Method for preparing tobacco leaves difficult to flue-cure by using high-nitrogen low-oxygen technology
By applying high nitrogen and low oxygen technology in tobacco leaf grilling rooms to monitor and control the environment of the grilling room, the problem of tobacco leaf grilling in the existing technology has been solved, and a higher quality tobacco leaf baking has been achieved.
Patent Information
- Application Number
- CN202510202107.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-24
- Publication Date
- 2025-06-06
AI Technical Summary
The existing air source heat pump tobacco leaf baking room is poorly moisturized in the later stage of yellowing and early stage of color fixation, resulting in frequent enzymatic browning reactions, resulting in the problem of tobacco leaf baking.
High nitrogen and low oxygen technology are used to monitor the temperature, humidity, nitrogen concentration and oxygen concentration in the grill room, and wet is discharged in the later stage of yellowing and coloring periods, and nitrogen is transported to the grill room according to process needs to control the oxygen concentration to prevent enzymatic browning reactions.
It effectively prevents enzymatic browning reactions, improves the baking quality of tobacco leaves, and reduces the incidence of bad tobacco.
Smart Images
Figure CN120093000A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of tobacco leaf processing and curing, and in particular relates to a method for curing difficult-to-cured tobacco leaves by applying a high-nitrogen and low-oxygen technology. Background Art
[0002] Flushing is the process of heat and moisture transfer between tobacco leaves and the environment and the solidification of tobacco leaf quality. It is an important link to achieve tobacco leaf quality improvement, efficiency enhancement, energy saving and carbon reduction. Flushing barns are the main places for tobacco leaf baking. Air source heat pump flushing barns are the main type of flushing barns for clean, low-carbon, safe and efficient production in my country's tobacco leaf baking field. At present, the existing air source heat pump tobacco flushing barns are mainly divided into closed, open and open and closed integrated types. Among them, closed flushing barns are the most widely used. Closed flushing barns use heat pump technology, low operating energy consumption, strong self-control performance, good drying quality, closed hot air circulation, and effective use of low-temperature heat energy in the atmospheric environment. It can efficiently utilize heat energy and save energy. However, closed flushing barns have problems such as poor moisture removal in the late yellowing period and early color fixing period, which leads to frequent browning reactions, resulting in bad tobacco. A large number of studies have shown that the loss rate of tobacco leaf baking in my country exceeds 15%, of which bad tobacco is the main type, and the proportion of bad tobacco caused by enzymatic browning reactions is far higher than 30%. The conditions for enzymatic browning reaction to occur are that polyphenols are in contact with polyphenol oxidase in large quantities under a temperature of 44℃-48℃, moisture and oxygen environment. Reducing the oxygen content in the baking room is one of the effective measures to prevent the occurrence of enzymatic browning reaction. Summary of the invention
[0003] The invention solves the problem that tobacco leaves are damaged due to an enzymatic browning reaction when tobacco leaves are baked in an existing baking house, and provides a method for preparing difficult-to-bake tobacco leaves by using a high-nitrogen and low-oxygen technology.
[0004] The technical solution claimed in the present invention is as follows:
[0005] A method for curing difficult-to-cured tobacco leaves by applying high-nitrogen and low-oxygen technology, wherein the curing refers to the process of curing the difficult-to-cured tobacco leaves in a curing room, and the curing process includes: a fire ignition period, a yellowing period, a color fixing period and a dry tendon period; the fire ignition period corresponds to a curing dry bulb temperature of 30°C-30.5°C in the curing room, a wet bulb temperature of 30°C, and a temperature increase of 0.5°C / h to an early yellowing period; the yellowing period is divided into an early yellowing period, a middle yellowing period and a late yellowing period, and moisture removal begins in the late yellowing period; the color fixing period is divided into an early color fixing period, a middle color fixing period and a late color fixing period, and moisture removal is performed during the whole curing process in the color fixing period; the temperature, humidity, nitrogen concentration and oxygen concentration in the curing room are monitored in the yellowing period and the color fixing period, and nitrogen is transported into the curing room according to process requirements; the process requirements are: nitrogen is transported into the curing room when the conditions in the curing room are: 44°C≤temperature≤48°C, nitrogen concentration≤89%, and oxygen concentration≥10%; otherwise, nitrogen is not transported into the curing room.
[0006] Preferably, the ignition period corresponds to a baking dry bulb temperature of 30°C-30.5°C, a wet bulb temperature of 30°C, and a temperature increase of 0.5°C / h to an early yellowing stage; the early yellowing stage corresponds to a baking dry bulb temperature of 32°C-34°C, a wet bulb temperature of 31°C-33°C, a temperature stabilization time of 15h-16h, and a temperature increase of 0.5°C / h to a middle yellowing stage; the middle yellowing stage corresponds to a baking dry bulb temperature of 38°C, a wet bulb temperature of 35°C, and a temperature stabilization time of 25h -28h, heating at 0.5℃ / h-1℃ / h to the middle yellowing stage; the late yellowing stage corresponds to a baking dry bulb temperature of 42℃, a wet bulb temperature of 35℃-35.5℃, a stabilization time of 18h-20h, heating at 0.5℃ / h-1℃ / h to the early color fixing stage, and moisture removal begins in the late yellowing stage; the dry rib stage is divided into the early dry rib stage and the late dry rib stage; the early color fixing stage corresponds to a baking dry bulb temperature of 44℃-45℃, a wet bulb temperature of 36℃-36.5℃ , 8h-10h stabilization time, 0.5℃ / h heating to the middle color fixing period; the middle color fixing period corresponds to a dry bulb temperature of 48℃, a wet bulb temperature of 36.5℃, 14h-16h stabilization time, 0.5℃ / h-1℃ / h heating to the late color fixing period; the late color fixing period corresponds to a dry bulb temperature of 54℃, a wet bulb temperature of 36.5℃, 20h-24h stabilization time, 1℃ / h-1.5℃ / h heating to the early dry rib period, and baking in the color fixing period Dehumidification is carried out throughout the whole process; the early stage of drying corresponds to a baking dry-bulb temperature of 62°C-65°C, a wet-bulb temperature of 37°C-38°C, a stabilizing time of 8h-10h, and the temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are dried by 80%, and the temperature is increased at a rate of 1°C / h-1.5°C / h to the late stage of drying; the late stage of drying corresponds to a dry-bulb temperature of 65°C-68°C, a wet-bulb temperature of 38°C-39°C, and the stabilizing time lasts for more than 15h, until the main veins of the tobacco leaves in the whole furnace are completely dried, and then the firing is stopped.
