A low turbidity removing process for grass-based liquor with Maotai flavor by coupling fractional crystallization and selective adsorption

Abstract

The present application relates to the technical field of liquor brewing and liquor body refining, and discloses a low-alcohol Luzhou-flavor herbal liquor turbidity removal process coupled with segmented crystallization and selective adsorption. The low-alcohol Luzhou-flavor base liquor is mixed with ethanol extracts of rhizoma polygonati, medlar, kudzu root and dried tangerine or orange peel, and is sequentially subjected to low-temperature treatment at 0-2 DEG C, deep cold treatment at -10 to -6 DEG C, and negative temperature warming treatment at -4 to -2 DEG C. No solid-liquid separation is performed from the end of the deep cold treatment to the beginning of the low-temperature adsorption, and then modified activated carbon of coconut shell, which is soaked in gluconic acid and subjected to nitrogen heat treatment, is added at -4 to -2 DEG C for adsorption. The liquor is sequentially subjected to coarse filtration and microporous membrane filtration under the condition that the temperature is not higher than 0 DEG C, and is subjected to stage-wise warming and maturation after filtration. The present application is suitable for turbidity removal and refining of low-alcohol Luzhou-flavor herbal liquor.

Description

Technical Field

[0001] This invention belongs to the field of liquor brewing and liquor refining technology, specifically involving a process for removing turbidity and stabilizing the liquor in a complex turbidity system formed by higher fatty acid esters, herbal colloids and fine suspended components in low-alcohol sauce-flavored herbal liquor, through segmented low-temperature crystallization, deep-cooling followed by negative-temperature warming, low-temperature selective adsorption and filtration. Background Technology

[0002] During the reduction of alcohol content in Maotai-flavor baijiu, as the volume fraction of ethanol decreases, the solubility equilibrium of some higher fatty acids and their ethyl esters that were originally dissolved or dispersed in the high-proof base liquor changes. In particular, components such as ethyl palmitate, ethyl oleate, and ethyl linoleate are prone to gradually precipitating out under lower temperatures or long-term storage conditions, causing the liquor to lose its luster, become milky white and cloudy, or develop flocculent precipitates. For low-proof baijiu, controlling these clouding components without excessively altering the original flavor system is a problem that needs to be solved during the refining process.

[0003] The introduction of herbal extracts into low-alcohol Maotai-flavor baijiu results in a more complex stabilizing system compared to ordinary low-alcohol baijiu. Besides introducing relatively soluble small molecules, the herbal extracts may also introduce polysaccharides, plant colloids, and colloidal, aggregated, or macromolecular components related to polyphenols and flavonoids. These components do not possess the same solubility and precipitation characteristics as the higher fatty acid ethyl esters in the baijiu. Therefore, the turbidity in low-alcohol Maotai-flavor herbal baijiu often manifests as a complex turbidity system containing lipid-soluble turbidity components, herbal-derived colloids, and fine suspended matter.

[0004] Currently, the main methods for removing turbidity from low-alcohol baijiu are cryogenic filtration, adsorption filtration, or a combination of both. Cryogenic treatment utilizes the characteristic that the solubility of different substances decreases at low temperatures, allowing some higher fatty acid ethyl esters and other low-temperature insoluble components in the baijiu to be precipitated before filtration. For low-alcohol baijiu with a relatively simple composition, the above methods can achieve certain results; however, when the baijiu contains both herbal colloids and fine aggregates, the precipitation temperature range, aggregation rate, and particle size of different turbidity components are not consistent. Simply maintaining a low temperature or filtering immediately after deep freezing may still result in small particle size of the fine precipitates, a high filtration load, and subsequent turbidity during storage.

[0005] Activated carbon adsorption is also a common method in the turbidity removal treatment of baijiu (Chinese liquor). Activated carbon can adsorb some higher fatty acid ethyl esters, colloids, and other impurities in the liquor using its porous structure. However, when the amount of activated carbon added is too large or the adsorption conditions are not properly controlled, some esters, alcohols, aldehydes, ketones, and other volatile components related to the soy sauce aroma style may also be adsorbed. For liquors containing herbal extracts, some herbal soluble components may also be lost. Therefore, simply relying on increasing the amount of activated carbon can easily create a contradiction between the degree of turbidity removal and the preservation of flavor and herbal components.

[0006] Existing cryogenic and adsorption combined treatment methods typically focus on combining the cryogenic and activated carbon steps sequentially, lacking control over the transitions between stages to address changes in the state of the combined turbidity system. Especially after cryogenic treatment results in a large amount of fine precipitates, if these are immediately separated or the conditions are changed to ambient temperature adsorption, the pre-crystallized state is unlikely to continue participating in subsequent adsorption and filtration processes, and the activated carbon still bears a significant load of residual turbidity.

