Method for optimizing sake quality by grinding rice

Abstract

The invention relates to a method for optimizing the quality of sake by grinding rice. By selecting rice with the milling degrees of 80%, 70%, 60%, 50% and 40% and combining physicochemical property analysis, aroma component analysis and sensory analysis of the rice, a correlation model between the milling degrees of the rice and the flavor of the sake is established, and the sake production process can be optimized according to different market requirements. Experimental results show that the sake brewed from the rice with the grinding degree of 50% has the best nutritional ingredients, fragrance and taste, and is suitable for production of high-quality sake; the grinding degree is 70%, and 60% of rice provides balanced alcoholic strength and taste, so that the rice wine is suitable for the taste of the public; the rice with the grinding degree of 40% is suitable for rapid fermentation and high-alcoholic-strength sake production. The method provides a new thought for optimization of a sake production process, and the flavor and quality of the sake can be flexibly adjusted according to market requirements.

Description

Technical Field

[0001] The invention provides a method for optimizing sake quality by adjusting rice milling degree, and belongs to the fields of food processing and wine brewing. Background Art

[0002] Sake is a traditional Japanese fermented alcoholic beverage. Its flavor and quality are influenced by a variety of factors, with rice playing a crucial role in the sake-making process. The degree of rice milling (polishing ratio) is the percentage of the weight of the remaining rice after milling compared to the original weight of brown rice. The degree of milling directly affects the rice's physical and chemical properties, such as starch, protein, and fat content, which in turn significantly influence the sensory qualities of sake, including alcohol content, aroma, and taste during fermentation.

[0003] Currently, some technologies have been used to improve sake quality by optimizing rice milling degree, thereby enhancing product quality. However, these technical solutions are still insufficient in depth and breadth: (1) there is a lack of systematic research on the relationship between rice milling degree and sake quality; (2) there is a failure to comprehensively consider the synergistic effects of rice physical and chemical properties, milling degree, and fermentation process; (3) there is insufficient research on optimizing sake's aroma, taste, amino acids, and other sensory qualities, resulting in limited improvement in sake flavor and market adaptability.

[0004] Therefore, it is necessary to systematically study the physical and chemical properties of rice with different milling degrees and, combined with fermentation process optimization, propose an innovative method for optimizing sake flavor. Establishing a correlation model between rice milling degree and sake flavor can help optimize sake production processes for different market demands. Summary of the Invention

[0005] To address the challenges of existing technologies, the present invention provides a novel method for optimizing sake brewing. By analyzing the physical and chemical properties of rice with varying milling degrees, combined with flavor and sensory analysis, the present invention significantly improves the overall quality of sake, particularly in terms of aroma and taste, thereby meeting the diverse market demands for sake flavor and quality.

[0006] A first object of the present invention is to provide a method for optimizing the quality of sake by milling rice, wherein the rice used for brewing sake is pre-milled, and the rice obtained after the milling process has a milling degree of 40% to 70% and satisfies any one of the following conditions: a. The rice is milled to a degree of 50% to obtain Class I rice, which is brewed to obtain Class I sake, wherein the Class I sake has an alcohol content of 14.0-15.0%vol, a total sugar content of 1.10-1.30 g / L, and amino acid nitrogen of less than 1.10 g / L; a free amino acid content of 30-34 mg / mL, of which the content of bitter amino acids is less than 15 mg / mL, and the content of sour amino acids is less than 6.5 mg / mL; the content of volatile flavor substances is not less than 2500µg / L, of which the content of esters is not less than 550µg / L, the content of alcohols is 1800-1900µg / L, and the content of acids is 200-220µg / L; b. The rice is milled to a degree of 60%-70% to obtain Class II rice, which is brewed to obtain Class II sake, wherein the alcohol content of the Class II sake is 13.0-14.5% vol, the total sugar content is 1.30-1.60 g / L, the amino acid nitrogen content is 1.20-1.40 g / L; the free amino acid content is 40-43.0 mg / mL, wherein the bitter amino acid content is less than 18 mg / mL, and the sour amino acid content is 7.0-8.0 mg / mL; the volatile flavor substance content is not less than 1400µg / L, wherein the ester content is not less than 300µg / L, the alcohol content is 1000-1200µg / L, and the acid content is 60-140µg / L; c. The rice is milled to a degree of 40% to obtain Class III rice, which is then brewed to obtain Class III sake. The Class III sake has an alcohol content of 16.0-17.0% vol, a total sugar content of less than 1.00 g / L, and an amino acid nitrogen content of less than 1.10 g / L; a free amino acid content of less than 34 mg / mL, of which the content of bitter amino acids is less than 14 mg / mL, and the content of sour amino acids is less than 6.5 mg / mL; and a volatile flavor compound content of less than 1200 µg / L, of which the content of esters is less than 170 µg / L, the content of alcohols is less than 900 µg / L, and the content of acids is 120-130 µg / L.