[0007] Preferably, dehumidification begins in the late yellowing stage when the baking dry-bulb temperature is 42°C±0.5°C and the wet-bulb temperature is 35±0.5°C; dehumidification occurs in the color fixing stage when the baking dry-bulb temperature is 44°C-54°C or the wet-bulb temperature is 36°C-36.5°C.
[0008] The difficult-to-cured tobacco leaves include: difficult-to-cured tobacco leaves formed by special flue-cured tobacco varieties and special climatic conditions in the field; the difficult-to-cured tobacco leaves include: difficult-to-cured tobacco leaves formed by special flue-cured tobacco varieties and special climatic conditions in the field, and the tobacco leaves have thicker leaf tissue structure and higher content of plastid pigments, fresh tobacco leaf enzyme activity and polyphenols.
[0009] The special flue-cured tobacco varieties include: Honghua Dajinyuan and Cuibi No. 1. The tobacco leaves of this variety have thicker leaf tissue structure and higher content of plastid pigments, fresh tobacco leaf enzyme activity and polyphenols; the difficult-to-cured tobacco leaves formed by the special field climatic conditions include: tobacco leaves with higher moisture content and tobacco leaves with lower moisture content; the special field climatic conditions include: heavy rain and little sunlight, long-term rainfall during the maturity period, and drought and high temperature.
[0010] In the above method, the special flue-cured tobacco variety baking process specifically includes the following steps:
[0011] S1: Ignition period: The ignition period corresponds to a baking dry bulb temperature of 30℃-30.5℃, a wet bulb temperature of 30℃, and a steady low fire with a temperature increase of 0.5℃ / h to the early yellowing stage;
[0012] S2: Yellowing stage: In the early stage of yellowing, the dry bulb temperature is 32℃-34℃, the wet bulb temperature is 31℃-33℃, and the temperature stabilization time is 15h-16h. The temperature is stabilized until the tips and edges of all tobacco leaves in the curing room turn yellow by 5cm-8cm. The dry bulb temperature is increased at a rate of 0.5℃ / h to the middle stage of yellowing; in the middle stage of yellowing, the dry bulb temperature is 38℃, the wet bulb temperature is 35℃, and the temperature stabilization time is 25h-28h. The temperature is stabilized until all tobacco leaves in the curing room have green veins and yellow pieces. The dry bulb temperature is increased at a rate of 1℃ / h to the late stage of yellowing; in the late stage of yellowing, the dry bulb temperature is 42℃, the wet bulb temperature is 35℃-35.5℃, and the moisture is slightly discharged. The temperature stabilization time is 18h-20h. The temperature is stabilized until more than 90% of the tobacco leaves in the curing room are completely yellow, begin to wither and collapse, the tips of the leaves curl, and 80% of the branches turn from green to white. The dry bulb temperature is increased at a rate of 0.5℃ / h-1℃ / h to the early stage of color fixation;
[0013] S3: Color fixing period: In the early stage of color fixing, the dry bulb temperature is 44℃-45℃, the wet bulb temperature is 36℃-36.5℃, the moisture is discharged, and the temperature stabilization time is 8h-10h. The temperature is stabilized until all tobacco leaves in the flue-curing room are completely yellow, the frame is fully collapsed, the side veins are completely white, soft and yellow, and the temperature is increased by 0.5℃ / h to the middle stage of color fixing; the dry bulb temperature in the middle stage of color fixing is 48℃, the wet bulb temperature is 36.5℃, the moisture is discharged, and the temperature stabilization time is 14h-16h. The temperature is stabilized until all tobacco leaves in the low temperature zone of the flue-curing room are yellow and yellow, and small rolls are formed. The temperature is increased by 0.5℃ / h-1℃ / h to the late stage of color fixing; the dry bulb temperature in the late stage of color fixing is 54℃, the wet bulb temperature is 36.5℃, and the temperature stabilization time is 20h-24h. The temperature is stabilized until all tobacco leaves in the low temperature zone of the flue-curing room are large rolls, the main veins are completely white, and the leaf flesh and side veins are completely dry. The temperature is increased by 1℃ / h-1.5℃ / h to the early stage of dry tendons.
[0014] S4: Drying period: In the early stage of drying period, the dry bulb temperature is 62℃-65℃, the wet bulb temperature is 37℃-38℃, and the temperature stabilization time is 8h-10h. The temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are 80% dry. The temperature is increased at 1℃ / h-1.5℃ / h to the late stage of drying period; the dry bulb temperature in the late stage of drying period is 65℃-68℃, the wet bulb temperature is 38℃-39℃, and the temperature stabilization time needs to last for more than 15h. The temperature is stabilized until the tobacco leaves in the whole furnace are completely dry, and then the fire is stopped;
[0015] Steps S2 and S3 deliver nitrogen into the baking room according to process requirements.
[0016] In an embodiment of the present invention, the baking process of tobacco leaves with a high moisture content specifically includes the following steps:
[0017] S1: Fire period: Run the fan for 6-7 hours before the fire breaks out. The fire period corresponds to a dry bulb temperature of 29℃-30℃ and a wet bulb temperature of 29℃. Steady low heat is used to increase the temperature at 0.5℃ / h until the early stage of yellowing.
