One-time stem-carrying curing method for middle-upper tobacco leaves of flue-cured tobaccos

Abstract

The invention provides a one-time stem-carrying curing method for middle-upper tobacco leaves of flue-cured tobacco, and relates to the technical field of tobacco. According to the one-time stem-carrying curing method for the middle-upper tobacco leaves of the flue-cured tobaccos, the relative humidity of air in the curing barn is regulated and controlled by adjusting the heating rate and the temperature stabilizing time of five stages of brewing fragrance, producing fragrance, increasing fragrance, increasing fragrance and fixing fragrance according to the quality of fresh tobacco leaves of the tobacco leaves harvested with the stems, the tobacco leaves are promoted to be fully yellowed, the proportion and the quality of the whole group of tobacco leaves are improved, and the tobacco leaves are cured. One-time baking of all middle and upper tobacco leaves with stems is realized; the modulated tobacco leaves have the advantages of obvious style characteristics, moderate strength, strong smoke concentration, clear and full aroma, sufficient aroma amount, obvious sweetness, small offensive odor and irritation and comfortable aftertaste.

Description

Technical Field

[0001] The present application relates to the technical field of tobacco, and in particular to a method for baking the upper and middle parts of flue-cured tobacco leaves with stems at one time. Background Art

[0002] Currently, the tobacco industry primarily focuses on harvesting and curing the top 4-6 leaves at once. Few studies have examined the effects of single-cut harvesting on physiological characteristics during curing and curing, as well as on the quality of the final tobacco leaves. Literature reports on the impact of single-cut harvesting on the physiological characteristics of tobacco leaves during curing and curing, and on the quality of the final tobacco leaves, are inconsistent. Most researchers believe that both harvesting the top 4-6 leaves with stems and harvesting them individually at once improve the quality of the final tobacco leaves, with the stems providing the best results. However, a few researchers believe that harvesting the top 4-6 leaves with stems has little or no significant effect on tobacco quality, and may even reduce it. This may be due to the research materials used or inadequate curing techniques for harvesting the top 4-6 leaves with stems. Due to the unique nature of moisture transport from the stems to the leaves, the critical temperature may differ from conventional curing, as may the temperature stabilization time and the requirements for leaf transition at the fire point. Currently, there are two widely accepted curing techniques for top-cut tobacco: the four-step curing process and the medium-temperature, medium-humidity curing process. Both methods offer potential improvements in the quality of tobacco produced by curing the top 4-6 leaves with stems. Summary of the Invention

[0003] The purpose of the present application is to provide a one-time method for baking the middle and upper tobacco leaves with stems, aiming to solve the problem that the quality of the flue-cured tobacco obtained by the existing process of baking the middle and upper tobacco leaves with stems needs to be improved.

[0004] To achieve the above objectives, the present application provides a one-time flue-cured tobacco leaf stemming method, comprising: The upper and middle tobacco leaves harvested with stems are clamped with tobacco clips, with the leaf tips facing downward, and placed in a curing room to start curing; the curing includes: an aroma brewing stage, an aroma producing stage, an aroma enhancing stage, an aroma increasing stage and an aroma fixing stage.

[0005] In some embodiments, the upper and middle tobacco leaves harvested with stems include 10 to 15 tobacco leaves.

[0006] In some embodiments, the aroma brewing stage includes: after loading the smoke, raising the dry-bulb temperature to 39°C at a rate of 1.0-1.5°C / h, stabilizing the temperature for 3 hours, then stopping the fire and cooling the temperature to a dry-bulb temperature of 30°C, and then using the same method to raise the dry-bulb temperature to 39°C at a rate of 1.0-1.5°C / h, stabilizing the temperature for 17-20 hours, and then stopping the fire and cooling the temperature to a dry-bulb temperature of 30°C.

[0007] In some embodiments, the wet-bulb temperature during the aroma brewing stage is maintained at 1-2°C lower than the dry-bulb temperature until the mesophyll of the bottom tobacco leaves is substantially completely yellow.

[0008] In some embodiments, the aroma production stage includes: raising the dry bulb temperature to 40°C at a rate of 0.5°C / h, maintaining the dry bulb temperature at 40-43°C and the wet bulb temperature at 36-37°C, until the tobacco leaves in the entire room turn completely yellow and the main veins are fully softened.

