Fragrant pure rice vinegar and preparation method thereof

Abstract

The invention discloses faint scent pure rice vinegar and a preparation method thereof. The preparation method comprises the following steps: S1, raw material treatment, S2, liquefaction and saccharification, S3, alcoholic fermentation, S4, rice wine treatment, S5, acetic fermentation, S6, filtration, S7, nanofiltration, S8, sterilization, filling and the like. According to the present invention, starch debranching enzyme is adopted to hydrolyze alpha-1, 6-glucosidic bonds, 20-28 DEG C micro-low temperature prolonged time fermentation is adopted, precipitation distillation, ultrafiltration and nanofiltration double filtration and other processes are adopted, full fermentation, full decoloration and odor removal are performed, high-quality and odor-free rice vinegar is produced, the fermentation speed is rapid, the fermentation is complete, the preparation method is simple, the operation is convenient, the cost is low, and the method is suitable for industrial production. The method is high in additional value and has good popularization and application value.

Description

Technical Field

[0001] The present invention relates to the technical field of rice vinegar production, and particularly relates to a delicate and pure rice vinegar and a preparation method thereof. Background Art

[0002] As the most common and essential condiment in daily life, the production and quality of rice vinegar are closely related to thousands of households. The traditional preparation process of rice vinegar mainly includes: (1) raw material selection and treatment; (2) saccharification and alcohol fermentation; (3) acetic acid fermentation; (4) aging and post-treatment; (5) vinegar leaching of vinegar grains; (6) post-treatment of raw vinegar, etc., and then the finished product can be obtained. The traditional method for brewing rice vinegar has the following disadvantages: (1) The brewing cycle is long. From raw material treatment to the final finished product, the entire brewing process takes several months; (2) It is greatly affected by environmental factors. The traditional brewing process has strict requirements for environmental conditions such as temperature and humidity; (3) The labor intensity is high. In the traditional brewing process, operations such as turning the vinegar grains mainly rely on manual labor; (4) The product quality is unstable. Due to the traditional brewing method being affected by various factors such as raw material quality, microbial community differences, and environmental conditions, the rice vinegar produced in different batches has certain differences in flavor, color, acidity, etc., and it is easy to produce rice vinegar with a yellowish color, unstable color, strange smell, and non-compliance of salt-free solids. Existing technologies have proposed some improvement measures in improving fermentation efficiency and the taste of rice vinegar, but the improvement of the quality and taste of rice vinegar is not obvious. Therefore, there is an urgent need in this field for a preparation process that can significantly improve the quality and taste of rice vinegar. Summary of the Invention

[0003] The object of the present invention is achieved through the following technical solutions:

[0004] The first aspect of the present invention provides a preparation method of a delicate and pure rice vinegar, comprising the following steps:

[0005] S1 Raw material treatment: Select plump and insect-free rice, rinse it, add drinking water to submerge the rice surface after rinsing, and grind it into rice slurry for standby after soaking;

[0006] S2 Liquefaction and saccharification: Steam the above-mentioned rice slurry, after completely steaming, add water and adjust the pH to 5 - 8, then add enzymes and stir to fully mix it with the steamed rice slurry, and react at 55 - 65 °C for more than 1 h to perform liquefaction and saccharification to obtain a saccharified liquid;

[0007] S3 Alcohol fermentation: Cool the above-mentioned saccharified liquid to 24 - 28 °C, then add active dry yeast for brewing and ferment to obtain fermented rice wine, and the alcohol content of the fermented rice wine is 6 - 8 vol%, with a normal new wine aroma and no other strange odors;

[0008] S4 Rice wine treatment: Let the above fermented rice wine stand for precipitation, take the supernatant for distillation until the alcohol content reaches 10-12 vol%, and obtain refined fermented rice wine;

[0009] S5 Acetic acid fermentation: Place the above refined fermented rice wine in a fermentation tank, inoculate acetic acid bacteria into the fermentation tank for acetic acid fermentation. When the total acid is greater than 9.0 g / 100 ml in terms of acetic acid, the fermentation is completed to obtain new vinegar;

