Red date table vinegar and preparation method thereof

Abstract

The invention discloses red date table vinegar and a preparation method thereof.The preparation method of the red date table vinegar mainly comprises the processes of precooking, enzymolysis, alcoholic fermentation and acetic fermentation, the red date table vinegar is mainly composed of red dates, water, pectinase and a leavening agent, and the leavening agent comprises saccharomycetes and lactic acid bacteria used for alcoholic fermentation and acetic bacteria used for acetic fermentation. The preparation process and formula of the red date table vinegar are optimized and improved by taking the total acid as an evaluation index, the red date table vinegar which is soft in sourness, mellow and fragrant, pure in color and luster and fragrant in sourness is finally obtained, the problems that the quality of a product obtained by an existing red date table vinegar preparation method is unstable, and the safety cannot be guaranteed are solved, and the production cost is reduced. And support is provided for large-scale production of the red date table vinegar.

Description

Technical Field

[0001] The present invention belongs to the field of vinegar production, and particularly relates to a production preparation method of red date vinegar. Background Art

[0002] Fruit vinegar uses the rich carbon source in fruits as the main fermentation substrate, and is brewed by alcohol fermentation and acetic acid fermentation using microorganisms such as yeasts and acetic acid bacteria. During the fermentation and aging processes of fruit vinegar, the microbial metabolism accumulates various flavor substances such as acids, esters, aldehydes, alcohols, aromatics, and terpenes, endowing it with a unique flavor. In addition, a number of studies have shown that fruit vinegar has health care effects such as blood sugar lowering, antioxidant, antidepressant, and anti-inflammatory properties.

[0003] Fruit vinegar can be classified into liquid fermentation and solid fermentation according to its fermentation method. The principle of both is that microorganisms use the nutrients in the fermentation substrate for alcohol fermentation and acetic acid fermentation, and are made after sterilization, aging, and clarification. There are obvious differences in the types and contents of volatile compounds and aroma characteristics of fruit vinegar obtained by the two different fermentation methods. Liquid fermentation has become a common fermentation method for fruit vinegar due to its advantages such as convenient operation, less contamination by miscellaneous bacteria, and scalable and standardized production.

[0004] Enterprises follow the traditional liquid fermentation process, with single raw materials and microorganisms for fermentation. Their red date vinegar products often have a light taste, poor aroma, a pungent sour aftertaste, and it is impossible to control the growth of microorganisms in the fermentation broth, and the fermentation broth is easily contaminated. In addition, the traditional natural aging process also has disadvantages such as a long cycle and difficult process control, which affect the fermentation cycle and the quality of red date vinegar, and is not conducive to the industrialized and standardized production of red date vinegar.

[0005] In view of the current situation of the difficulty in large-scale production of red date vinegar in the existing production of red date vinegar, especially the obvious differences in small-scale production, unstable product quality, inability to guarantee safety, and low production efficiency, a method suitable for large-scale production of red date vinegar, especially a red date vinegar and its production preparation method that are easy to carry out standard production, have stable product quality, and high production efficiency, have emerged as the times require. Summary of the Invention

[0006] The object of the present invention is to provide a method suitable for large-scale production of red date vinegar, especially a red date vinegar and its production preparation method that are easy to carry out standard production, have stable product quality, and high production efficiency.

[0007] The object of the present invention is mainly achieved by controlling comprehensive indexes such as total acid, alcohol content, pH value, soluble solids, and polysaccharide content during the production process, especially by carrying out alcohol fermentation and acetic acid fermentation separately during the fermentation process, thereby realizing precise control of the production indexes of red date vinegar.

[0008] The object of the present invention is achieved through the following process: The red date vinegar of the present invention mainly includes the processes of precooking, enzymatic hydrolysis, alcoholic fermentation, and acetic acid fermentation. The main raw materials are composed of red dates, water, pectinase, and a fermenting agent. The fermenting agent includes yeast and lactic acid bacteria for alcoholic fermentation, and acetic acid bacteria for acetic acid fermentation.

