Preparation method of coffee beans baked by hot air and coffee beans thereof

Abstract

The invention relates to a preparation method of coffee beans baked by hot air and coffee beans thereof, and belongs to the technical field of coffee beans, the preparation method comprises the following steps: S1, peeling fresh coffee fruits, and adding water for sterilization; s2, adding the mixed bacteria liquid into the sterilized fresh coffee fruits, sealing, and carrying out temperature-controlled fermentation; s3, after fermentation is finished, residual gum is removed from the fresh coffee fruits; s4, respectively soaking the coffee fresh fruits subjected to residual gum removal in a sucrose aqueous solution, fermenting, soaking in a borneol sugar aqueous solution, and fermenting to obtain raw coffee beans; and S5, baking the green coffee beans in a preheated hot air baking machine to obtain the finished coffee beans. In the step S2, the three strains are combined to generate an excellent synergistic effect, so that the content of chlorogenic acid in the coffee bean finished product is increased, and aroma components are enriched; meanwhile, double sugar soaking and closed fermentation are cooperated with fermentation of mixed bacteria liquid, the characteristics of the two sugars are combined, the flavor level of the coffee is further optimized, and the overall sensory quality of the coffee is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of coffee beans, and in particular relates to a method for preparing coffee beans roasted by hot air and the coffee beans. Background Art

[0002] As a popular beverage, coffee's quality and flavor have always been a focus for consumers. Traditional coffee bean preparation methods primarily involve picking, peeling, drying, and roasting. However, these methods have limitations in improving coffee bean quality. Furthermore, roasting is essential for developing coffee's distinctive color, aroma, and flavor. Coffee bean quality is primarily determined by the roasting process. Roasting involves subjecting coffee beans to a prolonged, high-temperature, oxygen-rich environment, where the Maillard reaction, caramelization, and thermal degradation reactions occur, producing coffee's distinctive aroma.

[0003] The chlorogenic acid content and sensory flavor richness in coffee beans are key factors in measuring coffee quality. Chlorogenic acid is a compound with multiple physiological activities. It has multiple functions such as cardioprotection, antioxidant, anti-inflammatory and anti-hypotensive effects, and has a positive impact on human health. However, traditional preparation methods often fail to effectively increase the chlorogenic acid content in coffee beans. In addition, the sensory flavor of coffee is also one of the important factors for consumers to choose coffee. Traditional preparation methods are insufficient in flavor richness and layering, and cannot meet consumers' increasingly diverse and high-quality taste demands. Therefore, developing a preparation method that can effectively increase the chlorogenic acid content in coffee beans and enhance the sensory flavor of coffee beans is of great practical significance. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing coffee beans by hot air roasting and the coffee beans thereof, which solves the problems of low chlorogenic acid content and poor sensory quality of finished coffee beans in the prior art.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for preparing coffee beans by hot air roasting, the method comprising the following steps:

[0007] S1. Peel the fresh coffee berries and sterilize them by adding water;

[0008] S2. Add the mixed bacterial solution to the sterilized coffee cherries, seal them, and then control the temperature for fermentation;

[0009] S3. After the fermentation is completed, the coffee berries are degummed;

[0010] S4, soaking the degummed coffee cherries in a sucrose aqueous solution and fermenting them, and soaking them in a borneol sugar aqueous solution and fermenting them, respectively, to obtain green coffee beans;

[0011] S5. Place the green coffee beans in a preheated hot air roaster and roast them to obtain finished coffee beans.

[0012] As a preferred technical solution of the present invention, step S1 specifically comprises: washing the picked coffee cherries, removing floating cherries and foreign matter, manually peeling the outer skin and screening out unripe cherries, and adding distilled water to the peeled and screened coffee cherries for temperature-controlled sterilization.

[0013] Furthermore, the amount of distilled water added is 2-2.5 times the volume of fresh coffee berries; the temperature of the temperature-controlled sterilization is 110° C., and the time is 5 minutes.

[0014] As a preferred technical solution of the present invention, the ratio of the sterilized fresh coffee cherries to the mixed bacterial solution in step S2 is 500-520 g:120-140 mL.

[0015] As a preferred technical solution of the present invention, the mixed bacterial solution in step S2 includes an activated solution of Leuconostoc mesenteroides, an activated solution of Pichia kluyveri, and an activated solution of Kluyveromyces marxianus.