[0010] S6 Filtration: First filter the above new vinegar through a 0.03-0.05 μm ceramic membrane, and then add water to adjust it to 4.5-5.5 g / 100 mL to obtain a preliminarily filtered vinegar solution;

[0011] S7 Nanofiltration: Filter the above preliminarily filtered vinegar solution again with a new hollow fiber membrane of 1-10 nm, with a molecular weight cut-off of 300-1000 kDa, to obtain a nanofiltrated vinegar solution;

[0012] S8 Sterilization and filling: Sterilize and fill the above refined filtered vinegar solution to obtain the said pure rice vinegar with a delicate fragrance;

[0013] Further, in S1, the soaking water temperature is 35-45 °C and the soaking time is 6-12 h;

[0014] Further, in S1, the grinding particle size is 40-80 mesh;

[0015] Further, in S2, the water addition amount is 0.6-0.8 times the mass of the raw rice;

[0016] Further, in S2, the added enzymes are a mixture composed of 8-15 U / g of α-amylase, 1-8 U / g of starch debranching enzyme, and 280-420 U / g of glucoamylase;

[0017] Further, in S3, the addition amount of the brewing active dry yeast is 1.0-1.2 wt% of the mass of the rice;

[0018] Further, in S3, the fermentation conditions are fermentation at 18-28 °C for at least 30-45 days;

[0019] Further, in S4, the standing precipitation time of the fermented rice wine is 12-18 h;

[0020] Further, in S6, the preliminary filtration conditions are a temperature of 25-27 °C, a pressure of 0.39-0.54 MPa, and an air flow rate of 40-60 m 3 / h;

[0021] Further, in S7, the nanofiltration conditions are a temperature of 25-27 °C, a pressure of 0.50-0.70 MPa, and an air flow rate of 80-110 m 3 / h;

[0022] The second aspect of the present invention provides rice vinegar prepared by any of the above methods;

[0023] Beneficial effects

[0024] 1. Conventional starch raw materials such as rice and glutinous rice contain 20 - 30% amylose and 70 - 80% amylopectin. Amylopectin is a complex branched structure formed by hundreds or thousands of glucose units connected by α-1,4-glycosidic bonds and α-1,6-glycosidic bonds formed by oxygen atoms at the C1 position. Commonly used enzymes for starch processing have high hydrolysis activity for α-1,4-glycosidic bonds, but cannot or can only slowly cleave α-1,6-glycosidic bonds, resulting in reduced starch utilization rate. Starch debranching enzyme can hydrolyze α-1,6-glycosidic bonds and other useful substances, which is beneficial to subsequent enzymatic reactions, improves the starch utilization rate, and increases the content of salt-free solids;

[0025] 2. The pure rice vinegar preparation process includes two stages: alcohol fermentation and acetic acid fermentation. In the rice wine fermentation process, too high temperature during the main fermentation period will lead to a high content of isoamyl alcohol in the rice wine, and an increase in the content of isovaleric acid in the final product will cause an off-flavor in the rice vinegar. The normal main fermentation temperature range is 32 - 36 °C. The present invention adopts a slightly low temperature of 20 - 28 °C and extends the fermentation time to 45 days, reducing the production of isoamyl alcohol and effectively reducing the off-flavor of the rice vinegar;

[0026] 3. Different from the traditional vat fermentation or vinegar production after pressing the wine mash, the rice wine is allowed to stand and sediment naturally, and the supernatant is taken and then the rice wine is distilled. While purifying the rice wine, the alcohol content is increased to more than 10 - 12 vol% to improve the acetic acid conversion rate.

[0027] 4. Ultrafiltration and nanofiltration double filtration. The two-stage filtration is carried out with a 0.05 μm ceramic membrane for primary filtration and a 10 nm new hollow fiber membrane for nanofiltration for repeated filtration. Conventional traditional rice vinegar manufacturing only undergoes ultrafiltration. The present invention adds nanofiltration operation. The membrane pore size is between 1 - 10 nm, which can block most substances such as suspended substances, proteins, and polysaccharides between several hundred and several thousand daltons (kDa) except for sucrose, glucose, polyvalent salt amino acids, achieving a sufficient decolorization and deodorization effect.