[0009] In some embodiments, the temperature is maintained at 40-43°C dry bulb temperature during the fragrance production phase for 8-10 hours.

[0010] In some embodiments, the aroma enhancement stage includes: raising the dry bulb temperature to 47°C to 49°C at a rate of 0.5-1.0°C / h, the wet bulb temperature to 36-37°C, and stabilizing the temperature for 8-10 hours.

[0011] In some embodiments, the fragrance enhancement stage includes: raising the dry bulb temperature to 50-54°C at a rate of 0.5-1.0°C / h and the wet bulb temperature to 38-40°C. The temperature stabilization time of the fragrance enhancement stage is shortened by 3-5 hours relative to the temperature stabilization time of the fragrance enhancement stage.

[0012] In some embodiments, the aroma fixing stage includes: raising the dry bulb temperature to 60-68°C at a rate of 0.5-1.0°C / h and the wet bulb temperature to 40-42°C until the veins of the tobacco leaves in the entire room are completely dry.

[0013] In some embodiments, the temperature stabilization time of the fragrance fixing stage is increased by 1 to 2 hours relative to the temperature stabilization time of the fragrance enhancing stage.

[0014] Compared with the prior art, the advantages of this application include: The present application provides a one-time baking method for the middle and upper parts of the flue-cured tobacco leaves with stems. Based on the quality of the fresh tobacco leaves harvested with stems, the method adjusts the heating rate and the stabilization time in the five stages of aroma brewing, aroma production, aroma enhancement, aroma enhancement, and aroma consolidation, thereby regulating the relative humidity of the air in the flue-curing room, promoting the full yellowing of the tobacco leaves, improving the proportion and quality of the entire group of tobacco leaves, and achieving one-time baking of all the middle and upper parts of the flue-cured tobacco leaves with stems. The tobacco leaves after curing have more obvious style characteristics, moderate strength, strong smoke concentration, clear and full aroma, sufficient aroma, obvious sweetness, little foreign smell and irritation, and a comfortable aftertaste. DETAILED DESCRIPTION

[0015] As used herein: "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0016] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0017] When an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed alone. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including the range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0018] In these examples, parts and percentages are by mass unless otherwise indicated.

[0019] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. For example, if we say that the parts by mass of component A are a parts and the parts by mass of component B are b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the parts by mass of all components is not limited to 100 parts.

[0020] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0021] The present application provides a one-time flue-cured tobacco leaf stem baking method, comprising: The upper and middle tobacco leaves harvested with stems are clamped with tobacco clips, with the leaf tips facing downward, and placed in a curing room to start curing; the curing includes: an aroma brewing stage, an aroma producing stage, an aroma enhancing stage, an aroma increasing stage and an aroma fixing stage.

[0022] The present application provides a one-time baking method for the middle and upper parts of the flue-cured tobacco leaves with stems. Based on the quality of the fresh tobacco leaves harvested with stems, the method adjusts the heating rate and the stabilization time in the five stages of aroma brewing, aroma production, aroma enhancement, aroma enhancement, and aroma consolidation, thereby regulating the relative humidity of the air in the flue-curing room, promoting the full yellowing of the tobacco leaves, improving the proportion and quality of the entire group of tobacco leaves, and achieving one-time baking of all the middle and upper parts of the flue-cured tobacco leaves with stems. The tobacco leaves after curing have more obvious style characteristics, moderate strength, strong smoke concentration, clear and full aroma, sufficient aroma, obvious sweetness, little foreign smell and irritation, and a comfortable aftertaste.

[0023] In some embodiments, the upper and middle tobacco leaves harvested with stems include 10 to 15 tobacco leaves, for example, 10, 11, 12, 13, 14 or 15 tobacco leaves.

