A method of identifying the barrel aging time of an oak barrel aged beer

Abstract

This invention discloses a method for identifying the barrel aging time of oak-aged beer, belonging to the field of beer testing technology. The technical solution includes calculating the barrel aging time of oak-aged beer using the chromatographic peak areas of three flavor markers; the three flavor markers are (Z)-oakolactone, ethyl furoate, and (2,2-diethoxyethyl)benzene; the specific calculation method is: T=[(A1+2×10] 7 The formula is: A1 = (Z)-oak lactone, A2 = ethyl furoate, A3 = (2,2-diethoxyethyl)benzene, and T = barrel aging time of oak barrel-aged beer. This invention addresses the lack of a simple and reliable method for determining the barrel aging time of oak barrel-aged beer in existing technologies.

Description

Technical Field

[0001] This invention belongs to the field of beer testing technology, and in particular relates to a method for determining the aging time of beer barrels aged in oak barrels. Background Technology

[0002] Beer is the world's third-largest consumed beverage, dominating the alcoholic beverage market. China is the world's largest beer market. Changing consumer preferences, the expansion of craft breweries, and intensifying market competition have driven a growing demand for higher quality and more diverse flavors, prompting breweries to innovate through new processing technologies such as barrel aging. Historically, before the widespread adoption of stainless steel, wooden barrels were the primary storage containers for alcoholic beverages. Modern barrel aging aims to enhance sensory characteristics by modulating volatile compounds, improving aroma complexity, and catering to consumer preferences. Barrel aging time is one of the key factors determining the flavor characteristics and market value of barrel-aged beer. Beer undergoes complex chemical changes during barrel aging, particularly the transformation and accumulation of volatile flavor compounds, which are potential biomarkers characterizing the barrel aging process.

[0003] Currently, the industry's assessment of barrel aging time for beer mainly relies on brewers' sensory experience or simple physicochemical indicators (such as color and total acidity), lacking objective, precise, and quantifiable scientific criteria. Therefore, developing a method for identifying barrel aging time for beer using biomarkers is of great significance for beer quality control, authenticity verification, process optimization, and product standardization. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is the lack of a simple and reliable method for identifying the aging time of barrel-aged beer. This invention proposes a simple and reliable method for identifying the aging time of barrel-aged beer using biomarkers.

[0005] To solve the aforementioned technical problem, the technical solution adopted by the present invention is as follows: A method for determining the barrel aging time of oak barrel-aged beer, which calculates the barrel aging time of oak barrel-aged beer by using the TIC peak area of ​​three flavor markers; The three flavor markers are (Z)-oak lactone, ethyl furoate, and (2,2-diethoxyethyl)benzene; The specific calculation method is as follows: T=[(A1+2×10 7 ) / 599942+(A2+852304) / 38613+(A3-574299) / 604282)] / 3 A1 is the TIC peak area of ​​(Z)-oak lactone, A2 is the TIC peak area of ​​ethyl furoate, A3 is the TIC peak area of ​​(2,2-diethoxyethyl)benzene, and T is the barrel aging time of oak barrel-aged beer.

[0006] In some embodiments, oak barrel-aged beer is a strong lager with an alcohol content of 10–12% that has been aged in oak barrels.

[0007] In some embodiments, the method further includes a sample pretreatment step; The sample pretreatment steps for the oak barrel aged beer are as follows: Take the oak barrel aged beer and NaCl together and place them in a headspace sample bottle, mix well, and extract with an extraction head to obtain an extracted sample; The mass-to-volume ratio of NaCl to the oak barrel-aged beer is 2:5; The extraction time is 55-65 min, and the extraction temperature is 45-55℃; the extraction head adopts an extraction head with a three-layer composite coating of DVB / CAR / PDMS.

[0008] In some preferred embodiments, the extraction time is 60 min and the extraction temperature is 50 °C.

[0009] In some embodiments, the method further includes a chromatographic separation step; The extracted sample is introduced into a gas chromatograph after thermal desorption for chromatographic separation. The thermal desorption temperature was 250℃, and the thermal desorption time was 2 min. The temperature program of the column in the gas chromatograph is set as follows: 40 °C for 10 min; increase to 200 °C at 3 °C / min and hold for 30 min; then increase to 250 °C at 30 °C / min and hold for 5 min.

