Yeast selection strategy method suitable for brewing vitis heyneana craft beer

Abstract

The invention discloses a yeast selection strategy method suitable for brewing craft downy grape beer, and relates to the field of beer brewing. Comprising the following steps: (1) aiming at the characteristics of a target wine body, selecting various saccharomyces cerevisiae as candidate yeasts; (2) respectively carrying out fermentation experiments on the vitis heyneana crafted beer by utilizing the candidate yeasts and recording data; (3) carrying out deep analysis and comparison on data obtained by the fermentation experiment; and (4) determining the type of the yeast most suitable for brewing the downy grape flavor beer according to analysis and evaluation results. The multiplication capacity, the fermentation capacity and the alcohol production capacity of various yeasts are compared and analyzed, the physical and chemical indexes and the flavor substance content of the vitis heyneana crafted beer obtained through yeast fermentation are detected, and the yeast suitable for brewing the vitis heyneana crafted beer is screened in combination with a sensory evaluation result. And a key technical support is provided for producing the craft beer with rich vitis heyneana flavor and remarkable nutrition and health-care effects.

Description

Technical Field

[0001] The present invention relates to the field of beer brewing, and particularly to a yeast selection strategy method suitable for the brewing of fine wine made from Vitis heyneana Roem. Background Art

[0002] The raw materials of fine wine made from Vitis heyneana Roem mainly include water, malt, hops and yeast. Malt infuses nutrients into the wort, such as fermentable sugars, amino acids, vitamins, inorganic salts, etc. Hops bring bitterness and aroma to the wort, while yeast is required to convert the wort into beer. The essence of the fermentation of fine wine made from Vitis heyneana Roem is a process in which yeast utilizes the nutrient substances in the wort for growth and development and produces flavor metabolites. Different yeasts have different fermentation characteristics and can bring different flavors to fine wine made from Vitis heyneana Roem. The fermentation performance of yeast mainly includes the number of yeast during the fermentation process, the sugar reduction rate of yeast, and the alcohol production ability of yeast. The main period for yeast to synthesize secondary metabolites (including off-flavor substances such as diacetyl and acetaldehyde) is the logarithmic growth phase. Yeast with too fast reproduction rate is likely to produce excessive off-flavor substances, while yeast with slow reproduction rate and low sugar reduction efficiency increases the time cost of fermentation.

[0003] The metabolic pathway of brewer's yeast is complex, and its metabolites can reach hundreds of kinds. These metabolites include higher alcohols, esters, aldehydes, organic acids, etc. Although their contents are very small, they have a significant impact on the flavor of beer. When the content of higher alcohols is within a certain range, it can make the wine body plump, but if the content is too high, it is easy to cause the beer to have an alcoholic taste and make people "feel dizzy". Ester substances include ethyl acetate, isobutyl acetate, isoamyl acetate, ethyl octanoate, etc., which can bring fruity aroma to beer, but if the content exceeds a certain range, it will bring off-flavors such as solvent flavor to beer. There are many types of brewer's yeast, and different yeasts can metabolize and produce different flavor substances, presenting different overall flavors and being suitable for different beer styles. How to improve the quality of fine wine made from Vitis heyneana Roem by selecting suitable yeast is the key concern of each brewer.

[0004] Fine wine made from Vitis heyneana Roem is favored by consumers because of its unique flavor and nutritional value. However, during the brewing process of fine wine made from Vitis heyneana Roem, the selection of yeast has an important impact on the physical and chemical properties, flavor substances and sensory evaluation of the product. For a specific fine wine made from Vitis heyneana Roem, such as fine wine made from Vitis heyneana Roem, it is necessary to select the best brewing yeast to ensure the flavor and quality of the product. Currently, the application research of Vitis heyneana Roem in beer brewing is not sufficient, and the selection of yeast lacks scientificity and systematicness, resulting in the inability to coordinate and integrate the flavor of Vitis heyneana Roem and the taste of beer, and even may produce adverse chemical reactions, affecting the overall flavor of beer. Summary of the Invention

[0005] The object of the present invention is to solve the above problems in the prior art, and to provide a yeast selection strategy method suitable for the brewing of fine wine made from Vitis heyneana, so as to provide key technical support for the brewing of fine wine made from Vitis heyneana.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A yeast selection strategy method suitable for fine wine made from Vitis heyneana includes the following steps:

[0008] (1) According to the characteristics of fine wine made from Vitis heyneana, select a variety of brewing yeasts as candidate yeasts;

[0009] In the present invention, based on the fact that Vitis heyneana juice is rich in natural organic acids and has a high acidity, and based on the yeast metabolic characteristics and flavor regulation potential, a variety of yeasts that can balance the sour taste of the raw materials and achieve a soft, fresh and harmonious taste of the wine body are screened out as candidate yeasts, and their adaptability to acidic environment and ester synthesis ability are mainly investigated. Therefore, five yeasts, namely Nottingham, Cologne, LONDON, S-04, and US-05, are selected as candidate yeasts;

[0010] (2) Use the candidate yeasts to conduct fermentation experiments on fine wine made from Vitis heyneana respectively and record the data;

[0011] (3) Deeply analyze the data obtained from the fermentation experiments, compare the proliferation ability, fermentation ability, alcohol production ability of each yeast, and the differences in flavor substances, physical and chemical properties, and sensory evaluation of the beers fermented by different yeasts, evaluate the influence of different yeasts on the flavor and quality of fine wine made from Vitis heyneana, and focus on considering indicators such as alcohol-ester ratio, ester fragrance, wine body sour taste, turbidity, etc.;

[0012] (4) According to the analysis and evaluation results, determine the yeast species most suitable for brewing fine wine with Vitis heyneana flavor.