[0009] The preparation of the red date vinegar of the present invention includes the following steps.

[0010] Precooking: Based on 100 kg of red dates, weigh red dates and water in proportion, add water at 3 - 10 times the weight of the red dates, precook at 95 - 105 °C for 20 - 60 min, cool to room temperature, remove the pits, and make a pulp to obtain date juice.

[0011] Enzymatic hydrolysis: Add cellulase and pectinase to the date juice in proportion, carry out enzymatic hydrolysis at 45 - 55 °C and a pH value of 3.5 - 4.5 for 4 - 6 h. The ratio of pectinase to cellulase is 4:1 - 4:2 by weight.

[0012] Alcoholic fermentation: After the enzymatic hydrolysis, inoculate lactic acid bacteria and yeast in proportion for alcoholic fermentation. The inoculation amount is 3 - 5%, ferment at 30 - 35 °C and a pH value of 4 - 5 for 4 - 6 d. The ratio of yeast to lactic acid bacteria is 2:1 - 2:8.

[0013] Acetic acid fermentation: After the alcoholic fermentation, inoculate acetic acid bacteria with an inoculation amount of 4 - 8% for acetic acid fermentation, and ferment at 25 - 35 °C and a pH value of 4 - 6 for 7 - 10 d.

[0014] After the fermentation is completed, pasteurization can be adopted, or sterilization can be carried out at 80 - 105 °C for 20 - 40 min. High-temperature sterilization at 95 - 105 °C is preferred. After sterilization, it can be stored at a low temperature in an environment of 3 - 5 °C.

[0015] In the preparation method of the red date vinegar with total acid as the main evaluation index provided by the present invention, the best process for alcoholic fermentation is as follows: fermentation temperature 31 - 33 °C, sugar content 17 - 19%, inoculation amount 3 - 5%, the strains are yeast and lactic acid bacteria with a ratio of 1:3 - 1:4, pH value 4.4 - 4.6, and fermentation time 4 - 5 d. Under these conditions, the alcohol content reaches 8%.

[0016] In the preparation method of the red date vinegar with total acid as the main evaluation index provided by the present invention, the best process for acetic acid fermentation is as follows: fermentation temperature 28 - 32 °C, alcohol content 6 - 9%, inoculation amount 5 - 8%, pH value 4.8 - 5.2, shaker speed 150 - 200 r / min, and fermentation time 7 - 10 d. Under these conditions, it is better to control the total acid content at 5.01 ± 0.22 g / 100 mL.

[0017] Furthermore, in the above precooking, it is preferred to add water at 6 - 8 times the weight of the red dates.

[0018] Through the above technical solutions, the present invention achieves the following technical effects.

[0019] (1) The present invention provides a method for preparing red date vinegar with comprehensive indexes such as total acid, alcohol content, pH value, soluble solids, and polysaccharide content. By screening the pretreatment process of jujube juice, suitable fermentation strains, optimizing the strain ratio, and fermentation time and other technological processes in each processing link, and using total acid as the evaluation index, the preparation process and formula of red date vinegar are optimized and improved. Finally, the sensory quality of the obtained red date vinegar is significantly improved; the sour taste is mild, mellow and fragrant, the color is pure, and the sour smell wafts. After fermentation, a unique fragrance is produced and mixed with the fragrance of jujube juice and the odor coordination is good. The color is dark red and darker. After fermentation, the sour taste of the product has an obvious retention in the mouth, the taste is delicious, and the acidity is moderate, suitable for people of all ages.

[0020] (2) The present invention provides a method for preparing red date vinegar with total acid as the main evaluation index. Under the fermentation of yeast and lactic acid bacteria, through the determination of alcohol content, on the basis of not masking the flavor of red dates, the special flavor substances produced by the fermentation of yeast and lactic acid bacteria are mixed and volatilized with the flavor substances in the jujube juice, making the jujube juice have a unique odor and the alcohol content is moderate, and the sensory is greatly improved.

