Method for improving quality of yellow clay for making pit mud

Abstract

This invention discloses a method for improving the quality of yellow clay used in cellar mud production, belonging to the field of brewing technology. The method involves inoculating yellow clay with *Lactobacillus paracasei* seed culture into MRS medium for anaerobic static cultivation. *Lactobacillus paracasei* weathers iron minerals, reducing the total iron and iron mineral content in the yellow clay. After cultivation, the upper culture medium is discarded, and the precipitate is collected to obtain improved yellow clay with significantly reduced iron content. Baijiu fermented using the improved yellow clay of this invention has a higher content of flavor compounds and better quality compared to baijiu prepared from unimproved yellow clay. This method for improving yellow clay quality is simple, low-cost, and widely applicable, effectively solving the problem of excessively high iron content in the original yellow clay used in existing cellars for preparing Luzhou-style baijiu.

Description

Technical Field

[0001] This invention belongs to the field of brewing technology and relates to the raw material of cellar mud used to make fermentation tanks for Luzhou-style baijiu. Specifically, it relates to a method for improving the quality of yellow mud used to make cellar mud. Background Technology

[0002] The most typical characteristic of strong-aroma baijiu brewing, exemplified by Luzhou Laojiao, is the use of mud-based fermentation pits for solid-state anaerobic fermentation. The pit mud is not only an important carrier for the growth and reproduction of various functional microorganisms in strong-aroma baijiu production, but also provides abundant nutrients for their growth and reproduction, facilitating the simultaneous saccharification and alcoholic fermentation of the brewing raw materials. However, the aging time of natural pit mud is at least 20 years, which has prompted attempts to shorten the aging time of new pits to improve the yield and quality of baijiu.

[0003] To date, research on promoting the aging of pit mud has mainly focused on adjusting the pit mud formula and inoculating functional bacteria such as caproic acid bacteria into the pit mud. In addition, existing literature indicates that changes in iron content are also an important potential factor affecting pit mud aging. For example, Zhuo Zhonghui (2002) found that a significant increase in the content of active iron (water-soluble iron, exchangeable iron, and complexed iron) in degraded pit mud is detrimental to the microbial activity of the pit mud. Xiang Zongfu (2007) believes that low active iron content can be considered a typical physicochemical characteristic of aged pit mud. Jiao et al. (2023) found that the total iron and free iron mineral content in pit mud decreased significantly with increasing pit age, suggesting that excessively high iron content in young pit mud may hinder the aging process. In summary, these studies all indicate that the iron content of pit mud is a crucial factor that must be controlled during pit mud preparation.

[0004] Yellow clay, an essential raw material for pit mud production, contributes the majority of the iron in the resulting pit mud. Therefore, the physicochemical properties of yellow clay significantly determine the quality of the pit mud. If the yellow clay itself has a high iron content and a poor physicochemical environment, the functional bacteria in the pit mud will struggle to grow and reproduce, failing to achieve the goal of rapidly improving the pit mud. To produce high-quality pit mud, it is necessary to reduce the iron content of yellow clay, a crucial raw material. Therefore, a method for improving the quality of yellow clay used in pit mud production requires further research. Summary of the Invention

[0005] The technical problem this invention aims to solve is the excessively high iron content in the original yellow mud used for preparing Luzhou-style baijiu fermentation pits. To address the issues in existing technologies, this invention provides a method that can quickly and effectively reduce the total iron and iron mineral content in the original yellow mud. Furthermore, this invention also tested the fermentation effect of the improved yellow mud.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for improving the quality of yellow clay used in the production of pit mud, comprising the following steps:

[0007] a. Pretreatment of yellow mud;

[0008] b. Add MRS medium to the pretreated yellow mud and inoculate with Lactobacillus paracasei seed culture for culture;

[0009] c. After cultivation, the upper liquid is extracted, and the resulting precipitate is the improved yellow mud with enhanced quality.

[0010] In the above-mentioned method for improving the quality of yellow mud, step a involves pretreatment to remove stones, roots and other impurities from the yellow mud, then grinding large soil particles and passing them through a 10-mesh sieve.