[0028] 5. The present invention has a fast fermentation speed, complete fermentation, a simple preparation method, convenient operation, low cost, and high added value, and has good promotion and application value. Brief description of the drawings

[0029] Figure 1 Process flow chart for preparing the light-flavor rice vinegar of the present invention Detailed implementation manners

[0030] The present invention will be further described below in conjunction with the drawings and embodiments.

[0031] Example 1

[0032] A production method of high-quality pure rice vinegar comprises the following steps:

[0033] S1 Raw material treatment: Select 100 kg of rice, which should be plump and free from insect damage. After rinsing, add drinking water to submerge the rice surface, control the water temperature at 35 - 45 °C, soak for 6 - 12 h, then take it out and grind it into a slurry with a fineness of 40 - 80 mesh for standby; S2 Liquefaction and saccharification: Steam the rice slurry. After complete steaming, add 60 kg - 80 kg of water, adjust the pH to about 5 - 8, add α-amylase at 8 - 15 U / g, pullulanase at 5 U / g, and glucoamylase at 280 - 420 U / g, stir and mix evenly with the material, keep it warm at 55 - 65 °C for more than 1 h for sufficient liquefaction and saccharification; S3 Alcohol fermentation: Cool the saccharified liquid to a temperature of 24 - 28 °C, add 1.0 - 1.2 kg of active dry yeast for brewing, ensure the temperature and ingredient ratio are accurate, control the fermentation temperature at 20 °C, aerobically ferment at 20 °C for 35 - 45 days, the alcohol content reaches 6 - 8 vol%, with a normal aroma of new wine and no other abnormal odors; S4 Rice wine treatment: Let the rice wine stand and sediment by itself for more than 12 - 18 h, take the supernatant and distill it until the alcohol content reaches 10 - 12 vol%, and pump the liquor into the fermentation tank; S5 Acetic acid fermentation: Inoculate acetic acid bacteria in the fermentation tank for acetic acid fermentation until the total acid (calculated as acetic acid) is greater than 9.0 g / 100 ml; S6 Filtration treatment: The fermented rice vinegar is first preliminarily filtered through a 0.03 - 0.05 μm ceramic membrane, then added with water to be adjusted to 4.5 - 5.5 degrees, at room temperature of 25 - 27 °C, pressure of 0.39 - 0.54 MPa, and flux of 40 - 60 m 3 / h; S7 Nanofiltration: At room temperature of 25 - 27 °C, pressure of 0.50 - 0.70 MPa, flux of 80 - 110 m 3 / h, use a new hollow fiber membrane with a membrane pore size of 1 - 10 nm and a retention molecular weight of 300 - 1000 kDa; S8 Sterilization and filling: Sterilize and fill the finished product to obtain the finished pure rice vinegar.

[0034] Example 2

[0035] A production method of high-quality pure rice vinegar comprises the following steps:

[0036] S1 Raw material treatment: Select 100 kg of rice, which is plump and free from insect damage. After rinsing, add drinking water to submerge the rice surface. Control the water temperature at 35 - 45 °C, soak for 6 - 12 h, then take it out and grind it into a slurry with a fineness of 40 - 80 mesh for standby; S2 Liquefaction and saccharification: Steam the rice slurry. After complete steaming, add 60 kg - 80 kg of water, adjust the pH to about 5 - 8, add α-amylase at 8 - 15 U / g, starch debranching enzyme at 1 U / g, and glucoamylase at 280 - 420 U / g, stir to mix evenly with the materials, and keep it warm at 55 - 65 °C for more than 1 h for sufficient liquefaction and saccharification; S3 Alcohol fermentation: Cool the saccharified liquid to a temperature of 24 - 28 °C and add 1.0 - 1.2 kg of active dry yeast for brewing. Ensure the accuracy of temperature and ingredient ratio. Control the fermentation temperature below 28 °C, and aerobically ferment at 24 - 28 °C for 30 - 40 days. The alcohol content reaches 6 - 8 vol%, with a normal aroma of new wine and no other abnormal odors; S4 Rice wine treatment: Let the rice wine stand and sediment for more than 12 - 18 h, and take the supernatant for distillation. Distill until the alcohol content reaches 10 - 12 vol%, and transfer the liquor to a fermentation tank; S5 Acetic acid fermentation: Inoculate acetic acid bacteria in the fermentation tank for acetic acid fermentation until the total acid (calculated as acetic acid) is greater than 9.0 g / 100 ml; S6 Filtration treatment: The matured rice vinegar is first preliminarily filtered through a 0.03 - 0.05 μm ceramic membrane, then adjusted with water to 4.5 - 5.5 degrees at room temperature of 25 - 27 °C, pressure of 0.39 - 0.54 MPa, and flux of 40 - 60 m 3 / h; S7 Nanofiltration: Use a new hollow fiber membrane with a membrane pore size of 1 - 10 nm and a retention molecular weight of 300 - 1000 kDa at room temperature of 26 °C, pressure of 0.50 - 0.70 MPa, and flux of 80 - 110 m