[0021] (3) The present invention provides a method for preparing red date vinegar with total acid as the main evaluation index. During the alcohol fermentation period, the fermentation time is effectively shortened through the mixed bacteria fermentation technology, and more acetic acid can be produced in a shorter time, quickly increasing the alcohol content of the jujube juice, providing a good fermentation environment for the subsequent acetic acid fermentation; at the same time, the total acid content of the product is increased, and the pH value of the product is reduced, which can effectively prevent the contamination of miscellaneous bacteria.

[0022] In the present invention, the red date juice jointly fermented by yeast and lactic acid bacteria during the alcohol fermentation process is richer in nutrients and has a stronger taste layer. At the same time, the alcohol content increases faster. On the basis of weakening the disadvantage of the poor taste of traditional single-strain fermented jujube vinegar, it also provides a good fermentation environment for acetic acid fermentation.

[0023] By screening the technological processes of various processing links such as the pretreatment process of jujube juice, suitable fermentation strains, optimizing the strain ratio, and fermentation time, etc., and taking the total acid as the main evaluation index, the preparation process and formula of red date vinegar were optimized and improved. Finally, the sensory quality of the obtained red date vinegar was significantly improved; the sour taste was mild, mellow and fragrant, the color was pure, and the sour smell was fragrant. After fermentation, a unique fragrance was produced and mixed with the fragrance of jujube juice and the odor coordination was good. The color was dark red and darker. The sour taste of the fermented product had an obvious retention in the mouth, the taste was delicious, and the acidity was moderate, suitable for people of all ages. It solved the problems of unstable product quality and unguaranteed safety in the existing preparation methods of red date vinegar, and provided support for the large-scale production of red date vinegar. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the single-factor optimization of the red date pre-cooking process in the present invention. Among them, A: single-factor optimization of pre-cooking temperature; B: single-factor optimization of pre-cooking time; C: single-factor optimization of solid-to-liquid ratio.

[0025] Figure 2 This is the optimization of the enzymatic hydrolysis process in the present invention. Among them, A: single-factor optimization of pectinase addition amount; B: single-factor optimization of the addition ratio of pectinase and cellulase.

[0026] Figure 3 This is the optimization of the enzymatic hydrolysis process in the present invention. Among them, A: single-factor optimization of enzymatic hydrolysis time of jujube juice; B: single-factor optimization of enzymatic hydrolysis temperature of jujube juice; C: single-factor optimization of enzymatic hydrolysis pH value of jujube juice.

[0027] Figure 4 This is the determination of the physicochemical properties of different lactic acid bacteria mixed fermentation of jujube wine in the present invention. Among them, Ⅰ: alcohol content; Ⅱ: soluble solids; Ⅲ: total acid; Ⅳ: pH value; A: Lactobacillus acidophilus; B: Lactobacillus plantarum; C: Lactobacillus fermentum; D: Lactobacillus casei; E: Lactobacillus bulgaricus; F: Bacillus subtilis.

[0028] Figure 5 This is the influence of inoculum size on the alcohol content of the fermentation broth in the present invention.

[0029] Figure 6 This is the influence of fermentation temperature on the alcohol content of the fermentation broth in the present invention.

[0030] Figure 7 This is the influence of pH value on the alcohol content of the fermentation broth in the present invention.

[0031] Figure 8 This is the influence of fermentation time on the alcohol content of the fermentation broth in the present invention.

[0032] Figure 9 This is the influence of sugar content on the alcohol content of the fermentation broth in the present invention.

[0033] Figure 10 For the optimization of acetic acid fermentation conditions in the present invention.

[0034] Figure 11 As shown in Table 1, it is the Box-Behnken test results of the enzymatic hydrolysis process optimization in the present invention.

[0035] Figure 12 As shown in Table 2, it is the variance analysis of the response surface test results in the present invention.