[0010] In some embodiments, the method further includes a mass spectrometry detection step; Mass spectrometry detection was performed using an electron impact ion source with an ionization energy of 70 eV; data acquisition was performed in full scan mode with a scan range of m / z 45–400; the mass analyzer was an Orbitrap high-resolution mass analyzer with a resolution of 60,000 at m / z 200; and both the ion source temperature and the GC-MS transfer line temperature were set to 250 °C.

[0011] In some embodiments, flavor markers are obtained by screening using the following methods: Select multiple oak barrel-aged beer samples with different aging times; HS-SPME-GC-Orbitrap-MS was used to analyze beer samples with different barrel aging times to obtain peak area data matrices of beer samples. Orthogonal partial least squares discriminant analysis was used to analyze the peak area data evidence to screen out the differential volatile substances in beer samples with different barrel aging times that changed in content, newly formed or disappeared with barrel aging time. Among the differentially volatile substances, compounds with flavor activity are selected to obtain flavor compounds; The flavor compounds were subjected to Mantel Test correlation analysis, and compounds with a correlation coefficient |r|>0.8 and a significance level p<0.01 with barrel aging time were selected to obtain flavor markers.

[0012] In some embodiments, oak barrel-aged beer samples were collected from five different barrel aging times: 0 days, 60 days, 100 days, 180 days, and 300 days.

[0013] In some embodiments, the selection criteria for differentially volatile substances are as follows: compounds whose variable importance projection value in the orthogonal partial least squares discriminant analysis model is greater than 1, whose significance level combined with the t-test is p<0.05, and whose difference fold FC is ≥2 or ≤0.5 are selected as differentially volatile substances.

[0014] In some embodiments, differentially volatile substances are compared with a flavor database to obtain flavor compounds.

[0015] In some embodiments, there are 162 differentially volatile substances, 28 flavor compounds, and 3 flavor markers.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for determining the barrel aging time of oak barrel-aged beer. The barrel aging time of oak barrel-aged beer is calculated by the chromatographic peak areas of three flavor markers ((Z)-oak lactone, ethyl furoate, and (2,2-diethoxyethyl)benzene). The method is simple to operate and the results are reliable. Attached Figure Description

[0017] Figure 1 This is a stacked diagram showing the quantity and chemical classification of differentially volatile substances provided in an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions in specific embodiments of the present invention will be described in detail and completely below. Obviously, the described embodiments are only some specific implementations of the overall technical solution of the present invention, and not all implementations. Based on the overall concept of the present invention, all other embodiments obtained by those skilled in the art fall within the protection scope of the present invention.

[0019] This invention provides a method for determining the aging time of oak barrels used for aging beer, comprising: The barrel aging time of oak barrel-aged beer was calculated by the TIC chromatographic peak areas of three flavor markers. The three flavor markers are (Z)-oak lactone, ethyl furoate, and (2,2-diethoxyethyl)benzene; The specific calculation method is as follows: T=[(A1+2×10 7 ) / 599942+(A2+852304) / 38613+(A3-574299) / 604282)] / 3 A1 is the TIC peak area of ​​(Z)-oak lactone, A2 is the TIC peak area of ​​ethyl furoate, A3 is the TIC peak area of ​​(2,2-diethoxyethyl)benzene, and T is the barrel aging time of oak barrel-aged beer.

[0020] In some embodiments, oak barrel-aged beer is a strong lager with an alcohol content of 10–12% that has been aged in oak barrels.

[0021] In some embodiments, the method further includes a sample pretreatment step; The sample pretreatment steps for oak barrel aged beer are as follows: Place oak barrel aged beer and NaCl together in a headspace sample vial, mix well, and extract with an extraction head to obtain the extracted sample; The mass-to-volume ratio of NaCl to oak barrel-aged beer is 2:5; The extraction time is 55-65 min, and the extraction temperature is 45-55℃; the extraction head adopts an extraction head with a three-layer composite coating of DVB / CAR / PDMS.

[0022] The purpose of adding NaCl to oak barrel-aged beer is to improve the extraction efficiency of flavor compounds through the salting-out effect, while suppressing matrix interference such as ethanol, resulting in more accurate quantification and more stable peak areas. A mass-to-volume ratio of 2:5 can produce sufficient salting-out effect, suitable for the ethanol concentration (10–12%) and flavor compound content of barrel-aged beer.