[0013] Further, in step (2), the inoculation amount of each yeast is wort. After inoculating the yeast, every Take a sample to measure the yeast number in the fermentation broth and the alcohol content of the fermentation broth. Record the mass of the fermentation flask once before and after sampling. The weight loss of the fermentation flask is the difference between the mass of the fermentation flask before the current sampling and the mass of the fermentation flask after the previous sampling, which is used to measure the fermentation situation.

[0014] Further, in step (3), the proliferation ability of the yeast is evaluated by measuring the change in the yeast number in the fermentation broth during the fermentation process, the fermentation ability of the yeast is evaluated by measuring the change in the carbon dioxide loss rate during the fermentation process to represent the change in the yeast's sugar reduction rate, and the alcohol production ability of the yeast is evaluated by measuring the alcohol content at different fermentation stages.

[0015] Further, in step (3), the content of flavor substances in the fermented beer is detected by a headspace gas chromatograph.

[0016] Further, in step (3), a tasting panel is composed of BJCP professional judges and professional teachers. Each taster conducts a sensory evaluation of the Vitis heyneana fine brewing beer in an independent tasting room from four aspects: appearance, foam, aroma, and taste according to the sensory evaluation standard table of Vitis heyneana fine brewing beer.

[0017] Further, in step (3), the characteristic flavor substance indexes of the Vitis heyneana fine brewing beer to be detected are: (1) total ester content ; (2) key ester concentration: ethyl acetate (fruity ester) 、isopentyl acetate (banana ester) 、phenethyl acetate (floral ester) ; (3) alcohol-ester ratio (higher alcohols / esters) ; (4) off-flavor esters: ethyl caprate (yeast flavor indicator) 、acetaldehyde (producing green flavor) .

[0018] Further, in step (3), the physical and chemical property indexes of the Vitis heyneana fine brewing beer to be detected are: final wort concentration 、final concentration 、fermentation degree 65%-75%, alcohol content 4.5%-6.0% vol, colority 13-16 EBC, turbidity 、total acid 、pH value 3.4-3.6, bitterness 12-16 BU.

[0019] Further, in step (4), the yeast most suitable for brewing Vitis heyneana flavored beer is determined to be Nottingham yeast.

[0020] Compared with the prior art, the beneficial effects obtained by the technical solution of the present invention are:

[0021] According to the fact that Vitis heyneana juice is rich in natural organic acids and has a high acidity, based on the metabolic characteristics of yeast and its flavor regulation potential, a variety of yeasts that can balance the sour taste of raw materials and achieve a soft, refreshing and harmonious taste of the wine body are selected as candidate yeasts, and their adaptability to acidic environments and ester synthesis ability are mainly investigated. Therefore, five yeasts, namely Nottingham, Cologne, LONDON, S-04, and US-05, are selected as candidate yeasts.

[0022] The present invention has successfully achieved the multi-index collaborative evaluation of fine-brewed beer from Vitis heyneana: determining the ranges of physical and chemical indexes such as total acid, turbidity, alcohol content, and fermentation degree to ensure the balance of the wine body and the process efficiency; quantitatively analyzing key esters (such as ethyl acetate and isoamyl acetate), higher alcohols (such as isoamyl alcohol), and off-flavor substances (such as acetaldehyde and ethyl caprate) by GC-MS to ensure harmonious flavor and no unpleasant off-flavors; professional judges quantify the scores through a sensory scoring system, verifying the product quality from multiple dimensions such as appearance, aroma, and taste, solving the problem that it is difficult to coordinate the flavor and the wine body in fine-brewed beer from Vitis heyneana, and greatly improving the sensory consistency of the product.

[0023] The present invention has successfully screened out Nottingham yeast as the most suitable yeast species for brewing fine-brewed beer from Vitis heyneana. Nottingham yeast has a moderate proliferation rate, moderate fermentation ability, and strong alcohol-producing ability. The fine-brewed beer from Vitis heyneana fermented with Nottingham yeast has the characteristics of a moderate alcohol-ester ratio, prominent ester fragrance, clear wine body, moderate acidity, etc., and has a high sensory score, bringing a new choice of a novel, unique, delicious, and healthy drink for consumers.

[0024] The innovation in the yeast selection strategy of the present invention lies in constructing a scientific and systematic yeast screening system for the raw material characteristics and flavor requirements of fine-brewed beer from Vitis heyneana. Traditional yeast selection mostly relies on experience and lacks in-depth research on the adaptability of yeast to specific raw materials. Based on the characteristics of Vitis heyneana juice being rich in natural organic acids and having a high acidity, the present invention accurately screens out five yeast species, namely Nottingham, Kolsch, LONDON, S-04, and US-05, as candidate yeasts, and focuses on investigating the adaptability of yeast to acidic environments and the ester synthesis ability, which is a direction that has not been fully concerned in previous studies. Description of the Drawings

[0025] Figure 1 Shows the changes in the number of yeasts in the fermentation broth during the fermentation of different yeasts;

[0026] Figure 2 Shows the changes in the carbon dioxide loss during the fermentation of different yeasts;

[0027] Figure 3 Shows the changes in the alcohol content during the fermentation of different yeasts;

[0028] Figure 4 Shows the comparison of the alcohol-ester ratios of fine-brewed beer from Vitis heyneana obtained by inoculating different yeasts. Detailed Embodiments

[0029] In order to make the technical problems, technical solutions, and beneficial effects to be solved by the present invention clearer and more understandable, the following further elaborates on the present invention in conjunction with the drawings and embodiments.