[0011] In the above-mentioned method for improving the quality of yellow clay, in step a, the total iron content in the yellow clay is 28.64–33.21 g / kg, the crystalline iron mineral content is 6.13–8.81 g / kg, the amorphous iron (hydrogen) oxide content is 4.32–6.37 g / kg, the pH value is 6.35–7.72, and the water content is 7.69–10.98%.

[0012] In the above-mentioned method for improving the quality of yellow mud, in step b, the mass-to-volume ratio of pretreated yellow mud to MRS culture medium is 1500g:700-1000mL.

[0013] In the above-mentioned method for improving the quality of yellow clay, step b involves using a Lactobacillus paracasei seed culture concentration of 8 × 10⁻⁶. 8 Inoculate the seed culture at a concentration of cfu / mL, at a volume of 25-40% of the MRS medium, and then mix it evenly with yellow mud.

[0014] Furthermore, the above-mentioned method for preparing Lactobacillus paracasei seed culture is as follows: inoculate 1-2 loops of Lactobacillus paracasei into MRS medium, seal the medium, and then culture it in a shaker at 37°C and 180 rpm for 10 hours to prepare the seed culture.

[0015] Furthermore, the composition (g / L) of the aforementioned MRS medium (DeMan-Rogosa-Sharpe medium, a medium specifically designed for the proliferation of Lactobacillus) is as follows: glucose 20.0, peptone 10.0, beef extract 5.0, yeast extract 4.0, sodium acetate 5.0, diammonium hydrogen citrate 2.0, dipotassium hydrogen phosphate 2.0, magnesium sulfate heptahydrate 0.2, manganese sulfate monohydrate 0.05, and Tween 80 1.0. The pH of the medium is approximately 6.5, and it is sterilized at 115°C for 30 minutes.

[0016] In the above-mentioned method for improving the quality of yellow clay, step b involves a culture condition of anaerobic static culture at 37℃ for 15–20 days.

[0017] In the above-mentioned method for improving the quality of yellow clay, step c involves improving the yellow clay to have a total iron content of 25.33–28.21 g / kg, a crystalline iron mineral content of 4.73–7.48 g / kg, an amorphous iron (hydrogen) oxide content of 3.02–4.36 g / kg, a pH value of 4.56–5.86, and a water content of 18.41–21.81%.

[0018] This invention provides the application of improved yellow mud obtained by the above-mentioned method for improving the quality of yellow mud used in cellar mud production in the fermentation of strong-aroma baijiu.

[0019] The beneficial effects of this invention are as follows: This invention utilizes *Lactobacillus paracasei*, a bacterium with strong weathering ability, to weather iron-containing minerals in yellow clay, effectively reducing the total iron and iron mineral content in the yellow clay. The lactic acid produced by *Lactobacillus paracasei* during its growth in yellow clay inhibits other bacteria in the clay, making the clay environment more suitable for the growth and reproduction of Daqu (fermentation starter) microorganisms. Baijiu (Chinese liquor) fermented using the improved yellow clay of this invention has a higher content of flavor compounds and is of better quality compared to baijiu made from unimproved yellow clay.

[0020] This invention presents a method for preparing improved yellow clay using Lactobacillus paracasei weathering yellow clay. This method is simple, inexpensive, and widely applicable. The yellow clay quality improvement method of this invention solves the problem of excessively high iron content in the original yellow clay, providing a new research approach for subsequently improving the quality of cellar mud and enhancing the quality of baijiu (Chinese liquor). Attached Figure Description

[0021] Figure 1 The images show the XRD characterization of the mineral components of Example 1, Example 1 Control, and the original yellow clay of the present invention. Detailed Implementation

[0022] The technical solution of the present invention can be implemented in the following manner.

[0023] The method for improving the quality of yellow clay used in making pit mud includes the following steps:

[0024] a. Yellow mud pretreatment: Remove stones, roots and other debris from the yellow mud, then grind large soil particles and pass them through a 10-mesh sieve;

[0025] b. Add 700-1000 mL of LMR S medium to 1500 g of pretreated yellow mud, and inoculate with 250-300 mL of Lactobacillus paracasei seed culture. Mix well and incubate at 37°C for anaerobic static culture for 15-20 days.

[0026] c. After cultivation, the upper liquid is extracted, and the resulting precipitate is the improved yellow mud with enhanced quality.