[0023] The extraction temperature is controlled at 45–55℃, which can improve the mass transfer efficiency of volatile components and increase detection sensitivity, while also taking into account thermal stability, avoiding decomposition or structural changes of the target analyte, and ensuring the accuracy of qualitative and quantitative analysis. At the same time, moderate heating can reduce the competitive adsorption of matrices such as ethanol and water, and improve peak shape and quantitative stability.

[0024] The extraction time is set to 55–65 min, which can achieve headspace extraction distribution balance, ensure quantitative reproducibility, and is suitable for quantitative calculation of barrel aging time based on peak area. This time is also conducive to the full enrichment of moderately volatile substances (such as (2,2-diethoxyethyl)benzene), avoiding linear distortion caused by insufficient extraction, while avoiding the introduction of impurities or accelerated aging of the extraction head caused by over-extraction.

[0025] It has a wide polarity coverage and can efficiently enrich different polarity markers such as lactones, esters, and benzene-substituted compounds; it has a large adsorption capacity, strong resistance to matrix interference, and reliable quantification.

[0026] The extraction head, employing a three-layer composite coating of DVB / CAR / PDMS, can achieve broad polarity coverage and efficiently enrich markers of different polarities, such as lactones, esters, and benzene-substituted compounds. Furthermore, this extraction head boasts a large enrichment capacity, high sensitivity, strong resistance to matrix interference, and reliable quantification.

[0027] In some preferred embodiments, the extraction time is 60 min and the extraction temperature is 50°C. This temperature-time synergistic condition achieves a mild and sufficient gas-liquid equilibrium: moderate heating at 50°C accelerates the release rate of the target analyte from the beer matrix to the headspace phase; combined with a sufficient extraction time of 60 min, the system reaches a stable partition equilibrium. This condition ensures the full release of markers such as (Z)-oakolactone, ethyl furoate, and (2,2-diethoxyethyl)benzene without damaging their structure or introducing interference, ensuring that the peak area accurately reflects their content.

[0028] In some embodiments, the sample pretreatment steps are as follows: 5 mL of beer sample and 2.0 g of NaCl are placed in a 20 mL headspace sample vial, mixed by vortexing, and then headspace extracted at 50 °C for 60 min using a DVB / CAR / PDMS coated extraction head; the vortexing conditions are: 500 rpm, 5 min, 50 °C; the extraction head model is 50 / 30 μm × 1 cm, Supelco, PA.

[0029] In some embodiments, the method further includes a chromatographic separation step; The extracted sample is introduced into a gas chromatograph after thermal desorption for chromatographic separation. The thermal desorption temperature was 250℃, and the thermal desorption time was 2 min. The temperature program of the column in the gas chromatograph is set as follows: 40 °C for 10 min; increase to 200 °C at 3 °C / min and hold for 30 min; then increase to 250 °C at 30 °C / min and hold for 5 min.

[0030] In some embodiments, the carrier gas for the gas chromatograph is helium, and the flow rate is 1.2 mL / min.

[0031] In some embodiments, the method further includes a mass spectrometry detection step; Mass spectrometry detection was performed using an electron impact ion source with an ionization energy of 70 eV; data acquisition was performed in full scan mode with a scan range of m / z 45–400; the mass analyzer was an Orbitrap high-resolution mass analyzer with a resolution of 60,000 at m / z 200; and both the ion source temperature and the GC-MS transfer line temperature were set to 250 °C.

[0032] In some embodiments, flavor markers are obtained by screening using the following methods: Select multiple oak barrel-aged beer samples with different aging times; Beer samples with different barrel aging times were analyzed using headspace solid phase microextraction-gas chromatography-electrostatic field orbital trap mass spectrometry (HS-SPME-GC-Orbitrap-MS) to obtain peak area data matrices of beer samples. Orthogonal partial least squares discriminant analysis was used to analyze the peak area data evidence to screen out differential volatile substances in beer samples with different barrel aging times that changed in content, newly formed or disappeared with barrel aging time. Among the differentially volatile substances, compounds with flavor activity are selected to obtain flavor compounds; The flavor compounds were subjected to Mantel Test correlation analysis, and compounds with a correlation coefficient |r|>0.8 and a significance level p<0.01 with barrel aging time were selected to obtain flavor markers.

[0033] In some embodiments, oak barrel-aged beer samples were collected from five different barrel aging times: 0 days, 60 days, 100 days, 180 days, and 300 days.

[0034] In some embodiments, each sample is set up in triplicate, collected directly from the oak barrel, rapidly frozen with liquid nitrogen, and stored in a -80°C freezer until analysis.