[0024] In some embodiments, the aroma brewing stage includes: after loading the smoke, raising the dry-bulb temperature to 39°C at a rate of 1.0-1.5°C / h, stabilizing for 3 hours, then stopping the fire and cooling to a dry-bulb temperature of 30°C, and then using the same method to raise the dry-bulb temperature to 39°C at a rate of 1.0-1.5°C / h, stabilizing for 17-20 hours, for example, it can be 17h, 18h, 19h, 20h or any value between 17 and 20h, and then stopping the fire and cooling to a dry-bulb temperature of 30°C.

[0025] The heating rate in the aroma brewing stage can be, for example, 1.0°C / h, 1.1°C / h, 1.2°C / h, 1.3°C / h, 1.4°C / h, 1.5°C / h, or any value between 1.0 and 1.5°C / h.

[0026] In some embodiments, the wet-bulb temperature during the aroma brewing stage is maintained at 1-2°C lower than the dry-bulb temperature, for example, 1°C, 1.5°C, 2°C or any value between 1-2°C, until the bottom tobacco leaf mesophyll is basically completely yellow.

[0027] In some embodiments, the aroma production stage includes: raising the dry-bulb temperature to 40°C at a rate of 0.5°C / h, maintaining the dry-bulb temperature at 40~43°C, for example, 40°C, 41°C, 42°C, 43°C or any value between 40~43°C, and the wet-bulb temperature at 36~37°C, for example, 36°C, 36.5°C, 37°C or any value between 36~37°C, until the whole room of tobacco leaves turns completely yellow and the main veins are fully softened.

[0028] In some embodiments, the temperature is maintained steady for 8 to 10 hours during the fragrance production stage at a dry bulb temperature of 40 to 43° C., for example, 8 hours, 9 hours, 10 hours, or any value between 8 and 10 hours.

[0029] In some embodiments, the fragrance enhancement stage includes: raising the dry-bulb temperature to 47°C to 49°C at a rate of 0.5-1.0°C / h, for example, 47°C, 48°C, 49°C or any value between 47°C and 49°C, the wet-bulb temperature to 36-37°C, for example, 36°C, 36.5°C, 37°C or any value between 36-37°C, and the stabilization time to 8-10h, for example, 8h, 9h, 10h or any value between 8-10h.

[0030] The heating rate in the aroma stage can be, for example, 0.5°C / h, 0.6°C / h, 0.7°C / h, 0.8°C / h, 0.9°C / h, 1.0°C / h or any value between 0.5 and 1.0°C / h.

[0031] In some embodiments, the fragrance enhancement stage includes: raising the dry bulb temperature to 50-54°C at a rate of 0.5-1.0°C / h, for example, it can be 50°C, 51°C, 52°C, 53°C, 54°C or any value between 50-54°C, and the wet bulb temperature is 38-40°C, for example, it can be 38°C, 39°C, 40°C or any value between 38-40°C. The temperature stabilization time of the fragrance enhancement stage is shortened by 3-5h relative to the temperature stabilization time of the aroma enhancement stage, for example, it can be 3h, 4h, 5h or any value between 3-5h.

[0032] The heating rate in the aroma enhancement stage may be, for example, 0.5°C / h, 0.6°C / h, 0.7°C / h, 0.8°C / h, 0.9°C / h, 1.0°C / h or any value between 0.5 and 1.0°C / h.

[0033] In some embodiments, the aroma fixing stage includes: raising the dry bulb temperature to 60-68°C at a rate of 0.5-1.0°C / h, for example, it can be 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C or any value between 60-68°C, and the wet bulb temperature is 40-42°C, for example, it can be 40°C, 41°C, 42°C or any value between 40-42°C, until the veins of the tobacco leaves in the whole room are completely dry.

[0034] The heating rate in the fragrance solidification stage may be, for example, 0.5°C / h, 0.6°C / h, 0.7°C / h, 0.8°C / h, 0.9°C / h, 1.0°C / h or any value between 0.5 and 1.0°C / h.

[0035] In some embodiments, the temperature stabilization time of the fragrance fixing stage is increased by 1 to 2 hours relative to the temperature stabilization time of the fragrance enhancing stage, for example, it can be 1 hour, 1.5 hours, 2 hours or any value between 1 and 2 hours.

[0036] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if specific conditions are not specified, the conditions are carried out according to conventional conditions or manufacturer recommendations. The reagents or instruments used are not specified by the manufacturer and are conventional products that can be purchased commercially.

