Upper leaf conditioning process in a down-draught bulk curing barn

Abstract

This invention discloses a process for softening tobacco leaves in the upper part of a descending intensive curing barn, comprising: pre-curing facilities and tobacco leaf preparation; loading the barn with dense upper and sparse lower sections, setting parameters for curing; early yellowing stage, slight dehumidification, yellowing of the tips; mid-yellowing stage, dehumidification based on tobacco observation, until fully yellow and soft; late yellowing stage, dehumidification based on observation window, small veins half-white, large veins fully soft; late yellowing stage, dehumidification based on observation window, small veins fully white, tip curling and edge rolling; early color fixing stage, dehumidification based on observation window, large veins fully white, small veins half-dry; early color fixing stage, dehumidification based on observation window, large veins fully yellow, base of small veins not dry; late color fixing stage, appropriate increase in humidity, small veins fully dry, color difference reduced; early drying stage, increase and stabilize humidity, large veins shrink and turn half purple; late drying stage, stabilize temperature and humidity, large veins completely shrink and turn purple. This invention is highly operable, can reduce problems such as mold, blackening, stunting, and greening during tobacco curing, improves the appearance quality of tobacco leaves, makes the chemical composition more harmonious, and increases the yield and usability of tobacco leaves.

Description

Technical Field

[0001] This invention relates to a process for softening tobacco leaves in the upper part of a descending intensive curing barn, belonging to the field of tobacco curing technology. Background Technology

[0002] Tobacco curing is the most crucial step affecting the quality, yield, and usability of tobacco leaves, and it is also a major factor influencing tobacco farmers' income, cigarette product quality, and economic benefits. The formation of tobacco leaf quality, use value, and economic value is jointly determined by field production management and scientific curing methods. Therefore, curing is of paramount importance in tobacco leaf quality and flue-cured tobacco production. The curing characteristics, processes, and quality of flue-cured tobacco leaves are closely related and form the fundamental basis for developing suitable curing methods and creating optimal curing conditions to produce the best quality tobacco leaves.

[0003] Currently, in the process of curing tobacco leaves in the upper part of the descending intensive curing barn, some tobacco areas still adopt the traditional curing technology of moisturizing and yellowing, and large ventilation and dehumidification. The specific process is as follows:

[0004] The first step is to load the tobacco onto the kang (heated brick bed), close the doors and windows, set the baking curve parameters, adjust the baking curve status indicator box to the initial position, set the circulating fan to high speed, and ignite the fire for baking.

[0005] The second step is to maintain the initial dry and wet bulb temperature at 32℃ after ignition and bake for 8-12 hours. The program automatically controls the opening of the cold air inlet door and keeps the circulating fan at high speed. After 4 hours of preheating, raise the dry and wet bulb temperature to 36℃ and bake at a stable temperature for 18-24 hours until the upper tobacco leaves sweat and the tips turn yellow.

[0006] The third step is to keep the circulating fan at high speed, control the opening of the cold air inlet door in the program, raise the dry bulb temperature to 38℃ in 4 hours, and the wet bulb temperature to 37-38℃, and bake at a stable temperature for 24-36 hours until the lower leaves are completely yellow and not soft but hard.

[0007] The fourth step is to keep the circulating fan running at high speed, control the opening of the cold air inlet door in the program, raise the dry bulb temperature to 40℃ in 8 hours, and the wet bulb temperature to 34-35℃. Maintain the temperature for baking for 12-18 hours until the small veins of the lower tobacco leaves are half white and the leaves are half soft.

[0008] Fifth step, manually open the cold air inlet door to the maximum to maintain maximum ventilation, keep the circulating fan running at high speed, raise the dry bulb temperature to 42℃ for 8 hours, and the wet bulb temperature to 28-30℃, and bake at a stable temperature for 16-24 hours until the lower layer of tobacco leaves are green and the leaves are semi-dry.

[0009] Step 6: Keep the cold air inlet door at its maximum opening, continue large-scale ventilation and dehumidification, run the circulating fan at high speed, raise the dry bulb temperature to 44℃ in 8 hours, stabilize the temperature for 12-18 hours, and bake at 28-30℃ for the wet bulb, until the large veins of the lower tobacco leaves are half white and the small veins are half dry.

[0010] Step 7: Keep the cold air inlet door at its maximum opening, continue to ventilate and dehumidify, raise the dry bulb to 48℃ in 8 hours, and bake at a stable temperature for 12-18 hours. Keep the wet bulb at 30-32℃, and run the circulating fan at high speed until the large veins of the lower layer of tobacco leaves are slightly green and the small veins are completely dry.

[0011] Step 8: Keep the cold air inlet door at its maximum opening, continue to ventilate and dehumidify, raise the dry bulb temperature to 54℃ in 6 hours, maintain a stable temperature for 8-16 hours, keep the wet bulb temperature at 30-32℃, run the circulating fan at high speed, and bake until the large veins of the lower tobacco leaves shrink.

[0012] Step 9: Keep the cold air inlet door at its maximum opening, continue to ventilate and dehumidify, raise the dry bulb temperature to 60℃ for 6 hours and stabilize it for 6-12 hours, keep the wet bulb temperature at 32-34℃, run the circulating fan at high speed, and bake until the large veins of the tobacco leaves shrink and turn half purple.