[0007] Preferably, the alcohol content of the Class I sake is 14.0-15.0%vol, the total sugar content is 1.10-1.30 g / L, and the amino acid nitrogen content is 1.00-1.10 g / L; the free amino acid content is 33-34 mg / mL, of which the content of bitter amino acids is 13-14 mg / mL, and the content of sour amino acids is 6.0-6.5 mg / mL; the content of volatile flavor substances is 2600-2700µg / L, of which the content of esters is 550-580µg / L, the content of alcohols is 1800-1900µg / L, and the content of acids is 200-220µg / .

[0008] Preferably, the alcohol content of the Class II sake is 13.5-14.5%vol, the total sugar content is 1.30-1.60 g / L, and the amino acid nitrogen content is 1.20-1.40 g / L; the free amino acid content is 40.0-43.0 mg / mL, of which the content of bitter amino acids is 15-18 mg / mL, and the content of sour amino acids is 7.0-8.0 mg / mL; the content of volatile flavor substances is 1400-1600µg / L, of which the content of esters is 300-400µg / L, the content of alcohols is 1000-1200µg / L, and the content of acids is 60-140µg / L.

[0009] Preferably, the alcohol content of the Class III sake is 16.0-17.0% vol, the total sugar content is 0.60-1.00 g / L, and the amino acid nitrogen content is 1.00-1.10 g / L; the free amino acid content is 30-34 mg / mL, of which the content of bitter amino acids is 13-14 mg / mL, and the content of sour amino acids is 6.0-6.5 mg / mL; the content of volatile flavor substances is 1100-1200 μg / L, of which the content of esters is 160-170 μg / L, the content of alcohols is 800-900 μg / L, and the content of acids is 120-130 μg / L.

[0010] Preferably, the Class I rice has a total starch content of 85-86%, a protein content of 6.0-6.5%, and a fat content of 0.3-0.4%.

[0011] Preferably, the total starch content of the Class II rice is 84-85%, the protein content is 6.5%-6.8%, and the fat content is 0.64%-1.25%.

[0012] Preferably, the Class III rice has a starch content of 87.78%, a protein content of less than 6%, and a fat content of less than 0.3%.

[0013] Preferably, the milling method comprises: ridge-forming, removing unripe grains, whitening with a whiteness meter to obtain white rice and passing through a 100-mesh sieve.

[0014] Preferably, the grinding degree is calculated according to the following formula: Specifically, the present invention conducts an in-depth study on the relationship between rice milling degree and sake quality through the following technical steps, thereby optimizing the sake production process.

[0015] Preferably, the present invention provides a method for preparing sake, the specific steps are as follows: (1) Raw material preparation: soaking the milled rice, steaming it, and cooling it to obtain cooled rice; (2) preparing a rice saccharification liquid: mixing the rice with water, rice koji, a medium-temperature α-amylase, and a saccharifying enzyme to obtain a rice saccharification liquid; (3) preparing distiller's yeast: adding yeast at a ratio of 5% to the rice saccharification solution and fermenting until the sugar content is ≥13 brix to obtain distiller's yeast; (4) Preparing fermented liquor: The cooled rice, yeast, rice koji and water are mixed and then fermented. The yeast is added once, and the rice, rice koji and water are added three times according to proportion to obtain the sake.

[0016] Preferably, the soaking time of the rice in step (1) is 0-30 min, and the soaking water absorption rate is required to be around 30%; and the cooking time is 40-50 min.

[0017] Preferably, the cooling temperature of the rice in step (1) is 28-34°C.

[0018] Preferably, in step (2), the mass ratio of rice, water, rice koji, medium-temperature α-amylase and saccharifying enzyme is 30g:120g:15g:3g:1.5g.

[0019] Preferably, in step (3), the fermentation temperature is 60° C. and the fermentation time is 10-12 h.

[0020] Preferably, based on the initial addition amount of rice, the mass ratio of the rice, rice koji and distiller's yeast is 500g:125g:50g.

[0021] Preferably, based on the initial amount of rice added, the mass ratio of water to rice is 1.3:1.

[0022] Preferably, the feeding ratio of the three feedings is calculated by mass as follows: the first feeding is 20% of the total amount, the second feeding is 30% of the total amount, and the third feeding is 50% of the total amount.

[0023] Preferably, the fermentation is sealed fermentation; the temperature of the sealed fermentation is 10-15°C, the fermentation is 2 days after the first feeding, the fermentation is 1 day after the second feeding, and the fermentation is 15-20 days after the third feeding.

[0024] Preferably, after the feeding is completed, the fermentation time of the Class I rice is 18 days, the fermentation time of the Class II rice is 19 days, and the fermentation time of the Class III rice is 15 days.

[0025] The second object of the present invention is to provide a sake prepared according to any one of the above methods.

[0026] Preferably, the sake is Class I sake, Class II sake, or Class III sake.