[0016] Furthermore, the volume ratio of the Leuconostoc mesenteroides activation solution, the Pichia kluyveri activation solution and the Kluyveromyces marxianus activation solution is 3-4:3-3.5:2-3 mL.

[0017] Furthermore, the concentration of the Leuconostoc mesenteroides activation solution is 2-2.1×10 7 CFU / g; the concentration of the Pichia kluyveri activation solution is 1-1.2×10 7 CFU / g; the concentration of the Kluyveromyces marxianus activation solution is 6.5-71 g CFU / mL.

[0018] Furthermore, the Leuconostoc mesenteroides activation solution is obtained by inoculating Leuconostoc mesenteroides into MRS broth and subculturing twice for 24 hours; the Pichia kluyveri activation solution is obtained by culturing Pichia kluyveri in YPD solid medium at a constant temperature of 28°C for 48 hours and subculturing twice; the Kluyveromyces marxianus activation solution is obtained by inoculating Kluyveromyces marxianus into YPD liquid medium at a constant temperature of 28°C for 48 hours and subculturing twice;

[0019] The aforementioned Leuconostoc mesenteroides was purchased from Zhengzhou Best Food Additive Co., Ltd. During the fermentation process, Leuconostoc mesenteroides can metabolize the sugars in the mucilage layer of fresh coffee cherries to produce organic acids such as lactic acid, thereby lowering the pH of the fermentation system, helping to provide a suitable acidic environment for the fermentation process and reducing the growth of other bacteria. Furthermore, the inoculation and fermentation of Leuconostoc mesenteroides can also increase the total amino acid and chlorogenic acid content in the green coffee beans, allowing them to be converted into compounds with unique aromas during the roasting process, thereby enhancing the complexity and layered flavor of the coffee.

[0020] The aforementioned Pichia kluyveri platform number is Bio-65054, purchased from Beijing Biobowei Biotechnology Co., Ltd. Pichia kluyveri can indirectly affect the environmental pH by secreting organic acids, thereby inhibiting the activity of chlorogenic acid-degrading enzymes, which contributes to the accumulation of chlorogenic acid. Pichia kluyveri can also efficiently decompose the pectin layer of fresh coffee cherries, releasing sugars, amino acids, and aroma precursors therein. These substances are more easily converted into aromatic compounds during the subsequent roasting process.

[0021] The aforementioned Kluyveromyces marxianus was purchased from Shaanxi Chenming Biotechnology Co., Ltd. Kluyveromyces marxianus can produce β-glucosidase and exoglucanase to degrade cellulose and hemicellulose in fresh coffee cherries. Kluyveromyces marxianus also contains a rich content of β-galactosidase, which can release the sugars required for fermentation for utilization by other bacterial species in the system, thereby enhancing the effects of other bacterial species. In addition, Kluyveromyces marxianus can also produce amino acid aroma precursors during the fermentation process, which facilitates the subsequent generation of complex aroma compounds in the green coffee beans through pathways such as the Maillard reaction during the roasting process, enriching the aroma of the finished coffee beans.

[0022] As a preferred technical solution of the present invention, the temperature-controlled fermentation in step S2 is a constant temperature fermentation at 28-30°C for 72 hours.

[0023] As a preferred technical solution of the present invention, step S3 specifically includes: after the fermentation is completed, the fresh coffee berries are soaked in clean water to remove residual gum.

[0024] Furthermore, the amount of clean water is 2-2.5 times the weight of the fresh coffee berries; the degree of soaking is such that the surface of the fresh coffee berries feels rough when touched by hand; this can effectively assist the fermentation step S2 in removing residual pectin.

[0025] As a preferred technical solution of the present invention, step S4 specifically comprises: soaking the degummed fresh coffee cherries in a sucrose aqueous solution, fermenting them once, and after the fermentation is completed, soaking the fermented fresh coffee cherries in a borneol sugar aqueous solution, fermenting them again, to obtain green coffee beans.

[0026] Furthermore, the concentrations of the sucrose aqueous solution and the borneol sugar aqueous solution are both 5-10 wt%; the amount of the sucrose aqueous solution added is 2-2.2 times the weight of the fresh coffee cherries after degumming; and the amount of the borneol sugar aqueous solution added is 2-2.2 times the weight of the fresh coffee cherries after primary fermentation.