[0013] Step 10: Keep the cold air inlet door at its maximum opening, continue to ventilate and dehumidify, raise the dry bulb temperature to 68℃ in 8 hours, and bake at a stable temperature for 16-24 hours, with the wet bulb temperature at 32-34℃. Run the circulating fan at high speed until all the large veins of the lower layer of tobacco leaves shrink and turn purple.

[0014] However, for the upper tobacco leaves, traditional curing techniques are prone to problems such as mold growth, ash buildup, blackening, floating green color, green veins, stiffness, poor oil content, and uneven color after curing. In particular, the problems of green and impure tobacco leaves, stiffness, and poor oil content are more prominent, and it is necessary to improve these aspects. Summary of the Invention

[0015] Based on the above, the present invention provides a process for softening tobacco leaves in the upper part of a descending intensive curing barn. This process is suitable for the tobacco curing process and can solve the problems of mold, ash, blackening, floating green, green veins, uneven color, and poor oil content that occur when using traditional descending intensive curing technology for the upper part of the tobacco leaves, thereby improving the quality of tobacco curing.

[0016] The technical solution of this invention is: a softening process for tobacco leaves in the upper part of a descending intensive curing barn, comprising the following steps:

[0017] First, install the smoke system with a denser smoke on top and a sparser smoke on the bottom, close the doors and windows, set the baking process parameters, adjust the baking curve status indicator box to the initial position, turn on the circulating fan at low speed, and start baking.

[0018] The second step is to maintain the initial target dry and wet bulb temperature of 32℃ and bake for 12-18 hours. After preheating the tobacco leaves, raise the dry bulb temperature to 36℃ and the wet bulb temperature to 35-34℃ for 4 hours and bake for 18-24 hours. The program automatically controls the opening of the cold air inlet door and keeps the circulating fan at a low speed. Bake until the tips of the upper tobacco leaves turn yellow, and there is water mist on the inner wall of the observation window and the tobacco leaves sweat.

[0019] The third step involves baking the tobacco leaves at 38°C (dry bulb) and 36°C (wet bulb) for 4 hours until the top layer turns 80% yellow and softens. Then, adjust the wet bulb temperature to 35°C and bake the middle layer until it turns 80% yellow and softens. Next, adjust the wet bulb temperature to 34°C and bake the bottom layer until it turns 80% yellow and softens. Maintain the wet bulb temperature at 34°C until the bottom layer is completely yellow and softened. For each 1°C decrease in wet bulb temperature, maintain this temperature for at least 6 hours. Then, bake at a stable 38°C for 24-36 hours. Once the tips of the top layer turn yellow, observe the inner wall of the observation window for water vapor. Hang up two leaves from each of the left and right dehumidification windows, control the opening of the cold air inlet door using the program, and set the circulating fan to high speed.

[0020] Fourth step: If there is still fog on the inner wall of the observation window, hang up all the blades of the left and right dehumidification windows, keep the circulating fan running at high speed, control the opening of the cold air inlet door according to the program, and place a small wooden block at the bottom of the cold air inlet door frame to prevent the door from closing completely and to keep the ventilation smooth; after 8 hours, raise the dry bulb temperature to 40℃ and the wet bulb temperature to 34℃ for about 6 hours. If there is still fog on the inner wall of the observation window, lower the wet bulb temperature by 1℃ every 6 hours or so until the fog disappears and no further lowering is needed. Bake at a stable temperature of 40℃ for 12-18 hours until the small veins of the lower tobacco leaves are half white and the large veins are completely soft.

[0021] Step 5: Keep all blades of the left and right exhaust windows hanging, keep the circulating fan running at high speed, control the opening of the cold air inlet door according to the program, and keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation; after 8 hours, raise the dry bulb temperature to 42℃ and the wet bulb temperature to 32℃ for about 6 hours. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃ every 6 hours or so until the wet bulb temperature can be lowered to below 30℃, until the fog disappears and no further lowering is required. Maintain a stable temperature of 42℃ for 12-18 hours, until the small veins of the lower layer of tobacco leaves are completely white and the tips are curled.

[0022] Step 6: Keep all blades of the left and right exhaust windows hanging, keep the circulating fan running at high speed, control the opening of the cold air inlet door according to the program, and keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure unobstructed ventilation; after 8 hours, raise the dry bulb temperature to 44℃ and the wet bulb temperature to 32℃ and bake for about 6 hours. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃ every 6 hours or so until the wet bulb temperature can be lowered to below 30℃, until the fog disappears and no further lowering is needed. Bake at a stable temperature of 44℃ for 12-18 hours until the large veins of the lower layer of tobacco leaves are completely white and the small veins are half dry.

[0023] Step 7: Keep all blades of the left and right exhaust windows hanging, keep the circulating fan running at high speed, control the opening of the cold air inlet door according to the program, and keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation; after 8 hours, raise the dry bulb temperature to 48℃ and the wet bulb temperature to 34℃ and bake for about 6 hours. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃. Lower the wet bulb temperature by 1℃ every 6 hours or so until the wet bulb temperature can be lowered to below 32℃, until the fog disappears and no further lowering is needed. Bake at a stable temperature of 48℃ for 10-16 hours until the large veins of the lower layer of tobacco leaves are completely yellow and the base of the small veins is not dry.