[0027] Beneficial effects: The present invention aims to improve the flavor and quality of sake: by adjusting the degree of rice grinding, the present invention can significantly enhance the aroma and taste of sake and optimize the overall quality of sake. Experimental results show that: Sake brewed from rice with a 50% grinding degree has an alcohol content of 14.0-15.0%vol, a free amino acid content of 33-34 mg / mL, with bitter amino acids below 14 mg / mL; and a volatile flavor compound content of no less than 2600 µg / L, including esters of no less than 550 µg / L. This rice has the best nutritional profile, aroma, and taste, making it suitable for the production of high-quality sake. Sake brewed from rice with a grinding degree of 70% or 60% has an alcohol content of 13.0-14.5%vol, a free amino acid content of 40.0-43.0 mg / mL, of which the content of bitter amino acids is less than 18 mg / mL; and a volatile flavor compound content of no less than 1400µg / L, of which the content of esters is no less than 300µg / L, which is suitable for the tastes of most consumers and provides a balanced alcohol content and taste. Sake brewed from rice with a grinding degree of 40% has an alcohol content of 16.0-17.0%vol, a free amino acid content of less than 34mg / mL, of which the content of bitter amino acids is less than 14mg / mL; the content of volatile flavor substances is less than 1200µg / L, of which the content of esters is less than 170µg / L. It has a fresh and elegant taste, but the raw material loss is relatively high, making it suitable for the fast-moving consumer goods market.

[0028] Sake brewed from rice with an 80% grinding degree has a very low alcohol content (less than 13% vol), a free amino acid content higher than 43 mg / mL, of which the bitter amino acid content exceeds 18 mg / mL; the volatile flavor compound content is 1500-1600 µg / L, of which the ester content is less than 170 µg / L. It has too many off-flavors and an unharmonious taste, making it unsuitable for production.

[0029] Meeting diverse market demands: By establishing a correlation model between rice milling degree and sake quality, the present invention can adjust the flavor of sake according to market demand, meet the diverse taste demands of different consumers, and has strong market adaptability.

[0030] Improve the technical level of the sake industry: The present invention provides a scientific theoretical basis and operation scheme for the sake production process, improves the technical level and production efficiency of the sake industry, and promotes technological progress in the sake industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The raw materials of rice with different milling degrees prepared in Example 1 are shown; Figure 2 Flowchart of the sake brewing process; Figure 3 The finished product of sake obtained in Examples 2 to 6; Figure 4 Sensory evaluation charts of sake prepared in Examples 2 to 6; Figure 5 The principal component analysis diagrams of sake were obtained in Examples 2 to 6. DETAILED DESCRIPTION

[0032] The present invention will be further explained below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. If technicians in this field make some non-essential adjustments and improvements to the present invention based on the above content of the present invention, they still fall within the scope of protection of the present invention.

[0033] Rice milling process: rice - weighing - ridge milling - removal of unripe rice - whitening with whiteness meter - weighing - white rice with different grinding degrees.

[0034] The obtained polished rice was ground through a 100-mesh sieve and sealed for subsequent use.

[0035] Determination of moisture content: refer to GB5009.3-2016 "National Food Safety Standard Determination of Moisture in Food".

[0036] Determination of protein: Determine according to GB 5009.5-2016 "National Food Safety Standard - Determination of Protein in Foods".

[0037] Determination of fat: Determined in accordance with GB5009.6-2016 "National Food Safety Standard - Determination of Fat in Foods".

[0038] Determination of amylose: Determine according to GB / T 15683-2008 “Determination of amylose content in rice”.

[0039] Determination of total starch: Use a total starch kit for determination.

[0040] Brewing process: rice, yeast, rice koji - fermentation - filtration - centrifugation - sterilization.

[0041] Determination of alcohol content, total sugar, total acid, and amino acid nitrogen: refer to GB / T 13662-2018 "Yellow Wine".

[0042] Determination of amino acids: Determined according to QB / T 4356-2012 "Determination of free amino acids in rice wine by high performance liquid chromatography".

[0043] Determination of volatile flavor substances: Sake fermentation broth treatment: Dilute sake to 6% vol. Take 6 mL of the diluted sake and add it to a 20 mL headspace vial. Add 3.0 g of NaCl and 10 μL of internal standard (100 mg / L 2-octanol). Use a 50 / 30 μm DVB / CAR / PDMS extraction tip (conditioned at 250°C for 30 min before use). Adsorb at 50°C for 40 min and desorb at 250°C for 7 min for GC-MS analysis.

[0044] GC conditions: TG-WAXMS column (30 m × 0.25 μm × 0.25 mm), inlet temperature 250°C. Temperature program: 40°C for 3 min, then increase to 100°C at 6°C / min, then increase to 230°C at 10°C / min, and hold for 7 min.

[0045] Carrier gas: high-purity helium (>99.999%), splitless, flow rate: 1.0 mL / min.