[0027] Preferably, in step a above, the total iron content of the yellow mud is 28.64–33.21 g / kg, the crystalline iron mineral content is 6.13–8.81 g / kg, the amorphous iron (hydrogen) oxide content is 4.32–6.37 g / kg, the pH value is 6.35–7.72, and the water content is 7.69–10.98%.

[0028] It should be further clarified that other forms of iron in the soil that are not part of layered silicates are defined as free iron minerals. Free iron minerals include crystalline iron minerals and amorphous iron (hydride) oxides. Free iron minerals in the soil were extracted using a sodium dithionite-sodium citrate-sodium bicarbonate solution; amorphous iron (hydride) oxides in the soil were extracted using an oxalic acid-ammonium oxalate solution; the content of crystalline iron minerals was the difference between the content of free iron minerals and the content of amorphous iron (hydride) oxides.

[0029] Preferably, in step b above, the concentration of Lactobacillus paracasei seed culture is 8 × 10⁻⁶. 8 cfu / mL.

[0030] More preferably, the above-mentioned method for preparing Lactobacillus paracasei seed culture is as follows: inoculate 1-2 loops of Lactobacillus paracasei into MRS medium, seal the medium, and then culture it in a shaker at 37°C and 180 rpm for 10 h to prepare the seed culture.

[0031] More preferably, the composition (g / L) of the above-mentioned MRS medium (DeMan-Rogosa-Sharpe medium, a medium specifically suitable for the proliferation of lactobacilli) is as follows: glucose 20.0, peptone 10.0, beef extract 5.0, yeast extract 4.0, sodium acetate 5.0, diammonium hydrogen citrate 2.0, dipotassium hydrogen phosphate 2.0, magnesium sulfate heptahydrate 0.2, manganese sulfate monohydrate 0.05, and Tween 80 1.0. The pH of the medium is approximately 6.5, and it is sterilized at 115°C for 30 min.

[0032] Preferably, in step c above, the improved yellow clay has a total iron content of 25.33–28.21 g / kg, a crystalline iron mineral content of 4.73–7.48 g / kg, an amorphous iron (hydrogen) oxide content of 3.02–4.36 g / kg, a pH value of 4.56–5.86, and a water content of 18.41–21.81%.

[0033] This invention provides the application of improved yellow mud obtained by the above-mentioned method for improving the quality of yellow mud used in cellar mud production in the fermentation of strong-aroma baijiu.

[0034] The technical solution and effects of the present invention will be further explained below through practical examples.

[0035] Example

[0036] 1. Preparation and testing of improved yellow clay

[0037] (1) Yellow mud pretreatment: Remove stones, roots and other debris from the yellow mud, then grind large soil particles and pass them through a 10-mesh sieve.

[0038] (2) Seed culture preparation: *Lactobacillus paracasei* seed culture medium: MRS medium was used, with the following components (g / L): glucose 20.0, peptone 10.0, beef extract 5.0, yeast extract 4.0, sodium acetate 5.0, diammonium hydrogen citrate 2.0, dipotassium hydrogen phosphate 2.0, magnesium sulfate heptahydrate 0.2, manganese sulfate monohydrate 0.05, and Tween 80 1.0. The pH of the medium was approximately 6.5, and it was sterilized at 115℃ for 30 min. One to two loops of *Lactobacillus paracasei* were inoculated into the MRS medium, sealed, and cultured at 37℃ and 180 rpm for 10 h. The resulting *Lactobacillus paracasei* seed culture concentration was approximately 8 × 10⁻⁶. 8 cfu / mL.

[0039] (3) Yellow mud improvement: In Examples 1-3, MRS medium was added to 1500g of pretreated yellow mud, and Lactobacillus paracasei seed culture was inoculated and mixed well. The mixture was then sealed and anaerobically cultured at 37℃. After the culture was completed, the supernatant was extracted and the precipitate was retained. This precipitate is the final product. In Examples 1-3 (control), MRS medium was added to 1500g of pretreated yellow mud, but Lactobacillus paracasei was not inoculated, and the final product was obtained. The specific improvement process parameters of Examples 1-3 and Examples 1-3 (control) are shown in Table 1.