[0037] Example 3

[0038] A production method of high-quality pure rice vinegar comprises the following steps:

[0039] S1 Raw material treatment: Select 100 kg of rice, which is plump and free from insect damage. After rinsing, add drinking water to submerge the rice surface. Control the water temperature at 35 - 45 °C, soak for 6 - 12 h, then take out and grind into a slurry with a fineness of 40 - 80 meshes for standby; S2 Liquefaction and saccharification: Steam the rice slurry until it is completely cooked. Then add 60 kg - 80 kg of water, adjust the pH to about 5 - 8, add α - amylase at 8 - 15 U / g, starch debranching enzyme at 3 - 8 U / g, and glucoamylase at 280 - 420 U / g, stir to mix evenly with the materials, and keep warm at 55 - 65 °C for more than 1 h for sufficient liquefaction and saccharification; S3 Alcohol fermentation: Cool the saccharified liquid to a temperature of 24 - 28 °C and add 1.0 - 1.2 kg of active dry yeast for brewing, ensuring accurate temperature and ingredient ratio. Control the fermentation temperature below 28 °C, aerobically ferment at 18 - 24 °C for 30 - 45 days, until the alcohol content reaches 6 - 8 vol%, with a normal aroma of new wine and no other abnormal odors; S4 Rice wine treatment: Let the rice wine stand and sediment for more than 12 - 18 h, and take the supernatant for distillation. Distill until the alcohol content reaches 10 - 12 vol%, and transfer the liquor to a fermentation tank; S5 Acetic acid fermentation: Inoculate acetic acid bacteria in the fermentation tank for acetic acid fermentation until the total acid (calculated as acetic acid) is greater than 9.0 g / 100 ml; S6 Filtration treatment: The finished rice vinegar is first preliminarily filtered through a 0.03 - 0.05 μm ceramic membrane, then adjusted to 4.5 - 5.5 degrees by adding water, at room temperature of 25 - 27 °C, pressure of 0.39 - 0.54 MPa, and flux of 40 - 60 m 3 / h; S7 Nanofiltration: Use a new hollow fiber membrane with a membrane pore size of 1 - 10 nm and a molecular weight cut - off of 300 - 1000 kDa, at room temperature of 25 - 27 °C, pressure of 0.50 - 0.70 MPa, and flux of 80 - 110 m 3 / h; S8 Sterilization and filling: Sterilize and fill the finished product to obtain the finished pure rice vinegar.

[0040] Comparative Example 1

[0041] A production method of high - quality pure rice vinegar comprises the following steps:

[0042] S1 Raw material treatment: Select 100 kg of rice, which is plump and free from insect damage. After rinsing, add drinking water to submerge the rice surface. Control the water temperature at 35 - 45 °C, soak for 6 - 12 h, then fish out and grind into a slurry with a fineness of 40 - 80 mesh for standby; S2 Liquefaction and saccharification: Steam the rice slurry. After complete steaming, add 60 kg - 80 kg of water, adjust the pH to about 5 - 8, add α - amylase at 8 - 15 U / g and glucoamylase at 280 - 420 U / g, stir and mix evenly with the materials. Keep warm at 55 - 65 °C for more than 1 h for sufficient liquefaction and saccharification; S3 Alcohol fermentation: Cool the saccharified liquid to a temperature of 24 - 28 °C and add 1.0 - 1.2 kg of active dry yeast for brewing. Ensure the accuracy of temperature and ingredient ratio. Control the fermentation temperature below 28 °C. After aerobic fermentation at 18 - 28 °C for 30 - 45 days, the alcohol content reaches 6 - 8 vol%, with a normal aroma of new wine and no other abnormal odors; S4 Rice wine treatment: Let the rice wine stand and sediment for more than 12 - 18 h, and take the supernatant for distillation. Distill until the alcohol content reaches 10 - 12 vol%, and transfer the liquor to a fermentation tank; S5 Acetic acid fermentation: Inoculate acetic acid bacteria in the fermentation tank for acetic acid fermentation until the total acid (calculated as acetic acid) is greater than 9.0 g / 100 ml; S6 Filtration treatment: The finished rice vinegar is first preliminarily filtered through a 0.03 - 0.05 um ceramic membrane, then adjusted with water to 4.5 - 5.5 degrees, at room temperature of 25 - 27 °C, pressure of 0.39 - 0.54 MPa, and flux of 40 - 60 m 3 / h; S7 Nanofiltration: Use a new hollow fiber membrane with a membrane pore size of 1 - 10 nm and a retention molecular weight of 300 - 1000 kDa, at room temperature of 25 - 27 °C, pressure of 0.50 - 0.70 MPa, and flux of 80 - 110 m 3 / h; S8 Sterilization and filling: Sterilize and fill the finished product to obtain the finished pure rice vinegar.

[0043] Comparative Example 2

[0044] A production method of high - quality pure rice vinegar comprises the following steps:

[0045] S1 Raw material treatment: Select 100 kg of rice, which is plump and free from insect damage. After rinsing, add drinking water to submerge the rice surface. Control the water temperature at 35 - 45 °C, soak for 6 - 12 h, then fish out and grind it into a slurry with a fineness of 40 - 80 meshes for standby; S2 Liquefaction and saccharification: Steam the rice slurry until it is completely cooked. Then add 60 kg - 80 kg of water, adjust the pH to about 5 - 8, add α - amylase at 8 - 15 U / g, starch debranching enzyme at 1 - 5 U / g, and glucoamylase at 280 - 420 U / g, stir to mix evenly with the materials, and keep it at 55 - 65 °C for more than 1 h for sufficient liquefaction and saccharification; S3 Alcohol fermentation: Cool the saccharified liquid to a temperature of 24 - 28 °C, add 1.0 - 1.2 kg of active dry yeast for brewing. Ensure the accuracy of temperature and ingredient ratio, control the fermentation temperature at 30 - 35 °C, and ferment aerobically for 30 - 45 days until the alcohol content reaches 6 - 8 vol%, with a normal aroma of new wine and no other abnormal odors; S4 Rice wine treatment: Let the rice wine stand and sediment for more than 12 - 18 h, take the supernatant and distill it until the alcohol content reaches 10 - 12 vol%, and transfer the liquor to a fermentation tank; S5 Acetic acid fermentation: Inoculate acetic acid bacteria in the fermentation tank for acetic acid fermentation until the total acid (calculated as acetic acid) is greater than 9.0 g / 100 ml; S6 Filtration treatment: The finished rice vinegar is first preliminarily filtered through a 0.03 - 0.05 um ceramic membrane, then adjusted with water to 4.5 - 5.5 degrees, at room temperature of 25 - 27 °C, pressure of 0.39 - 0.54 MPa, and flux of 40 - 60 m 3 / h; S7 Nanofiltration: Use a new hollow fiber membrane with a membrane pore size of 1 - 10 nm and a retention molecular weight of 300 - 1000 kDa, at room temperature of 25 - 27 °C, pressure of 0.50 - 0.70 MPa, and flux of 80 - 110 m 3 / h; S8 Sterilization and filling: Sterilize and fill the finished product to obtain the finished pure rice vinegar.

