guaranteeing the purity and stability of the beer's flavor. This combined low-temperature fermentation process is suitable for the production needs of small and medium-sized craft breweries, shortening the production cycle, reducing energy consumption and inventory burden, and providing reliable technical support for the high-quality production of craft sour beer. Attached Figure Description

[0018] Figure 1 This is a flowchart of the craft sour beer preparation process; Figure 2 This is a schematic diagram of the structure of the low-temperature fermentation stage; Figure 3 This is a flowchart of the saccharification process. Detailed Implementation

[0019] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0020] like Figure 1-3 As shown, this embodiment of the invention provides a process for preparing craft sour beer using a low-temperature fermentation wort containing multiple strains of bacteria and lager yeast. The process includes: S1. Mixing and saccharifying malt and brewing water to form raw wort. The mixed saccharification process includes crushing, saccharification, filtration, and boiling. The brewing water has a hardness of 75 mg / L and a pH of 6.2. The mixed saccharification steps are as follows: S11. The malt is crushed to form crushed malt material, with a husk breakage rate of ≥90% and an endosperm mesh of 14 mesh.

[0021] S12. The crushed wheat material and brewing water are mixed in a certain proportion to form a saccharification mixture, and the mass ratio of the mixed mixture is 1:2.02.

[0022] S13. The saccharification mixture is subjected to constant temperature saccharification treatment to form a fermentable sugar solution. The constant temperature saccharification treatment includes keeping the mixture at 50℃ for 20 minutes to generate small molecule peptides, which provide nutrients for the complex bacteria and promote aroma production. Then, the mixture is kept at 68.5℃ for 70 minutes to slowly decompose starch, retain some medium molecule sugars, and improve the taste of the wine.

[0023] S14. The fermentable sugar solution is filtered and boiled to form raw wort. The boiling time is 15 minutes. The saccharified sugar solution is then guided to a filtering tank. The liquid in the filtering tank is gradually filtered out by natural flow or slight pressure to remove malt bran, chaff, and other solid impurities. After filtration, a clear sugar solution with a light color and low impurity content is obtained, which facilitates subsequent boiling.

[0024] The filtered wort is transferred to a boiling kettle for boiling. During boiling, the proteins in the wort react with other substances to form insoluble compounds. This sediment precipitates out during boiling, helping to remove unwanted components and improving the beer's clarity and flavor.

[0025] Preliminary sterilization: The high temperature during boiling kills any microorganisms that may be present, preventing off-flavors or unstable fermentation results during subsequent fermentation. Moisture evaporation control: During boiling, some moisture in the wort will evaporate; the amount of moisture evaporation needs to be monitored regularly. After boiling, the wort concentration is approximately 13°P.

[0026] S2. The original wort is inoculated with a complex microbial culture to form acid-producing wort. This inoculation process involves adding a lactic acid fermentation microbial community for co-fermentation. The lactic acid fermentation microbial community includes *Lactobacillus plantarum*, *Lactobacillus casei*, *Streptococcus thermophilus*, and *Bifidobacterium*, with a mass ratio of 4:5:2:3. *Lactobacillus casei* produces lactic acid esters to enhance the milky aroma, *Lactobacillus plantarum* produces malic acid and isoamyl acetate to enhance the fruity aroma, *Streptococcus thermophilus* promotes the metabolism of *Lactobacillus casei* and *Lactobacillus plantarum*, and *Bifidobacterium* regulates the acidity of the original wort to maintain flavor balance. Co-fermentation is carried out under anaerobic conditions at a temperature of 36℃-38℃ for 6-7 days and a pressure of 0.03 MPa within the tank.

[0027] S3. The acidified wort is subjected to boiling inactivation treatment to form flavor-fixing wort. The boiling inactivation treatment temperature is 98℃-100℃ and the time is 60 minutes ± 5 minutes. Qingdao daphne is added at the 5th minute of the boiling inactivation treatment, and Cascatel is added at the 50th minute of the boiling inactivation treatment. After the boiling inactivation treatment is completed, the wort is cooled to 18℃ to form flavor-fixing wort. The proportion of Qingdao daphne added is 0.010%–0.015% of the total mass of acidified wort, and the proportion of Cascatel added is 0.040%–0.050% of the total mass of acidified wort.