[0040] Table 1. Process parameters for improving yellow mud

[0041]

[0042] (4) Physicochemical property determination: XRD was used to analyze the mineral composition of the improved yellow clay (with Example 1 as a control and Example 1 as an example) and the original yellow clay. The results are as follows: Figure 1 As shown in Table 2, the total iron, crystalline iron minerals, amorphous iron (hydride) oxides, and pH values ​​in improved yellow clay (with Example 1 as a control and Example 1 as an example) and original yellow clay were determined by chemical methods.

[0043] Table 2 Physicochemical Properties

[0044] Physicochemical indicators Original yellow mud Example 1 Comparison Example 1 2-year-old pit mud Total iron (g / kg) 30.54 29.13 26.95 24.26 Amorphous iron (hydrogen) oxides (g / kg) 5.55 4.24 3.64 1.51 Crystalline iron minerals (g / kg) 7.71 6.88 6.17 10.93 pH value 7.23 6.57 5.15 6.16

[0045] The changes in the mineral composition characteristics of the inoculated modified yellow mud prepared in Examples 1-3 were analyzed by XRD. Figure 1The results (taking Example 1 as an example) showed that after weathering by *Lactobacillus paracasei*, the XRD diffraction peaks related to iron minerals in the inoculated improved yellow clay 1 all decreased to varying degrees. Furthermore, the changes in the XRD diffraction peaks related to iron minerals in the control of Example 1 were not significant, indicating that the MRS medium had almost no weathering effect on the yellow clay. In conclusion, it can be reasonably inferred that the iron mineral content in the improved yellow clay decreased under the weathering action of *Lactobacillus paracasei*.

[0046] As shown in Table 2, the total iron and amorphous iron (hydrogen) oxide content of the inoculated improved yellow mud 1 prepared in Example 1 of the present invention is close to that of 2-year-old pit mud, while the crystalline iron mineral content is lower than that of 2-year-old pit mud. This indicates that using Lactobacillus paracasei to weather the original yellow mud can effectively reduce the total iron and iron mineral content in the original yellow mud.

[0047] 2. Experiment on the use of improved yellow mud for Baijiu fermentation

[0048] (1) Sorghum crushing: Wash the sorghum with ultrapure water, soak it in 60℃ hot water for 24 hours, filter out excess water with gauze, then crush it into 6-8 pieces with a soymilk maker, collect the sorghum and store it for later use.

[0049] (2) Fermentation Experiment: A 16×16cm food-grade 304 stainless steel tank was used as the fermentation container to simulate the fermentation process. For Examples 4-6, the control of Examples 4-6, and Control Example 2, 1000g of yellow mud was used to cover the bottom and four walls of the fermentation container. Control Example 1 did not use yellow mud and used the original fermentation container directly. Then, 150g of Daqu powder and 1500g of sorghum were mixed and placed into the fermentation container. After sealing, the container was kept at a constant temperature of 25℃ for anaerobic fermentation for 30 days. The specific process of covering the fermentation container with yellow mud is shown in Table 3.

[0050] Table 3 Improvements to Fermentation Vessels

[0051] Fermentation containers were covered with yellow mud. Example 4 Inoculation Improved Yellow Mud 1 Example 5 Inoculation Improved Yellow Mud 2 Example 6 Inoculation Improved Yellow Mud 3 Example 4 (Comparative) Non-inoculated improved yellow mud 1 Example 5 (Comparative Study) Non-inoculated improved yellow mud 2 Example 6 (Comparative Study) Non-inoculated improved yellow mud 3 Compare with Example 1 Not covered Compare with Example 2 Original yellow mud

[0052] (3) Results detection: After fermentation, the moisture content, acidity, alcohol content and volatile flavor substance content of the mash were measured (using Example 4, Example 4 control, and Control Examples 1-2 as examples). The results are shown in Table 4.

[0053] Table 4. Physicochemical properties of fermented mash and content of flavor compounds in distilled spirits made from fermented mash.