[0027] Furthermore, the soaking temperature in the sucrose aqueous solution is room temperature, and the time is 3-4 hours; the conditions for the primary fermentation are temperature control at 30-32°C, closed conditions, and fermentation for 8-10 hours; the soaking temperature in the borneol sugar aqueous solution is room temperature, and the time is 2-3 hours; the conditions for the secondary fermentation are temperature control at 30-32°C, closed conditions, and fermentation for 8-10 hours.

[0028] As a preferred technical solution of the present invention, the preheating in step S5 is to preheat the hot air baking machine to 220-230° C. and stabilize it for 2-3 minutes; the baking time is 15-16 minutes.

[0029] As a preferred technical solution of the present invention, the present invention also provides coffee beans prepared by the above-mentioned hot air roasting coffee bean preparation method.

[0030] Beneficial effects of the present invention:

[0031] (1) The present invention ferments a mixture of Leuconostoc mesenteroides, Pichia kluyveri and Kluyveromyces marxianus, producing an excellent synergistic effect, which effectively increases the content of chlorogenic acid in the finished coffee beans to a certain extent; in addition, the combination of these three strains can also produce rich aroma components, which has a positive effect on improving the flavor quality of coffee beans and significantly enhances the aroma complexity and pleasantness of coffee.

[0032] (2) The present invention combines the characteristics of two sugars through double sugar immersion and closed fermentation with fermentation of mixed bacteria, further optimizing the flavor level of coffee and improving the overall sensory quality of coffee. Specifically, the compounds produced by the decomposition of the sucrose solution attached to the fresh coffee cherries increase the sweetness and aroma complexity of coffee. At the same time, the generated 5-hydroxymethylfurfural (5-HMF) can also increase the caramel flavor of coffee beans. The borneol sugar solution attached to the fresh coffee cherries decomposes into monosaccharides during the roasting process and participates in the Maillard reaction, generating a variety of flavor compounds, thereby significantly improving the flavor quality of coffee beans and making them more rich.

[0033] (3) The present invention constructs a main process design of "peeling + fermentation + degumming + double sugar immersion, fermentation + hot air roasting". The peeling step retains pectin to the maximum extent, laying a good foundation for the fermentation step, and the soaking degumming can assist the fermentation step in removing residual pectin. The final hot air roasting can complement the above steps to complete the flavor of the coffee beans. The entire process flow is consistent and can better stimulate the production of flavor substances in the coffee beans. DETAILED DESCRIPTION

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] The Leuconostoc mesenteroides used in the present invention was purchased from Zhengzhou Best Food Additive Co., Ltd.; Pichia kluyveri platform number: Bio-65054, purchased from Beijing Biobowei Biotechnology Co., Ltd.; Kluyveromyces marxianus was purchased from Shaanxi Chenming Biotechnology Co., Ltd.;

[0036] The activated solution of Leuconostoc mesenteroides used in the present invention is obtained by inoculating Leuconostoc mesenteroides into MRS broth and subculturing twice for 24 hours; the activated solution of Pichia kluyveri used in the present invention is obtained by culturing Pichia kluyveri in YPD solid culture medium at a constant temperature of 28°C for 48 hours and subculturing twice; the activated solution of Kluyveromyces marxianus used in the present invention is obtained by inoculating Kluyveromyces marxianus into YPD liquid culture medium at a constant temperature of 28°C for 48 hours and subculturing twice;

[0037] The above is not repeated here.

[0038] Example 1

[0039] A method for preparing coffee beans by hot air roasting, the method comprising the following steps:

[0040] S1. Wash the picked coffee cherries, remove floating cherries and foreign matter, manually peel the cherries and sieve out unripe cherries. Add distilled water twice the volume of the cherries to the cherries and sterilize at 110°C for 5 minutes.

[0041] S2. Add the mixed bacterial solution to the sterilized coffee cherries at a ratio of 500 g:130 mL, seal the mixture, and ferment at a constant temperature of 30°C for 72 hours.