[0024] Step 8: Keep all blades of the left and right exhaust windows hanging, keep the circulating fan running at high speed, control the opening of the cold air inlet door according to the program, and keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation; after 9 hours, raise the dry bulb temperature to 54℃ and the wet bulb temperature to 36℃ for about 6 hours. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃. Lower the wet bulb temperature by 1℃ every 6 hours or so until the wet bulb temperature can be lowered to below 34℃, until the fog disappears and no further lowering is needed. Maintain a stable temperature of 54℃ for 12-18 hours, until the lower small veins are completely dry and the color difference between the front and back of the tobacco leaves becomes smaller.

[0025] Step 9: Close all blades of the dehumidification window, adjust the circulating fan to run at low speed, control the opening of the cold air inlet door through the program, and remove the small wooden block at the bottom of the cold air inlet door frame; raise the dry bulb temperature to 60℃ and the wet bulb temperature to 38℃ for 6 hours, and bake at a stable temperature for 8-12 hours until the large veins of the lower layer of tobacco leaves shrink and turn half purple.

[0026] Step 10: Control the opening of the cold air inlet and the exhaust outlet, and keep the circulating fan running at low speed; raise the dry bulb to 68℃ and the wet bulb to 39℃ in 8 hours, and bake at a stable temperature for 16-24 hours until all the large veins of the lower layer of tobacco leaves shrink, turn purple and harden.

[0027] Preferably, in the first step, the tobacco leaves are of the same variety as those used in the kiln, and the maturity of the tobacco leaves in the same layer is consistent. They are then loaded into the upper, middle, and lower layers according to their maturity levels (high, medium, and low), with the upper layer being denser and the lower layer sparser, ensuring that the filling is full and even.

[0028] Preferably, in the first step, the baking process parameters are ten target dry-bulb stable temperature points: the first stable temperature point has a dry-bulb temperature of 32℃ and a wet-bulb temperature of 32℃, with a stable temperature period of 12-18 hours; the second stable temperature point has a dry-bulb temperature of 36℃ and a wet-bulb temperature of 35-34℃, with a stable temperature period of 18-24 hours and a heating time of 4 hours; the third stable temperature point has a dry-bulb temperature of 38℃ and a wet-bulb temperature of 36-34℃, with a stable temperature period of 24-36 hours and a heating time of 4 hours; the fourth stable temperature point has a dry-bulb temperature of 40℃ and a wet-bulb temperature of 34-31℃, with a stable temperature period of 12-18 hours and a heating time of 8 hours; and the fifth stable temperature point has a dry-bulb temperature of 42℃ and a wet-bulb temperature of 32-30℃, with a stable temperature period of 4 hours. 12-18h, heating time 8h; sixth stable temperature point: dry bulb temperature 44℃, wet bulb temperature 32-30℃; stable temperature for 12-18h, heating time 8h; seventh stable temperature point: dry bulb temperature 48℃, wet bulb temperature 34-32℃; stable temperature for 10-16h, heating time 8h; eighth stable temperature point: dry bulb temperature 54℃, wet bulb temperature 36-34℃; stable temperature for 12-18h, heating time 9h; ninth stable temperature point: dry bulb temperature 60℃, wet bulb temperature 38℃; stable temperature for 8-12h, heating time 6h; tenth stable temperature point: dry bulb temperature 68℃, wet bulb temperature 39℃; stable temperature for 16-24h, heating time 8h.

[0029] Preferably, the low-speed setting of the circulating fan corresponds to a rotational speed of 720 r / min, and the high-speed setting corresponds to a rotational speed of 1440 r / min.

[0030] The applicant's research revealed the following problems with the traditional curing technique used in the intensive curing of upper tobacco leaves: During the mid-yellowing stage, with a dry-bulb temperature of 38℃ and a wet-bulb temperature of 37.5-37℃, high humidity and low ventilation result in leaves that are not fully softened and do not fully swell, making them prone to blackening, stiffening, and mold. In the late-yellowing stage, with a dry-bulb temperature of 40℃ and a wet-bulb temperature of 36-35℃, low ventilation results in leaves with half-white veins and semi-soft leaves, making them prone to blackening and stiffening. Finally, in the late-yellowing stage, with a dry-bulb temperature of 42℃ and a wet-bulb temperature of 30-28℃, high ventilation and high humidity result in leaves with green veins and semi-dry leaves, but the humidity drop is too rapid, leading to excessively rapid drying. Tobacco leaves are easily blackened, stiffened, or turned green during roasting. In the early stage of color setting, the dry-bulb temperature is 44℃ and the wet-bulb temperature is 30-28℃. Continuous high ventilation and high humidity are maintained until the large veins of the tobacco leaves are half-white and the small veins are half-dry. The dry-bulb temperature is 48℃ and the wet-bulb temperature is 32-30℃. Continuous high ventilation and high humidity are maintained until the large veins of the tobacco leaves are slightly green and the small veins are completely dry. If the tobacco leaves dry too quickly, the veins will not have time to turn white, and green smoke will easily be produced during roasting. In the later stage of color setting, the dry-bulb temperature is 54℃ and the wet-bulb temperature is 32-30℃. Continuous high ventilation and high humidity are maintained until the large veins of the tobacco leaves shrink. The tobacco leaves are dry, but if the humidity is too low, there will be a large color difference between the front and back of the leaves. During the rib-drying stage, the dry-bulb temperature is 60-68℃ and the wet-bulb temperature is 32-34℃. Continuous high ventilation and high humidity are maintained until all the large veins of the tobacco leaves in the entire kiln have shrunk, turned purple, and dried. If the humidity is too low, the oil content of the tobacco leaves will be poor.