[0046] MS conditions were as follows: EI ionization mode, emission current 50 μA, electron energy 70 eV, ion source temperature 230 °C, transfer line temperature 250 °C, and scan range 33–400 amu.

[0047] The internal standard method was used for semi-quantitative calculation. The specific calculation method is as follows: C i —Content of analyte in sake solution μg / L; C S —Concentration of internal standard μg / L; A i —peak area of ​​the analyte in sake liquid; As—peak area of ​​the internal standard.

[0048] Determination of sensory scores: Table 1 Sake sensory evaluation table Example 1 Preparation of rice with different grinding degrees Moisture determination: Use a moisture meter to measure the moisture content of rice grains to ensure that the moisture content of rice grains is below 18%; Ridge and rice: put the rice with qualified moisture into the rice ridger to remove the rice husk, 1000 g at a time, and weigh it; Remove unripe grains: Put the hulled brown rice into a thickness machine and sieve for 1 minute; Polishing: Select rice of relatively uniform size for milling; weigh 100 g of brown rice sample and pour it into the VP-32 rice polisher for milling. Weigh the rice after each polishing until the desired polishing degree is achieved. The polishing degree is calculated using the following formula: For specific products, see Figure 1 .

[0049] The five rices with different milling degrees (80%, 70%, 60%, 50%, and 40%) prepared in Example 1 were tested for nutritional component indicators. Each rice was used as a treatment, and three parallel experiments were conducted for each treatment. The results are shown in the table below.

[0050] Table 2 Chemical composition of rice with different milling degrees Table 2 shows that the moisture content of the five samples ranged from 12.53% to 13.05%, a variation likely due to friction between the rice grains and the inner wall of the mill. The total starch (dry basis) content increased slightly, ranging from 82.92% to 87.78%, while the amylose content varied from 9.76% to 10.55%, with no significant pattern. This may be related to the uneven distribution of starch content in the rice endosperm. Protein content varied significantly among the five samples, with the 80% milling degree being the highest, with the protein content of the 80% milling rice being 28.7% higher than that of the 40% milling rice. Fat content was higher in the 80% and 70% milling degrees, with fat contents being 709% and 468.1% higher than those of the 40% milling degree. Lipids in the outer layer of the rice grain are primarily present as acylglycerols or in a free form. Milling largely removes these lipids, resulting in a lower ratio of unsaturated fatty acids to total fatty acids in the rice, which facilitates ester formation during sake fermentation. Furthermore, protein and fat are key factors influencing rice gelatinization. Research has shown that protein and lipids increase the gelatinization and swelling resistance of starch granules. Protein forms a thin film around starch granules, inhibiting swelling and improving their high-temperature shear tolerance. Lipids not only form a protective layer on the surface of starch granules but also form starch-lipid complexes with the starch, improving the integrity of the starch granules and protecting them from damage. Low-milling rice has lower protein and lipid content, retaining more of the internal starch structure. This allows for stronger interaction with water during gelatinization, facilitating the dissolution of starch and amylose, and promoting saccharification and alcohol fermentation during sake fermentation.

[0051] Example 2 Preparation method of 80% rice brewed sake Sake brewing process Figure 2 As shown, the specific steps include: (1) Rice soaking: Weigh 300 g of rice with a grinding degree of 80% and wash it. After washing, add water to a container so that the water level does not exceed the rice. Soak for 30 minutes until the water absorption rate reaches about 30%, and obtain the soaked raw material.

[0052] (2) Steaming rice: Rinse the soaked rice in step (1) and steam it in a steamer. Pour hot water over the rice twice during the steaming process (taking 300 g as an example, generally 300 g is steamed for 40-45 min). The more rice you have, the longer it takes to steam. Steam the rice until there is no hard core and it breaks when you gently twist it with your fingernail. If the rice does not break, it is not yet cooked. Continue steaming until it is cooked and then let it cool to 32°C to obtain cooled rice.

[0053] (3) Rice saccharification liquid: Mix rice and water in a ratio of 1:4. Add 10% liquefaction enzyme, 5% saccharification enzyme, and 50% rice koji by weight, based on the amount of rice added. Saccharify in a 60°C water bath for approximately 8 h, until the sugar content reaches above 13°Brix. After saccharification, filter the liquid with gauze and place it in a conical flask. Sterilize the liquid by steam at 121°C for 15 min.

[0054] (3) Preparation of yeast: The activated yeast was inoculated into the above rice saccharification solution and cultured at 28°C for 24 h.

[0055] (4) Feeding: The yeast was added once, and steamed rice, rice koji, and water were added three times. The second feeding was done 2 days after the first feeding, and the third feeding was done 1 day after the second feeding. The three feeding ratios are shown in Table 3. Before adding the raw materials, the prepared yeast was placed in a 15℃ constant temperature box for standby use (water-rice ratio 1:1.3).