[0036] Figure 13 As shown in Table 3, it is the influence of the mixed bacteria ratio on the alcohol content and total acid of jujube vinegar during alcoholic fermentation in the present invention. Detailed implementation manners

[0037] The following examples are used to illustrate the present invention. However, the present invention is not limited to the following examples.

[0038] The red dates and bacterial powder used in the present invention can be purchased through public channels, and the equipment and instruments used in the process are common equipment in the field.

[0039] All the materials, experiments and determination methods of the instruments selected in the present invention are well-known in the art but do not limit the implementation of the present invention. Some other reagents and equipment well-known in the art can also be applied to the implementation of the following embodiments of the present invention.

[0040] Example 1: A preparation method of jujube vinegar, which consists of two fermentation processes: alcoholic fermentation and acetic acid fermentation. The main raw materials include red dates, water, pectinase and fermenting agent. The fermenting agent includes yeast and lactic acid bacteria for alcoholic fermentation, and acetic acid bacteria for acetic acid fermentation.

[0041] Taking 100 kg of red dates as the basic unit, add water according to 3 - 5 times the weight of the red dates, pre-cook at 95 - 105 °C for 20 - 60 min, cool to room temperature, and then remove the pits and make a pulp to obtain jujube juice.

[0042] Add cellulase and pectinase to the jujube juice in proportion, and carry out enzymatic hydrolysis at 45 - 55 °C and pH value of 3.5 - 4.5 for 4 - 6 h; the weight ratio of pectinase to cellulase is 4:1 - 4:2.

[0043] After the enzymatic hydrolysis, inoculate lactic acid bacteria and yeast in proportion for alcoholic fermentation, and ferment at 30 - 35 °C and pH value of 4 - 5 for 4 - 6 d. The strain is a mixed bacteria of yeast: lactic acid bacteria = 1:3 - 1:4, and the pH value is 4.4 - 4.6. Under this condition, the alcohol content can reach 7 - 10%.

[0044] After the alcohol fermentation is completed, inoculate acetic acid bacteria in proportion for acetic acid fermentation, and ferment at 25-35 °C and pH 4-6 for 7-10 d; after the fermentation is completed, sterilize at 95-105 °C for 20-40 min and store at low temperature of 3-5 °C. In the acetic acid fermentation, the inoculation amount of acetic acid bacteria is 5-8%, the pH value is 4.8-5.2, the shaking table speed is 150-200 r / min, and the fermentation time is 7-10 d. Under these conditions, it is better to control the total acid content at 5.01±0.22 g / 100 mL.

[0045] After the fermentation is completed, it can be pasteurized at 80-85 °C for 20-40 min and stored at low temperature of 3-5 °C. The sterilization is preferably carried out at 95-105 °C.

[0046] Example 2: In this example, Design-Expert.11 software was used for experimental design and variance analysis, Origin 2021 software was used for drawing, and SPSS 26 was used for variance analysis, with a significance level of 0.05. Each experiment was repeated 3 times, and the results were expressed as mean ± standard deviation.

[0047] Optimization of the precooking process: The weight ratio of the equivalent amount of red dates to the feed liquid is 1:5, and the precooking time is 30 min. The enzymolysis process is: enzymolysis at 50 °C, the addition amount of pectinase is 0.2%, the addition amount of cellulase is 0.067%, the pH value of enzymolysis is 5, and enzymolysis and filtration are carried out for 4 h.

[0048] Furthermore, 1:7 was selected as the optimal feed liquid ratio for the precooking process.

[0049] Optimization of the enzymolysis process: In order to fully enzymolyze the pectin and cellulose in red dates that are difficult to be utilized by fermenting bacteria and obtain sufficient fermentable sugars. Taking the extraction rate of jujube juice as an index, single factors such as the addition amount of pectinase, the ratio of pectinase to cellulase, enzymolysis time, enzymolysis temperature, and enzymolysis pH value were optimized for the process.

[0050] The optimal addition amount of pectinase was determined to be 0.18-0.22%, and the mixing ratio of pectinase to cellulase was best at 4:1.2-4:1.4.