[0031] The beneficial effects of this invention are as follows: Addressing the problems of mold, stunting, blackening, greening, large color differences, and poor oil content in the upper tobacco leaves after traditional baking techniques, this invention, based on the tobacco packing density and changes during the baking process, employs measures such as segmented dehumidification and softening, adjusting the opening of the cold air inlet and exhaust window blades, and adjusting the fan speed. According to the applicant's experiments, this invention can reduce problems such as mold, stunting, blackening, greening, large color differences, and poor oil content in the upper tobacco leaves during intensive downward baking. In particular, it solves the problems of stunting, blackening, and greening of the tobacco leaves, thus improving the quality of tobacco leaf baking. Detailed Implementation

[0032] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0033] First, let's describe the curing barn. The existing descending-type intensive curing barn includes a heating chamber and a smoke-loading chamber. An observation window is installed on the side of the smoke-loading chamber closest to the heating chamber. A cold air inlet is located at the lower part of one side of the heating chamber. The opening of the cold air inlet can be automatically controlled by the curing program or manually. Dehumidification louvers are installed on both sides of the lower part of the smoke-loading chamber closest to the heating chamber, with eight blades on each side. The circulating fan in the curing barn operates at a low speed of 720 r / min and a high speed of 1440 r / min.

[0034] The present invention provides a process for softening tobacco leaves in the upper part of a descending intensive curing barn, comprising the following steps:

[0035] The first step is to prepare the facilities and tobacco leaves before curing. Before loading the curing barn, remove any accumulated dust from the heating equipment to prevent blockages, ensure the curing barn enclosure is airtight, seal the heating equipment to prevent smoke leakage, and ensure the equipment is powered on and functions normally. Harvest the tobacco leaves according to the current mature harvest standards, classify and bundle them, and install the sensors in place.

[0036] In this step, the upper tobacco leaves are harvested when they are mainly yellow with a hint of green. They are then sorted and bundled, with the tobacco leaves on the same stalk (bundle) having basically the same maturity. There are about 60 bundles per stalk, with 2-3 leaves per bundle, and the number of tobacco leaves per bundle is consistent. The bundles are filled and evenly packed, which ensures that the tobacco leaves on the same stalk (bundle) change in a basically consistent manner. The sensors are installed in place, the water bottle is filled with clean water, the degreased cotton yarn is clean, the upper end is wrapped with the wet bulb thermometer bulb, and the lower end is completely placed in the water bottle. The temperature and humidity sensors are installed in the corresponding positions on the bottom and top of the shed.

[0037] The second step is to load the tobacco leaves into the drying rack with a denser top layer and a sparser bottom layer, and then set the parameters for drying. The leaves are loaded into the upper, middle, and lower layers of the drying rack according to their maturity levels (high, medium, and low), with a denser top layer and a sparser bottom layer. The number of racks (or poles) should be reduced by 8 from top to bottom to prevent excessive humidity in the middle and lower layers, which could lead to insufficient softening and stiffness after drying. Each layer should be fully and evenly loaded, with 4 layers totaling approximately 400 racks (or poles). After loading, close the doors and windows. After powering on the equipment, set the dry-bulb temperature display box on the controller to "upper rack" on the left. Set ten target dry-bulb temperature stabilization points according to the current drying process. Based on the drying characteristics of the upper tobacco leaves and the loading density, set the corresponding target wet-bulb temperature, stabilization time, and heating time. The drying scheme parameters are shown in Table 1 below. After setting the parameters, adjust the status indicator box to the initial position, turn on the circulating fan at low speed, and ignite the drying rack.

[0038] Baking Program Parameter Table 1

[0039]

[0040] In this step, the left side of the dry bulb temperature display box is set to "Upper Shelf," displaying the actual temperature and humidity values ​​of the tobacco leaves during baking. Baking parameters are set to prevent significant fluctuations in temperature and humidity, which could affect tobacco quality. These parameters are characterized by setting ten stable temperature points at ignition, with the wet bulb temperature and stabilization time set to their upper limits. During baking, the initial wet bulb temperature at each stable point is set to its upper limit. The wet bulb temperature is then gradually reduced based on the tobacco leaf's changing stage and the water mist index in the observation window. Once the stage target is reached, the temperature is no longer reduced. The baking time can vary depending on the target tobacco leaf changes at the stable temperature points. The baking curve status indicator box is adjusted to its initial position to prevent the indicator box from being in other positions, resulting in a high ignition temperature and causing the tobacco leaves to turn green. The circulating fan is adjusted to a low speed to maintain proper moisture during the yellowing process and prevent premature moisture loss in the tobacco leaves.