[0042] The mixed bacterial solution includes Leuconostoc mesenteroides activated solution, Pichia kluyveri activated solution and Kluyveromyces marxianus activated solution in a volume ratio of 3:3.2:3 mL;

[0043] The concentration of the Leuconostoc mesenteroides activation solution is 2×10 7 CFU / g; the concentration of the Pichia kluyveri activation solution is 1×10 7 CFU / g; the concentration of the Kluyveromyces marxianus activation solution is 6.8lgcfu / mL;

[0044] S3. After fermentation is complete, soak the coffee cherries in clean water 2.5 times their weight to remove residual gum until the surface of the cherries feels rough to the touch.

[0045] S4, soaking the degummed coffee cherries in a 5 wt% sucrose aqueous solution at room temperature for 3 hours, then fermenting them in a sealed container at a temperature of 31° C. for 8 hours. After the fermentation is complete, soaking the fermented coffee cherries in a 10 wt% borneol sugar aqueous solution at room temperature for 3 hours, then fermenting them in a sealed container at a temperature of 31° C. for 8 hours to obtain green coffee beans;

[0046] S5. Preheat the hot air roaster to 225°C and stabilize for 3 minutes. Place the green coffee beans in the hot air roaster and roast for 15 minutes to obtain finished coffee beans.

[0047] Example 2

[0048] A method for preparing coffee beans by hot air roasting, the method comprising the following steps:

[0049] S1. Wash the picked coffee cherries, remove floating cherries and foreign matter, manually peel the cherries and sieve out unripe cherries. Add 2.5 times the volume of the coffee cherries to distilled water and sterilize at 110°C for 5 minutes.

[0050] S2. Add the mixed bacterial solution to the sterilized coffee cherries at a ratio of 520 g:120 mL, seal the mixture, and ferment at 28°C for 72 hours.

[0051] The mixed bacterial solution includes Leuconostoc mesenteroides activated solution, Pichia kluyveri activated solution and Kluyveromyces marxianus activated solution in a volume ratio of 3.5:3.5:2.5 mL;

[0052] The concentration of the Leuconostoc mesenteroides activation solution is 2.1×10 7 CFU / g; the concentration of the Pichia kluyveri activation solution is 1.2×10 7 CFU / g; the concentration of the Kluyveromyces marxianus activation solution is 6.5lgcfu / mL;

[0053] S3. After fermentation is complete, soak the coffee cherries in clean water twice their weight to remove residual gum until the surface of the cherries feels rough to the touch.

[0054] S4, soaking the degummed coffee cherries in a 10 wt% sucrose aqueous solution at room temperature for 3.5 hours, then fermenting them in a sealed container at a temperature of 30° C. for 10 hours. After the fermentation is complete, soaking the fermented coffee cherries in a 7.5 wt% borneol sugar aqueous solution at room temperature for 2 hours, then fermenting them in a sealed container at a temperature of 30° C. for a second time for 9 hours to obtain green coffee beans;

[0055] S5. Preheat the hot air roaster to 220°C and stabilize for 2 minutes. Place the green coffee beans in the hot air roaster and roast for 15.5 minutes to obtain finished coffee beans.

[0056] Example 3

[0057] A method for preparing coffee beans by hot air roasting, the method comprising the following steps:

[0058] S1. Wash the picked coffee cherries, remove floating cherries and foreign matter, manually peel the cherries and sieve out unripe cherries. Add 2.2 times the volume of the cherries to the dehulled and sieved cherries in distilled water and sterilize at 110°C for 5 minutes.

[0059] S2. Add the mixed bacterial solution to the sterilized coffee cherries at a ratio of 510 g:140 mL, seal the mixture, and ferment at a constant temperature of 29°C for 72 hours.

[0060] The mixed bacterial solution includes Leuconostoc mesenteroides activated solution, Pichia kluyveri activated solution and Kluyveromyces marxianus activated solution in a volume ratio of 4:3:2 mL;

[0061] The concentration of the Leuconostoc mesenteroides activation solution is 2.1×10 7 CFU / g; the concentration of the Pichia kluyveri activation solution is 1.1×10 7 CFU / g; the concentration of the Kluyveromyces marxianus activation solution is 7lgcfu / mL;

[0062] S3. After fermentation is complete, soak the coffee cherries in clean water at a volume 2.3 times their weight to remove residual gum until the surface of the cherries feels rough to the touch.