[0018] S2: Yellowing stage: In the early stage of yellowing, the dry bulb temperature is 33℃-35℃, the wet bulb temperature is 33℃-34℃, and the temperature stabilization time is 14h-16h. The temperature is stabilized until the tips and edges of all tobacco leaves in the cantilevered flue-curing room turn yellow. The dry bulb temperature is increased at a rate of 0.5℃ / h-1℃ / h to the middle stage of yellowing. In the middle stage of yellowing, the dry bulb temperature is 37℃-38℃, the wet bulb temperature is 35℃-36℃, the moisture is discharged in the middle stage, the temperature stabilization time is 22h-25h, and the temperature is stabilized. The temperature is set until all tobacco leaves in the cantilevered flue-curing room have green veins and yellow flakes, and the dry bulb temperature is raised at a rate of 1℃ / h to the late yellowing stage; the dry bulb temperature in the late yellowing stage is 41℃-42℃, and the wet bulb temperature is 36℃-36.5℃. The moisture is removed in large quantities and the temperature is stabilized for 20h-22h. The temperature is stabilized until all tobacco leaves in the cantilevered flue-curing room are completely yellow, the tips are curled, and 80% of the veins turn from green to white. The dry bulb temperature is raised at a rate of 1℃ / h-1.5℃ / h to the early color fixation stage;
[0019] S3: Color fixing period: In the early stage of color fixing, the dry bulb temperature is 44℃-45℃, the wet bulb temperature is 36℃-36.5℃, and moisture is discharged. The temperature is kept stable for 10h-12h. The temperature is kept stable until all tobacco leaves in the flue-curing room are completely yellow, the frame is fully collapsed, and the branch veins are completely white, soft and yellow. The dry bulb temperature is increased at a rate of 1℃ / h to the middle stage of color fixing; the dry bulb temperature in the middle stage of color fixing is 47℃-48℃, the wet bulb temperature is 36℃-36.5℃, and moisture is discharged. The temperature is kept stable for 13h-15h. The temperature is kept stable until all tobacco leaves in the low temperature zone of the flue-curing room are yellow in pieces and tendons, and small rolls are formed. The temperature is increased at a rate of 1℃ / h to the late stage of color fixing; the dry bulb temperature in the late stage of color fixing is 52℃-54℃, the wet bulb temperature is 37℃, and moisture is discharged. The temperature is kept stable until all tobacco leaves in the flue-curing room are large rolls, the main veins are completely white, and the leaf flesh and branch veins are completely dry. The dry bulb temperature is increased to 65℃ at a rate of 1℃ / h-1.5℃ / h;
[0020] S4: Drying period: In the drying period, the dry bulb temperature is 62℃-65℃, the wet bulb temperature is 36.5℃-37℃, and the temperature stabilization time is 9h-10h. The temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are dried by 80%, and the temperature is increased at 2℃ / h to the late drying period; the dry bulb temperature in the late drying period is 65℃-68℃, the wet bulb temperature is 38℃-39℃, and the temperature stabilization time needs to last for more than 15h. The temperature is stabilized until the tobacco leaves in the whole furnace are completely dry, and then the fire is stopped;
[0021] Steps S2 and S3 deliver nitrogen into the baking room according to process requirements.
[0022] In an embodiment of the present invention, the baking process of tobacco leaves with a low moisture content specifically includes the following steps:
[0023] S1: Ignition period: The ignition period corresponds to a dry bulb temperature of 30°C, a wet bulb temperature of 30°C, and a steady low fire at a rate of 0.5°C / h until the early stage of yellowing;
[0024] S2: Yellowing stage: In the early stage of yellowing, the dry bulb temperature is 32℃-34℃, the wet bulb temperature is 32℃-33℃, and the temperature stabilization time is 15h-16h. The temperature is stabilized until the tips and edges of all tobacco leaves in the curing room turn yellow. The dry bulb temperature is increased at a rate of 0.5℃ / h to the middle stage of yellowing; in the middle stage of yellowing, the dry bulb temperature is 36℃-38℃, the wet bulb temperature is 34℃-35℃, and the temperature stabilization time is 24h-26h. The temperature is stabilized until all tobacco leaves in the curing room have green veins and yellow pieces. The dry bulb temperature is increased at a rate of 0.5℃ / h to the late stage of yellowing; in the late stage of yellowing, the dry bulb temperature is 40℃-42℃, the wet bulb temperature is 36℃-37℃, and the moisture is slightly discharged. The temperature stabilization time is 16h-18h. The temperature is stabilized until all tobacco leaves in the curing room are completely yellow, the tips are curled, and 80% of the branch veins turn from green to white. The dry bulb temperature is increased at a rate of 1℃ / h to the early stage of color fixation;
[0025] S3: Color fixing period: In the early stage of color fixing, the dry bulb temperature is 43℃-44℃, the wet bulb temperature is 36℃, the moisture is discharged in the middle stage, and the temperature is kept stable for 10h-12h. The temperature is kept stable until all tobacco leaves in the flue-curing room are completely yellow, the frame is fully collapsed, and the branch veins are completely white, soft and yellow. The temperature is raised at 0.5℃ / h to the middle stage of color fixing; the dry bulb temperature in the middle stage of color fixing is 46℃-48℃, the wet bulb temperature is 37℃, the moisture is discharged in the large stage, and the temperature is kept stable for 14h-16h. The temperature is kept stable until all tobacco leaves in the low temperature zone of the flue-curing room are yellow in pieces and tendons, and are in the shape of small rolls. The temperature is raised at 0.5℃ / h-1℃ / h to the late stage of color fixing; the dry bulb temperature in the late stage of color fixing is 53℃-54℃, the wet bulb temperature is 37℃-37.5℃, the moisture is discharged in the large stage, and the temperature is kept stable until all tobacco leaves in the low temperature zone of the flue-curing room are in the shape of large rolls, the main veins are completely white, and the leaf flesh and branch veins are completely dry. The temperature is raised at 1.5℃ / h to the early stage of dry tendons;
[0026] S4: Drying period: In the early stage of drying period, the dry bulb temperature is 62℃-64℃, the wet bulb temperature is 37℃, and the temperature stabilization time is 8h-10h. The temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are 80% dry. The temperature is increased at 1.5℃ / h to the late stage of drying period. In the late stage of drying period, the dry bulb temperature is 66℃-68℃, the wet bulb temperature is 38℃-39℃, and the temperature stabilization time needs to last for more than 15h. The temperature is stabilized until the tobacco leaves in the whole furnace are completely dry, and then the fire is stopped;
[0027] Steps S2 and S3 deliver nitrogen into the baking room according to process requirements.
[0028] Beneficial effects:
[0029] The invention provides a method for preparing difficult-to-cure tobacco leaves by applying high-nitrogen and low-oxygen technology, wherein the yellowing period is divided into an early yellowing period, a middle yellowing period and a late yellowing period, the color fixing period is divided into an early color fixing period, a middle color fixing period and a late color fixing period, the tendon drying period is divided into an early tendon drying period and a late tendon drying period, and different temperatures are set respectively to bake the tobacco leaves, which is more targeted. Compared with the traditional three-stage baking method, the baking quality of the tobacco leaves is higher; when the humidity in a baking room in the late yellowing period and the color fixing period of baking is too high, the difficult-to-cure tobacco leaves are dehumidified, and at the same time, the nitrogen delivery in the baking room is started and stopped according to the temperature and nitrogen oxygen concentration in the baking room, and the oxygen concentration in the baking room is reduced to a certain proportion, so as to prevent the occurrence of an enzymatic browning reaction, thereby solving the problem that the enzymatic browning reaction occurs when baking tobacco leaves in the existing baking room, causing the tobacco leaves to be damaged, and greatly improving the baking quality of the tobacco leaves. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 The present invention is a flow chart of a method for preparing difficult-to-cured tobacco leaves using high-nitrogen and low-oxygen technology according to an embodiment of the present invention. DETAILED DESCRIPTION
[0031] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:
[0032] The present invention provides a method for curing difficult-to-cured tobacco leaves using a high-nitrogen and low-oxygen technology, wherein the curing refers to a process of curing the difficult-to-cured tobacco leaves in a curing room, such as Figure 1 As shown, the baking process includes: ignition period, yellowing period, color fixing period and dry period; the ignition period corresponds to a baking dry bulb temperature of 30°C-30.5°C in the baking room, a wet bulb temperature of 30°C, and a temperature increase of 0.5°C / h to the early yellowing stage; the yellowing stage is divided into the early yellowing stage, the middle yellowing stage and the late yellowing stage, and moisture removal begins in the late yellowing stage; the color fixing stage is divided into the early color fixing stage, the middle color fixing stage and the late color fixing stage, and moisture removal is performed during the entire baking process during the color fixing stage; the temperature, humidity, nitrogen concentration and oxygen concentration in the baking room are monitored during the yellowing stage and the color fixing stage, and nitrogen and oxygen concentrations are transported to the baking room according to process requirements.