[0041] The third step, the early yellowing stage, involves slightly reducing humidity until the tips turn yellow. Maintain the initial target dry-bulb and wet-bulb temperatures at 32℃ for 12-18 hours of baking. After preheating the tobacco leaves, increase the dry-bulb temperature to 36℃ and the wet-bulb temperature to 35-34℃ for 4 hours, baking for 18-24 hours. Reduce humidity appropriately to prevent mold growth. The program automatically controls the opening of the cold air inlet door, and the circulating fan is kept at a low speed. Baking continues until the tips of the upper layer of tobacco leaves turn yellow, and water vapor appears on the inner wall of the observation window, indicating the tobacco leaves are sweating.

[0042] Step 4, Mid-Yellowing Stage: Observe the tobacco leaves as they decrease moisture and become completely yellow and soft. After the tips of the upper layer of tobacco leaves turn yellow, raise the dry bulb temperature to 38℃ and the wet bulb temperature to 36℃ for 4 hours. Bake until the upper layer of tobacco leaves are 80% yellow and soft. Adjust the wet bulb temperature to 35℃ and bake until the middle layer of tobacco leaves are 80% yellow and soft. Adjust the wet bulb temperature to 34℃ and bake until the lower layer of tobacco leaves are 80% yellow and soft. Maintain the wet bulb temperature at 34℃ and bake until the lower layer of tobacco leaves are completely yellow and soft. For each 1℃ decrease in wet bulb temperature, maintain this temperature for at least 6 hours to prevent excessive yellowing and insufficient moisture loss, which would result in stiff and unsoft leaves after baking. Maintain a stable temperature of 38℃ for 24-36 hours. After the tips of the upper layer of tobacco leaves turn yellow, observe the inner wall of the observation window for condensation. Hang up two leaves from each of the left and right dehumidification windows, control the opening of the cold air inlet valve, and adjust the circulating fan to high speed to prevent mold growth on the tobacco leaves.

[0043] Step 5, late yellowing stage: Observe the leaves through the window to reduce humidity. The smaller veins should be half-white, and the larger veins should be completely soft. After the lower layer of tobacco leaves has turned completely yellow and is collected, if there is fog on the inner wall of the observation window, hang up all the blades of the left and right dehumidification windows, keep the circulating fan running at high speed, and control the opening of the cold air inlet door according to the program. Place a small wooden block at the bottom of the cold air inlet door frame to prevent the door from closing completely, ensuring smooth ventilation and preventing the tobacco leaves from being scorched. After 8 hours, raise the dry bulb temperature to 40℃ and the wet bulb temperature to 34℃ for about 6 hours. If there is still fog on the inner wall of the observation window, lower the wet bulb temperature by 1℃ every 6 hours or so until the bulb temperature drops below 31℃, until the fog disappears and no further lowering is needed. Maintain a stable temperature of 40℃ for 12-18 hours, until the smaller veins of the lower layer of tobacco leaves are half-white and the larger veins are completely soft. This is to prevent the leaves from being scorched and hardened due to insufficient softening of the veins caused by high humidity in the curing room.

[0044] Step 6, in the later stage of yellowing, observe the dehumidification through the windows. The small veins should be completely white, and the tips and edges should be curled. After the small veins of the lower tobacco leaves are half white and the large veins are completely soft, keep all the blades of the left and right dehumidification windows hanging up, keep the circulating fan running at high speed, and control the opening of the cold air inlet door according to the program. Place a small wooden block at the bottom of the cold air inlet door frame to ensure smooth ventilation and prevent the tobacco leaves from turning black. Bake at 42℃ for 8 hours with the dry bulb and 32℃ for about 6 hours with the wet bulb. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃ every 6 hours or so, until the wet bulb temperature can be below 30℃, until the fog disappears and no further lowering is allowed. Maintain a stable temperature of 42℃ for 12-18 hours, until the small veins of the lower tobacco leaves are completely white, and the tips and edges are curled. Avoid insufficient whitening of the small veins, which may result in green veins after baking.

[0045] Step 7, Pre-coloring stage: Observe the dehumidification windows. The main veins should be completely white, and the smaller veins should be semi-dry. After the smaller veins of the lower layer of tobacco leaves are completely white and the tips are hooked and curled, keep all the leaves of the left and right dehumidification windows hanging up, keep the circulating fan running at high speed, and control the opening of the cold air inlet door according to the program. Keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation and prevent the tobacco leaves from turning black. After 8 hours, raise the dry bulb temperature to 44℃ and the wet bulb temperature to 32℃ for about 6 hours. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃ every 6 hours or so, until the wet bulb temperature can be below 30℃, until the fog disappears and no further lowering is allowed. Maintain a stable temperature of 44℃ for 12-18 hours, until the main veins of the lower layer of tobacco leaves are completely white and the smaller veins are semi-dry. Avoid excessive humidity causing blackening and excessive humidity causing greening and stiffening.