[0035] In some embodiments, the method also includes raw data processing of HS-SPME-GC-Orbitrap-MS: peak extraction, alignment, denoising, and normalization; and compound identification: the identification of volatile compounds is completed by comparing retention time, mass spectrometry similarity (>60%), and mass-to-charge ratio, in conjunction with standards referenced to the NIST database.

[0036] In some embodiments, the selection criteria for differentially volatile substances are as follows: compounds whose variable importance projection value in the orthogonal partial least squares discriminant analysis model is greater than 1, whose significance level combined with the t-test is p<0.05, and whose difference fold FC is ≥2 or ≤0.5 are selected as differentially volatile substances.

[0037] In some embodiments, the flavor compounds are obtained by comparing differentially volatile substances with a flavor database.

[0038] In some embodiments, the flavor database is FlavorDB, PubChem, etc.

[0039] In some embodiments, there are 162 differentially volatile substances, 28 flavor compounds, and 3 flavor markers.

[0040] To provide a clearer and more detailed description of the method for determining the aging time of oak barrels used in beer brewing, as provided in the embodiments of the present invention, the following description will be based on specific embodiments.

[0041] Example 1 1) Sample collection All beer samples were produced using the same batch of whole wheat wort and fermented in the same batch, ultimately yielding strong lagers with an alcohol content of 10–12% (v / v). During the barrel aging process, these strong lagers were placed in American bourbon whiskey barrels and aged for 360 days under controlled conditions (0–5°C; relative humidity 30–50%). Beer samples were collected at five different barrel aging times (0, 60, 100, 180, and 300 days). Each sample was replicated in triplicate, collected directly from the oak barrels, rapidly frozen in liquid nitrogen, and stored at -80°C until analysis.

[0042] 2) Data Acquisition High-resolution mass spectrometry data acquisition: Volatile compound analysis was performed using headspace solid-phase microextraction-gas chromatography-electrostatic field orbital trap mass spectrometry (HS-SPME-GC-Orbitrap-MS), equipped with a TG-5SilMS capillary column (25 m × 0.25 mm × 0.25 µm).

[0043] The sample pretreatment steps were as follows: 5 mL of beer sample and 2.0 g of NaCl were placed in a 20 mL headspace vial and vortexed (500 rpm, 5 min, 50 ℃). Then, headspace extraction was performed at 50 ℃ for 60 min using a DVB / CAR / PDMS coated extraction head (50 / 30 μm × 1 cm). The extraction head was then thermally desorbed at the gas chromatograph inlet at 250 ℃ for 2 min (splitless mode). Helium was used as the carrier gas, and the flow rate was kept constant (1.2 mL / min). The column temperature program was set as follows: 40 ℃ for 10 min; increased to 200 ℃ at 3 ℃ / min and held for 30 min; then increased to 250 ℃ at 30 ℃ / min and held for 5 min.

[0044] Mass spectrometry was performed using electron impact ionization (EI) mode with an ionization energy of 70 eV, and data were acquired at full scan (m / z 45–400). The Orbitrap mass analyzer had a resolution of 60,000 (at m / z 200). The ion source and transfer line temperatures were both set to 250 °C.

[0045] Data processing and compound identification: Raw data processing: peak extraction, alignment, noise reduction, and normalization.

[0046] Compound identification: The identification of volatile compounds was completed by comparing retention time, mass spectrometry similarity (>60%), and mass-to-charge ratio, combined with reference to standards and the mass spectrometry database of the National Institute of Standards and Technology (NIST).

[0047] 3) Screening for differentially volatile substances Statistical analysis was performed on the normalized peak area data matrix. Specifically, orthogonal partial least squares discriminant analysis (OPLS-DA) was conducted on samples aged 60 days and 0 days, 100 days and 60 days, 180 days and 100 days, and 300 days and 180 days, respectively. Differentially volatile compounds were screened based on the following criteria: the variable importance projection value (VIP) in the OPLS-DA model was greater than 1, and the significance level of the t-test (T-test) was p < 0.05, with a fold change (FC) ≥ 2 or ≤ 0.5. Figure 1 As shown, a total of 162 differential substances were identified. Among them, 60 differential substances were found between 60-day barrel-aged beer and non-barrel-aged beer; 22 differential substances were found between 100-day barrel-aged beer and 60-day barrel-aged beer; 76 differential substances were found between 180-day barrel-aged beer and 100-day barrel-aged beer; and 54 differential substances were detected between 300-day barrel-aged beer and 180-day barrel-aged beer. The number of differential substances was most significant in the 180-day barrel-aged beer versus 100-day barrel-aged beer comparison. In other words, the effect of barrel aging on volatile compounds exhibits a non-steady-state characteristic as aging time increases. Notably, esters, aromatic compounds, ketones, and heterocyclic compounds are the main chemical categories that undergo changes during barrel aging.