[0028] S4. The wort is subjected to low-temperature fermentation to form a low-temperature fermented spirit. This low-temperature fermentation process includes inoculation with lager yeast, segmented temperature control, and segmented pressure control. The lager yeast dosage is 1 g / L. The low-temperature fermentation process includes a primary fermentation stage, a warming fermentation stage, a sealed fermentation stage, and a post-fermentation stage. The primary fermentation stage is conducted at 10℃±0.5℃ for 4 days at a pressure of 0 MPa. The warming fermentation stage is conducted at 12℃±0.5℃ for 5 days at a pressure of 0 MPa. The sealed fermentation stage is conducted for 7 days at a pressure of 0.18 MPa. The post-fermentation stage includes two phases: the first phase is conducted at 4℃±0.5℃ for 1 day at a pressure of 0.18 MPa, and the second phase is conducted at 0℃ for 6 days at a pressure of 0.18 MPa.

[0029] S5. The low-temperature fermented beer is filtered and bottled to produce the finished craft sour beer. Filtration and bottling are performed without sterilization to remove residual yeast and impurities. Microporous membranes with a pore size of 0.55 μm are used for filtration and bottling. Example

[0030] This embodiment compares the intensity of milk and fruit aromas in sour beer under different proportions of compound bacteria, evaluates the flavor performance of the optimal strain ratio with other control groups, and verifies the effect of the optimal strain ratio on the flavor of sour beer.

[0031] 1. Experimental Materials raw material: Barley malt: 50 kg, used for 100 L of wort; brewing water: 105 L, hardness 75 mg / L, pH 6.2.

[0032] Hops: Cascade: 42g, Tsingtao hops: 12g, Lager yeast: 100g.

[0033] Compound bacteria ratio: Group A: Lactobacillus plantarum: Lactobacillus casei: Streptococcus thermophilus: Bifidobacterium = 4:5:2:3; Group B: Compound bacteria ratio is 3:4:1:2; Group C: Compound bacteria ratio is 5:6:3:4; Group D: Compound bacteria ratio is 4:3:2:3; Group E: Compound bacteria ratio is 2:5:4:3; Group F: Compound bacteria ratio is 4:5:4:5.

[0034] Controlling a single variable: Group A: Active bacterial strains: Lactobacillus plantarum: 4g, Lactobacillus casei: 5g, Streptococcus thermophilus: 2g, Bifidobacterium: 3g. Groups B, C, D, E, and F added quantitative amounts of active bacterial strains according to the predetermined compound bacterial ratio.

[0035] 2. Experimental Procedure 2.1 Wort Preparation Malt grinding: Grind the barley malt to ensure a husk breakage rate of ≥90% and an endosperm mesh of 14 mesh. Saccharification: Mix the ground malt and brewing water at a ratio of 1:2.02 and perform low-temperature saccharification. Protein rest is held at 50℃ for 20 minutes; saccharification rest is held at 68.5℃ for 70 minutes.

[0036] Filtration and Boiling: After saccharification, the wort is filtered and collected. It is then boiled for 15 minutes to precipitate proteins, yielding clarified wort. Cooling: The wort is cooled to 37°C using a plate heat exchanger in preparation for inoculation.

[0037] 2.2 Bacterial Inoculation and Fermentation Activation of bacterial strains: Add each type of bacteria separately to 50 mL of sterile wort at 36°C and agitate for 60 minutes. Inoculation and fermentation: Inoculate the bacterial strains into the cooled wort according to the specified ratio for each group. Maintain a fermentation temperature of 37°C and carry out anaerobic fermentation for 6-7 days. Monitor the pH; fermentation ends when the acidity reaches 3.5°T.

[0038] 2.3 Secondary boiling and addition of hops Secondary boiling: Transfer the acidified wort to a boiling kettle and boil for 60 minutes. Add Tsingtao hops after 5 minutes and Cascade hops after 50 minutes.