[0046] Step 8, Pre-coloring stage: Observe the dehumidification windows. The main veins should be completely yellow, while the base of the smaller veins should not be dry. After the main veins of the lower layer of tobacco leaves are completely white and the smaller veins are half-dry, keep all the leaves of the left and right dehumidification windows hanging up, keep the circulating fan running at high speed, and control the opening of the cold air inlet door according to the program. Keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation and prevent the tobacco leaves from turning black. After 8 hours, raise the dry bulb temperature to 48℃ and the wet bulb temperature to 34℃ for about 6 hours. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃. Lower the wet bulb temperature by 1℃ every 6 hours or so until the fog disappears and no further lowering is allowed. Maintain a stable temperature of 48℃ for 10-16 hours, until the main veins of the lower layer of tobacco leaves are completely yellow and the base of the smaller veins is not dry. Avoid excessive humidity causing discoloration of the tobacco leaves and excessive humidity causing them to turn green and stiff.

[0047] Step 9, Post-coloring stage: Increase humidity appropriately until the small veins are completely dry and the color difference decreases. After the large veins of the lower layer of tobacco leaves turn completely yellow, keep all the leaves of the left and right exhaust windows hanging, keep the circulating fan running at high speed, and control the opening of the cold air inlet door according to the program. Place small wooden blocks at the bottom of the cold air inlet door frame to ensure smooth ventilation and prevent the tobacco leaves from darkening. Bake at 54℃ for 9 hours and 36℃ for 6 hours for wet bulb. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃. Lower the wet bulb temperature by 1℃ every 6 hours or so until the fog disappears and no further lowering is needed. Maintain a stable temperature of 54℃ for 12-18 hours until the small veins of the lower layer are completely dry and the color difference between the front and back of the tobacco leaves decreases. Avoid excessive humidity, as this will cause the inner leaves to not dry properly and develop mixed colors.

[0048] Step 10: In the early stage of drying the tobacco leaves, increase and stabilize the humidity until the larger ribs shrink and turn half purple. After the smaller ribs in the lower layer are completely dry, close all the blades of the exhaust window, adjust the circulating fan to run at low speed, control the opening of the cold air inlet damper using the program, and remove the small wooden block at the bottom of the cold air inlet damper frame. After 6 hours, raise the dry bulb temperature to 60℃ and the wet bulb temperature to 38℃, and maintain the temperature for 8-12 hours, until the larger ribs of the lower layer of tobacco leaves shrink and turn half purple. Avoid excessive humidity causing the leaves to turn red, and avoid excessive humidity resulting in poor oil content.

[0049] Step 11, late drying stage: Stabilize temperature and humidity until all the large ribs of the tobacco leaves shrink and turn purple. After half of the large ribs of the lower layer of tobacco leaves have shrunk and turned purple, control the opening of the cold air inlet and outlet, and keep the circulating fan running at low speed. Raise the dry bulb temperature to 68℃ and the wet bulb temperature to 39℃ for 8 hours, and maintain the temperature for 16-24 hours until all the large ribs of the lower layer of tobacco leaves have shrunk, turned purple, and hardened. Avoid excessively high temperature and humidity causing the tobacco leaves to turn red, and avoid drastic temperature reduction causing the ribs and leaves to become infiltrated, and excessively low humidity causing poor oil content in the tobacco leaves.

[0050] The baking effect of the present invention will be verified by the following experiment:

[0051] The experiment was conducted in Liupanshui City, Guizhou Province in 2024. The tested flue-cured tobacco variety was Yunyan 87, with the upper leaves used as the experimental material. The tested tobacco leaves were cultivated and managed according to local standardized practices for high-quality tobacco production, and harvested at maturity according to the standards and procedures for tobacco leaf maturity. The tested curing barn was a descending, intensive curing barn. A comparative experiment was conducted, using the curing process of this invention as the treatment and traditional curing technology as the control. Except for the process conditions and the amount of tobacco loaded in each layer, all other factors, such as the curing barn structure and the tobacco variety, were the same.

[0052] Traditional baking process:

[0053] The first step is to load the tobacco onto the drying rack and set the parameters. Based on the degree of maturity (high, medium, low), load the tobacco into the upper, middle, and lower layers of the drying rack, respectively, from top to bottom. Load 100 bundles of tobacco per layer, ensuring they are full and evenly distributed. Load 4 layers, for a total of 400 bundles. Set the drying program parameters as shown in Table 2 below. After setting the parameters, adjust the status indicator box to its initial position, set the circulating fan to high speed, and ignite the drying process.

[0054] Table 2 Baking Scheme Parameters

[0055]

[0056] The second step, the early yellowing stage, involves simultaneous temperature and humidity control, causing the tobacco leaves to sweat and the tips to turn yellow. After ignition, maintain the initial dry-bulb and wet-bulb temperature at 32℃ for 12 hours of baking. The program automatically controls the opening of the cold air inlet valve, and the circulating fan is kept at high speed to adapt to the tobacco leaf baking environment. After preheating for 4 hours, raise the dry-bulb and wet-bulb temperature to 36℃ and bake at a stable temperature for 20 hours. The upper layer of tobacco leaves sweats and the tips turn yellow.

[0057] The third step is the mid-yellowing stage, where the leaves are kept moist and turn completely yellow without becoming soft or hard. After the tips of the upper tobacco leaves turn yellow, the circulating fan is kept at high speed, and the opening of the cold air inlet is controlled by the program. The dry bulb temperature is raised to 38°C in 4 hours, and the wet bulb temperature is raised to 37°C. The temperature is maintained for 30 hours until the lower leaves are completely yellow without becoming soft or hard.