[0046] Comparative Example 3

[0047] A production method of high - quality pure rice vinegar comprises the following steps:

[0048] S1 Raw material treatment: Select 100 kg of rice, which is plump and free from insect damage. After rinsing, add drinking water to submerge the rice surface. Control the water temperature at 35 - 45 °C, soak for 6 - 12 h, then fish out and grind into a slurry with a fineness of 40 - 80 mesh for standby; S2 Liquefaction and saccharification: Steam the rice slurry. After complete steaming, add 60 kg - 80 kg of water, adjust the pH to about 5 - 8, add α - amylase at 8 - 15 U / g, starch debranching enzyme at 1 - 5 U / g, and glucoamylase at 280 - 420 U / g, stir and mix evenly with the materials. Keep warm at 55 - 65 °C for more than 1 h for sufficient liquefaction and saccharification; S3 Alcohol fermentation: Cool the saccharified liquid to a temperature of 24 - 28 °C and add 1.0 - 1.2 kg of active dry yeast for brewing. Ensure the accuracy of temperature and ingredient ratio. Control the fermentation temperature below 28 °C. After aerobic fermentation at 18 - 28 °C for 30 - 45 days, the alcohol content reaches 6 - 8 vol%, with a normal aroma of new wine and no other abnormal odors; S4 Acetic acid fermentation: Transfer the fermented mash into a fermentation tank, and inoculate acetic acid bacteria in the fermentation tank for acetic acid fermentation until the total acid (calculated as acetic acid) is greater than 9.0 g / 100 ml; S5 Filtration treatment: The fermented rice vinegar is first preliminarily filtered through a 0.03 - 0.05 μm ceramic membrane, then diluted with water to 4.5 - 5.5 degrees. At room temperature of 25 - 27 °C, with a pressure of 0.39 - 0.54 MPa and a flux of 40 - 60 m 3 / h; S6 Nanofiltration: Use a new hollow fiber membrane with a membrane pore size of 1 - 10 nm and a retention molecular weight of 300 - 1000 kDa. At room temperature of 25 - 27 °C, with a pressure of 0.50 - 0.70 MPa and a flux of 80 - 110 m 3 / h; S7 Sterilization and filling: Sterilize and fill the finished product to obtain the finished pure rice vinegar.

[0049] Comparative Example 4

[0050] A production method of high - quality pure rice vinegar comprises the following steps:

[0051] S1 Raw material treatment: Select 100 kg of rice, which is plump and free from insect damage. After rinsing, add drinking water to submerge the rice surface. Control the water temperature at 35 - 45 °C, soak for 6 - 12 h, then fish out and grind into a slurry with a fineness of 40 - 80 meshes for standby; S2 Liquefaction and saccharification: Steam the rice slurry. After complete steaming, add 60 kg - 80 kg of water, adjust the pH to about 5 - 8, add α - amylase at 8 - 15 U / g, starch debranching enzyme at 1 - 5 U / g, and glucoamylase at 280 - 420 U / g, stir and mix evenly with the materials. Keep warm at 55 - 65 °C for more than 1 h for sufficient liquefaction and saccharification; S3 Alcohol fermentation: Cool the saccharified liquid to a temperature of 24 - 28 °C and add 1.0 - 1.2 kg of active dry yeast for brewing. Ensure the accuracy of temperature and ingredient ratio. Control the fermentation temperature below 28 °C. After aerobic fermentation at 18 - 28 °C for 30 - 45 days, the alcohol content reaches 6 - 8 vol%, with a normal aroma of new wine and no other abnormal odors; S4 Rice wine treatment: Let the rice wine stand and sediment for more than 12 - 18 h, and take the supernatant and pump it into the fermentation tank; S5 Acetic acid fermentation: Add acetic acid bacteria into the fermentation tank for acetic acid fermentation until the total acid (calculated as acetic acid) is greater than 9.0 g / 100 ml; S6 Filtration treatment: The finished rice vinegar is first pre - filtered through a 0.03 - 0.05 μm ceramic membrane and then diluted with water to 4.5 - 5.5 degrees. At room temperature of 25 - 27 °C, with a pressure of 0.39 - 0.54 MPa and a flux of 40 - 60 m 3 / h; S7 Nanofiltration: Use a new hollow fiber membrane with a membrane pore size of 1 - 10 nm and a molecular weight cut - off of 300 - 1000 kDa. At room temperature of 25 - 27 °C, with a pressure of 0.50 - 0.70 MPa and a flux of 80 - 110 m 3 / h; S8 Sterilization and filling: Sterilize and fill the finished product to obtain the finished pure rice vinegar.