[0033] The leaves of the flue-cured tobacco varieties Cuibi No. 1 and Honghua Dajinyuan have thicker leaf tissue structures and higher content of plastid pigments, fresh tobacco leaf enzyme activity and polyphenols. During the baking process, the leaves turn yellow slowly, lose water easily, and are prone to enzymatic browning reactions. The baking process specifically includes the following steps:
[0034] S1: Ignition period: The ignition period corresponds to a baking dry bulb temperature of 30℃-30.5℃, a wet bulb temperature of 30℃, and a steady low fire with a temperature increase of 0.5℃ / h to the early yellowing stage;
[0035] S2: Yellowing stage: In the early stage of yellowing, the dry bulb temperature is 32℃-34℃, the wet bulb temperature is 31℃-33℃, and the temperature stabilization time is 15h-16h. The temperature is stabilized until the tips and edges of all tobacco leaves in the curing room turn yellow by 5cm-8cm. The dry bulb temperature is increased at a rate of 0.5℃ / h to the middle stage of yellowing; in the middle stage of yellowing, the dry bulb temperature is 38℃, the wet bulb temperature is 35℃, and the temperature stabilization time is 25h-28h. The temperature is stabilized until all tobacco leaves in the curing room have green veins and yellow pieces. The dry bulb temperature is increased at a rate of 1℃ / h to the late stage of yellowing; in the late stage of yellowing, the dry bulb temperature is 42℃, the wet bulb temperature is 35℃-35.5℃, and the moisture is slightly discharged. The temperature stabilization time is 18h-20h. The temperature is stabilized until more than 90% of the tobacco leaves in the curing room are completely yellow, begin to wither and collapse, the tips of the leaves curl, and 80% of the branches turn from green to white. The dry bulb temperature is increased at a rate of 0.5℃ / h-1℃ / h to the early stage of color fixation;
[0036] S3: Color fixing period: In the early stage of color fixing, the dry bulb temperature is 44-45℃, the wet bulb temperature is 36-36.5℃, the moisture is discharged, and the temperature is stabilized for 8h-10h. The temperature is stabilized until all tobacco leaves in the flue-curing room are completely yellow, the frame is fully collapsed, and the branch veins are completely white, soft and yellow. The temperature is raised at 0.5℃ / h to the middle stage of color fixing; the dry bulb temperature in the middle stage of color fixing is 48℃, the wet bulb temperature is 36.5℃, the moisture is discharged, and the temperature is stabilized for 14h-16h. The temperature is stabilized until all tobacco leaves in the low temperature zone of the flue-curing room are yellow and yellow, and small rolls are formed. The temperature is raised at 0.5℃ / h-1℃ / h to the late stage of color fixing; the dry bulb temperature in the late stage of color fixing is 54℃, the wet bulb temperature is 36.5℃, and the temperature is stabilized for 20h-24h. The temperature is stabilized until all tobacco leaves in the low temperature zone of the flue-curing room are large rolls, the main veins are completely white, and the leaf flesh and branch veins are completely dry. The temperature is raised at 1℃ / h-1.5℃ / h to the early stage of dry tendons;
[0037] S4: Drying period: In the early stage of drying period, the dry bulb temperature is 62℃-65℃, the wet bulb temperature is 37℃-38℃, and the temperature stabilization time is 8h-10h. The temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are 80% dry. The temperature is increased at 1℃ / h-1.5℃ / h to the late stage of drying period; the dry bulb temperature in the late stage of drying period is 65℃-68℃, the wet bulb temperature is 38℃-39℃, and the temperature stabilization time needs to last for more than 15h. The temperature is stabilized until the tobacco leaves in the whole furnace are completely dry, and then the fire is stopped;
[0038] Steps S2 and S3 deliver nitrogen into the baking room according to process requirements.
[0039] Embodiment 2, the method for baking tobacco leaves with high water content
[0040] Tobacco with high moisture content is rainy and light-poor tobacco, rain-soaked tobacco, and green tobacco. It is characterized by high moisture content and protein, less dry matter accumulation, poor maturity, and thin identity. During the baking process, the tobacco leaves are difficult to turn yellow, and are prone to hard yellowing and enzymatic browning reactions. The baking process of tobacco leaves with high moisture content is:
[0041] S1: Fire period: The fan is operated for 6-7 hours before the fire occurs. The fire period corresponds to a baking dry bulb temperature of 29℃-30℃ and nitrogen. The process requirements are: nitrogen is delivered to the baking room when the conditions in the baking room are 44℃≤temperature≤48℃, nitrogen concentration≤89%, and oxygen concentration≥10%; otherwise, nitrogen is not delivered to the baking room. In a specific embodiment of the present invention, there are multiple groups of dry bulb + wet bulb probes in the baking room (generally 2 groups, separated in different shelf baking rooms), which are connected to a controller outside the baking room, and the dry bulb temperature and wet bulb temperature in the baking room are monitored and transmitted to the sensor display screen in real time, and then provided to the baking technicians for reference, real-time feedback and appropriate adjustment of the baking process.