[0030] The following provides a detailed description of specific embodiments of the present invention, but the scope of the present invention is not limited by these embodiments. Without departing from the spirit and scope of the present invention, various changes and improvements will occur. What is described in the following embodiments only illustrates the principles of the present invention, and various processes and methods not described in detail are conventional methods well known in the art. It should be understood that these embodiments are only for exemplifying the present invention and not limiting the scope of the present invention in any way.

[0031] Example 1

[0032] A yeast selection strategy method suitable for fine brewing beer with Vitis heyneana, the steps are as follows:

[0033] S1. Yeast species screening: In view of the characteristics of fine brewing beer with Vitis heyneana, five dry yeast powders, namely Nottingham, Kolsch, LONDON, S-04, and US-05 yeasts, are selected as candidate yeasts. The characteristic of these five yeasts is that they can bring a relatively soft and refreshing body to the beer. S-04 yeast (model: S-04), US-05 yeast (model: US-05), these two yeasts are purchased from Fermentis SAS; Nottingham yeast (model: ), LONDON yeast (model: London ), Kolsch yeast (model: ) are purchased from Lallemand Brewing.

[0034] S2. Yeast fermentation experiment: Use the candidate yeasts to conduct fermentation experiments on fine brewing beer with Vitis heyneana respectively and record the data. The inoculation amount of each yeast is 0.5 g / L of wort. After inoculating the yeast, samples are taken every 12 h, and the sampling amount is 1.5 mL, which is used to measure the yeast count in the fermentation broth and the alcohol content of the fermentation broth. Record the mass of the fermentation flask once before and after sampling. The weight loss of the fermentation flask is the difference between the mass of the fermentation flask before the current sampling and the mass of the fermentation flask after the previous sampling.

[0035] S3. Compare the properties of each yeast: Evaluate the proliferation ability of the yeast by measuring the change in the yeast count in the fermentation broth during the fermentation process, evaluate the fermentation ability of the yeast by measuring the carbon dioxide loss during the fermentation process to represent the change in the yeast sugar reduction rate, and evaluate the alcohol production ability of the yeast by measuring the alcohol content at different fermentation stages.

[0036] S4. Compare the differences in flavor substances and physical and chemical properties of beers fermented by different yeasts: The content of flavor substances in the fermented beer is detected using a GC9270PLUS headspace gas chromatograph. The main physical and chemical properties investigated are the final wort concentration, terminal concentration, fermentation degree, alcohol content, color, turbidity, total acid, pH, bitterness, etc.

[0037] S5. Sensory evaluation: A 10-person evaluation panel consisting of 6 BJCP professional judges and 4 professional teachers, with 5 males and 5 females in total. Each evaluator conducts a sensory evaluation of the Vitis heyneana fine beer from four aspects: appearance, foam, aroma, and taste in an independent sensory evaluation room according to the sensory evaluation standard table for Vitis heyneana fine beer.

[0038] S6. Determine the optimal yeast: Based on the analysis and evaluation results, determine the yeast type most suitable for brewing Vitis heyneana flavored beer.

[0039] Index determination

[0040] Determination of alcohol content: Referring to GB / T4928-2008 "Beer Analysis Method", the alcohol content of the obtained Vitis heyneana fine beer is determined by high-performance liquid chromatography. The sample is degassed by ultrasound and then centrifuged, and the supernatant is taken and filtered through a 0.45μm filter membrane for standby. The detection conditions are: the chromatographic column model is ; the injection volume is 20μL; the column temperature is 35°C; the detector temperature is 35°C; the mobile phase is sulfuric acid solution; the flow rate is 0.6mL / min; the detector is an RI detector. The retention time of the ethanol standard is and the standard curve is .

[0041] Determination of apparent concentration: Measuring the concentration of a sample is actually measuring the density of the sample and then converting it to the concentration of the sample. When the alcohol in the sample is not removed, the measured concentration is the apparent concentration; when the alcohol in the sample is removed, the measured concentration is the true concentration (alcohol will reduce the density of the sample, resulting in the measured concentration of the sample being smaller than the true concentration). The concentration of the sample obtained by measuring the sample with a saccharimeter is the apparent sugar content of the sample, also known as the apparent concentration. Pour an appropriate amount of the sample into a graduated cylinder, gently place the saccharimeter into the graduated cylinder, and after the saccharimeter stabilizes, read the value on the upper part of the saccharimeter. This value needs to be calibrated. Measure the beer temperature with the thermometer at the lower part of the saccharimeter. If the temperature is 20°C, no calibration is required. If it is lower than 20°C or higher than 20°C, calibration needs to be carried out according to the actual temperature.