[0063] S4, soaking the degummed coffee cherries in a 7.5 wt% sucrose aqueous solution at room temperature for 4 hours, then performing a primary fermentation at 32° C. in a sealed container for 9 hours. After the primary fermentation is complete, soaking the fermented coffee cherries in a 5 wt% borneol sugar aqueous solution at room temperature for 2.5 hours, then performing a secondary fermentation at 32° C. in a sealed container for 10 hours to obtain green coffee beans;

[0064] S5. Preheat the hot air roaster to 230°C and stabilize it for 2.5 minutes. Place the green coffee beans in the hot air roaster and roast them for 16 minutes to obtain finished coffee beans.

[0065] Comparative Example 1

[0066] Compared with Example 3, the difference is that no Leuconostoc mesenteroides activation solution is added to the mixed bacterial solution in step S2 of Comparative Example 1, that is, the mixed bacterial solution includes Pichia kluyveri activation solution and Kluyveromyces marxianus activation solution in a volume ratio of 5:4 mL; the other operating steps and parameters remain unchanged.

[0067] Comparative Example 2

[0068] Compared with Example 3, the difference is that the Pichia kluyveri activation solution is not added to the mixed bacterial solution in step S2 of Comparative Example 2, that is, the mixed bacterial solution includes the Leuconostoc mesenteroides activation solution and the Kluyveromyces marxianus activation solution in a volume ratio of 5.5:3.5 mL; the other operating steps and parameters remain unchanged.

[0069] Comparative Example 3

[0070] Compared with Example 3, the difference is that the Kluyveromyces marxianus activation solution is not added to the mixed bacterial solution in step S2 of Comparative Example 3, that is, the mixed bacterial solution includes the Leuconostoc mesenteroides activation solution and the Pichia kluyveri activation solution in a volume ratio of 5:4 mL; the other operating steps and parameters remain unchanged.

[0071] Comparative Example 4

[0072] Compared with Example 3, the difference is that the operation of step S4 is not performed in Comparative Example 4, and the remaining operation steps and parameters remain unchanged.

[0073] Comparative Example 5

[0074] Compared with Example 3, the difference is that step S4 of Comparative Example 5 is specifically as follows:

[0075] S4. Soak the degummed coffee cherries in a 7.5 wt% sucrose aqueous solution at room temperature for 4 hours, and then ferment them in a sealed container at a temperature of 32° C. for 9 hours to obtain green coffee beans.

[0076] Comparative Example 6

[0077] Compared with Example 3, the difference is that step S4 of Comparative Example 5 is specifically as follows:

[0078] S4. Soak the degummed coffee cherries in a 5 wt% borneol sugar aqueous solution at room temperature for 2.5 hours, and then perform secondary fermentation at 32° C. in a sealed environment for 10 hours to obtain green coffee beans.

[0079] Test Example 1

[0080] Chlorogenic acid content test: Referring to GB / T 22250-2008, the chlorogenic acid content of the finished coffee beans prepared in Examples 1-3 and Comparative Examples 1-3 was tested by HPLC. The results are shown in Table 1. 18 Column (particle size 5 μm, column length 250 mm × diameter 4.6 mm); mobile phase: 0.5% acetic acid solution + acetonitrile = 85 + 15; flow rate: 1.0 mL / min; column temperature: 35°C; injection volume: 10 μL; detection wavelength 327 nm.

[0081] Table 1

[0082] Chlorogenic acid content (g / kg) Example 1 0.739 Example 2 0.735 Example 3 0.743 Comparative Example 1 0.701 Comparative Example 2 0.710 Comparative Example 3 0.716

[0083] As can be seen in Table 1, the finished coffee beans produced by the present invention have a high chlorogenic acid content. This is because the mixed fermentation of Leuconostoc mesenteroides, Pichia kluyveri, and Kluyveromyces marxianus produces an excellent synergistic effect, effectively increasing the chlorogenic acid content of the finished coffee beans to a certain extent.