[0037] The middle and upper tobacco leaves harvested with stems used in the flue-cured tobacco curing methods of the following examples and comparative examples are obtained by a planting and harvesting method for flue-cured tobacco suitable for one-time harvesting of the middle and upper tobacco leaves developed by the applicant. The planting and harvesting method for one-time harvesting of the middle and upper tobacco leaves comprises the following steps: (1) Land preparation: Purple soil with a pH of 6.8 was selected as the tobacco planting soil, and the flue-cured tobacco variety was NX212; (2) Nitrogen fertilizer application rate: 10.5 kg / 666.7 m 2 , nitrogen, phosphorus and potassium ratio 1:1:3; (3) Strengthen the prevention of rhizome diseases: every 666.7m 2 Apply 160ml of rhizome disease resistance inducer (Labotan 10% microemulsion) to the soil of the area by root irrigation; (4) Transplanting density: 900 tobacco seedlings / 666.7m 2 ; (5) Increase the application of cake fertilizer: When transplanting flue-cured tobacco, add rapeseed cake fertilizer 50kg / 666.7m 2 , applied to the root soil as base fertilizer; (6) Tobacco leaf harvesting: 15 days after topping, the five lower tobacco leaves are harvested early according to the traditional harvesting method; when the nine upper tobacco leaves are mature, the 14 upper and middle tobacco leaves are harvested at one time by cutting with stems.

[0038] Example 1 Example 1 provides a one-time flue-cured tobacco leaf with stems, comprising the following steps: The upper and middle tobacco leaves harvested with stems (with 14 tobacco leaves on the stems) are clamped with tobacco clips, with the tips of the leaves facing downwards, and placed in the drying room to start baking.

[0039] "Aroma brewing" stage: After loading the tobacco, raise the dry-bulb temperature to 39°C at a rate of 1.2°C / h, stabilize for 3 hours, then stop the fire and cool down to a dry-bulb temperature of 30°C; then use the same method to raise the dry-bulb temperature to 39°C at a rate of 1.2°C / h, stabilize for 18 hours, then stop the fire and cool down to a dry-bulb temperature of 30°C; the wet-bulb temperature is kept 1.5°C lower than the dry-bulb temperature until the bottom tobacco leaf flesh is basically completely yellow.

[0040] "Aroma production" stage: Raise the dry-bulb temperature to 40°C at a rate of 0.5°C / h, maintain the dry-bulb temperature at 42°C and the wet-bulb temperature at 36.5°C, until the tobacco leaves in the entire room turn completely yellow and the main veins soften completely; in the "aroma production" stage with a dry-bulb temperature of 40-43°C, maintain a steady temperature for 9 hours.

[0041] "Perfume" stage: increase the dry-bulb temperature to 48°C at a rate of 0.5°C / h, the wet-bulb temperature to 36.5°C, and the temperature stabilization time to 9 hours.

[0042] "Fragrance enhancement" stage: the dry bulb temperature is raised to 52°C at a rate of 0.5°C / h, and the wet bulb temperature is 39°C. The stabilization time is shortened by 4 hours compared to the stabilization time in the fragrance enhancement stage.

[0043] "Fragrance fixation" stage: the dry-bulb temperature is raised to 68°C at a rate of 0.5°C / h, and the wet-bulb temperature is 41°C. The temperature stabilization time is increased by 1 h compared to the temperature stabilization time in the fragrance enhancement stage; until the veins of the tobacco leaves in the entire room are completely dry.

[0044] Comparative Example 1 Comparative Example 1 provides a one-time flue-cured tobacco leaf with stems, using conventional technology, including the following steps: The upper and middle tobacco leaves harvested with stems (with 14 tobacco leaves on the stems) are clamped with tobacco clips, with the tips of the leaves facing downwards, and placed in the drying room to start baking.

[0045] Yellowing period: After loading the tobacco, increase the dry bulb temperature to 38°C at a rate of 1°C / h, maintain the dry bulb temperature at 38°C and the wet bulb temperature at 37°C until the bottom tobacco leaves are basically completely yellow.