[0042] Determination of true concentration: Use Determine the true concentration by the following method. Accurately measure 100.0 g of the sample into a round-bottom distillation flask, then rinse the measuring cylinder with 50.0 mL of distilled water and pour it all into the flask. Add a few pieces of porcelain chips to the flask and start distillation. When the liquid volume is about 1 / 3 of the original volume, stop distillation (the distillation time is controlled within 30 - 60 min). Remove the distillation flask and wait for it to cool to room temperature, then add distilled water to make up to 100.0 g. Pour the residue into a clean and dry density bottle, measure the relative density of the residue, and then look up the number of grams of extract in 100 g of the sample ( ), which is the true concentration of the beer. The relative density of the residue is calculated according to the formula:

[0043]

[0044] In the formula:

[0045] m2—the sum of the mass of the density bottle and the residue, in grams (g);

[0046] m1—the sum of the mass of the density bottle and distilled water, in grams (g);

[0047] m—the mass of the density bottle, in grams (g).

[0048] Determination of fermentation degree: The fermentation degree is calculated according to the formula:

[0049]

[0050] In the formula:

[0051] OG—the original wort concentration of the sample, in ;

[0052] FG—the final concentration of the sample, in .

[0053] Determination of total acid: Use the indicator method in to determine the total acid content of the sample. Add 100.0 mL of water to a 250 mL conical flask, heat to boiling, keep it for 2 min, then add 10.0 mL of degassed beer, continue heating for 1 min, and make the solution boil again within the last 30 s, then quickly take it out and let it cool naturally for 5 min, and then quickly rinse the outer wall of the conical flask with tap water to cool the solution to room temperature rapidly. Add 0.5 mL of phenolphthalein solution and titrate with 0.1 mol / L sodium hydroxide solution until the solution turns light pink, which is the titration end point, and record the volume of sodium hydroxide solution consumed. The total acid content of the sample (i.e., the number of milliliters of 1.0 mol / L sodium hydroxide standard titrant consumed by 100 mL of the sample) is calculated according to the formula:

[0054]

[0055] Where:

[0056] X—the total acid content of the sample ( );

[0057] —the concentration of the standard sodium hydroxide titrant ( );

[0058] —the volume of the standard sodium hydroxide titrant consumed (mL);

[0059] 10—the coefficient for converting to 100 mL of the sample.

[0060] Determination of bitterness: Accurately pipette 10.0 mL of the non-degassed beer sample (at 10 °C) into a 50 mL centrifuge tube, add a drop of octanol, add hydrochloric acid solution and 20.0 mL of isooctane, tighten the centrifuge tube cap, and shake for 15 min using an electric shaker. The liquid after shaking should be milky. Then centrifuge for 10 min using a centrifuge and pipette the upper isooctane layer liquid into a 10 mm quartz cuvette. Using isooctane as the blank control, measure the absorbance of the sample at a wavelength of 275 nm. The bitterness of the sample is calculated according to the formula:

[0061]

[0062] Where:

[0063] X—the bitterness of the sample, in bitterness units (BU);

[0064] —the absorbance of the sample measured at a wavelength of 275 nm;

[0065] 50—conversion coefficient.

[0066] Determination of color: Determine the color of the beer according to the spectrophotometer method in GB / T 4928-2008. After the sample is pre-degassed, centrifuge at 4000 r / min for 10 min using a centrifuge, take an appropriate amount of the sample and inject it into a 10 mm glass cuvette. First, adjust the instrument zero with ultrapure water, and then measure the absorbance of the sample at wavelengths of 430 nm and 700 nm respectively.

[0067] If , indicating that the sample is transparent, then calculate the color of the sample according to the formula. If , indicating that the sample is turbid, it needs to be centrifuged or filtered before measuring again. If , then the sample needs to be diluted before measuring.

[0068]

[0069] Where:

[0070] S—the chromaticity of the sample, in EBC units;

[0071] —the absorbance of the sample measured at a wavelength of 430 nm using a 10-mm glass cuvette;

[0072] 25—the thickness converted to a standard cuvette, in millimeters (mm);

[0073] n—the dilution factor.

[0074] Determination of turbidity: Use a turbidimeter to measure the turbidity of the beer sample. First, calibrate the instrument with a standard turbidity solution. After calibration, add the degassed but unfiltered beer sample to the sample bottle. The sample temperature is , shake well, and place it in the turbidimeter for reading.

[0075] Determination of total sugar content: The phenol-sulfuric acid method is used to determine the total sugar content. Accurately prepare a 6% aqueous phenol solution, which needs to be stored in the dark and refrigerated. Take 200 μL of the diluted wort in a centrifuge tube, and successively add 100 μL of the 6% phenol solution and 500 μL of sulfuric acid. Shake well, let stand for 5 min, heat in a water bath at 40 °C for 30 min, then measure the absorbance at a wavelength of 490 nm, and substitute it into the standard curve ( , ) to obtain the total sugar content in the diluted wort, and then multiply by the corresponding dilution factor to obtain the total sugar content in the wort.

[0076] Determination of fermentable sugar content: The high-performance liquid chromatography method is used to determine the fermentable sugar content in the wort. Use chromatographic column ( , 4 μm); the mobile phase is sulfuric acid solution, the flow rate is 0.6 mL / min; the injection volume is 10 μL; the column temperature: 30 °C; the detector: RI detector.