[0084] Test Example 2

[0085] Sensory evaluation: The cupping method of the Specialty Coffee Association (SCAA) was used. The coffee beans prepared in Examples 1-3 and Comparative Examples 1-6 were ground to an average particle size of approximately 0.7 mm. 8.25 g of coffee powder was accurately weighed and added to 150 mL of 93°C hot water. The sensory evaluation was completed within 20 minutes after brewing. The sensory evaluation panel consisted of 8 well-trained members, 4 men and 4 women, aged 20-35 years. The coffee liquid was scored based on 10 indicators: aroma (dry and wet), flavor, aftertaste, acidity, body, balance, consistency, cleanliness, sweetness, and overall evaluation. The sum of the 10 sensory indicators was the final score of each coffee sample. Each sensory indicator was scored out of 10 points, with a score ranging from 0 to 10 representing non-existent, unacceptable, very poor, poor, acceptable, fair, good, very good, excellent, very excellent, and perfect, respectively. The scoring interval was 0.25 points.

[0086] Scoring order: After grinding the coffee beans, smell and score the dry aroma. After 4 minutes of water infusion, use a spoon to break the grounds and score the wet aroma. After 8 minutes of water infusion, use a cupping spoon to taste and score the flavor, aftertaste, acidity, body and balance. After 15 minutes of water infusion, score the consistency, cleanliness, sweetness and overall evaluation.

[0087] The final scores of each test sample are shown in Table 2.

[0088] Table 2

[0089]

[0090]

[0091] As can be seen from Table 2, the finished coffee beans prepared by the present invention have excellent sensory quality.

[0092] Throughout the specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0093] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing coffee beans by hot air roasting, characterized in that: The preparation method comprises the following steps: S1. Peel the fresh coffee berries and sterilize them by adding water; S2. Add the mixed bacterial solution to the sterilized coffee cherries, seal them, and then control the temperature for fermentation; S3. After the fermentation is completed, the coffee berries are degummed; S4, soaking the degummed coffee cherries in a sucrose aqueous solution and fermenting them, and soaking them in a borneol sugar aqueous solution and fermenting them, respectively, to obtain green coffee beans; S5. Place the green coffee beans in a preheated hot air roaster and roast them to obtain finished coffee beans.

2. The method for preparing coffee beans by hot air roasting according to claim 1, wherein: Step S1 specifically includes: washing the picked coffee cherries, removing floating cherries and foreign matter, manually peeling the outer skin and screening out unripe cherries, and adding distilled water to the peeled and screened coffee cherries for temperature control and sterilization.

3. The method for preparing coffee beans by hot air roasting according to claim 1, wherein: The ratio of the sterilized fresh coffee cherries to the mixed bacterial solution in step S2 is 500-520 g:120-140 mL.

4. The method for preparing coffee beans by hot air roasting according to claim 3, wherein: The mixed bacterial solution in step S2 includes an activated solution of Leuconostoc mesenteroides, an activated solution of Pichia kluyveri, and an activated solution of Kluyveromyces marxianus.

5. The method for preparing coffee beans by hot air roasting according to claim 4, wherein: The volume ratio of the Leuconostoc mesenteroides activation solution, the Pichia kluyveri activation solution and the Kluyveromyces marxianus activation solution is 3-4:3-3.5:2-3 mL.

6. The method for preparing coffee beans by hot air roasting according to claim 4, wherein: The concentration of the Leuconostoc mesenteroides activation solution is 2-2.1×10 7 CFU / g; the concentration of the Pichia kluyveri activation solution is 1-1.2×10 7 CFU / g; the concentration of the Kluyveromyces marxianus activation solution is 6.5-71 g CFU / mL.

7. The method for preparing coffee beans by hot air roasting according to claim 1, wherein: Step S3 specifically includes: after fermentation is completed, the fresh coffee berries are soaked in clean water to remove residual gum.

8. The method for preparing coffee beans by hot air roasting according to claim 1, wherein: Step S4 specifically comprises: soaking the coffee cherries after the residual gum is removed in a sucrose aqueous solution, fermenting them once, and after the fermentation is completed, soaking the coffee cherries after the primary fermentation in a borneol sugar aqueous solution, fermenting them again, and obtaining green coffee beans.

9. The method for preparing coffee beans by hot air roasting according to claim 9, wherein: The concentrations of the sucrose aqueous solution and the borneol sugar aqueous solution are both 5-10wt%; the amount of the sucrose aqueous solution added is 2-2.2 times the weight of the fresh coffee cherries after degumming; and the amount of the borneol sugar aqueous solution added is 2-2.2 times the weight of the fresh coffee cherries after primary fermentation.

10. Coffee beans prepared by the method for preparing hot air roasted coffee beans according to any one of claims 1 to 9.

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