[0046] Wilting period: Raise the dry bulb temperature to 40℃, maintain the dry bulb temperature at 40℃ and the wet bulb temperature at 37℃ until the tobacco leaves in the whole room turn completely yellow and the main veins are fully softened.

[0047] Color fixing period: Raise the dry bulb temperature to 55℃ at a rate of 1℃ every 2 hours, maintain the dry bulb temperature at 55℃ and the wet bulb temperature at 39℃ until the tobacco leaves in the whole room are completely dry.

[0048] Drying period: Raise the dry bulb temperature to 68℃ at a rate of 1℃ / h, maintain the dry bulb temperature at 68℃ and the wet bulb temperature at 41.5℃ until the veins of the tobacco leaves in the entire room are completely dry.

[0049] Result Analysis 1. Analysis of the appearance quality of tobacco leaves with different curing processes The appearance quality of tobacco leaves prepared by different baking processes was evaluated, and the results are shown in Tables 1 and 2. The data show that, for upper tobacco leaves: the maturity, identity, oil content, and chroma scores of the tobacco leaves baked by the baking process of Example 1 are significantly better than those of the conventional baking process of Comparative Example 1, and the comprehensive score of appearance quality is also higher than that of the conventional baking process. The baking process of Example 1 can significantly improve the appearance quality of the upper tobacco leaves that are cut and baked in one go. For middle tobacco leaves: the maturity and leaf structure scores of the tobacco leaves baked by the baking process of Example 1 are significantly better than those of the conventional baking process of Comparative Example 1, and the comprehensive score of appearance quality is higher than that of the conventional baking process of Comparative Example 1. The baking process of Example 1 can significantly improve the appearance quality of the middle tobacco leaves that are cut and baked in one go.

[0050] Table 1 Comparison of the appearance quality of upper leaves under different baking processes

[0051] Table 2 Comparison of the appearance quality of middle leaves under different baking processes

[0052] 2. Analysis of conventional chemical components of tobacco leaves with different curing processes 2.1 Effects of different curing processes on the content of conventional chemical components in tobacco leaves The conventional chemical components of the middle and upper tobacco leaves prepared by different baking processes were tested and analyzed by variance, and the results are shown in Tables 3 and 4. The data show that 1) compared with the conventional baking process of Comparative Example 1, the baking process of Example 1 can significantly increase the total sugar content, reducing sugar content and sugar-alkali ratio of the middle tobacco leaves after baking, significantly reduce the starch content of the tobacco leaves after baking; and significantly reduce the total nitrogen content of the middle tobacco leaves. 2) Compared with the conventional baking process of Comparative Example 1, the baking process of Example 1 can significantly increase the total sugar content, reducing sugar content and sugar-alkali ratio of the upper tobacco leaves after baking, and significantly reduce the starch content of the tobacco leaves after baking.

[0053] Table 3 Significance analysis of conventional chemical components in middle tobacco leaves with different curing processes

[0054] Table 4 Significance analysis of conventional chemical components of upper tobacco leaves with the same curing process

[0055] 2.2 Effects of different curing processes on the scores of conventional chemical components of tobacco leaves The conventional chemical components of tobacco leaves prepared by different baking processes were assigned values and variance analysis was performed, and the results are shown in Tables 5 and 6. The data show that 1) the chemical component content and coordination of the middle tobacco leaves after the baking process of Example 1 was adjusted were better than those of the conventional baking process of Comparative Example 1, especially the impact on the scores of nicotine, reducing sugar, sugar-alkali ratio and nitrogen-alkali ratio reached a significant level; the total score of conventional chemical components of the baking process of Example 1 was significantly higher than that of the conventional baking process of Comparative Example 1. 2) The chemical component content and coordination of the upper tobacco leaves after the baking process of Example 1 was adjusted were better than those of the conventional baking process of Comparative Example 1, especially the impact on nicotine, reducing sugar, sugar-alkali ratio and nitrogen-alkali ratio reached a significant level; the total score of conventional chemical components was significantly higher than that of the conventional baking process of Comparative Example 1.