[0077] Determination of flavor substances: The content of flavor substances is detected using a GC9270PLUS headspace gas chromatograph. The sample treatment and detection conditions are as follows: Sample pretreatment: Take out the beer sample placed in the refrigerator and wait for it to return to room temperature. Take an appropriate amount of beer and place it in an ultrasonic cleaner for 10 min of degassing. After degassing, measure 20 mL and place it in a headspace bottle for standby; Headspace conditions: The equilibrium temperature is 80 °C, the sampling needle temperature is 95 °C, the valve box temperature is 110 °C, the transfer line temperature is 120 °C, the equilibrium time is 30 min, and the flow rate is 15 mL / min; Gas chromatography conditions: The chromatographic column model ( ), the detector is an FID detector. The carrier gas is nitrogen. Sampling is carried out in constant flow mode with a flow rate of 1.5 mL / min and a split ratio of 15%. The column temperature is raised from room temperature to 90 °C and held for 5 min, the target temperature is 180 °C with a heating rate of 15 °C / min and held for 5 min, the target temperature is 240 °C with a heating rate of 20 °C / min and held for 15 min, and the total running time is 34 min.

[0078] The retention times and standard curves of each standard product are shown in Table 1.

[0079] Table 1 Retention times and standard curves of flavor substance standard products

[0080]

[0081] Sensory evaluation of Vitis heyneana fine brewing beer: When conducting the sensory evaluation of beer, the samples need to be coded secretly first and kept at a constant temperature of 12 - 15 °C. Then, at the same height (3 cm from the cup mouth) and injection flow rate, the samples are injected into clean and dry beer tasting cups according to the numbers. Then, several professional beer tasters are invited to observe, evaluate, and score the appearance, aroma, taste, and mouthfeel according to the scoring table. The sensory evaluation standards of Vitis heyneana fine brewing beer are shown in Table 2.

[0082] Table 2 Sensory evaluation standard table of Vitis heyneana fine brewing beer

[0083]

[0084] Note: This sensory evaluation standard table is designed and modified by referring to the scoring items and score design of the BJCP scoring table, combining the scoring rules of fruit beer and the fruit characteristics of Vitis heyneana.

[0085] Test result 1:

[0086] The changes in the number of yeasts in the fermentation broth during the fermentation process of different yeasts were measured as Figure 1 shown. Initially, the inoculation amounts of the five yeasts were the same, all being 2.50×10 6 cells / mL. After inoculation, the proliferation rate of LONDON yeast was the fastest, followed by S - 04 yeast, and the other three yeasts all had a certain lag phase. Almost all five yeasts reached the peak number of yeasts at 48 h. The peak number of yeasts of LONDON yeast was the largest, being 1.50×10 7 cells / mL, followed by Kölsch yeast and Nottingham yeast, being 1.46×10 7 cells / mL and 1.35×10 7 cells / mL respectively, and the proliferation rates of these three yeasts were the fastest. The proliferation rate of US - 05 yeast was the slowest, with a lag phase of about 24 h. Its quantity was small in the initial stage of fermentation and only 9.51×10 6After the peak of fermentation, yeast activity decreased, and the yeast with insufficient activity settled to the bottom of the fermentation bottle. The number of yeast in the fermentation liquid decreased significantly. The number of Nottingham yeast decreased the fastest and had the best cohesion, which was conducive to the recovery and removal of yeast. Cologne yeast and S-04 yeast were second, and both could drop to 0.35×10 at 144h. 6 The LONDON yeast had poor cohesion and the yeast count was 1.30×10 at 144h. 6 The US-05 yeast had the worst cohesion, with 3.24×10 6 A yeast.

[0087] It can be seen that the proliferation rate of LONDON yeast is too fast in the early stage, which is easy to produce odor, while the proliferation rate of US-05 yeast is slow, which increases the time cost invisibly and is not suitable for fermenting hairy grape craft beer. The proliferation rates of S-04, Nottingham and Cologne yeasts are moderate, which reduces the risk of producing too many odor substances while ensuring the fermentation rate, and are suitable for fermenting hairy grape craft beer.

[0088] Test Result 2:

[0089] At the start of beer fermentation, yeast uses O2 dissolved in the wort for aerobic respiration and reproduces rapidly. When O2 is exhausted, yeast starts anaerobic respiration and converts fermentable sugars into alcohol and CO2. In the early stage of fermentation, the fermentation bottle is indirectly connected to the outside world through a water seal, and the generated CO2 escapes directly into the air. Because pressure inhibits yeast activity, yeast produces more acetaldehyde and less ester substances. The more vigorous the yeast fermentation, the more CO2 escapes, the more the fermentation liquid loses quality, and the faster the yeast reduces sugar.

[0090] The changes in carbon dioxide loss during fermentation of different yeasts were measured. Figure 2 As shown. London yeast started fermentation at the fastest rate, with CO2 loss reaching 2.27g from 0 to 12h. The rate was faster than other yeasts in the early stage of fermentation, but after the peak of fermentation, the fermentation rate dropped rapidly. Except for US-05 yeast, which reached the peak mass loss at 60h, the other four yeasts reached the peak mass loss at 48h, among which London yeast and Cologne yeast had the highest mass loss, at 4.86g and 4.64g respectively. At 144h, US-05 yeast still produced CO2, and the fermentation was not yet completed, while the carbon dioxide loss of the other four yeasts was less than 0.20g, and the fermentation basically stopped.