[0007] Therefore, it is necessary to provide a segmented processing technology for low-alcohol Maotai-flavored herbal liquor. By controlling the sequential relationship between low-temperature pretreatment, further deep cooling, negative temperature recovery after deep cooling, and low-temperature adsorption, different turbidity components can form a suitable precipitation and aggregation state before entering the adsorption and filtration stages, and reduce the dependence on high-intensity adsorption treatment while obtaining low-temperature and storage stability. Summary of the Invention

[0008] In view of this, the present invention proposes a segmented crystallization and selective adsorption coupling process for turbidity removal in low-alcohol Maotai-flavor herbal baijiu. The technical problem to be solved by this invention is to address the complex turbidity system in low-alcohol Maotai-flavor baijiu containing herbal extracts, which comprises higher fatty acid ethyl esters, herbal-derived colloids, and fine suspended components, while simultaneously ensuring low-temperature stability and storage stability, and reducing the load on subsequent adsorption treatments and the loss of Maotai-flavor flavor and herbal soluble components. To this end, the present invention alters the state of the complex turbidity system before entering the adsorption and filtration stages through segmented low-temperature treatment, and ensures that cryogenic treatment, negative temperature warming, and low-temperature adsorption are sequentially linked.

[0009] The technical solution of this invention is implemented as follows: The base liquor of the sauce-flavored type is diluted and mixed with an herbal extract obtained by extracting Polygonatum sibiricum, Lycium barbarum, Pueraria lobata, and Citrus reticulata peel in a dry weight ratio of 4:3:2:1 using a 45% vol ethanol aqueous solution. The herbal extract accounts for 5%–10% of the total volume of the liquor to be treated after mixing, resulting in a liquor body of 33–42 vol%. The liquor body is then subjected to a first-stage low-temperature treatment at 0–2℃, a second-stage cryogenic treatment at -10–-6℃, and a third-stage negative-temperature warming treatment at -4–-2℃. No solid-liquid separation is performed from the end of the cryogenic treatment until the start of low-temperature adsorption. Subsequently, 0.20–0.40 g / L of modified activated carbon is added at -4–-2℃ for adsorption. The modified activated carbon is food-grade coconut shell activated carbon soaked in a 5%–8% gluconic acid solution for 1–3 hours, followed by heat treatment at 180–200℃ under a nitrogen atmosphere for 1–2 hours. h, then washed and dried; after adsorption, coarse filtration and microporous membrane filtration are carried out in sequence at a temperature not higher than 0℃, and finally the temperature is restored and matured in stages.

[0010] In some embodiments, the herbal extract is prepared from Polygonatum sibiricum, Lycium barbarum, Pueraria lobata, and Citrus reticulata peel, with a dry weight ratio of 4:3:2:1. A 45% (v / v) aqueous ethanol solution is used as the extractant. The extract is prepared at a ratio of 1 g:8 mL (dry weight of the herbal raw materials to the extractant volume) at 35°C for 2 h, followed by filtration. The residue is extracted again under the same conditions. The two filtrates are combined and concentrated under reduced pressure at a temperature not exceeding 45°C. When the herbal extract is mixed with the diluted soy sauce-flavored base liquor, the liquor temperature can be controlled at 20–25°C, and the mixture is stirred at 30–50 r / min for 15–20 min, followed by standing for 20–40 min after stirring.

[0011] In some implementations, the first stage of low-temperature treatment involves cooling the wine to 0–2°C at a rate of 0.2–0.4°C / h and maintaining the temperature for 4–6 hours; the second stage, following the first stage, continues cooling to -10–-6°C at a rate of 0.4–0.6°C / h and maintaining the temperature for 8–12 hours. The first and second stages constitute a temperature path that gradually changes from a higher low-temperature range to a cryogenic range.

[0012] In some embodiments, after the second stage of cryogenic treatment, instead of filtration, centrifugation or other solid-liquid separation, the wine is warmed to -4 to -2°C and kept warm for 4 to 8 hours; the final temperature of the warming is 2 to 8°C higher than the cryogenic holding temperature of the second stage but still below 0°C.

[0013] In some implementations, after the third stage of negative temperature recovery is completed, the temperature of the wine is maintained at -4 to -2°C, and modified activated carbon is added for stirring and static adsorption, so that the precipitation system formed by deep cryogenics enters the negative temperature recovery and low temperature adsorption stages in sequence without undergoing intermediate solid-liquid separation.

[0014] In some embodiments, the modified activated carbon is prepared by soaking 120-180 mesh food-grade coconut shell activated carbon in a 5%-8% gluconic acid solution for 1-3 hours, then heat-treating it at 180-200°C for 1-2 hours under a nitrogen atmosphere, and finally washing and drying it with deionized water.