[0058] Step 4: In the later stage of yellowing, dehumidify and quickly exhaust the leaves until the veins are half-white and the leaves are half-soft. After the lower leaves are completely yellow, keep the circulating fan running at high speed, control the opening of the cold air inlet damper by program, raise the dry bulb temperature to 40℃ and the wet bulb temperature to 35℃ for 8 hours, and bake at a stable temperature for 12 hours until the veins of the lower tobacco leaves are half-white and the leaves are half-soft.

[0059] Step 5, in the later stage of yellowing, reduce humidity and drastically remove pollutants until the large veins are green and the leaves are semi-dry. When the small veins of the lower tobacco leaves are half-white and the leaves are semi-soft, manually open the cold air inlet to the maximum to maintain maximum ventilation and keep the circulating fan running at high speed. After 8 hours, raise the dry bulb temperature to 42℃ and the wet bulb temperature to 30℃, and bake at a stable temperature for 20 hours until the large veins of the lower tobacco leaves are green and the leaves are semi-dry.

[0060] Step 6, in the early stage of color setting, continue vigorous ventilation until the large veins of the tobacco leaves are half-white and the small veins are half-dry. After the large veins of the lower layer of tobacco leaves are green and the leaves are half-dry, keep the cold air inlet door at maximum opening and continue to ventilate and dehumidify, with the circulating fan running at high speed; raise the dry bulb to 44℃ for 8 hours, stabilize the temperature for 16 hours, and then bake at 30℃ until the large veins of the lower layer of tobacco leaves are half-white and the small veins are half-dry.

[0061] Step 7, in the early stage of color setting, continue vigorous ventilation until the large veins of the tobacco leaves are slightly green and the small veins are completely dry. After the large veins of the lower layer of tobacco leaves are half white and the small veins are half dry, keep the cold air inlet door at its maximum opening and continue to ventilate and dehumidify. After 8 hours, raise the dry bulb to 48℃ and maintain the temperature for 16 hours, with the wet bulb at 32℃ and the circulating fan running at high speed; continue to bake until the large veins of the lower layer of tobacco leaves are slightly green and the small veins are completely dry.

[0062] Step 8, in the later stage of color setting, continue to ventilate vigorously until the large veins of the tobacco leaves begin to shrink. After the small veins of the lower layer of tobacco leaves are completely dry, keep the cold air inlet door at its maximum opening and continue to ventilate and dehumidify. After 6 hours, raise the dry bulb temperature to 54°C and bake at a stable temperature for 12 hours. At a wet bulb temperature of 32°C, run the circulating fan at high speed until the large veins of the lower layer of tobacco leaves shrink.

[0063] Step 9, early drying stage: Maintain high ventilation until the large ribs of the lower tobacco leaves shrink and turn half purple. After the large ribs of the lower tobacco leaves begin to shrink, keep the cold air inlet door at its maximum opening and continue high ventilation to remove moisture. Raise the dry bulb to 60℃ in 6 hours and stabilize the temperature for 8 hours. Keep the wet bulb at 34℃ and run the circulating fan at high speed until the large ribs of the tobacco leaves shrink and turn half purple.

[0064] Step 10, late drying stage: Maintain high ventilation until all the large ribs shrink and turn purple. After half of the large ribs of the tobacco leaves have shrunk and turned purple, keep the cold air inlet door at maximum opening and continue high ventilation to remove moisture. Raise the dry bulb temperature to 68℃ for 8 hours, maintain a stable temperature for 20 hours, and bake at 34℃ with the wet bulb temperature. Run the circulating fan at high speed until all the large ribs of the lower layer of tobacco leaves have shrunk and turned purple.

[0065] Baking process of this invention:

[0066] The first step is to pack the tobacco leaves densely on top and sparsely on the bottom to prevent stiffness. Based on high, medium, and low maturity, the leaves are packed in the upper, middle, and lower layers of the curing barn, respectively, with 112, 104, 96, and 88 clamps respectively from top to bottom. This prevents excessive humidity in the middle and lower layers, which could lead to insufficient softening and stiffness after curing. Each layer should be fully and evenly packed, for a total of 4 layers and 400 clamps. Set the curing parameters as shown in Table 3 below. After setting the parameters, adjust the status indicator box to the initial position, turn on the circulating fan at low speed, and ignite the curing process.

[0067] Table 3 Baking Program Parameters

[0068]

[0069] The second step, the early yellowing stage, involves slightly reducing humidity until the tips turn yellow. Maintain the initial target dry-bulb and wet-bulb temperatures at 32℃ for 12 hours of preheating. After 4 hours of preheating, increase the dry-bulb temperature to 36℃ and the wet-bulb temperature to 35℃ for 20 hours of baking, appropriately reducing humidity to prevent mold growth. The program automatically controls the opening of the cold air inlet valve, and the circulating fan remains at a low speed. Baking continues until the tips of the upper layer of tobacco leaves turn yellow, and water vapor appears on the inner wall of the observation window, indicating the tobacco leaves are sweating.