[0051] The optimal enzymolysis temperature is 48-52 °C, and the pH value of the enzymolysis system is preferably 4.4-4.6.

[0052] The analysis results of the optimized enzymolysis process are shown in Table 1, which are the results of the Box-Behnken test for the optimized enzymolysis process.

[0053] Table 2 is the variance analysis of the response surface test results of the present invention.

[0054] As can be seen from Table 2, the optimal enzymatic hydrolysis temperature is 50.168 °C, the enzymatic hydrolysis time is 4.226 h, and the enzymatic hydrolysis pH value is 4.698. The theoretical alcohol content can reach 8.503%. Therefore, the optimal enzymatic hydrolysis process conditions are set as enzymatic hydrolysis temperature 50 °C, enzymatic hydrolysis time 4.2 h, and enzymatic hydrolysis pH value 4.7.

[0055] Physicochemical properties of jujube wine fermented by mixed strains of different lactic acid bacteria: Since the growth abilities of different lactic acid bacteria are different under different fermentation systems, in order to screen the most suitable lactic acid bacteria strains for jujube vinegar fermentation. Six lactic acid bacteria, namely Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus casei, Lactobacillus bulgaricus, and Bacillus subtilis, were used as representative strains and cultured in pure jujube juice and jujube juice inoculated with yeast respectively to observe their respective growth conditions.

[0056] In the examples, the physicochemical properties of jujube wine brewed by mixed strains of different lactic acid bacteria, including alcohol content, soluble solids, total acid content, and pH value, were measured. The different abilities of the six lactic acid bacteria to utilize sugars in jujube juice and their sugar-to-alcohol conversion abilities led to the alcohol content of the jujube wine after fermentation, as shown in Figure 4 Ⅰ, soluble solids, as shown in Figure 4 Ⅱ, with significant differences. Among them, Lactobacillus plantarum has the strongest sugar consumption and alcohol production abilities. The alcohol content of the jujube wine after 3 days of fermentation reaches 7.1%, and the soluble solids are 5.3%. Previously, it was verified that Lactobacillus plantarum has a strong ability to decompose jujube polysaccharides, decomposing the jujube polysaccharides that are difficult to be fermented and utilized into fermentable sugars, which may also be one of the reasons for the high sugar consumption and alcohol production rates of Lactobacillus plantarum in the fermentation of jujube wine. In addition, lactic acid bacteria will utilize the fermentable carbohydrates in jujube juice to produce acidic metabolites such as lactic acid and acetic acid, resulting in an increase in the TA content in the fermentation system ( Figure 4 Ⅲ), and a decrease in the pH value ( Figure 4 Ⅳ), providing an acidic environment for subsequent jujube vinegar fermentation and also endowing it with a unique lactic acid flavor. Among them, the jujube wine fermented by the mixed culture of Lactobacillus plantarum and yeast has the highest total acid content (0.83%), and the pH value is 3.55.

[0057] Lactobacillus plantarum has good growth ability in jujube juice and a strong ability to decompose jujube polysaccharides, and can decompose the sugars that are difficult to be fermented and utilized into fermentable carbon sources, thereby improving the fermentation efficiency. In addition, Lactobacillus plantarum has strong acid production and alcohol production abilities, which can provide a good fermentation environment for subsequent acetic acid fermentation. Therefore, Lactobacillus plantarum is selected as the lactic acid bacteria strain for mixed culture fermentation of jujube vinegar.

[0058] Optimization of the mixed culture jujube vinegar fermentation process: Regarding the influence of the mixed culture ratio on the alcohol content of jujube juice, the present invention preferably selects the ratio of yeast-Lactobacillus plantarum as 1:3 as the mixed culture fermentation ratio.

[0059] Table 3 shows the effects of the mixed culture ratio on the alcohol content and total acid of jujube vinegar alcohol fermentation.

[0060] The influence of inoculum size on the alcohol content of jujube juice is as Figure 5 , and the preferred inoculum size is selected as 4%.