[0039] Cooling: After boiling, the wort is quickly cooled to 18°C ​​to obtain flavored wort.

[0040] 2.4 Low-temperature fermentation of Lager yeast Yeast inoculation: Add 100g of Lager yeast at a ratio of 1g / L.

[0041] Low-temperature fermentation: Primary fermentation: 10℃, ferment for 4 days, monitor wort concentration. Secondary fermentation: Increase temperature to 12℃, ferment for 5 days. Sealed fermentation: Seal the fermentation tank, maintain a pressure of 0.18 MPa, ferment for 7 days. Secondary fermentation: Reduce temperature to 4℃, continue fermentation for 1 day; then reduce to 0℃, ferment for 6 days.

[0042] 2.5 Finished Product Processing and Packaging Filtration: Filter using a 0.55μm microporous membrane to remove yeast residue. Packaging: Bottle or can the beer without sterilization.

[0043] 4. Sensory analysis: Sensory analysis was performed after each batch of beer fermentation was completed: Milk aroma intensity: The richness of the milk aroma is assessed by a team of professional tasters using standard milk aroma descriptive terms. Fruit aroma intensity: The complexity and intensity of the fruit aroma are assessed by professional tasters, with a focus on key fruit aroma components such as malic acid.

[0044] Comprehensive flavor analysis: The overall flavor balance and harmony are evaluated based on the synergistic effect of milky and fruity aromas. The overall flavor profile of different groups is compared, with particular emphasis on the harmony between milky and fruity aromas.

[0045] 5. Data recording and statistical analysis: Sensory rating: Record the intensity of creaminess, fruitiness, and overall flavor score for each group of beers.

[0046] Table 1: Comparison of "milky aroma - fruity aroma intensity" under different proportions of compound bacteria.

[0047] Group Ratio of four bacteria Milk flavor intensity rating Fruit aroma intensity rating Group A 4:5:2:3 9.2 8.8 Group B 3:4:1:2 7.5 7.2 Group C 5:6:3:4 8.9 7 Group D 4:3:2:3 6.8 8.5 Group E 2:5:4:3 8 6.5 Group F 4:5:4:5 7.8 7.5 The ratio of the four bacteria is Lactobacillus plantarum: Lactobacillus casei: Streptococcus thermophilus: Bifidobacterium, and the intensity of milk and fruit aromas is scored from 1 to 10.

[0048] Chemical analysis: The content of flavor compounds such as diacetone and malic acid was determined to verify the differences in flavor components among the groups: Group A: Rich in milky aroma and fresh in fruity aroma, with the best synergy between the two. The content of diacetone reaches 20mg / L, malic acid reaches 14mg / L, and the acidity is stable at 3.5°T, with an overall balanced and harmonious flavor.

[0049] Group B: The addition of each strain was low, resulting in insufficient accumulation of flavor compounds. The milky aroma was weak, the fruity aroma was underdeveloped, and the overall flavor was bland.

[0050] Group C: High proportion of Lactobacillus casei, with a prominent milky aroma, but the production of acid and fruity substances by Lactobacillus plantarum is inhibited; the fruity aroma is weak, the acidity is slightly high at 3.8°T, and the flavor balance is not good.

[0051] Group D: Lactobacillus plantarum has a good ability to produce fruity aroma, but the insufficient proportion of Lactobacillus casei results in a weak milky aroma; the overall flavor is dominated by fruity aroma, lacking the soft accompaniment of milky aroma.

[0052] Group E: The proportion of thermophilic streptococci is too high. Although it promotes the metabolism of some strains, it consumes too many nutrients; the production of fruity aroma substances is limited, and the overall flavor is too simple.

[0053] Group F: The proportion of thermophilic streptococci and bifidobacteria is relatively high, which intensifies the competition for nutrients with other strains; the milk and fruit aromas are not fully developed, and the acidity fluctuates greatly, ranging from 3.2 to 3.9°T. Example

[0054] This embodiment optimizes the alcohol content, flavor stability, and taste of craft all-malt lager beer through a low-temperature fermentation process that controls temperature and pressure in stages.