[0091] It can be seen that the fermentation rate of LONDON yeast is too fast, while that of US-05 yeast is too slow, so they are not suitable for fermenting and producing fine Vitis heyneana beer. The fermentation rates of S-04 yeast, Nottingham yeast and Kolsch yeast are roughly the same, with a moderate fermentation rate, and they are more suitable for fermenting and producing fine Vitis heyneana beer.

[0092] Test result 3:

[0093] The changes in alcohol content during the fermentation of different yeasts are measured as Figure 3 shown. LONDON yeast produces more alcohol in the early stage because its fermentation rate is faster in the initial stage of fermentation, converting more sugar into alcohol. After 60 h, the content of fermentable sugar in the fermentation broth is less, the fermentation rate drops significantly, and the alcohol content in the fermentation broth tends to be stable. The fermentation rates of S-04, Nottingham and Kolsch yeasts are similar, and their alcohol-producing abilities are similar. The alcohol content tends to be stable after 120 h. The fermentation rate of US-05 yeast is the slowest, and the alcohol content has not yet stabilized at 144 h. Finally, the alcohol contents in the beer samples fermented by Kolsch, Nottingham and S-04 yeasts are relatively high, 5.31%vol, 5.22%vol and 5.24%vol respectively, while the alcohol contents in the beer samples fermented by LONDON yeast and US-05 yeast are relatively low, 4.83%vol and 4.91%vol respectively. This is because different yeasts have different metabolic degrees of maltotriose, and yeasts with lower metabolic ability of maltotriose produce less alcohol.

[0094] It can be seen that LONDON yeast has the fastest fermentation rate, but its alcohol-producing ability is weak. Kolsch, Nottingham and S-04 yeasts have a relatively fast fermentation rate and a strong alcohol-producing ability, while US-05 yeast has the slowest fermentation rate and a weak alcohol-producing ability.

[0095] Test result 4:

[0096] The main flavor substances and their contents of the fine Vitis heyneana beer obtained by inoculating different yeasts are measured as shown in Table 3.

[0097] Table 3 Main flavor substances and their contents of the fine Vitis heyneana beer

[0098]

[0099] The ratio of higher alcohols to esters is the ratio of the content of higher alcohols to esters in beer, and it is an index used to measure the content of higher alcohols and main esters in beer. Generally, it is appropriate to control the ratio of higher alcohols to esters between 3 and 5. As Figure 4 can be seen, the ratios of higher alcohols to esters of S-04, US-05, LONDON, Nottingham and Kolsch yeasts are 3.16, 4.04, 3.84, 3.48 and 3.99 respectively. The ratios of higher alcohols to esters of US-05 yeast and Kolsch yeast are relatively high, but both are between 3 and 5, and the body flavor is balanced and coordinated.

[0100] The esters in beer are mainly divided into volatile esters and non-volatile esters. The volatile esters mainly include ethyl acetate, phenethyl acetate, isobutyl acetate, isoamyl acetate, citronellyl acetate, etc. Among the five yeasts, S-04 yeast has the strongest ability to produce ethyl acetate, which is 46.90 mg / L. S-04 yeast also has the strongest ester-producing ability, with an ester production of 113.34 mg / L. Nottingham yeast has the second-strongest ester-producing ability, which is 95.09 mg / L, while the ester-producing abilities of US-05, LONDON, and Cologne yeast are relatively close, being 76.49 mg / L, 81.70 mg / L, and 77.62 mg / L respectively.

[0101] Common off-flavors in beer include yeast flavor, and its indicator is ethyl caprate. The threshold of ethyl caprate in beer is 1.5 mg / L. The ethyl caprate of the five yeasts is less than 1.5 mg / L, and there is no yeast odor.

[0102] α-Terpineol, geraniol, and linalool in beer mainly come from hops. The terpene compounds in hops have low solubility in water and strong volatility. Most of them volatilize during the boiling process, while substances such as esters and alcohols have relatively weak volatility and can be well retained during the boiling process. Affected by the technological process and the intensity of fermentation, the contents of α-terpineol, geraniol, and linalool in the five beers are slightly different, but the difference is not significant.

[0103] Acetaldehyde is a by-product of yeast fermentation, mainly obtained by the oxidation and conversion of ethanol. Excessive acetaldehyde will not only give the beer an off-flavor of "green flavor" but also be harmful to health. The acetaldehyde contents produced by the five yeasts are all less than their thresholds, with relatively low contents, and the beer has no green flavor.

[0104] Citral, ethyl isovalerate, and ethyl isobutyrate are unique to the fine-fermented beer of Vitis heyneana with the addition of Vitis heyneana juice. Since the addition amounts of Vitis heyneana juice in the five fine-fermented beers of Vitis heyneana are the same, the contents of the three substances are not very different.

[0105] Thus, it can be seen that the contents of off-flavor components in the fine-fermented beer of Vitis heyneana fermented with the above five yeasts are all lower than the thresholds. The alcohol-ester ratios of the five fine-fermented beers of Vitis heyneana are all relatively moderate. However, the alcohol-ester ratios of the fine-fermented beer of Vitis heyneana fermented with S-04 and Nottingham yeast are relatively low, and their ester production is also the highest. The ester fragrance is more prominent, which can add some floral and fruity aromas to the beer and make the aroma layer of the beer richer. Considering from the perspective of the flavor of fine-fermented beer, S-04 and Nottingham yeast are more suitable for brewing the fine-fermented beer of Vitis heyneana.