[0015] In some embodiments, the nitrogen adsorption-desorption isotherm of the modified activated carbon is measured at 77 K, and the pore volume distribution within the measurable pore size range is calculated using a DFT model. The sum of the pore volumes within this measurable pore size range is used as the total statistical pore volume, wherein the pore volume of micropores with a pore size less than 2 nm accounts for 5% to 10%, and the pore volume of mesopores with a pore size of 2 to 50 nm accounts for 65% to 70%. In the preparation example, the pore volume with a pore size greater than 50 nm and within the measurable range of the above method accounts for 20% to 25%, and this data serves as an auxiliary characterization of the pore structure.

[0016] In some embodiments, the modified activated carbon is added at a rate of 0.20–0.40 g / L, and after addition, it is stirred at 40–50 r / min for 10–20 min, and then allowed to stand in a sealed container at -4–-2℃ for 3–5 h for adsorption. The amount of modified activated carbon added can be selected within the above range according to the alcohol content of the wine to be treated, the proportion of herbal extract, and the initial stable state.

[0017] In some embodiments, low-temperature filtration includes coarse filtration and microporous membrane filtration; the coarse filtration employs plate and frame filtration, and the coarsely filtered wine is then filtered through a microporous membrane with a pore size of 0.22 μm at a filtration pressure of 0.15–0.25 MPa. The wine to be filtered, the filtration equipment, and the delivery pipeline are kept at a temperature not exceeding 0°C.

[0018] In some implementations, after precision filtration, the wine is first warmed to 10-12°C and maintained for 1-3 days, then warmed to 20-25°C and aged for 7-15 days, so that the wine gradually returns from a low-temperature refined state to a room-temperature storage state.

[0019] In some embodiments, the alcohol content of the wine to be treated is preferably 36-40 vol%, more preferably 38-40 vol%; the temperature of the first stage low-temperature treatment is preferably 1-2℃, the temperature of the second stage cryogenic treatment is preferably -9 to -7℃, and the temperature of the third stage negative temperature recovery is preferably -4 to -3℃.

[0020] In some embodiments, the segmented crystallization and selective adsorption coupling means that the first stage of low-temperature treatment, the second stage of cryogenic treatment, and the third stage of negative temperature recovery and low-temperature adsorption are carried out in the order described above, and no solid-liquid separation step is set from the end of the second stage cryogenic treatment to the start of low-temperature adsorption.

[0021] The present invention has the following advantages over the prior art: Compared with existing technologies, this invention constructs a non-unidirectional temperature path through a first-stage low-temperature treatment, a second-stage cryogenic treatment, and a subsequent negative-temperature recovery. This allows the precipitated system formed during cryogenic treatment to continue into the negative-temperature recovery and low-temperature adsorption stages without intermediate solid-liquid separation, thus connecting the pre-stage crystallization state with the subsequent adsorption and filtration. Furthermore, modified coconut shell activated carbon treated with gluconic acid and nitrogen heat is used for low-temperature adsorption, enabling the removal of residual turbidity components under a lower adsorbent load and reducing reliance on high-intensity adsorption. Low-temperature coarse filtration and microporous membrane filtration further remove precipitates and activated carbon, while staged recovery and maturation gradually restore the liquor to its room-temperature storage state. Therefore, this invention can simultaneously ensure the low-temperature stability, long-term storage stability, filtration performance, and retention of the soy sauce aroma and herbal soluble components of the low-alcohol Maotai-flavored herbal liquor. Attached Figure Description

[0022] To more clearly illustrate the technical solution of the present invention, the accompanying drawings are briefly described below.

[0023] Figure 1 This is a schematic diagram of the turbidity removal process of the present invention; Figure 2 This is a schematic diagram of the segmented low-temperature processing temperature program of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to embodiments. The overall turbidity removal process of the present invention is as follows: Figure 1 As shown, the temperature program for segmented low-temperature processing is as follows: Figure 2 As shown. Unless otherwise specified, all embodiments and comparative examples used the same batch of soy sauce-flavored base liquor, herbal extract, and filtration equipment; all test results were obtained from parallel experiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0025] I. Experimental Materials The same batch of Kunsha-style sauce-flavored base liquor was used as the base liquor. The herbal extract was prepared from Polygonatum sibiricum, Lycium barbarum, Pueraria lobata, and Citrus reticulata peel, with a dry weight ratio of 4:3:2:1. After crushing and mixing the raw materials, a 45% (v / v) ethanol-water solution was used as the extractant. Extraction was carried out at 35°C for 2 hours at a ratio of 1 g:8 mL (dry weight of the herbal raw materials to the volume of the extractant), based on the total dry weight of the herbal raw materials and the volume of the extractant. The mixture was then filtered. The residue was extracted again under the same conditions. The two filtrates were combined and concentrated under reduced pressure at a temperature not exceeding 45°C. The alcohol content of the extract was adjusted with an ethanol-water solution. The herbal extract used in Example 1 had an alcohol content of 39 vol% and a soluble solids content of 8.4%. This indicator was used to characterize the herbal extract used in this example.