[0061] The influence of fermentation temperature on the alcohol content of jujube juice is as Figure 6 , and the preferred fermentation temperature for mixed bacteria is 32 °C.

[0062] The influence of pH value on the alcohol content of jujube juice is as Figure 7 , and the preferred pH value is 5.

[0063] The influence of fermentation time on the alcohol content of jujube juice is as Figure 8 , and the preferred fermentation time for mixed bacteria alcohol fermentation is set as 4 d.

[0064] The influence of sugar content on the alcohol content of jujube juice. Too low sugar content will lead to low alcohol content in the fermentation broth and cannot meet the requirements of subsequent acetic acid fermentation; however, too high sugar content will result in too high alcohol content in the fermentation broth, which will not only affect the activities of yeast and lactic acid bacteria, but also inhibit the growth of acetic acid bacteria. The preferred sugar content for alcohol fermentation is 18%.

[0065] Optimization of the fermentation process in the acetic acid fermentation stage: As Figure 10 shown in A, with the increase of the inoculum size of acetic acid bacteria, the total acid content of jujube vinegar shows a trend of first increasing and then decreasing. When the inoculum size is 6%, the total acid content of jujube vinegar reaches the maximum value of 4.89 g / 100 mL. Therefore, the selected inoculum size of acetic acid bacteria is 6% as the most suitable. The total acid content first increases and then decreases with the increase of temperature, as Figure 10 shown in B. This is because acetic acid bacteria are sensitive to temperature. Too high or too low temperature will greatly affect the activity of acetic acid bacteria, making it difficult to maintain the growth and metabolism of acetic acid bacteria, resulting in a rapid decrease in acid production. Therefore, the selected fermentation temperature of 30 °C is appropriate, and the total acid content reaches 4.32 g / 100 mL at this time. The total acid content of jujube vinegar first continuously increases with the increase of fermentation time, but after continuous fermentation for 8 d, the total acid content gradually decreases Figure 10 as shown in C. This is because, in the later stage of fermentation, the acid production rate of acetic acid bacteria is lower than the acetic acid volatilization rate, resulting in a decrease in the total acid. As can be seen from Figure 10 D, the acid production ability of acetic acid bacteria in jujube wine with different alcohol contents varies greatly. The maximum total acid production reaches 4.80 g / 100 mL under the condition of 8% alcohol content. This is because too high alcohol content will inhibit the growth and metabolism of acetic acid bacteria, and alcohol is the main carbon source for acetic acid bacteria fermentation. When its content is too low, it will reduce the alcohol-to-acid conversion rate of acetic acid bacteria. Too high alcohol content in the fermentation environment will inhibit the activity of acetic acid bacteria. Therefore, 8% is selected as the optimal alcohol content of the fermentation broth. The pH value of the fermentation environment will also affect the activity of acetic acid bacteria. As Figure 10As can be seen from Table E, the optimum pH value is 5, and the maximum total acid production reaches 4.30 g / 100 mL at this time. Acetic acid bacteria are extremely aerobic microorganisms. To increase the dissolved oxygen content in the vinegar body, the acetic acid fermentation stage of the jujube vinegar in this experiment was carried out by shaking culture in a shaker. Therefore, a single-factor optimization of the shaker speed of the shaking incubator was carried out, as Figure 10 shown in Figure F. The total acid content of the jujube vinegar first increased and then decreased with the increase of the shaker speed. The total acid content reached the highest at 4.81±0.16 g / 100 mL when the shaker speed was 160 r / min. If the shaker speed is too slow, the dissolved oxygen in the fermentation system will be insufficient, reducing the activity of acetic acid bacteria. When the shaker speed is too fast, although acetic acid bacteria can fully contact oxygen, improving the activity of acetic acid bacteria and increasing the acid production rate, a large amount of volatile acid will volatilize from the fermentation broth, resulting in a decrease in the total acid content of the jujube vinegar after fermentation. Therefore, the shaker speed of 160 r / min was selected.