[0106] Test result 5:

[0107] The physical and chemical properties and contents of the fine-fermented beer of Vitis heyneana obtained with different inoculated yeasts are listed in Table 4.

[0108] Table 4 Physicochemical properties of different Vitis heyneana fine brewing beers

[0109]

[0110] The true fermentation degrees of US-05 yeast and LONDON yeast are relatively low because their metabolism of maltotriose is relatively low, so the alcohol content is relatively low. While the fermentation degrees of S-04, Nottingham and Kolsch yeast are relatively high, all exceeding 70%, the residual sugar in the beer is relatively less, and the alcohol content is relatively high. The flocculation properties of US-05 yeast and LONDON yeast are weak, the turbidity of the beer is large, and the light transmittance of the wine body is poor. The total acid content of the Vitis heyneana fine brewing beer fermented by US-05 yeast and Nottingham yeast is relatively low, the pH value is relatively high, and the acid feeling of the wine body is relatively low.

[0111] The colority of beer is greatly affected by factors such as the type and dosage of malt, wort concentration, boiling time, boiling intensity, colority of fruit juice, addition amount of fruit juice, and addition time of fruit juice; the bitterness of beer mainly comes from hops and is greatly affected by the α-acid content of hops, addition amount of hops, and addition time of hops. The above two indicators are less affected by yeast type and the numerical differences are also small.

[0112] Thus, it can be seen that Nottingham yeast is more suitable for brewing Vitis heyneana fine brewing beer. Although the fermentation degree of Nottingham yeast is relatively high, the total acid of the final beer is relatively low. The flocculation property of Nottingham yeast is good, and the turbidity of the Vitis heyneana fine brewing beer fermented by Nottingham yeast is relatively low, and the wine body is relatively clear.

[0113] Test result 6:

[0114] The Vitis heyneana fine brewing beers obtained by inoculating different yeasts were scored using the sensory evaluation method, and the results are shown in Table 5. The Vitis heyneana fine brewing beer fermented by Nottingham yeast has the highest score of 82 points; followed by that of LONDON yeast, which is 79 points; those of S-04, US-05, and Kolsch yeast are lower. The flocculation properties of S-04, Nottingham and Kolsch yeast are relatively high, and the wine body is relatively clear. The flocculation properties of US-05 and LONDON yeast are weak, the wine body is slightly turbid, and the score is slightly lower. Thus, it can be known that Nottingham yeast is more suitable for fermenting Vitis heyneana fine brewing beer.

[0115] Table 5 Sensory evaluation of different Vitis heyneana fine brewing beers

[0116]

[0117] In the above experimental process, the present invention adopts an innovative method of collaborative evaluation of multiple indicators. It not only measures conventional physical and chemical indicators such as total acid, turbidity, alcohol content, and fermentation degree to ensure the balance of the wine body and the process efficiency, but also quantitatively analyzes key flavor substances such as esters (such as ethyl acetate, isoamyl acetate), higher alcohols (such as isoamyl alcohol), and off-flavor substances (such as acetaldehyde, ethyl caprate) by GC-MS to precisely control the flavor of the beer from a chemical level. At the same time, professional judges are introduced to conduct quantitative scoring based on a scientific sensory scoring system to verify the product quality from multiple dimensions such as appearance, aroma, and taste. This multi-index and multi-dimensional evaluation method comprehensively and deeply reveals the influence of different yeasts on the flavor and quality of the wild grape craft beer, and can more accurately screen out the best yeast compared with the traditional single or few-index evaluation methods.

[0118] In summary, the present invention provides a yeast selection strategy method suitable for wild grape craft beer, and finally selects Nottingham yeast as the inoculated yeast, providing key technical support for the production of craft beer with rich wild grape flavor and significant nutritional and health care effects.

[0119] Compared with the prior art, the present invention screens out Nottingham yeast as the most suitable yeast for brewing wild grape craft beer, which has significant advantages.

[0120] From the perspective of fermentation performance, the proliferation rate of Nottingham yeast is moderate, effectively avoiding problems such as the excessive proliferation of LONDON yeast in the early stage, which produces off-flavors, and the slow proliferation of US-05 yeast, which increases the time cost. Its moderate fermentation ability ensures the stability and efficiency of the fermentation process, with a reasonable sugar reduction rate, reaching the peak of carbon dioxide loss at about 48h, which is roughly similar to that of S-04 yeast and Kolsch yeast, ensuring the smooth progress of fermentation. At the same time, Nottingham yeast has a strong alcohol-producing ability, and the alcohol content of the fermented beer sample can reach about 5.22% vol, which is higher than that of LONDON yeast and US-05 yeast. This is due to its efficient metabolic ability for sugars such as maltotriose, providing an appropriate alcohol content for the beer.