[0026] The activated carbon used was 120-180 mesh food-grade coconut shell activated carbon. Unless otherwise specified, the same batch of base wine, herbal extract and activated carbon were used in all examples and comparative examples.

[0027] II. Preparation of Modified Activated Carbon Preparation Example 1 Food-grade coconut shell activated carbon (120-180 mesh) was washed with deionized water and dried at 90℃. The dried activated carbon was then added to a 5% (w / w) gluconic acid aqueous solution (1 g:10 mL by mass volume) and soaked at room temperature for 2 h. After soaking, the free liquid was removed, and the activated carbon was placed in a nitrogen-protected environment. The temperature was increased to 190℃ at 3℃ / min and held for 1.5 h. After naturally cooling to below 80℃, the activated carbon was removed. It was then rinsed with deionized water until the pH of the final rinse solution was 6.5-7.2, and subsequently dried at 100℃ to constant weight to obtain modified activated carbon M1.

[0028] Preparation Example 2 Modified activated carbon was prepared according to the method of Preparation Example 1, except that a 6% gluconic acid solution was used, the soaking time was 2.5 h, and the nitrogen-protected heat treatment temperature was 185℃ for 2 h to obtain modified activated carbon M2.

[0029] Preparation Example 3 Modified activated carbon was prepared according to the method of Preparation Example 1, except that an 8% gluconic acid solution was used, the soaking time was 1.5 h, and the nitrogen-protected heat treatment temperature was 200℃ and the holding time was 1 h, resulting in modified activated carbon M3.

[0030] III. Detection Methods 1. Pore structure of activated carbon After degassing the activated carbon sample under vacuum at 200℃ for 8 h, the nitrogen adsorption-desorption isotherm was measured at 77 K. The specific surface area was calculated using the BET method within a relative pressure P / P0 range of 0.05–0.30, and the pore volume distribution within the measurable pore size range was calculated using the DFT pore size distribution model. The sum of the pore volumes within the measurable pore size range was used as the total statistical pore volume. Pores smaller than 2 nm were defined as micropores, pores between 2 and 50 nm as mesopores, and pores larger than 50 nm as macropores. The percentage of pore volume in each pore size range relative to the total statistical pore volume was calculated.

[0031] Table 1. Pore structure of ordinary coconut shell activated carbon and modified activated carbon

[0032] As shown in Table 1, after gluconic acid treatment and nitrogen atmosphere heat treatment, the pore volume distribution of M1 to M3 all showed a high proportion of mesopores and a low proportion of micropores. Subsequent examples used M1 to M3 for wine processing.

[0033] 2. Turbidity and storage stability Turbidity of the wine was measured using a scattering turbidimeter, expressed as NTU. For room temperature turbidity measurement, the wine sample was equilibrated at 20±1℃ for 2 hours before measurement. In the low-temperature stability test, the finished wine sample was continuously stored at -5±0.5℃ for 7 days, and the presence of luster loss, flocculent matter, or sediment was observed and turbidity was measured while maintaining the low temperature. For shelf stability testing, the wine was stored in a sealed, light-protected environment at 20–25℃ for 90 days, and the wine's condition was observed and turbidity was measured. Three replicates were set up for each group.

[0034] 3. Higher fatty acid ethyl esters Ethyl palmitate, ethyl oleate, and ethyl linoleate were determined using gas chromatography-mass spectrometry (GC-MS). A DB-WAX capillary column (30 m × 0.25 mm × 0.25 μm) was used, with an injection temperature of 250 °C, a helium flow rate of 1.0 mL / min, and a split ratio of 10:1. The column temperature was initially set at 50 °C for 3 min, then increased to 200 °C at a rate of 5 °C / min, and finally increased to 240 °C at a rate of 10 °C / min and held for 10 min. Mass spectrometry used an EI source of 70 eV, an ion source temperature of 230 °C, and a scan range of m / z 40–500. Qualitative analysis was performed using appropriate standards, and ethyl heptadecanoate was used as an internal standard for quantification. The removal rate of higher fatty acid ethyl esters was calculated as the percentage difference between the total amount of the three higher fatty acid ethyl esters before and after treatment relative to the total amount before treatment.

[0035] 4. Representative flavor components Ethyl acetate, ethyl lactate, ethyl hexanoate, ethyl butyrate, n-propanol, isobutanol, isoamyl alcohol, acetal, and furfural were determined according to the corresponding analytical methods specified in GB / T 10345-2022. 2,3,5,6-Tetramethylpyrazine was determined by gas chromatography-mass spectrometry (GC-MS), with retention time and characteristic ion confirmation using 2,3,5,6-tetramethylpyrazine standards, and quantification using a standard curve. The total retention rate of the target flavor components after treatment was calculated based on the sum of the mass concentrations of the above target flavor components before treatment.