[0056] Table 5 Comparison of significance of conventional chemical components of middle leaves under different baking processes

[0057] Table 6 Comparison of significance of conventional chemical components of upper leaves under different baking processes

[0058] In summary, the tobacco leaves prepared by the baking process of the present application have better identity, oil content and color than those prepared by the existing conventional process; the impact on the conventional chemical composition of the tobacco leaves after baking is mainly manifested in increasing the sugar content, reducing the starch content, and improving the coordination of the sugar-alkali ratio.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

[0060] Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and to form distinct embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background of this application and should not be construed as an admission or any implication that such information constitutes prior art known to those skilled in the art.

Claims

1. A one-time flue-cured tobacco leaf with stems, characterized in that: include: The upper and middle tobacco leaves harvested with stems are clamped with tobacco clips, with the leaf tips facing downward, and placed in a curing room to start curing; the curing includes: an aroma brewing stage, an aroma producing stage, an aroma enhancing stage, an aroma increasing stage and an aroma fixing stage.

2. The one-time flue-cured tobacco leaf with stems of the upper and middle parts of the flue-cured tobacco according to claim 1, characterized in that: The middle and upper tobacco leaves harvested with stems include 10 to 15 tobacco leaves.

3. The one-time flue-cured tobacco leaf with stems of the upper and middle parts of the flue-cured tobacco according to claim 1, characterized in that: The aroma brewing stage includes: after loading the tobacco, raising the dry-bulb temperature to 39°C at a rate of 1.0-1.5°C / h, stabilizing the temperature for 3 hours, then stopping the fire and cooling the temperature to a dry-bulb temperature of 30°C, then using the same method to raise the dry-bulb temperature to 39°C at a rate of 1.0-1.5°C / h, stabilizing the temperature for 17-20 hours, and then stopping the fire and cooling the temperature to a dry-bulb temperature of 30°C.

4. The one-time flue-cured tobacco leaf with stems of the upper and middle parts of the flue-cured tobacco according to claim 3, characterized in that: The wet bulb temperature during the aroma brewing stage is kept 1-2°C lower than the dry bulb temperature until the mesophyll of the bottom tobacco leaves is substantially completely yellow.

5. The one-time flue-cured tobacco leaf with stems of the upper and middle parts of the flue-cured tobacco according to claim 1, characterized in that: The aroma production stage includes: raising the dry bulb temperature to 40°C at a rate of 0.5°C / h, maintaining the dry bulb temperature at 40-43°C and the wet bulb temperature at 36-37°C, until the tobacco leaves in the entire room turn completely yellow and the main veins become fully softened.

6. The one-time flue-cured tobacco leaf with stems of the upper and middle parts of the flue-cured tobacco according to claim 5, characterized in that: During the fragrance production stage, the dry bulb temperature is maintained at 40~43℃ for 8~10 hours.

7. The one-time flue-cured tobacco leaf with stems of the upper and middle parts of the flue-cured tobacco according to claim 1, characterized in that: The aroma enhancement stage includes: raising the dry bulb temperature to 47°C to 49°C at a rate of 0.5-1.0°C / h, the wet bulb temperature to 36-37°C, and stabilizing the temperature for 8-10 hours.

8. The one-time flue-cured tobacco leaf with stems of the upper and middle parts of the flue-cured tobacco according to claim 1, characterized in that: The aroma enhancement stage includes: raising the dry bulb temperature to 50-54°C at a rate of 0.5-1.0°C / h and the wet bulb temperature to 38-40°C. The temperature stabilization time of the aroma enhancement stage is shortened by 3-5h compared with the temperature stabilization time of the aroma enhancement stage.

9. The one-time flue-cured tobacco leaf with stems of the upper and middle parts of the flue-cured tobacco according to claim 1, characterized in that: The aroma fixing stage includes: raising the dry bulb temperature to 60-68°C at a rate of 0.5-1.0°C / h and the wet bulb temperature to 40-42°C until the veins of the tobacco leaves in the entire room are completely dry.

10. The one-time flue-cured tobacco leaf with stems of the upper and middle parts of the flue-cured tobacco according to claim 9, characterized in that: The temperature stabilization time of the fragrance fixing stage is increased by 1 to 2 hours compared with the temperature stabilization time of the fragrance enhancing stage.

Images