[0048] 4) Mantel Test association analysis to screen time-related biomarkers. Literature and flavor databases were consulted to obtain flavor descriptions of differentially volatile compounds, and compounds with flavor activity were screened for further analysis. Mantel Test correlation analysis was performed on 28 differentially volatile components with flavor activity. The results are shown in Table 1. Three compounds showed a strong correlation with barrel aging time (|r|>0.8, p<0.01): (Z)-oak-lactone, ethyl 2-furoate, and (2,2-diethoxyethyl)benzene. Four other compounds showed moderate correlation (0.7 < |r| < 0.8): acetoxyacetic acid 3-methylbut-2-yl ester, butanedioic acid diethyl ester, methoxyacetaldehyde diethyl acetal, and trans-geranic acid methyl ester. The stable accumulation trends of (Z)-oak lactone, ethyl furoate, and (2,2-diethoxyethyl)benzene over time support their reliability as potential chemical markers for monitoring barrel aging processes.

[0049] Table 1. Results of Mantel Test correlation analysis between flavor compounds and barrel aging time.

[0050] Example 2 1) Sample collection All beer samples were produced using the same batch of whole wheat wort and fermented in the same batch, ultimately yielding strong lagers with an alcohol content of 10–12% (v / v). During the barrel aging process, these strong lagers were placed in American bourbon whiskey barrels and aged for 360 days under controlled conditions (0–5°C; relative humidity 30–50%). Beer samples were collected at three different barrel aging times. Each sample was replicated in triplicate, collected directly from the oak barrels, rapidly frozen with liquid nitrogen, and stored at -80°C until analysis.

[0051] 2) Data Acquisition High-resolution mass spectrometry data acquisition: Volatile compound analysis was performed using headspace solid-phase microextraction-gas chromatography-electrostatic field orbital trap mass spectrometry (HS-SPME-GC-Orbitrap-MS) equipped with a TG-5SilMS capillary column (25 m × 0.25 mm × 0.25 µm).

[0052] The sample pretreatment steps were as follows: 5 mL of beer sample and 2.0 g of NaCl were placed in a 20 mL headspace vial and vortexed (500 rpm, 5 min, 50 ℃). Then, headspace extraction was performed at 50 ℃ for 60 min using a DVB / CAR / PDMS coated extraction head (50 / 30 μm × 1 cm; Supelco, PA). The extraction head was then subjected to thermal desorption at the gas chromatograph inlet at 250 ℃ for 2 min (splitless mode). Helium was used as the carrier gas, and the flow rate was kept constant (1.2 mL / min). The column temperature program was set as follows: 40 ℃ for 10 min; increased to 200 ℃ at 3 ℃ / min and held for 30 min; then increased to 250 ℃ at 30 ℃ / min and held for 5 min.

[0053] Mass spectrometry was performed using electron impact ionization (EI) mode with an ionization energy of 70 eV, and data were acquired at full scan (m / z 45–400). The Orbitrap mass analyzer had a resolution of 60,000 (at m / z 200). The ion source and transfer line temperatures were both set to 250 °C.

[0054] Data processing and compound identification: Raw data processing: peak extraction, alignment, noise reduction, and normalization.

[0055] 3) Calculation of barrel aging time Use the following formula to calculate the barrel aging time. T=[(A1+2×10 7 ) / 599942+(A2+852304) / 38613+(A3-574299) / 604282)] / 3 (A1 is the TIC peak area of ​​(Z)-oak lactone, A2 is the TIC peak area of ​​ethyl furoate, A3 is the TIC peak area of ​​(2,2-diethoxyethyl)benzene, and T is the barrel aging time of oak barrel-aged beer.) Three samples with different barrel aging times were taken, and after testing and analysis, the peak areas were substituted into the above formula to predict the barrel aging time. The predicted results were compared with the actual barrel aging results as follows:

[0056] Verification shows that the time deviation is less than 10%, indicating that the barrel aging time determination method is effective and reliable.