[0036] 5. Total polyphenols and total flavonoids Total polyphenols were determined using the Folin-Ciocalteu colorimetric method, with a standard curve established using gallic acid, and absorbance measured at 765 nm. Total flavonoids were determined using the sodium nitrite-aluminum nitrate-sodium hydroxide colorimetric method, with a standard curve established using rutin, and absorbance measured at 510 nm. The retention rates of total polyphenols and total flavonoids were calculated as percentages of their content after treatment to their content before treatment, respectively.

[0037] 6. Particle size of precipitated particles The particle size of the precipitated particles was determined using a laser diffractometer with a circulating temperature control unit. The sampling container, delivery pipeline, and detection cell were pre-adjusted to the corresponding process stage temperature. The sample was not diluted after sampling, and the detection cell temperature was controlled within ±0.5℃ of the sampling stage temperature. Measurements were completed within 3 minutes of sampling. The median volumetric particle size (D50) and the volume fraction of particles smaller than 2 μm were recorded.

[0038] 7. Filtration performance Each group used 0.22 μm microporous membranes of the same material and with the same effective filtration area, and filtration was carried out at a filtration pressure of 0.20 MPa. The average membrane flux J was calculated according to J=V / (A×t), where V is the volume of filtered wine, A is the effective filtration area, and t is the filtration time.

[0039] IV. Examples Example 1 The base liquor of Kunsha sauce-flavored liquor was diluted, and 5% (v / v) of herbal extract was added to bring the alcohol content of the resulting liquor to 39 vol%. The liquor was stirred at 40 r / min for 15 min at 22℃ and allowed to stand for 30 min. The liquor was then cooled to 2℃ at a rate of 0.3℃ / h and held for 5 h; subsequently, it was cooled further to -8℃ at a rate of 0.5℃ / h and held for 10 h. After cryogenic treatment, no filtration or other solid-liquid separation was performed. The liquor was then warmed to -3℃ and held for 6 h. Maintaining the temperature at -3℃, 0.28 g / L of M1 was added, and the mixture was stirred at 45 r / min for 15 min, followed by sealed standing for adsorption for 4 h. After adsorption, plate and frame filtration was performed under conditions where the temperature of the liquor and the filtration system did not exceed 0℃, followed by filtration using a 0.22 μm microporous membrane at a pressure of 0.20 MPa. After filtration, the wine is warmed to 12°C and kept there for 2 days, then warmed to 22°C and aged for 10 days.

[0040] Example 2 Using the same base wine and herbal extract as in Example 1, with the herbal extract added at 8% (v / v), the alcohol content of the wine to be treated was 36 vol%. The mixture was stirred at 50 r / min for 18 min at 20°C, then allowed to stand for 30 min. The temperature was then lowered to 1°C at 0.25°C / h and maintained for 6 h, followed by a further cooling to -9°C at 0.45°C / h and maintained for 9 h. Subsequently, without solid-liquid separation, the wine was warmed to -4°C and maintained for 8 h. Maintaining at -4°C, 0.34 g / L of M2 was added, and the mixture was stirred at 50 r / min for 12 min, then allowed to stand for adsorption for 3.5 h. After low-temperature plate and frame filtration, the mixture was filtered through a 0.22 μm microporous membrane, maintained at 10°C for 3 days, and then aged at 20°C for 15 days.

[0041] Example 3 The herbal extract was added at a rate of 10% (v / v), and the alcohol content of the wine to be treated was 42 vol%. The mixture was stirred at 35 r / min for 20 min at 25℃, then allowed to stand for 40 min. The temperature was then lowered to 0℃ at 0.4℃ / h and held for 4 h, followed by a further cooling to -6℃ at 0.6℃ / h and held for 12 h. Subsequently, without solid-liquid separation, the mixture was warmed back to -2℃ and held for 4 h. At -2℃, 0.22 g / L of M3 was added, and the mixture was stirred at 40 r / min for 15 min, followed by sealed standing for adsorption for 5 h. After low-temperature plate and frame filtration, the mixture was filtered through a 0.22 μm microporous membrane. The filtered wine was kept at 12℃ for 1 day, and then aged at 25℃ for 7 days.

[0042] Example 4 The herbal extract was added at a rate of 7.5% (v / v), and the alcohol content of the wine to be treated was 33 vol%. The mixture was stirred at 45 r / min for 18 min at 22℃, and then allowed to stand for 35 min. The temperature was then lowered to 0℃ at a rate of 0.2℃ / h and maintained for 6 h, followed by a further cooling to -10℃ at a rate of 0.4℃ / h and maintained for 12 h. After cryogenic treatment, no solid-liquid separation was performed; the mixture was then warmed to -4℃ and maintained for 8 h. At -4℃, 0.40 g / L of M1 was added, and the mixture was stirred at 45 r / min for 15 min, followed by adsorption for 5 h. Low-temperature plate and frame filtration and 0.22 μm membrane filtration were performed according to the method in Example 1, followed by maintenance at 10℃ for 3 days, and then aging at 22℃ for 15 days.