[0042] In a specific embodiment of the present invention, the ignition period corresponds to a baking dry bulb temperature of 30°C-30.5°C and a wet bulb temperature of 30°C in the baking room, and the temperature is increased at 0.5°C / h to the early yellowing stage; the early yellowing stage corresponds to a baking dry bulb temperature of 32°C-34°C, a wet bulb temperature of 31°C-33°C, a stabilization time of 15h-16h, and the temperature is increased at 0.5°C / h to the middle yellowing stage; the middle yellowing stage corresponds to a baking dry bulb temperature of 38°C, a wet bulb temperature of 35°C, and a stabilization time of 15h-16h. The temperature is kept at 25h-28h, and the temperature is raised at 0.5℃ / h-1℃ / h to the middle yellowing stage; the late yellowing stage corresponds to a baking dry bulb temperature of 42℃, a wet bulb temperature of 35℃-35.5℃, and the temperature is kept at 18h-20h, and the temperature is raised at 0.5℃ / h-1℃ / h to the early color fixing stage. Moisture is discharged in the late yellowing stage; the dry rib stage is divided into the early dry rib stage and the late dry rib stage; the early color fixing stage corresponds to a baking dry bulb temperature of 44℃-45℃, a wet bulb temperature of 36℃-3 6.5℃, stabilization time 8h-10h, heating at 0.5℃ / h to the middle color fixing period; the middle color fixing period corresponds to a baking dry bulb temperature of 48℃, a wet bulb temperature of 36.5℃, stabilization time 14h-16h, heating at 0.5℃ / h-1℃ / h to the late color fixing period; the late color fixing period corresponds to a baking dry bulb temperature of 54℃, a wet bulb temperature of 36.5℃, stabilization time 20h-24h, heating at 1℃ / h-1.5℃ / h to the early dry tendon period, in the color fixing period Dehumidification is carried out during the whole baking process; the early stage of drying corresponds to a drying dry bulb temperature of 62℃-65℃, a wet bulb temperature of 37℃-38℃, and a stabilization time of 8h-10h. The temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are 80% dry, and the temperature is raised to the late stage of drying at 1℃ / h-1.5℃ / h; the late stage of drying corresponds to a dry bulb temperature of 65℃-68℃, a wet bulb temperature of 38℃-39℃, and a stabilization time of more than 15h, until the main veins of the tobacco leaves in the whole furnace are completely dry, and then the fire is stopped. Dehumidification begins in the late yellowing stage when the drying dry bulb temperature is 42℃±0.5℃ and the wet bulb temperature is 35±0.5℃; dehumidification is carried out in the color fixing stage when the drying dry bulb temperature is 44℃-54℃ or the wet bulb temperature is 36℃-36.5℃.
[0043] In some embodiments of the present invention, the difficult-to-cured tobacco leaves are special flue-cured tobacco varieties, and the special flue-cured tobacco varieties include: Honghua Dajinyuan and Cuibi No. 1; in other embodiments of the present invention, the difficult-to-cured tobacco leaves are difficult-to-cured tobacco leaves formed by special climatic conditions in the field; the special field climatic conditions include: heavy rain and little sunlight, long-term rainfall during the maturity period, drought and high temperature; the difficult-to-cured tobacco leaves formed by special field climatic conditions include: tobacco leaves with higher moisture content and tobacco leaves with lower moisture content.
[0044] Example 1, flue-cured tobacco leaf baking method of Honghua Dajinyuan and Cuibi No. 1 flue-cured tobacco varieties
[0045] The wet bulb temperature is 29℃, burn steadily at low heat and increase the temperature at 0.5℃ / h until the early stage of yellowing;
[0046] S2: Yellowing stage: In the early stage of yellowing, the dry bulb temperature is 33℃-35℃, the wet bulb temperature is 33℃-34℃, and the temperature stabilization time is 14h-16h. The temperature is stabilized until the tips and edges of all tobacco leaves in the cantilevered flue-curing room turn yellow. The dry bulb temperature is increased at a rate of 0.5℃ / h-1℃ / h to the middle stage of yellowing. In the middle stage of yellowing, the dry bulb temperature is 37℃-38℃, the wet bulb temperature is 35℃-36℃, the moisture is discharged in the middle stage, the temperature stabilization time is 22h-25h, and the temperature is stabilized. The temperature is set until all tobacco leaves in the cantilevered flue-curing room have green veins and yellow flakes, and the dry bulb temperature is raised at a rate of 1℃ / h to the late yellowing stage; the dry bulb temperature in the late yellowing stage is 41℃-42℃, and the wet bulb temperature is 36℃-36.5℃. The moisture is removed in large quantities and the temperature is stabilized for 20h-22h. The temperature is stabilized until all tobacco leaves in the cantilevered flue-curing room are completely yellow, the tips are curled, and 80% of the veins turn from green to white. The dry bulb temperature is raised at a rate of 1℃ / h-1.5℃ / h to the early color fixation stage;
[0047] S3: Color fixing period: In the early stage of color fixing, the dry bulb temperature is 44℃-45℃, the wet bulb temperature is 36℃-36.5℃, and moisture is discharged. The temperature is kept stable for 10h-12h. The temperature is kept stable until all tobacco leaves in the flue-curing room are completely yellow, the frame is fully collapsed, and the branch veins are completely white, soft and yellow. The dry bulb temperature is increased at a rate of 1℃ / h to the middle stage of color fixing; the dry bulb temperature in the middle stage of color fixing is 47℃-48℃, the wet bulb temperature is 36℃-36.5℃, and moisture is discharged. The temperature is kept stable for 13h-15h. The temperature is kept stable until all tobacco leaves in the low temperature zone of the flue-curing room are yellow in pieces and tendons, and small rolls are formed. The temperature is increased at a rate of 1℃ / h to the late stage of color fixing; the dry bulb temperature in the late stage of color fixing is 52℃-54℃, the wet bulb temperature is 37℃, and moisture is discharged. The temperature is kept stable until all tobacco leaves in the flue-curing room are large rolls, the main veins are completely white, and the leaf flesh and branch veins are completely dry. The dry bulb temperature is increased to 65℃ at a rate of 1℃ / h-1.5℃ / h;
[0048] S4: Drying period: In the drying period, the dry bulb temperature is 62℃-65℃, the wet bulb temperature is 36.5℃-37℃, and the temperature stabilization time is 9h-10h. The temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are dried by 80%, and the temperature is increased at 2℃ / h to the late drying period; the dry bulb temperature in the late drying period is 65℃-68℃, the wet bulb temperature is 38℃-39℃, and the temperature stabilization time needs to last for more than 15h. The temperature is stabilized until the tobacco leaves in the whole furnace are completely dry, and then the fire is stopped;
[0049] Steps S2 and S3 deliver nitrogen into the baking room according to process requirements.