[0054] Example 4 Compare with Example 1 Compare with Example 2 Example 4 (Comparative) Moisture (%) 66.11 55.25 56.30 62.26 acidity 31.33 16.33 14.33 13.67 Alcohol content (°) 8.68 2.07 0.83 1.93 Acetic acid (μg / mL) 46.31 11.83 0.00 0.00 Isobutanol (μg / mL) 14.35 2.51 0.00 0.00 Ethyl acetate (μg / mL) 265.58 105.78 81.26 81.13 Ethyl butyrate (μg / mL) 101.51 6.91 10.88 6.34 Ethyl hexanoate (μg / mL) 6.27 0.00 0.00 0.00

[0055] As shown in Table 4, the moisture content, acidity, and alcohol content of the fermented mash produced in Example 4 were higher than those in Control Examples 1-2 and the control of Example 4. This indicates that the metabolic activity of the Daqu microorganisms in Example 4 was higher, resulting in more complete decomposition of the grain mash and thus producing more moisture, organic acids, and alcohol. Furthermore, the strong-aroma baijiu brewed in Example 4 had a higher content of flavor compounds, further demonstrating that the improved yellow mud prepared by inoculating Lactobacillus paracasei seed solution has a significantly improved quality compared to the original unimproved yellow mud, and the quality of the brewed strong-aroma baijiu is also better.

[0056] In summary, the contents of total iron, crystalline iron minerals, and amorphous iron (hydride) oxides in the inoculated and improved yellow mud prepared in Examples 1-3 of this invention are significantly lower than those in the original yellow mud and the uninoculated and improved yellow mud. Furthermore, after the inoculated and improved yellow mud is mixed with Daqu (a type of starter culture) for fermentation, the physicochemical properties of the mash are better, and the content of flavor compounds is higher. Therefore, the method for preparing improved yellow mud in Examples 1-3 of this invention can effectively reduce the iron content in the original yellow mud, and the inoculated and improved yellow mud can enhance the microbial activity of the mash, promote fermentation, and improve the quality of strong-aroma baijiu.

Claims

1. A method for improving the quality of yellow clay used in the production of pit mud, characterized in that, Includes the following steps: a. Pretreatment of yellow mud; The yellow mud has a pH value of 6.35-7.72 and a water content of 7.69-10.98%; its total iron content is 28.64-33.21 g / kg, its crystalline iron mineral content is 6.13-8.81 g / kg, and its amorphous iron (hydrogen) oxide content is 4.32-6.37 g / kg. b. Add MRS medium to the pretreated yellow mud and inoculate with Lactobacillus paracasei seed culture, and incubate at 37℃ for anaerobic static culture for 15-20 days; The mass-to-volume ratio of pretreated yellow mud to MRS culture medium was 1500 g: 700-1000 mL; the concentration of Lactobacillus paracasei seed culture was 8 × 10⁻⁶. 8 CFU / mL, inoculate the seed culture at 25-40% of the volume of MRS medium, and then mix it evenly with yellow mud; c. After cultivation, the upper liquid is extracted, and the resulting precipitate is the improved yellow mud with enhanced quality. The modified yellow mud has a pH value of 4.56-5.86 and a water content of 18.41-21.81%; its total iron content is 25.33-28.21 g / kg, its crystalline iron mineral content is 4.73-7.48 g / kg, and its amorphous iron (hydrogen) oxide content is 3.02-4.36 g / kg.

2. The method for improving the quality of yellow clay used in making pit mud according to claim 1, characterized in that: In step a, the pretreatment involves removing stones, roots, and other debris from the yellow mud, then grinding large soil particles and passing them through a 10-mesh sieve.

3. The method for improving the quality of yellow clay used in making pit mud according to claim 1, characterized in that: The method for preparing the Lactobacillus paracasei seed culture is as follows: inoculate 1-2 loops of Lactobacillus paracasei into MRS medium, seal the culture, and then incubate at 37°C and 180 rpm in a shaker for 10 h.

4. The method for improving the quality of yellow clay used in making pit mud according to claim 1 or 3, characterized in that: The MRS medium has a pH of approximately 6.5 and is sterilized at 115°C for 30 min. Its formula is as follows: glucose 20.0 g / L, peptone 10.0 g / L, beef extract 5.0 g / L, yeast extract 4.0 g / L, sodium acetate 5.0 g / L, diammonium hydrogen citrate 2.0 g / L, dipotassium hydrogen phosphate 2.0 g / L, magnesium sulfate heptahydrate 0.2 g / L, manganese sulfate monohydrate 0.05 g / L, and Tween 80 1.0 g / L.

5. The application of the improved yellow mud obtained by the method for improving the quality of yellow mud used to make cellar mud as described in any one of claims 1 to 4 in the fermentation of strong-aroma baijiu.

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