[0043] V. Comparative Examples Comparative Example 1: Combination of single cryogenic and ordinary activated carbon Using the same wine as in Example 1, the wine was directly cooled to -8°C at a rate of 0.5°C / h and kept at that temperature for 10h. Then, the temperature was adjusted to -3°C, and 0.28 g / L of unmodified ordinary coconut shell activated carbon was added. The remaining adsorption, filtration, and aging conditions were the same as in Example 1.

[0044] Comparative Example 2: Segmented temperature treatment without activated carbon adsorption The same low-temperature treatment at 2°C, deep freezing at -8°C, and negative temperature recovery at -3°C as in Example 1 were used, but without the addition of activated carbon. After the negative temperature recovery was completed, low-temperature plate and frame filtration and 0.22 μm microporous membrane filtration were performed directly.

[0045] Comparative Example 3: Single Cryogenic Modified Activated Carbon The first stage of low-temperature treatment at 0-2℃ as described in Example 1 was not performed. Instead, the wine was directly cooled to -8℃ and kept warm for 10 hours. Subsequently, the temperature of the wine was adjusted to -3℃. After reaching -3℃, M1 0.28 g / L was added for adsorption. The third stage of treatment, which involved keeping the wine at -3℃ for 6 hours as described in Example 1, was not performed. The remaining steps were the same as in Example 1.

[0046] Comparative Example 4: Complete temperature program combined with ordinary activated carbon The same three-stage temperature program as in Example 1 was used, but M1 was replaced with an equal amount of unmodified ordinary coconut shell activated carbon, and the other conditions were the same as in Example 1.

[0047] Comparative Example 5: Removal of negative temperature recovery and adsorption at cryogenic temperature Following Example 1, a first-stage low-temperature treatment at 2°C and a second-stage cryogenic treatment at -8°C were performed. After holding at -8°C for 10 hours, a third-stage negative temperature recovery was not performed. Instead, M1 0.28 g / L was directly added at -8°C for adsorption, followed by low-temperature filtration and ripening. This comparative example is used to evaluate the overall process differences after eliminating the third-stage negative temperature recovery and changing the subsequent adsorption connection method.

[0048] Comparative Example 6: Separation after cryogenic treatment followed by reheat adsorption Following Example 1, a first-stage low-temperature treatment at 2°C and a second-stage cryogenic treatment at -8°C were performed. After holding at -8°C for 10 hours, low-temperature plate and frame filtration was first conducted to remove the precipitates that had formed. The filtered wine was then warmed to -3°C and held for 6 hours, and then M1 0.28 g / L was added for adsorption. After adsorption, plate and frame filtration and 0.22 μm microporous membrane filtration were performed in the same manner as in Example 1, followed by the same warming and aging process.

[0049] VI. Results of Turbidity Removal and Component Retention by Different Processes Both the example and the comparative examples had three parallel samples, and the test results are shown in Table 2.

[0050] Table 2 Treatment effects of different turbidity removal processes

[0051] Examples 1-4 all achieved low turbidity at room temperature, low temperature, and 90-day storage under conditions of 33-42 vol% alcohol content and different amounts of herbal extract added. Comparative Example 2, without activated carbon adsorption, showed higher retention of flavor components and herbal polyphenols and flavonoids, but the removal rate of higher fatty acid ethyl esters and long-term stability were lower than in Examples 1. Comparative Example 3, using only cryogenic combined with modified activated carbon, showed lower low-temperature and 90-day storage turbidity and membrane flux than Example 1. Comparative Example 4, using a complete temperature program but ordinary activated carbon, showed significantly lower retention rates of target flavor components, total polyphenols, and total flavonoids than in Example 1. Comparative Example 5 was used to evaluate the overall process differences after eliminating the third-stage negative temperature reheat and directly adsorbing at cryogenic temperature; the effect of the third-stage negative temperature reheat itself on the state of the precipitated particles is evaluated separately in Table 3. Comparative Example 6 shows that even after cryogenic separation followed by reheat adsorption, the low-temperature and long-term stability were still lower than in Example 1.

[0052] VII. The Influence of the Negative Temperature Recovery Stage on the State of Precipitated Particles Taking Example 1 as an example, samples were taken at the end of the first stage, the end of the second stage of deep freezing, and the end of the third stage of negative temperature recovery. The particle size distribution of the precipitated particles in the wine was determined according to the aforementioned constant temperature particle size detection method. The results are shown in Table 3.

[0053] Table 3. Particle size changes of precipitated particles in the wine at different temperature stages.