[0050] Embodiment 3, the method for baking tobacco leaves with low water content
[0051] Tobacco leaves with low moisture content are dry yellow tobacco leaves, which are characterized by premature yellowing and false ripening after encountering drought weather during the growth and maturity periods. The tobacco leaves have a tight tissue structure, low moisture content but are difficult to lose water, and have a high protein content. The specific baking process of tobacco leaves with low moisture content is as follows:
[0052] S1: Ignition period: The ignition period corresponds to a dry bulb temperature of 30°C, a wet bulb temperature of 30°C, and a steady low fire at a rate of 0.5°C / h until the early yellowing stage;
[0053] S2: Yellowing stage: In the early stage of yellowing, the dry bulb temperature is 32℃-34℃, the wet bulb temperature is 32℃-33℃, and the temperature stabilization time is 15h-16h. The temperature is stabilized until the tips and edges of all tobacco leaves in the curing room turn yellow. The dry bulb temperature is increased at a rate of 0.5℃ / h to the middle stage of yellowing; in the middle stage of yellowing, the dry bulb temperature is 36℃-38℃, the wet bulb temperature is 34℃-35℃, and the temperature stabilization time is 24h-26h. The temperature is stabilized until all tobacco leaves in the curing room have green veins and yellow pieces. The dry bulb temperature is increased at a rate of 0.5℃ / h to the late stage of yellowing; in the late stage of yellowing, the dry bulb temperature is 40℃-42℃, the wet bulb temperature is 36℃-37℃, and the moisture is slightly discharged. The temperature stabilization time is 16h-18h. The temperature is stabilized until all tobacco leaves in the curing room are completely yellow, the tips are curled, and 80% of the branch veins turn from green to white. The dry bulb temperature is increased at a rate of 1℃ / h to the early stage of color fixation;
[0054] S3: Color fixing period: In the early stage of color fixing, the dry bulb temperature is 43℃-44℃, the wet bulb temperature is 36℃, the moisture is discharged in the middle stage, and the temperature is kept stable for 10h-12h. The temperature is kept stable until all tobacco leaves in the flue-curing room are completely yellow, the frame is fully collapsed, and the branch veins are completely white, soft and yellow. The temperature is raised at 0.5℃ / h to the middle stage of color fixing; the dry bulb temperature in the middle stage of color fixing is 46℃-48℃, the wet bulb temperature is 37℃, the moisture is discharged in the large stage, and the temperature is kept stable for 14h-16h. The temperature is kept stable until all tobacco leaves in the low temperature zone of the flue-curing room are yellow in pieces and tendons, and are in the shape of small rolls. The temperature is raised at 0.5℃ / h-1℃ / h to the late stage of color fixing; the dry bulb temperature in the late stage of color fixing is 53℃-54℃, the wet bulb temperature is 37℃-37.5℃, the moisture is discharged in the large stage, and the temperature is kept stable until all tobacco leaves in the low temperature zone of the flue-curing room are in the shape of large rolls, the main veins are completely white, and the leaf flesh and branch veins are completely dry. The temperature is raised at 1.5℃ / h to the early stage of dry tendons;
[0055] S4: Drying period: In the early stage of drying period, the dry bulb temperature is 62℃-64℃, the wet bulb temperature is 37℃, and the temperature stabilization time is 8h-10h. The temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are 80% dry. The temperature is increased at 1.5℃ / h to the late stage of drying period. In the late stage of drying period, the dry bulb temperature is 66℃-68℃, the wet bulb temperature is 38℃-39℃, and the temperature stabilization time needs to last for more than 15h. The temperature is stabilized until the tobacco leaves in the whole furnace are completely dry, and then the fire is stopped;
[0056] Steps S2 and S3 deliver nitrogen into the baking room according to process requirements.
[0057] It should be noted that the above-described specific implementations can enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way. Therefore, although this specification has described the invention in detail with reference to the drawings and embodiments, those skilled in the art should understand that the invention can still be modified or replaced by equivalents. In short, all technical solutions and improvements that do not deviate from the spirit and scope of the invention should be included in the protection scope of the patent for the invention.
Claims
1. A method for preparing difficult-to-cured tobacco leaves using high-nitrogen and low-oxygen technology, characterized in that: The modulation refers to the process of baking the difficult-to-bake tobacco leaves in a flue-curing room, and the baking process includes: a fire ignition period, a yellowing period, a color fixing period and a dry tendon period; the fire ignition period corresponds to a baking dry bulb temperature of 30°C-30.5°C in the flue-curing room, a wet bulb temperature of 30°C, and a temperature increase of 0.5°C / h to the early yellowing stage; the yellowing stage is divided into an early yellowing stage, a middle yellowing stage and a late yellowing stage, and dehumidification begins in the late yellowing stage; the color fixing stage is divided into an early color fixing stage, a middle color fixing stage and a late color fixing stage, and dehumidification is performed during the entire baking process in the color fixing stage; the temperature, humidity, nitrogen concentration and oxygen concentration in the flue-curing room are monitored during the yellowing stage and the color fixing stage, and nitrogen is transported into the flue-curing room according to process requirements; the process requirements are: nitrogen is transported into the flue-curing room when the conditions in the flue-curing room are: 44°C≤temperature≤48°C, nitrogen concentration≤89%, and oxygen concentration≥10%; otherwise, nitrogen is not transported into the flue-curing room.
2. The method for preparing difficult-to-cured tobacco leaves using high-nitrogen and low-oxygen technology according to claim 1, characterized in that: The fire period corresponds to a baking dry bulb temperature of 30°C-30.5°C, a wet bulb temperature of 30°C, and a temperature increase of 0.5°C / h to the early yellowing stage in the baking room; the early yellowing stage corresponds to a baking dry bulb temperature of 32°C-34°C, a wet bulb temperature of 31°C-33°C, a temperature stabilization time of 15h-16h, and a temperature increase of 0.5°C / h to the middle yellowing stage; the middle yellowing stage corresponds to a baking dry bulb temperature of 38°C, a wet bulb temperature of 35°C, and a temperature stabilization time of 25h-28 h, and the temperature is raised at 0.5℃ / h-1℃ / h to the middle yellowing stage; the late yellowing stage corresponds to a baking dry bulb temperature of 42℃, a wet bulb temperature of 35℃-35.5℃, and a stabilization time of 18h-20h, and the temperature is raised at 0.5℃ / h-1℃ / h to the early color fixing stage, and moisture is discharged in the late yellowing stage; the dry rib stage is divided into the early dry rib stage and the late dry rib stage; the early color fixing stage corresponds to a baking dry bulb temperature of 44℃-45℃, a wet bulb temperature of 36℃-36.5℃, and a stabilization time of 18h-20h. The temperature is kept at 8h-10h, and the temperature is increased at 0.5℃ / h to the middle color fixing period; the middle color fixing period corresponds to a dry bulb temperature of 48℃, a wet bulb temperature of 36.5℃, and a stabilizing time of 14h-16h, and the temperature is increased at 0.5℃ / h-1℃ / h to the late color fixing period; the late color fixing period corresponds to a dry bulb temperature of 54℃, a wet bulb temperature of 36.5℃, and a stabilizing time of 20h-24h, and the temperature is increased at 1℃ / h-1.5℃ / h to the early dry rib period. During the color fixing period, the whole The process is dehumidified; the early stage of drying corresponds to a baking dry-bulb temperature of 62°C-65°C, a wet-bulb temperature of 37°C-38°C, a stabilizing time of 8h-10h, and the temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are dried by 80%, and the temperature is increased by 1°C / h-1.5°C / h to the late stage of drying; the late stage of drying corresponds to a dry-bulb temperature of 65°C-68°C, a wet-bulb temperature of 38°C-39°C, and the stabilizing time lasts for more than 15h, until the main veins of the tobacco leaves in the whole furnace are completely dried and the firing is stopped.