[0056] (5) Fermentation: Place the fermentation tank in step (4) in a constant temperature box at 15°C. Stir once every 12 hours after each feeding, and then do not stir again. After the third feeding, ferment in a constant temperature box at 15°C for 20 days.

[0057] (6) Filtration: First, filter the finished wine with gauze, then centrifuge at 5000 rpm for 10 min, and pour out the supernatant; (7) Sterilization: Sterilize at 68℃ for 30 min after canning.

[0058] The final finished sake is recorded as NFQP1, see Figure 3 .

[0059] Table 3 Three-time feeding ratio Example 3 Preparation method of 70% rice brewed sake The difference from Example 1 is that in step (1), 300 g of rice with a grinding degree of 70% is weighed to replace the rice with a grinding degree of 80% in Example 1. The final finished sake is recorded as NFQP2. The specific product is shown in Figure 3 .

[0060] Example 4 Preparation Method of 60% Rice Brewing Sake The difference from Example 1 is that in step (1), 300 g of rice with a grinding degree of 60% is weighed to replace the rice with a grinding degree of 80% in Example 1. The final finished sake is recorded as NFQP3. The specific product is shown in Figure 3 .

[0061] Example 5 Preparation method of 50% rice brewed sake The difference from Example 1 is that in step (1), 300 g of rice with a grinding degree of 50% is weighed to replace the rice with a grinding degree of 80% in Example 1. The final finished sake is recorded as NFQP4. The specific product is shown in Figure 3 .

[0062] Example 6 Preparation Method of 40% Rice Brewing Sake The difference from Example 1 is that in step (1), 300 g of rice with a grinding degree of 40% is weighed to replace the rice with a grinding degree of 80% in Example 1. The final finished sake is recorded as NFQP5. The specific product is shown in Figure 3 .

[0063] The chemical composition and aroma index of the five sakes (NFQP1, NFQP2, NFQP3, NFQP4, and NFQP5) prepared in Examples 2 to 6 were tested. Each sake was treated as one, and three parallel experiments were conducted for each treatment. The results are shown in the table below.

[0064] Table 4 Chemical composition of sake brewed from rice with different milling degrees Total acidity and pH are important indicators of sake quality. Excessively low acidity cannot inhibit bacterial growth and prevents proper yeast growth and reproduction, while excessive acidity can affect the overall flavor balance of sake. Table 4 shows that the pH of the five sakes ranged from 4.66 to 4.82. Total acidity was highest in NFQP2 and NFQP3. A total acidity exceeding 4 g / L results in a pronounced sourness and an unbalanced flavor. A total acidity of 3.7-3.9 g / L is optimal for yeast growth. NFQP1 has a high total sugar content but an alcohol content of less than 13% vol, indicating incomplete fermentation and failing to meet the standard for sake alcohol content. NFQP2, NFQP3, and NFQP4 have moderate total sugar content and alcohol content. NFQP5 has a total sugar content of less than 1.0 g / L and an alcohol content exceeding 16% vol, indicating more complete fermentation within a short period of time. This indicates that as the degree of milling decreases, the rice becomes increasingly gelatinized, making starch more easily hydrolyzed into fermentable sugars by enzymes. This ultimately leads to yeast metabolism and the production of more alcohol, improving the quality of sake. Amino acid nitrogen content is another key parameter for evaluating sake quality. Excessive amino acid nitrogen can impart a bitter taste to sake. Additionally, amino acid nitrogen can be used to measure the degree of rice fermentation and protein hydrolysis. NFQP1 has an amino acid nitrogen value exceeding 1.5 g / L. Excessive amino nitrogen produces excessive bitter amino acids, leading to a pronounced bitterness in sake. NFQP2 and NFQP3 have more moderate amino nitrogen values, while NFQP4 and NFQP5 have values ​​below 1.20 g / L, which are optimal for sake brewing.

[0065] Table 5 Amino acid composition of sake brewed with rice of different milling degrees Table 5 shows that the free amino acid content of the five sakes varies considerably. NFQP1 has the highest total amino acid content, while NFQP2 and NFQP3 have amino acid contents of 42-43 mg / mL, which are moderate values ​​for fermented sake. NFQP1's bitter amino acid content exceeds 18 mg / mL, resulting in a pronounced bitterness. NFQP4 and NFQP5 have bitter amino acid contents below 14 mg / mL, representing optimal values ​​for sake brewing, indicating that milling has alleviated the excessive bitterness of sake. Sweet and umami amino acids decreased slightly, indicating that milling gradually softens the sake's taste, resulting in a lighter, more refreshing flavor. Sour and aromatic amino acids also exhibit subtle differences with milling treatment, with NFQP1 having the highest content. The order of flavor amino acid content in sake, from highest to lowest, is bitter amino acids > sour amino acids > sweet amino acids > umami amino acids. The reduction in bitter and sour amino acids is most significant, reducing the excessive bitterness and sourness in sake. This shows that reducing the grinding degree not only affects the total content of amino acids in sake, but also adjusts the ratio of the four amino acids, thereby achieving the effect of blending the flavor of sake.