[0054] As shown in Table 3, a significant number of precipitated particles were formed after the second stage of cryogenic treatment. After further rewarming to -3°C and maintaining this temperature for 6 hours without intermediate solid-liquid separation, the D50 increased further, and the proportion of fine particles smaller than 2 μm decreased. This change corresponds to the higher membrane filtration flux of Example 1.

[0055] VIII. The effect of pretreatment temperature on the minimum effective activated carbon dosage The activated carbon dosage was varied under different pretreatment methods, with a gradient of 0.04 g / L. Stable turbidity removal was determined by the following criteria: the finished wine was clear at room temperature with no visible suspended matter; after storage at -5℃ for 7 days, the turbidity was no higher than 1.50 NTU with no significant loss of luster or precipitation; and after sealed storage at 20–25℃ for 90 days, the turbidity was no higher than 1.50 NTU with no visible precipitation. The minimum activated carbon dosage required to meet these conditions is shown in Table 4.

[0056] Table 4 Minimum effective activated carbon dosage under different pretreatment methods

[0057] As shown in Table 4, using M1 modified activated carbon can reduce the dosage required to achieve stable turbidity removal compared to ordinary activated carbon. Furthermore, when using the same M1 modified activated carbon, the minimum effective dosage is further reduced to 0.20 g / L when fully implementing the three-stage temperature program. This result indicates a process correlation between the pre-stage segmented temperature treatment and the subsequent low-temperature adsorption; the pre-treatment can reduce the adsorbent load required to achieve the same stability.

[0058] IX. The effect of modified activated carbon dosage on the retention of wine components Using the three-stage temperature program of Example 1, only the amount of M1 added was changed to investigate the effect of activated carbon dosage on the stability of the wine and the retention of target components. The results are shown in Table 5.

[0059] Table 5. Effect of M1 addition amount on treatment effect

[0060] Table 5 shows that under the complete three-stage temperature program, when the amount of M1 added increased from 0.16 g / L to 0.20 g / L, the turbidity at low temperature and after 90 days of storage reached the aforementioned stable turbidity removal criteria. Further increasing the amount of M1 added could further reduce turbidity, but the retention rates of target flavor components and total polyphenols gradually decreased with increasing adsorbent dosage. Considering both stability and component retention results, an M1 addition amount of 0.20–0.40 g / L is feasible, with 0.20–0.32 g / L being suitable for balancing stability and component retention.

[0061] X. Results Analysis As can be seen from the comprehensive examples and comparative examples, for low-alcohol Maotai-flavor liquor containing both higher fatty acid ethyl esters and herbal-derived colloidal and fine suspended components, single cryogenic treatment, single segmented low-temperature treatment, or simply increasing the adsorption intensity of activated carbon are all insufficient to simultaneously ensure low-temperature stability, long-term storage stability, and component retention. This invention first establishes staged precipitation conditions through a first-stage low-temperature treatment at 0–2℃ and a second-stage cryogenic treatment at -10–-6℃. After cryogenic treatment, no intermediate solid-liquid separation is performed; instead, the temperature is restored to -4–-2℃ and maintained, followed by modified activated carbon adsorption within the same negative temperature range. The particle size and minimum effective activated carbon dosage results show that the initial temperature path not only plays a role in precipitation but also affects the particle state and adsorbent load when entering the subsequent adsorption and filtration stages. The comparison between ordinary activated carbon and modified activated carbon further indicates that the pore structure of the subsequent adsorption medium is related to the flavor of the liquor and the retention of herbal soluble components. Therefore, this invention achieves continuous treatment of the complex turbidity system through a sequential combination of segmented crystallization, negative temperature restoration, low-temperature selective adsorption, and filtration.

[0062] The above embodiments are used to illustrate the technical solution of the present invention. For those skilled in the art, without departing from the technical concept disclosed in the present invention, non-critical process parameters can be routinely adjusted according to the specific state of the wine.