[0055] 1. Preparation of flavored wort After boiling and cooling, flavored wort is obtained. The wort is then boiled twice to deactivate it and cooled to 18°C ​​for low-temperature fermentation.

[0056] 2. Lager yeast inoculation Yeast type: Active lager yeast is used to ensure high fermentation activity and low by-product formation in the wort. Dosage ratio: The amount of lager yeast added is controlled at 1g / L to ensure effective yeast fermentation and avoid unclear or unstable beer caused by excessive yeast.

[0057] 3. Low-temperature fermentation stage Low-temperature fermentation is divided into four stages: primary fermentation, warm-up fermentation, sealed fermentation, and post-fermentation. Temperature and pressure are strictly controlled at each stage to ensure the beer's flavor and stability.

[0058] 3.1 Primary Fermentation Stage Temperature control: Maintain fermentation temperature at 10℃±0.5℃. Low-temperature fermentation reduces the formation of byproducts such as esters and higher alcohols, ensuring a pure beer flavor. Fermentation time: Primary fermentation lasts for 4 days to ensure the yeast can fully convert the sugars in the wort into alcohol. Tank pressure: Control the tank pressure at 0MPa to ensure the yeast ferments in a pressure-free environment, reducing excessive esterification and preserving the beer's fresh flavor.

[0059] 3.2 Heating and Fermentation Stage Temperature control: Increasing the temperature to 12℃±0.5℃ at this stage helps enhance yeast activity, further promoting sugar fermentation and reducing byproducts. Fermentation time: The fermentation time during the heating stage is 5 days. As the temperature increases, the yeast fermentation efficiency improves. Internal pressure: Maintain the internal pressure at 0MPa; fermentation should be carried out under pressure-free conditions to avoid affecting yeast activity.

[0060] 3.3 Sealed fermentation stage Temperature control: During the sealed fermentation stage, the temperature is maintained at 12℃±0.5℃ to ensure the yeast completes the final sugar conversion. Fermentation time: Continues for 7 days, during which most of the fermentation is complete, and the yeast completes the remaining sugar conversion, reducing the formation of undesirable flavors. Tank pressure: After sealing, the tank pressure is maintained at 0.18MPa to promote bubble formation and enhance the smoothness of the wine's texture.

[0061] 3.4 Post-fermentation stage The post-fermentation stage includes two sub-stages: refining the wine, stabilizing the flavor, and making the wine clearer through refrigeration.

[0062] Phase 1: Temperature control: Lower the temperature to 4℃±0.5℃. Low-temperature refrigeration helps reduce yeast activity, decreases the formation of excess byproducts, and accelerates wine clarification. Tank pressure: Maintain the tank pressure at 0.18MPa to stabilize the wine and prevent excessive carbon dioxide escape. Fermentation time: The first stage of post-fermentation lasts for 1 day to promote wine clarity and reduce turbidity.

[0063] Phase Two: Temperature control: The temperature is lowered to 0℃ to enter the late maturation stage, ensuring a more stable beer body and a more mature flavor. Tank pressure: The tank pressure is maintained at 0.18MPa to continue stabilizing the beer body through appropriate pressure. Fermentation time: Continues for 6 days, during which the beer flavor is optimized, sediment settles, and the beer's clarity and taste are improved.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for preparing craft sour beer using a low-temperature fermentation wort incorporating multiple strains of bacteria and lager yeast, characterized in that, include: S1. The malt and brewing water are mixed and saccharified to form raw wort, wherein the mixed saccharification process includes crushing, saccharification, filtration and boiling; S2. The original wort is subjected to compound microbial inoculation treatment to form acid-producing wort, wherein the compound microbial inoculation treatment includes adding lactic acid complex fermentation bacteria for synergistic fermentation; S3. The acid-producing wort is boiled and inactivated to form flavored wort; S4. The flavored wort is subjected to low-temperature fermentation to form a low-temperature fermented wine, wherein the low-temperature fermentation includes inoculation with Lager yeast, segmented temperature control, and segmented pressure control. S5. The low-temperature fermented beer is filtered and bottled to form a finished craft sour beer.