[0066] Table 6 Flavor composition of sake brewed with rice of different milling degrees Table 6 shows significant differences in the flavor compounds of the five sake samples. NFQP4's total volatile flavor compound content exceeded 2600 µg / L, the optimal value for sake brewing. This indicates that moderate milling (50% milling) significantly increases the flavor compound content in sake. However, a 40% milling significantly decreases the flavor compound content, resulting in a bland taste. Alcohols and esters in sake form the backbone of its aroma, while acids are important flavor compounds in rice wine. Alcohols and acids are also important precursors of ester compounds produced during wine aging. Ester content varied significantly among the five samples. NFQP4 exceeded 500µg / L, reaching the optimal value for sake brewing. NFQP2 and NFQP3 ranged from 300-350µg / L, a moderate value for sake brewing. When over-grinded to 40% grinding, ester content fell below 170µg / L, a significant 246.2% reduction compared to NFQP4. NFQP4 also achieved optimal alcohol and acid content, exceeding NFQP1 by 46.1% and 136.3%, respectively.

[0067] Sensory analysis: Invite 10 sake tasting experts to conduct a blind test and score the wines. The scoring content includes color, aroma, taste and style. Figure 4 As shown, among the five sakes, NFQP5 is the clearest and most transparent, without sediment or impurities; NFQP4 has the strongest aroma, with a pure and elegant mellow fragrance, followed by NFQP5; NFQP2 and NFQP3 have strong aromas without foreign aromas, and NFQP1 has no obvious mellow aroma; NFQP4 has the best taste, with a soft and rich taste, a harmonious taste, and a relatively mellow taste; NFQP2, NFQP3, and NFQP5 have a mellow taste with a slight off-flavor (slightly bitter, slightly sour); NFQP1 has a thin and unharmonious body, with obvious off-flavors; NFQP3, NFQP4, and NFQP5 have a pure and light fragrance with a distinctive style; NFQP2 has a more harmonious body that suits the taste of the general public, while NFQP1 has an unharmonious body, a general style, and lacks elegance.

[0068] Analysis of the optimal rice grinding degree: The chemical composition, free amino acid content, key volatile flavor compounds and sensory scores of sake were used as evaluation indicators to conduct principal component analysis on sake brewed with rice of different grinding degrees. Figure 5 The red dots in the figure represent the scores (95% confidence ellipses) of sake samples brewed with rice of different polishing rates.

[0069] As can be seen in the figure, sake samples with different rice polishing rates are distributed in different quadrants. Samples in the first quadrant scored higher in flavor, aroma, and taste, indicating that NFQP4 sake scores well in these areas. While achieving a rich flavor content and high sensory scores, it also minimizes waste caused by over-grinding. The optimal milling degree is 50%, and sake brewed with rice polished to a 50% milling degree is considered Class I sake.

[0070] NFQP2 and NFQP3 sakes scored higher in terms of free amino acids and chemical composition, and were classified as Class II sakes.

[0071] Sake brewed from rice with a grinding degree of NFQP5 has excellent alcohol content, but the content of flavor substances is too low and the taste is light, so it is classified as Class III sake.

[0072] The amino acid content of NFQP1 sake is too high, resulting in a strong off-flavor, an unbalanced body, and a low sensory score, making it a Class IV sake.