Claims

1. A process for removing turbidity from low-alcohol soy sauce-flavored herbal liquor using a segmented crystallization and selective adsorption coupling method, characterized in that, Includes the following steps: S1. The base liquor of the sauce aroma type is diluted and mixed with the herbal extract obtained by extracting Polygonatum sibiricum, Lycium barbarum, Pueraria lobata and Citrus reticulata in a dry base mass ratio of 4:3:2:1 with a volume fraction of 45% ethanol aqueous solution. The herbal extract accounts for 5% to 10% of the total volume of the liquor to be treated after mixing, and the liquor to be treated has an alcohol content of 33 to 42 vol%. S2. Cool the wine to be treated to 0-2℃ at a rate of 0.2-0.4℃ / h and keep it at that temperature for 4-6 h; S3. The wine treated in S2 is further cooled to -10 to -6℃ at a rate of 0.4 to 0.6℃ / h and kept at that temperature for 8 to 12 hours. S4. Warm the wine treated in S3 to -4 to -2°C and keep it warm for 4 to 8 hours. S5. Maintain the temperature of the wine at -4 to -2℃, add 0.20 to 0.40 g / L of modified activated carbon, stir at 40 to 50 r / min for 10 to 20 min, and then allow it to stand in a sealed container at -4 to -2℃ for 3 to 5 h for adsorption. The modified activated carbon is obtained by soaking food-grade coconut shell activated carbon in a 5% to 8% gluconic acid solution for 1 to 3 h, then heat-treating it at 180 to 200℃ for 1 to 2 h under a nitrogen atmosphere, and then washing and drying it. S6. Under conditions not exceeding 0℃, the liquor treated in S5 is subjected to coarse filtration and microporous membrane filtration in sequence; S7. The filtered liquor is warmed and aged to obtain low-alcohol soy sauce-flavored herbal liquor; wherein, S2 to S5 are carried out sequentially, and no solid-liquid separation is performed from the end of S3 to the beginning of S5.

2. The turbidity removal process for low-alcohol soy sauce-flavored herbal liquor according to claim 1, characterized in that, In S1, based on the total dry weight of Polygonatum sibiricum, Lycium barbarum, Pueraria lobata, and Citrus reticulata and the volume of the extractant, the material-to-liquid ratio was 1 g:8 mL. The extract was prepared at 35℃ for 2 h and filtered. The residue was extracted again under the same conditions. The two filtrates were combined and concentrated under reduced pressure at a temperature not exceeding 45℃. When the herbal extract was mixed with the diluted soy sauce-flavored base liquor, the liquor temperature was controlled at 20-25℃, and the mixture was stirred at 30-50 r / min for 15-20 min, followed by standing for 20-40 min.

3. The turbidity removal process for low-alcohol soy sauce-flavored herbal liquor according to claim 1, characterized in that, The alcohol content of the wine to be treated in S1 is 36-40 vol%; the holding temperature in S2 is 1-2℃; the holding temperature in S3 is -9 to -7℃; and the final temperature of the rewarming in S4 is -4 to -3℃.

4. The turbidity removal process for low-alcohol soy sauce-flavored herbal liquor according to claim 1, characterized in that, In step S5, the food-grade coconut shell activated carbon is 120-180 mesh, and the mass-to-volume ratio of activated carbon to gluconic acid solution is 1 g: 10 mL. After soaking, the free liquid is removed, and the temperature is increased to the heat treatment temperature at 3℃ / min under a nitrogen atmosphere. The activated carbon after heat treatment is washed with deionized water until the pH of the final washing solution is 6.5-7.2, and then dried at 100℃ to constant weight.

5. The turbidity removal process for low-alcohol soy sauce-flavored herbal liquor according to claim 4, characterized in that, In S5, the gluconic acid solution has a mass fraction of 5%, the soaking time is 2 h, and the heat treatment temperature is 190℃ and the heat treatment time is 1.5 h.

6. The turbidity removal process for low-alcohol soy sauce-flavored herbal liquor according to claim 1, characterized in that, In S5, the amount of modified activated carbon added is 0.20 to 0.32 g / L.

7. The turbidity removal process for low-alcohol soy sauce-flavored herbal liquor according to claim 1, characterized in that, In S6, the coarse filtration is performed using plate and frame filtration, and the wine after coarse filtration is filtered using a microporous membrane with a pore size of 0.22 μm and a filtration pressure of 0.15 to 0.25 MPa.

8. The turbidity removal process for low-alcohol soy sauce-flavored herbal liquor according to claim 7, characterized in that, In S6, the temperature of the wine to be filtered, the filtration equipment, and the conveying pipeline is not higher than 0°C, and the filtration pressure of the microporous membrane filtration is 0.20 MPa.

9. The turbidity removal process for low-alcohol soy sauce-flavored herbal liquor according to claim 1, characterized in that, In S7, the filtered wine is first warmed to 10-12°C and kept there for 1-3 days, then warmed to 20-25°C and aged for 7-15 days.

10. The turbidity removal process for low-alcohol soy sauce-flavored herbal liquor according to claim 5, characterized in that, The alcohol content of the wine to be treated in S1 is 39 vol%. In S2, the temperature is lowered to 2℃ at 0.3℃ / h and held for 5 h. In S3, the temperature is further lowered to -8℃ at 0.5℃ / h and held for 10 h. In S4, the temperature is restored to -3℃ and held for 6 h. In S5, 0.28 g / L of the modified activated carbon is added at -3℃, stirred at 45 r / min for 15 min, and then allowed to stand for adsorption for 4 h. In S6, after coarse filtration by plate and frame filter, the wine is filtered through a 0.22 μm microporous membrane. In S7, the filtered wine is kept at 12℃ for 2 days and then aged at 22℃ for 10 days.

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