[0121] In terms of beer flavor, the wild grape craft beer fermented by Nottingham yeast has a moderate alcohol-ester ratio, about 3.48, which is in the ideal range of 3-5, making the wine body flavor balanced and harmonious. Its ester fragrance is prominent, and the ester production reaches about 95.09mg / L, ranking among the top among the five yeasts. The contents of key ester substances such as ethyl acetate and isoamyl acetate are appropriate, adding rich fruity and floral aromas to the beer and enhancing the aroma hierarchy. Moreover, the content of off-flavor components in the beer fermented by this yeast is low, with ethyl caprate less than 1.5mg / L and acetaldehyde less than 10mg / L, avoiding off-flavors such as yeast flavor and green flavor, and greatly optimizing the beer flavor.

[0122] Nottingham yeast shows excellent performance in the physical and chemical properties and sensory quality of beer. The beer fermented has a relatively low turbidity, about 10.17 EBC, with a clear body and good light transmittance, making it more appealing in appearance compared to the beer fermented by US-05 yeast and LONDON yeast. The total acid content is about , and the pH value is about 3.50, with a moderate acidity and a soft taste, enhancing the drinking experience. In the sensory evaluation, the beer fermented by Nottingham yeast has an overall score as high as 82 points, showing balanced and excellent performance in terms of appearance, aroma, foam, and taste, far exceeding the beer fermented by other yeasts, and bringing high-quality fine brewed beer made from Vitis quinquangularis Rehd. to consumers.

Claims

1. A yeast selection strategy method suitable for the brewing of fine grape beer, characterized in that It includes the following steps: 1) According to the characteristics of wild grape craft beer, select a variety of brewing yeasts as candidate yeasts, and the candidate yeasts include five yeasts: Nottingham, Kolsch, LONDON, S-04, and US-05; 2) Use the above candidate yeasts to conduct fermentation experiments on wild grape craft beer respectively and record the data; 3) Conduct in-depth analysis on the data obtained from the fermentation experiments, compare the proliferation ability, fermentation ability, alcohol production ability of each yeast, and the differences in flavor substances, physical and chemical properties, and sensory evaluation of the beer fermented by different yeasts, evaluate the influence of different yeasts on the flavor and quality of wild grape craft beer, and focus on considering the alcohol-ester ratio, ester fragrance, body acidity, and turbidity index; 4) According to the analysis and evaluation results, determine the yeast type most suitable for brewing wild grape flavor beer.

2. The yeast selection strategy method suitable for the brewing of fine wine made from Vitis heyneana as described in claim 1, characterized in that: In step 2), the inoculation amount of each yeast is 0.3 - 0.7 g / L of wort. After inoculating the yeast, samples are taken every 8 - 16 h for measuring the change in the number of yeast cells and alcohol content in the fermentation broth during the fermentation process; record the mass of the fermentation bottle during the fermentation process, and judge the fermentation situation according to the weight loss during the fermentation process.

3. A yeast selection strategy method suitable for the brewing of fine wine made from Vitis heyneana as claimed in claim 1, characterized in that: In step 3), evaluate the proliferation ability of the yeast by measuring the change in the number of yeast cells in the fermentation broth during the fermentation process.

4. The yeast selection strategy method suitable for the brewing of fine wine made from Vitis heyneana as described in claim 1, wherein: In step 3), evaluate the fermentation ability of the yeast by measuring the change in the carbon dioxide loss during the fermentation process to represent the change in the yeast's sugar reduction rate.

5. A yeast selection strategy method suitable for the brewing of fine wine made from Vitis heyneana as described in claim 1, characterized in that: In step 3), evaluate the alcohol production ability of the yeast by measuring the alcohol content at different fermentation stages.

6. The yeast selection strategy method suitable for the brewing of fine wine made from wild grapes as claimed in claim 1, wherein: In step 3), the content of flavor substances in the beer obtained by fermentation is detected using a headspace gas chromatograph.

7. A yeast selection strategy method suitable for the brewing of fine wine made from Vitis heyneana as described in claim 1, characterized in that: In step 3), a tasting panel is composed of BJCP professional judges and professional teachers. Each taster conducts a sensory evaluation of the wild grape craft beer in an independent tasting room from four aspects: appearance, foam, aroma, and taste, according to the sensory evaluation standard table for wild grape craft beer.

8. A yeast selection strategy method suitable for the brewing of fine wine from Vitis heyneana as claimed in claim 1, characterized in that: In step 3), the characteristic flavor substance indexes of the detected wild grape craft beer include: total ester content 60 - 120 mg / L, ethyl acetate 15 - 50 mg / L, isoamyl acetate 10 - 25 mg / L, phenethyl acetate 5 - 15 mg / L, alcohol-ester ratio 3 - 5, ethyl caprate ≤1.5 mg / L, acetaldehyde ≤10 mg / L.

9. A yeast selection strategy method suitable for the brewing of fine wine made from Vitis heyneana as claimed in claim 1, characterized in that: In step 3), the physical and chemical property indexes of the detected wild grape craft beer are: final wort concentration 13.0 - 14.0 °P, terminal concentration 3.5 - 4.5 °P, degree of fermentation 65% - 75%, alcohol content 4.5% - 6.0% vol, colority 13 - 16 EBC, turbidity ≤15 EBC, total acid 3.5 - 4.5 mL / 100 mL, pH value 3.4 - 3.6, bitterness 12 - 16 BU.

10. A yeast selection strategy method suitable for the brewing of fine wine from Vitis heyneana as described in claim 1, characterized in that: In step 4), the yeast most suitable for brewing wild grape flavor beer is determined to be Nottingham yeast.

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