[0073] In summary, the use of the milled rice provided by the present invention to prepare sake greatly improves the flavor and sensory properties of sake. Based on the data of chemical composition, free amino acid content, flavor substance content and sensory score, the five kinds of sake were classified and a comprehensive analysis showed that: a. The total volatile flavor compound content of sake brewed with rice of 50% grinding degree increased by 71.6% compared with that of 80%, of which the content of esters increased by 231.7%; the free amino acid content decreased to the moderate value of 30-34 mg / mL for fermented sake, and the sensory score increased significantly, indicating that the quality of sake was significantly improved. This was defined as Class I sake. The alcohol content of Class I sake was 14.0-15.0%vol, the total sugar content was 1.10-1.30 g / L, and the amino acid nitrogen content was less than 1.10 g / L; the free amino acid content was 30-34 mg / mL, of which the content of bitter amino acids was less than 15 mg / mL, and the content of sour amino acids was less than 6.5 mg / mL; the content of volatile flavor substances is not less than 2500µg / L, of which the content of esters is not less than 550µg / L, the content of alcohols is 1800-1900µg / L, and the content of acids is 200-220µg / L; b. Sake brewed from rice with a grinding degree of 70% and 60% had a moderate content of total volatile flavor compounds, with ester content increasing by 90.9% and 85.4% compared to rice with a grinding degree of 80%, reaching moderate values. The sensory scores were moderate, in line with general tastes, and were defined as Class II sake. This Class II sake had an alcohol content of 13.0-14.5%vol, a total sugar content of 1.30-1.60g / L, and an amino acid nitrogen content of 1.20-1.40g / L. The free amino acid content was 40.0-43 mg / mL, with the bitter amino acid content below 18mg / mL and the sour amino acid content of 7.0-8.0 mg / mL. The volatile flavor compound content was no less than 1400.0 µg / L, with the ester content no less than 300 µg / L, the alcohol content of 1000-1200µg / L, and the acid content of 60-140µg / L. c. Sake brewed from rice with a grinding degree of 40% has a volatile flavor compound content of less than 1200 µg / L and a free amino acid content of less than 34 mg / mL. It has a light and refreshing taste, but the raw material loss is relatively high, making it suitable for the fast-moving consumer market. This is defined as Class III sake. The alcohol content of Class III sake is 16.0-17.0%vol, the total sugar content is less than 1.00g / L, and the amino acid nitrogen content is less than 1.10g / L; the free amino acid content is less than 34 mg / mL, of which the bitter amino acid content is less than 14 mg / mL and the sour amino acid content is less than 6.5mg / mL; the volatile flavor compound content is less than 1200 µg / L, of which the ester content is less than 170 µg / L, the alcohol content is less than 900µg / L, and the acid content is 120-130µg / L; d. Sake brewed from rice with an 80% grinding degree has an alcohol content of less than 13% vol, which does not meet the standard. The free amino acid content is greater than 43 mg / mL, of which the bitter amino acid content exceeds 18 mg / mL. The ester content of volatile flavor substances is less than 170 µg / L, resulting in an unbalanced wine body and a low sensory score. It is not suitable for production and is defined as Class IV sake. This Class IV sake has an alcohol content of less than 13% vol, a free amino acid content greater than 43 mg / mL, and a volatile flavor substance content of 1500-1600 µg / L, of which the ester content is less than 170 µg / L.

[0074] This paper establishes a correlation model between rice milling degree and sake flavor, which can optimize sake production process according to different market demands: High-end market: Using rice with a grinding degree of 50% to brew sake, producing high-end sake with complex aroma and rich body; Mass market: Sake brewed with rice of 70% and 60% grinding degrees provides moderate alcohol content and a balanced taste, with a moderate content of flavor substances, meeting the needs of the general public; Fast-moving consumer goods market: Utilizing the high-speed fermentation characteristics of 40% milled rice, high-alcohol, fast-fermenting sake is produced.

[0075] It should be understood that the above detailed embodiments of the present disclosure are merely for the purpose of illustrating or explaining the principles of the present disclosure, and are not intended to limit the present invention. Therefore, any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present disclosure shall be included within the scope of protection of the present invention.

Claims

1. A method for optimizing sake quality by milling rice, characterized in that: The rice used for sake brewing is pre-milled, and the rice obtained after milling has a grinding degree of 40%-70% and meets any of the following conditions: a. The rice is milled to a degree of 50% to obtain Class I rice, which is brewed to obtain Class I sake, wherein the Class I sake has an alcohol content of 14.0-15.0%vol, a total sugar content of 1.10-1.30 g / L, and amino acid nitrogen of less than 1.10 g / L; a free amino acid content of 30-34 mg / mL, of which the content of bitter amino acids is less than 15 mg / mL, and the content of sour amino acids is less than 6.5 mg / mL; a content of volatile flavor substances of not less than 2500µg / L, of which the content of esters is not less than 550µg / L, the content of alcohols is 1800-1900µg / L, and the content of acids is 200-220µg / L; b. The rice is milled to a degree of 60%-70% to obtain Class II rice, which is brewed to obtain Class II sake, wherein the alcohol content of the Class II sake is 13.0-14.5% vol, the total sugar content is 1.30-1.60 g / L, the amino acid nitrogen content is 1.20-1.40 g / L; the free amino acid content is 40-43.0 mg / mL, wherein the bitter amino acid content is less than 18 mg / mL, and the sour amino acid content is 7.0-8.0 mg / mL; the volatile flavor substance content is not less than 1400µg / L, wherein the ester content is not less than 300µg / L, the alcohol content is 1000-1200µg / L, and the acid content is 60-140µg / L; c. The rice is milled to a degree of 40% to obtain Class III rice, which is then brewed to obtain Class III sake. The Class III sake has an alcohol content of 16.0-17.0% vol, a total sugar content of less than 1.00 g / L, and an amino acid nitrogen content of less than 1.10 g / L; a free amino acid content of less than 34 mg / mL, of which the content of bitter amino acids is less than 14 mg / mL, and the content of sour amino acids is less than 6.5 mg / mL; and a volatile flavor compound content of less than 1200 µg / L, of which the content of esters is less than 170 µg / L, the content of alcohols is less than 900 µg / L, and the content of acids is 120-130 µg / L.