[0066] Based on the above data, the method for preparing red date vinegar provided by the present invention optimizes the processes of each processing link such as the pretreatment process and fermentation process of red date vinegar, and optimizes and improves the preparation process and formula of red date vinegar with the total acid as the evaluation index. Finally, the sensory quality of the obtained red date vinegar is significantly improved; the sour taste is soft, mellow and fragrant, the color is pure, and the sour smell is fragrant. After fermentation, a unique fragrance is produced and mixed with the fragrance of jujube juice and the odor coordination is good. The color is dark red and darker. The sour taste of the fermented product has an obvious retention in the mouth, the taste is delicious, and the acidity is moderate, suitable for people of all ages.

[0067] Compared with the red date vinegar fermented by single bacteria, this product has a shorter fermentation time, a richer taste, effectively reduces the production cost of the factory, and improves the nutritional value of the product at the same time. At the same time, for the mixed bacteria fermentation technology of lactic acid bacteria and yeast, more lactic acid and alcohol can be produced in a shorter time. The total acid content of the product increases, the pH value decreases, and the alcohol content increases, making it difficult for other miscellaneous bacteria to grow at a lower pH value, and the higher alcohol in the jujube juice provides a good environment for acetic acid fermentation.

[0068] The above embodiments are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for preparing red date vinegar, characterized in that: It mainly includes the processes of precooking, enzymatic hydrolysis, alcoholic fermentation and acetic acid fermentation. The main raw materials consist of red dates, water, pectinase and starter cultures. The starter cultures include yeast and lactic acid bacteria for alcoholic fermentation, and acetic acid bacteria for acetic acid fermentation. The specific process is as follows: Precooking: Based on 100 kg of red dates, weigh red dates and water in proportion, add water at 3 - 10 times the weight of red dates, precook at 80 - 105 °C for 20 - 60 min, cool to room temperature, remove the pits and make a pulp to obtain jujube juice; Enzymatic hydrolysis: Add cellulase and pectinase to the jujube juice in proportion, carry out enzymatic hydrolysis at 45 - 55 °C and pH value of 3.5 - 4.5 for 4 - 6 h. The ratio of pectinase to cellulase is 4:1 - 4:2 by weight; Alcoholic fermentation: After enzymatic hydrolysis, inoculate lactic acid bacteria and yeast in proportion for alcoholic fermentation. The inoculation amount is 3 - 5%, ferment at 30 - 35 °C and pH value of 4 - 5 for 4 - 6 d. The ratio of yeast to lactic acid bacteria is 2:1 - 2:8; Acetic acid fermentation: After alcoholic fermentation, inoculate acetic acid bacteria with an inoculation amount of 4 - 8% for acetic acid fermentation, and ferment at 25 - 35 °C and pH value of 4 - 6 for 7 - 10 d.

2. The preparation method of red date vinegar according to claim 1, wherein: In the alcoholic fermentation described above, the fermentation temperature is 31 - 33 °C, the sugar content is 17 - 19%, the inoculation amount is 3 - 5%, the strains are yeast and lactic acid bacteria with a ratio of 1:3 - 1:4, the pH value is 4.4 - 4.6, and the fermentation time is 4 - 5 d.

3. The preparation method of the red date vinegar according to claim 1 or 2, characterized in that: In the acetic acid fermentation described above, the fermentation temperature is 28 - 32 °C, the alcohol content is 6 - 9%, the inoculation amount is 5 - 7%, the pH value is 4.8 - 5.2, the shaker speed is 150 - 200 r / min, and the fermentation time is 7 - 10 d.

4. The preparation method of the red date vinegar according to claim 1 or 2, characterized in that: In the precooking described above, add water at 6 - 8 times the weight of red dates.

5. The preparation method of red date vinegar according to claim 3, characterized in that: In the precooking described above, add water at 6 - 8 times the weight of red dates.

6. A red date vinegar, characterized in that: Prepared by the method according to any one of claims 1 - 5.

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