[0052] Comparative Example 5

[0053] A production method of high - quality pure rice vinegar comprises the following steps:

[0054] S1 Raw material treatment: Select 100 kg of rice, which is plump and free from insect damage. After rinsing, add drinking water to submerge the rice surface. Control the water temperature at 35 - 45 °C, soak for 6 - 12 h, then fish out and grind into a slurry with a fineness of 40 - 80 meshes for standby; S2 Liquefaction and saccharification: Steam the rice slurry. After complete steaming, add 60 kg - 80 kg of water, adjust the pH to about 5 - 8, add α-amylase at 8 - 15 U / g, starch debranching enzyme at 1 - 5 U / g, and glucoamylase at 280 - 420 U / g, stir and mix evenly with the materials. Keep warm at 55 - 65 °C for more than 1 h for sufficient liquefaction and saccharification; S3 Alcohol fermentation: Cool the saccharified liquid to a temperature of 24 - 28 °C, add 1.0 - 1.2 kg of active dry yeast for brewing, ensure the accuracy of temperature and ingredient ratio. Control the fermentation temperature below 28 °C. After aerobic fermentation at 18 - 28 °C for 30 - 45 days, the alcohol content reaches 6 - 8 vol%, with a normal aroma of new wine and no other abnormal odors; S4 Rice wine treatment: Let the rice wine stand and sediment by itself for more than 12 - 18 h, take the supernatant for distillation until the alcohol content reaches 10 - 12 vol%, and pump the liquor into the fermentation tank; S5 Acetic acid fermentation: Inoculate acetic acid bacteria in the fermentation tank for acetic acid fermentation until the total acid (calculated as acetic acid) is greater than 9.0 g / 100 ml; S6 Filtration treatment: The matured rice vinegar is first preliminarily filtered through a 0.03 - 0.05 μm ceramic membrane and then adjusted with water to 4.5 - 5.5 degrees at room temperature of 25 - 27 °C and a pressure of 0.39 - 0.54 MPa; S7 Sterilization and filling: Sterilize and fill the finished product to obtain the finished pure rice vinegar.

[0055] Comparative example 6: Commercial pure rice vinegar 1.

[0056] Comparative example 7: Commercial pure rice vinegar 2.

[0057] The performance of the examples and comparative examples after detection and comparison is as shown in the following table:

[0058]

[0059] Conclusion:

[0060] As shown in the results of Table 1:

[0061] Adding starch debranching enzyme within the numerical range of the present invention can achieve the above technical effects. Among them, Example 1 is the best example. The optimal addition amount of starch debranching enzyme is 5 U / g, and the optimal fermentation temperature is 20 °C at low temperature. The results show that the non-volatile acid, salt-free solids, and ammonia nitrogen are high. And there is no abnormal odor and the color is transparent.

[0062] In comparative example 1, starch debranching enzyme was not added and the inorganic salt content was low after nanofiltration.

[0063] In comparative example 2, fermentation was carried out at normal temperature, and the contents of isoamyl alcohol and isoamyl acid were high, with abnormal odors, but less than those of commercial products.

[0064] Comparative Example 3: The normal rice wine mash was directly fermented into rice vinegar. The content of isovaleric acid in the wine was the highest, with a strong off-flavor and a slightly yellow color. However, even after nanofiltration, it was still lower than that of the commercially available products.

[0065] Comparative Example 4: The supernatant of rice wine was used for fermentation. The content of isovaleric acid was high, with an off-flavor, a light yellow color, and a low total acid content.

[0066] Comparative Example 5: Only ceramic membrane filtration was used, which was equivalent to the ordinary traditional process, with an off-flavor, a yellow color, and poor effects.