3. The method for preparing difficult-to-cured tobacco leaves using high-nitrogen and low-oxygen technology according to claim 1 or 2, characterized in that: In the late yellowing stage, when the baking dry-bulb temperature is 42℃±0.5℃ and the wet-bulb temperature is 35±0.5℃, dehumidification begins; in the color fixing stage, when the baking dry-bulb temperature is 44℃-54℃ or the wet-bulb temperature is 36℃-36.5℃, dehumidification occurs.
4. The method for preparing difficult-to-cured tobacco leaves using high-nitrogen and low-oxygen technology according to claim 3, characterized in that: The difficult-to-cured tobacco leaves include: difficult-to-cured tobacco leaves formed by special flue-cured tobacco varieties and special climatic conditions in the field.
5. The method for preparing difficult-to-cured tobacco leaves using high-nitrogen and low-oxygen technology according to claim 4, characterized in that: The special flue-cured tobacco varieties include: Honghua Dajinyuan and Cuibi No.
1. The tobacco leaves of this variety have thicker leaf tissue structure and higher content of plastid pigments, fresh tobacco leaf enzyme activity and polyphenols.
6. The method for preparing difficult-to-cured tobacco leaves using high-nitrogen and low-oxygen technology according to claim 4, characterized in that: The difficult-to-cure tobacco leaves formed under the special climatic conditions in the field include: tobacco leaves with higher moisture content and tobacco leaves with lower moisture content.
7. The method for preparing difficult-to-cured tobacco leaves using high-nitrogen and low-oxygen technology according to claim 6, characterized in that: The special field climate conditions include: heavy rain and little sunlight, long rainfall during the ripening period, and drought and high temperature.
8. The method for preparing difficult-to-cured tobacco leaves using high-nitrogen and low-oxygen technology according to claim 5, characterized in that: The special flue-cured tobacco variety baking process specifically comprises the following steps: S1: Ignition period: The ignition period corresponds to a baking dry bulb temperature of 30℃-30.5℃, a wet bulb temperature of 30℃, and a steady low fire with a temperature increase of 0.5℃ / h to the early yellowing stage; S2: Yellowing stage: In the early stage of yellowing, the dry bulb temperature is 32℃-34℃, the wet bulb temperature is 31℃-33℃, and the temperature stabilization time is 15h-16h. The temperature is stabilized until the tips and edges of all tobacco leaves in the curing room turn yellow by 5cm-8cm. The dry bulb temperature is increased at a rate of 0.5℃ / h to the middle stage of yellowing; in the middle stage of yellowing, the dry bulb temperature is 38℃, the wet bulb temperature is 35℃, and the temperature stabilization time is 25h-28h. The temperature is stabilized until all tobacco leaves in the curing room have green veins and yellow pieces. The dry bulb temperature is increased at a rate of 1℃ / h to the late stage of yellowing; in the late stage of yellowing, the dry bulb temperature is 42℃, the wet bulb temperature is 35℃-35.5℃, and the moisture is slightly discharged. The temperature stabilization time is 18h-20h. The temperature is stabilized until more than 90% of the tobacco leaves in the curing room are completely yellow, begin to wither and collapse, the tips of the leaves curl, and 80% of the branches turn from green to white. The dry bulb temperature is increased at a rate of 0.5℃ / h-1℃ / h to the early stage of color fixation; S3: Color fixing period: In the early stage of color fixing, the dry bulb temperature is 44-45℃, the wet bulb temperature is 36-36.5℃, the moisture is discharged, and the temperature is stabilized for 8h-10h. The temperature is stabilized until all tobacco leaves in the flue-curing room are completely yellow, the frame is fully collapsed, and the branch veins are completely white, soft and yellow. The temperature is raised at 0.5℃ / h to the middle stage of color fixing; the dry bulb temperature in the middle stage of color fixing is 48℃, the wet bulb temperature is 36.5℃, the moisture is discharged, and the temperature is stabilized for 14h-16h. The temperature is stabilized until all tobacco leaves in the low temperature zone of the flue-curing room are yellow and yellow, and small rolls are formed. The temperature is raised at 0.5℃ / h-1℃ / h to the late stage of color fixing; the dry bulb temperature in the late stage of color fixing is 54℃, the wet bulb temperature is 36.5℃, and the temperature is stabilized for 20h-24h. The temperature is stabilized until all tobacco leaves in the low temperature zone of the flue-curing room are large rolls, the main veins are completely white, and the leaf flesh and branch veins are completely dry. The temperature is raised at 1℃ / h-1.5℃ / h to the early stage of dry tendons; S4: Drying period: In the early stage of drying period, the dry bulb temperature is 62℃-65℃, the wet bulb temperature is 37℃-38℃, and the temperature stabilization time is 8h-10h. The temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are 80% dry. The temperature is increased at 1℃ / h-1.5℃ / h to the late stage of drying period; the dry bulb temperature in the late stage of drying period is 65℃-68℃, the wet bulb temperature is 38℃-39℃, and the temperature stabilization time needs to last for more than 15h. The temperature is stabilized until the tobacco leaves in the whole furnace are completely dry, and then the fire is stopped; Steps S2 and S3 deliver nitrogen into the baking room according to process requirements.