2. The process for preparing craft sour beer using a multi-strain and lager yeast compound low-temperature fermentation wort according to claim 1, characterized in that: The brewing water has a hardness of 75 mg / L and a pH of 6.

2. The steps of the mixed saccharification treatment are as follows: S11. The malt is pulverized to form broken malt material, wherein the husk breakage rate of the pulverization process is ≥90% and the endosperm is 14 mesh; S12. The crushed wheat material and the brewing water are mixed in a certain proportion to form a saccharification mixture, wherein the mass ratio of the mixture is 1:2.0-1:2.1; S13. The saccharification mixture is subjected to constant temperature saccharification treatment to form a fermentable sugar solution, wherein the constant temperature saccharification treatment includes holding at 50°C for 20 minutes and holding at 68-69°C for 70 minutes. S14. The fermentable sugar solution is filtered and boiled to form the original wort, and the boiling time is 15 minutes.

3. The process for preparing craft sour beer using a multi-strain and lager yeast compound low-temperature fermentation wort according to claim 1, characterized in that: The lactic acid complex fermentation microbial community includes Lactobacillus plantarum, Lactobacillus casei, Streptococcus thermophilus, and Bifidobacterium, and the mass ratio of Lactobacillus plantarum, Lactobacillus casei, Streptococcus thermophilus, and Bifidobacterium is 4:5:2:

3.

4. The process for preparing craft sour beer using a multi-strain and lager yeast compound low-temperature fermentation wort according to claim 3, characterized in that: The *Lactobacillus casei* produces lactic acid esters to enhance the milky aroma, the *Lactobacillus plantarum* produces malic acid and isoamyl acetate to enhance the fruity aroma, the *Streptococcus thermophilus* promotes the metabolism of the *Lactobacillus casei* and the *Lactobacillus plantarum*, and the *Bifidobacterium* regulates the acidity of the original wort.

5. The process for preparing craft sour beer using a multi-strain and lager yeast compound low-temperature fermentation wort according to claim 1, characterized in that: The co-fermentation is carried out in an anaerobic environment, with a fermentation temperature of 36℃-38℃, a fermentation time of 6-7 days, and an internal pressure of 0.02MPa-0.04MPa.

6. The process for preparing craft sour beer using a multi-strain and lager yeast compound low-temperature fermentation wort according to claim 1, characterized in that: The boiling inactivation treatment is performed at a temperature of 98℃-100℃ for 60 minutes ± 5 minutes. Qingdao daphne is added at the 5th minute of the boiling inactivation treatment, and Cascatel is added at the 50th minute of the boiling inactivation treatment. After the boiling inactivation treatment is completed, the wort is cooled to 18℃ to form the flavor-fixing wort. The addition ratio of Qingdao daphne is 0.010%–0.015% of the total mass of the acid-producing wort, and the addition ratio of Cascatel is 0.040%–0.050% of the total mass of the acid-producing wort.

7. The process for preparing craft sour beer using a multi-strain and lager yeast compound low-temperature fermentation wort according to claim 1, characterized in that: The dosage of the Lager yeast is 1 g / L. The low-temperature fermentation treatment includes a main fermentation stage, a heated fermentation stage, a sealed fermentation stage, and a post-fermentation stage. The temperature of the main fermentation stage is 10℃±0.5℃, the fermentation time is 4 days, and the internal pressure is 0 MPa. The temperature of the heated fermentation stage is 12℃±0.5℃, the internal pressure is 0 MPa, and the fermentation time is 5 days. The fermentation time of the sealed fermentation stage is 7 days, and the internal pressure is 0.18 MPa. The post-fermentation stage includes a first stage and a second stage. The temperature of the first stage is 4℃±0.5℃, the internal pressure is 0.18 MPa, and the fermentation time is 1 day. The temperature of the second stage is 0℃, the internal pressure is 0.18 MPa, and the fermentation time is 6 days.

8. The process for preparing craft sour beer using a multi-strain and lager yeast compound low-temperature fermentation wort according to claim 1, characterized in that: The filtration and filling process uses a microporous membrane with a pore size of 0.55 μm.

Images