[0067] The results showed that the overall effect of the process of the present invention was good, and the sensory evaluation of the pure rice vinegar was good. The remaining physical and chemical indexes all met the requirements of GB / T 18187-2000 "Brewed Vinegar".

[0068] Although the present invention has been described above with reference to the embodiments, various improvements can be made to it and its components can be replaced with equivalents without departing from the scope of the present invention. In particular, as long as there is no structural conflict, the various features in the disclosed embodiments of the present invention can be combined with each other in any way. The exhaustive description of these combinations is not given in this specification only for the sake of saving space and resources. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing fragrant pure rice vinegar, characterized in that: The following steps are involved: S1 Raw material processing: Select full and insect-free rice and rinse it. After rinsing, add drinking water to cover the rice surface and soak it. After soaking, grind it into rice slurry for later use; S2 liquefaction and saccharification: steaming the rice slurry, adding water and adjusting the pH to 5-8 after it is completely steamed, then adding enzymes and stirring to fully mix it with the steamed rice slurry, reacting at 55-65° C. for more than 1 hour to perform liquefaction and saccharification to obtain saccharified liquid; preferably, the amount of water added is 0.6-0.8 times the mass of the raw rice; S3 alcohol fermentation: cooling the saccharified liquid to 24-28° C., then adding active dry yeast for fermentation to obtain fermented rice wine, wherein the alcohol content of the fermented rice wine is 6-8 vol%, with a normal new wine aroma and no other foreign odors; S4 rice wine treatment: the fermented rice wine is allowed to settle, and the supernatant is distilled to an alcohol content of 10-12 vol% to obtain refined fermented rice wine; S5 acetic acid fermentation: placing the refined fermented rice wine in a fermentation tank, inoculating acetic acid bacteria into the fermentation tank for acetic acid fermentation, and when the total acid is greater than 9.0 g / 100 ml in terms of acetic acid, the fermentation is completed to obtain new vinegar; S6 filtration: The new vinegar is first filtered through a 0.03-0.05 μm ceramic membrane and then water is added to adjust the concentration to 4.5-5.5 g / 100 mL to obtain a primary filtered vinegar solution; S7 Nanofiltration: The above-mentioned initially filtered vinegar solution is filtered again using a 1-10 nm new hollow fiber membrane with a molecular weight cutoff of 300-1000 kDa to obtain a nanofiltered vinegar solution; S8 sterilization and filling: sterilize and can the refined filtered vinegar liquid to obtain the fragrant pure rice vinegar.

2. The method for preparing the fragrant pure rice vinegar according to claim 1, characterized in that: In S1, the soaking water temperature is 35-45° C. and the soaking time is 6-12 hours.

3. The method for preparing the fragrant pure rice vinegar according to claim 1, characterized in that: In S1, the grinding particle size is 40-80 meshes.

4. The method for preparing the fragrant pure rice vinegar according to claim 1, characterized in that: In S2, the added enzyme is a mixture of 8-15 U / g of α-amylase, 1-8 U / g of starch debranching enzyme, and 280-420 U / g of saccharifying enzyme.

5. The method for preparing the fragrant pure rice vinegar according to claim 1, characterized in that: In S3, the amount of brewing active dry yeast added is 1.0-1.2 wt % of the rice mass.

6. The method for preparing the fragrant pure rice vinegar according to claim 1, characterized in that: In S3, the fermentation condition is 18-28° C. for at least 30-45 days.

7. The method for preparing the fragrant pure rice vinegar according to claim 1, characterized in that: In S4, the fermented rice wine is allowed to settle for 12 to 18 hours.

8. The method for preparing the fragrant pure rice vinegar according to claim 1, characterized in that: In S6, the initial filtration conditions are temperature 25-27°C, pressure 0.39-0.54MPa, ventilation volume 40-60m 3 / h.

9. The method for preparing the fragrant pure rice vinegar according to claim 1, characterized in that In S7, the nanofiltration conditions are temperature 25-27°C, pressure 0.50-0.70 MPa, flux 80-110 m 3 / h.

10. A rice vinegar, characterized in that Prepared by any of the above methods.

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