Claims

1. A method for determining the aging time of oak barrels used for aging beer, characterized in that, The barrel aging time of oak barrel-aged beer was calculated by the TIC peak area of ​​three flavor markers. The three flavor markers are (Z)-oak lactone, ethyl furoate, and (2,2-diethoxyethyl)benzene; The specific calculation method is as follows: T = [(A1+2x10 7 ) / 599942 + (A2+852304) / 38613 + (A3-574299) / 604282)] / 3 A1 is the TIC peak area of ​​(Z)-oak lactone, A2 is the TIC peak area of ​​ethyl furoate, A3 is the TIC peak area of ​​(2,2-diethoxyethyl)benzene, and T is the barrel aging time of oak barrel-aged beer.

2. The method for determining the aging time of oak barrels and beer barrels according to claim 1, characterized in that, The oak barrel-aged beer is a strong lager with an alcohol content of 10–12% that has been aged in oak barrels.

3. The method for determining the aging time of oak barrels and beer barrels according to claim 1 or 2, characterized in that, The method further includes a sample pretreatment step; The sample pretreatment steps for the oak barrel aged beer are as follows: Take the oak barrel aged beer and NaCl together and place them in a headspace sample bottle, mix well, and extract with an extraction head to obtain an extracted sample; The mass-to-volume ratio of NaCl to the oak barrel-aged beer is 2:5 (g:ml). The extraction time is 55-65 min, and the extraction temperature is 45-55℃; the extraction head adopts a DVB / CAR / PDMS composite coating extraction head.

4. The method for determining the aging time of oak barrels and beer barrels according to claim 3, characterized in that, The method further includes a chromatographic separation step; The extracted sample is introduced into a gas chromatograph after thermal desorption for chromatographic separation. The thermal desorption temperature was 250℃, and the thermal desorption time was 2 min. The temperature program of the column in the gas chromatograph is set as follows: 40℃ for 10 min; increase to 200℃ at 3℃ / min and hold for 30 min; then increase to 250℃ at 30℃ / min and hold for 5 min.

5. The method for determining the aging time of oak barrels and beer barrels according to claim 4, characterized in that, The method also includes a mass spectrometry detection step; Mass spectrometry detection uses an electron impact ion source for ionization at an ionization energy of 70 eV; data acquisition mode is full scan mode, with a scan range of m / z 45–400; The mass analyzer was an Orbitrap high-resolution mass analyzer, with a resolution of 60,000 at m / z 200; the ion source temperature and GC-MS transfer line temperature were both set to 250 °C.

6. The method for determining the aging time of oak barrels and beer barrels according to claim 1, characterized in that, The flavor markers were obtained by screening using the following method: Select multiple oak barrel-aged beer samples with different aging times; Beer samples with different barrel aging times were analyzed using headspace solid phase microextraction-gas chromatography-electrostatic field orbital trap mass spectrometry (HS-SPME-GC-Orbitrap-MS) to obtain peak area data matrices of beer samples. Orthogonal partial least squares discriminant analysis was used to analyze the peak area data evidence to screen out differential volatile substances in beer samples with different barrel aging times that changed in content, newly formed or disappeared with barrel aging time. Among the differentially volatile substances, compounds with flavor activity are selected to obtain flavor compounds; The flavor compounds were subjected to Mantel Test correlation analysis, and compounds with a correlation coefficient |r|>0.8 and a significance level p<0.01 with barrel aging time were selected to obtain flavor markers.

7. The method for determining the aging time of oak barrels and beer barrels according to claim 6, characterized in that, The oak barrel-aged beer samples were collected from five different barrel aging times: 0 days, 60 days, 100 days, 180 days, and 300 days.

8. The method for determining the aging time of oak barrels and beer barrels according to claim 6, characterized in that, The selection criteria for differentially volatile substances are as follows: compounds with a variable importance projection value greater than 1 in the orthogonal partial least squares discriminant analysis model, a significance level of p < 0.05 in the t-test, and a difference fold FC ≥ 2 or ≤ 0.5 are selected as differentially volatile substances.

9. The method for determining the aging time of oak barrels and beer barrels according to claim 6, characterized in that, The flavor compounds are obtained by comparing the differentially volatile substances with a flavor database.

10. The method for determining the aging time of oak barrels and beer barrels according to claim 6, characterized in that, There are 162 differentially volatile substances, 28 flavor compounds, and 3 flavor markers.

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