2. The method according to claim 1, characterized in that The Class I sake has an alcohol content of 14.0-14.5%vol, a total sugar content of 1.10-1.30 g / L, and an amino acid nitrogen content of 1.00-1.10 g / L; a free amino acid content of 33-34 mg / mL, of which the bitter amino acid content is 13-14 mg / mL and the sour amino acid content is 6.0-6.5 mg / mL; a volatile flavor substance content of 2600-2700µg / L, of which the ester content is 550-580µg / L, the alcohol content is 1800-1900µg / L, and the acid content is 200-220µg / L; and / or Preferably, the alcohol content of the Class II sake is 13.5-14.5% vol, the total sugar content is 1.30-1.60 g / L, the amino acid nitrogen content is 1.20-1.40 g / L; the free amino acid content is 40.0-43.0 mg / mL, of which the bitter amino acid content is 15-18 mg / mL, and the sour amino acid content is 7.0-8.0 mg / mL; the volatile flavor substance content is 1400-1600 μg / L, of which the ester content is 300-400 μg / L, the alcohol content is 1000-1200 μg / L, and the acid content is 60-140 μg / L; and / or Preferably, the alcohol content of the Class III sake is 16.0-17.0% vol, the total sugar content is 0.6-1.00 g / L, and the amino acid nitrogen content is 1.00-1.10 g / L; the free amino acid content is 30-34 mg / mL, of which the content of bitter amino acids is 13-14 mg / mL, and the content of sour amino acids is 6.0-6.5 mg / mL; the content of volatile flavor substances is 1100-1200 μg / L, of which the content of esters is 160-170 μg / L, the content of alcohols is 800-900 μg / L, and the content of acids is 120-130 μg / L.

3. The method according to claim 1, characterized in that The Class I rice has a total starch content of 85-86%, a protein content of 6.0-6.5%, and a fat content of 0.3-0.4%; and / or Preferably, the total starch content of the Class II rice is 84-85%, the protein content is 6.5%-6.8%, and the fat content is 0.64%-1.25%; and / or Preferably, the total starch content of the Class III rice is 87.78%, the protein content is less than 6%, and the fat content is less than 0.3%.

4. The method according to claim 1, wherein The milling method comprises: ridge rice, removing unripe grains, polishing rice with a polishing meter to obtain polished rice, and passing the polished rice through a 100-mesh sieve; The grinding degree is calculated according to the following formula: 。 5. The method according to claim 1, characterized in that The method for brewing sake comprises the following steps: (1) Raw material preparation: soaking the milled rice, steaming it, and cooling it to obtain cooled rice; (2) preparing a rice saccharification liquid: mixing the rice with water, rice koji, a medium-temperature α-amylase, and a saccharifying enzyme to obtain a rice saccharification liquid; (3) preparing distiller's yeast: inoculating yeast at a ratio of 5% into the rice saccharification solution and fermenting until the sugar content reaches ≥13 brix to obtain distiller's yeast; (4) Preparing fermented liquor: The cooled rice, yeast, rice koji and water are mixed and then added for fermentation. The yeast is added once, and the rice, rice koji and water are added three times according to a certain proportion to obtain sake.

6. The method according to claim 5, characterized in that In the step (1), the soaking time of the rice is 0-30 min, and the soaking water absorption rate is required to be 30%-40%; the cooking time is 40-50 min; and / or Preferably, the cooling temperature of the rice in step (1) is 28-34° C.; and / or Preferably, in step (2), the mass ratio of rice, water, rice koji, medium-temperature α-amylase and saccharifying enzyme is 1:4:0.5:0.1:0.

05.

7. The method according to claim 5, characterized in that Preferably, in step (3), the fermentation temperature is 60°C and the fermentation time is 10-12 h; and / or Preferably, based on the initial addition amount of rice, the mass ratio of the rice, rice koji and distiller's yeast is 1:0.25:0.1; and / or Preferably, the mass ratio of water to rice is 1.3:1 based on the initial amount of rice added; and / or Preferably, the feeding ratio of the three feedings is calculated by mass as follows: the first feeding is 20% of the total amount, the second feeding is 30% of the total amount, and the third feeding is 50% of the total amount; and / or Preferably, the fermentation is sealed fermentation; the temperature of the sealed fermentation is 10-15°C, the fermentation is 2 days after the first feeding, the fermentation is 1 day after the second feeding, and the fermentation is 15-20 days after the third feeding.

8. The method according to any one of claims 1 to 7, characterized in that: After the feeding is completed, the fermentation time of the Class I rice is 16-18 days, the fermentation time of the Class II rice is 19-21 days, and the fermentation time of the Class III rice is 14-16 days.

9. Sake prepared according to any one of claims 1 to 8.

10. The sake according to claim 9, characterized in that The sake is Class I sake, Class II sake, or Class III sake.

Images