9. The method for preparing difficult-to-cured tobacco leaves using high-nitrogen and low-oxygen technology according to claim 4, characterized in that: The baking process of tobacco leaves with high moisture content specifically includes the following steps: S1: Fire period: Run the fan for 6-7 hours before the fire breaks out. The fire period corresponds to a dry bulb temperature of 29℃-30℃ and a wet bulb temperature of 29℃. Steady low heat is used to increase the temperature at 0.5℃ / h until the early stage of yellowing. S2: Yellowing stage: In the early stage of yellowing, the dry bulb temperature is 33℃-35℃, the wet bulb temperature is 33℃-34℃, and the temperature stabilization time is 14h-16h. The temperature is stabilized until the tips and edges of all tobacco leaves in the cantilevered flue-curing room turn yellow. The dry bulb temperature is increased at a rate of 0.5℃ / h-1℃ / h to the middle stage of yellowing. In the middle stage of yellowing, the dry bulb temperature is 37℃-38℃, the wet bulb temperature is 35℃-36℃, the moisture is discharged in the middle stage, the temperature stabilization time is 22h-25h, and the temperature is stabilized. The temperature is set until all tobacco leaves in the cantilevered flue-curing room have green veins and yellow flakes, and the dry bulb temperature is raised at a rate of 1℃ / h to the late yellowing stage; the dry bulb temperature in the late yellowing stage is 41℃-42℃, and the wet bulb temperature is 36℃-36.5℃. The moisture is removed in large quantities and the temperature is stabilized for 20h-22h. The temperature is stabilized until all tobacco leaves in the cantilevered flue-curing room are completely yellow, the tips are curled, and 80% of the veins turn from green to white. The dry bulb temperature is raised at a rate of 1℃ / h-1.5℃ / h to the early color fixation stage; S3: Color fixing period: In the early stage of color fixing, the dry bulb temperature is 44℃-45℃, the wet bulb temperature is 36℃-36.5℃, and moisture is discharged. The temperature is kept stable for 10h-12h. The temperature is kept stable until all tobacco leaves in the flue-curing room are completely yellow, the frame is fully collapsed, and the branch veins are completely white, soft and yellow. The dry bulb temperature is increased at a rate of 1℃ / h to the middle stage of color fixing; the dry bulb temperature in the middle stage of color fixing is 47℃-48℃, the wet bulb temperature is 36℃-36.5℃, and moisture is discharged. The temperature is kept stable for 13h-15h. The temperature is kept stable until all tobacco leaves in the low temperature zone of the flue-curing room are yellow in pieces and tendons, and small rolls are formed. The temperature is increased at a rate of 1℃ / h to the late stage of color fixing; the dry bulb temperature in the late stage of color fixing is 52℃-54℃, the wet bulb temperature is 37℃, and moisture is discharged. The temperature is kept stable until all tobacco leaves in the flue-curing room are large rolls, the main veins are completely white, and the leaf flesh and branch veins are completely dry. The dry bulb temperature is increased to 65℃ at a rate of 1℃ / h-1.5℃ / h; S4: Drying period: In the drying period, the dry bulb temperature is 62℃-65℃, the wet bulb temperature is 36.5℃-37℃, and the temperature stabilization time is 9h-10h. The temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are dried by 80%, and the temperature is increased at 2℃ / h to the late drying period; the dry bulb temperature in the late drying period is 65℃-68℃, the wet bulb temperature is 38℃-39℃, and the temperature stabilization time needs to last for more than 15h. The temperature is stabilized until the tobacco leaves in the whole furnace are completely dry, and then the fire is stopped; Steps S2 and S3 deliver nitrogen into the baking room according to process requirements.
10. The method for curing difficult-to-cured tobacco leaves using high nitrogen and low oxygen technology according to claim 4, characterized in that: The baking process of tobacco leaves with low moisture content specifically includes the following steps: S1: Ignition period: The ignition period corresponds to a dry bulb temperature of 30°C, a wet bulb temperature of 30°C, and a steady low fire at a rate of 0.5°C / h until the early stage of yellowing; S2: Yellowing stage: In the early stage of yellowing, the dry bulb temperature is 32℃-34℃, the wet bulb temperature is 32℃-33℃, and the temperature stabilization time is 15h-16h. The temperature is stabilized until the tips and edges of all tobacco leaves in the curing room turn yellow. The dry bulb temperature is increased at a rate of 0.5℃ / h to the middle stage of yellowing; in the middle stage of yellowing, the dry bulb temperature is 36℃-38℃, the wet bulb temperature is 34℃-35℃, and the temperature stabilization time is 24h-26h. The temperature is stabilized until all tobacco leaves in the curing room have green veins and yellow pieces. The dry bulb temperature is increased at a rate of 0.5℃ / h to the late stage of yellowing; in the late stage of yellowing, the dry bulb temperature is 40℃-42℃, the wet bulb temperature is 36℃-37℃, and the moisture is slightly discharged. The temperature stabilization time is 16h-18h. The temperature is stabilized until all tobacco leaves in the curing room are completely yellow, the tips are curled, and 80% of the branch veins turn from green to white. The dry bulb temperature is increased at a rate of 1℃ / h to the early stage of color fixation; S3: Color fixing period: In the early stage of color fixing, the dry bulb temperature is 43℃-44℃, the wet bulb temperature is 36℃, the moisture is discharged in the middle stage, and the temperature is kept stable for 10h-12h. The temperature is kept stable until all tobacco leaves in the flue-curing room are completely yellow, the frame is fully collapsed, and the branch veins are completely white, soft and yellow. The temperature is raised at 0.5℃ / h to the middle stage of color fixing; the dry bulb temperature in the middle stage of color fixing is 46℃-48℃, the wet bulb temperature is 37℃, the moisture is discharged in the large stage, and the temperature is kept stable for 14h-16h. The temperature is kept stable until all tobacco leaves in the low temperature zone of the flue-curing room are yellow in pieces and tendons, and are in the shape of small rolls. The temperature is raised at 0.5℃ / h-1℃ / h to the late stage of color fixing; the dry bulb temperature in the late stage of color fixing is 53℃-54℃, the wet bulb temperature is 37℃-37.5℃, the moisture is discharged in the large stage, and the temperature is kept stable until all tobacco leaves in the low temperature zone of the flue-curing room are in the shape of large rolls, the main veins are completely white, and the leaf flesh and branch veins are completely dry. The temperature is raised at 1.5℃ / h to the early stage of dry tendons; S4: Drying period: In the early stage of drying period, the dry bulb temperature is 62℃-64℃, the wet bulb temperature is 37℃, and the temperature stabilization time is 8h-10h. The temperature is stabilized until the main veins of the tobacco leaves in the whole furnace are 80% dry. The temperature is increased at 1.5℃ / h to the late stage of drying period. In the late stage of drying period, the dry bulb temperature is 66℃-68℃, the wet bulb temperature is 38℃-39℃, and the temperature stabilization time needs to last for more than 15h. The temperature is stabilized until the tobacco leaves in the whole furnace are completely dry, and then the fire is stopped; Steps S2 and S3 deliver nitrogen into the baking room according to process requirements.