[0070] The third step, mid-yellowing stage, involves observing the tobacco's moisture reduction until it is completely yellow and soft. After the tips of the upper layer of tobacco leaves turn yellow, raise the dry bulb temperature to 38℃ and the wet bulb temperature to 36℃ for 4 hours, and bake for 6 hours until the upper layer of tobacco leaves are 80% yellow and the leaves are soft. Then adjust the wet bulb temperature to 35℃ and bake for 6 hours until the middle layer of tobacco leaves are 80% yellow and the leaves are soft. Then adjust the wet bulb temperature to 34℃ and bake for 6 hours until the lower layer of tobacco leaves are 80% yellow and the leaves are soft. Maintain the wet bulb temperature at 34℃ and bake for 14 hours until the lower layer of tobacco leaves are completely yellow and soft. This process prevents the tobacco leaves from over-yellowing and insufficient moisture loss, which would result in stiff and unsoft leaves after baking. After the tips of the upper layer of tobacco leaves turn yellow, observe the water vapor on the inner wall of the observation window. Hang up two leaves on each side of the dehumidification window, control the opening of the cold air inlet door according to the program, and adjust the circulating fan to high speed to prevent the tobacco leaves from becoming moldy.

[0071] Step 4, the later stage of yellowing: Observe the leaves through the window to reduce humidity. The smaller veins should be half-white, and the larger veins should be completely soft. After the lower layer of tobacco leaves has turned completely yellow and is collected, if there is fog on the inner wall of the observation window, hang up all the blades of the left and right dehumidification windows, keep the circulating fan running at high speed, and control the opening of the cold air inlet door according to the program. Place small wooden blocks at the bottom of the cold air inlet door frame to prevent the door from closing completely, ensuring smooth ventilation and preventing the tobacco leaves from being scorched. After 8 hours, raise the dry bulb temperature to 40℃ and the wet bulb temperature to 34℃ for 6 hours. If there is still fog on the inner wall of the observation window, adjust the wet bulb temperature to 33℃ and bake for 6 hours. If there is still fog on the inner wall of the lower layer's observation window, adjust the wet bulb temperature to 32℃ and bake for 4 hours. The inner wall of the lower layer's observation window should be clean and fog-free, and the smaller veins of the lower layer of tobacco leaves should be half-white, while the larger veins should be completely soft. This is to prevent the tobacco leaves from being scorched and hardened due to insufficient softening of the veins caused by high humidity in the curing room.

[0072] Step 5, late yellowing stage: Observe the dehumidification windows. The small veins should be completely white, and the tips and edges should be curled. After the small veins of the lower layer of tobacco leaves are half white and the large veins are completely soft, keep all the blades of the left and right dehumidification windows hanging, keep the circulating fan running at high speed, and control the opening of the cold air inlet door according to the program. Keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation and prevent the tobacco leaves from turning black. Bake for 8 hours at a dry bulb temperature of 42℃ and a wet bulb temperature of 32℃ for 6 hours. When there is no fog on the inner wall of the glass of the lower observation window, maintain a dry bulb temperature of 42℃ and a wet bulb temperature of 32℃ for 10 hours, until the small veins of the lower layer of tobacco leaves are completely white and the tips and edges are curled. Avoid insufficient whitening of the small veins, which may result in green veins after baking.

[0073] Step 6, Pre-coloring stage: Observe the dehumidification windows. The main veins should be completely white, and the smaller veins should be semi-dry. After the smaller veins of the lower layer of tobacco leaves are completely white and the tips are hooked and curled, keep all the blades of the left and right dehumidification windows hanging up, keep the circulating fan running at high speed, and control the opening of the cold air inlet door according to the program. Keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation and prevent the tobacco leaves from turning black. After 8 hours, raise the dry bulb temperature to 44℃, and maintain the wet bulb temperature at 32℃ for 6 hours. Observe that there is no fog on the inner wall of the observation window glass. Maintain the dry bulb temperature of 44℃ and the wet bulb temperature of 32℃ for 6 hours, until the main veins of the lower layer of tobacco leaves are completely white and the smaller veins are semi-dry. Avoid excessive humidity causing blackening and excessive humidity causing greening and stiffening.

[0074] Step 7, Pre-coloring stage: Observe the dehumidification windows. The main veins should be completely yellow, while the base of the smaller veins should not be dry. After the main veins of the lower layer of tobacco leaves are completely white and the smaller veins are half-dry, keep all the blades of the left and right dehumidification windows hanging, keep the circulating fan running at high speed, and control the opening of the cold air inlet door according to the program. Keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation and prevent the tobacco leaves from turning black. After 8 hours, raise the dry bulb temperature to 48℃ and the wet bulb temperature to 34℃, and bake at a stable temperature for 6 hours. Observe that there is no fog on the inner wall of the observation window glass, and maintain the dry bulb temperature of 48℃ and the wet bulb temperature of 34℃ for 6 hours, until the main veins of the lower layer of tobacco leaves are completely yellow and the base of the smaller veins is not dry. Avoid excessive humidity causing discoloration of the tobacco leaves, and avoid excessive humidity causing the leaves to turn green and stiff.

[0075] Step 8, Post-Color Fixation: Increase humidity appropriately until the small veins are completely dry and the color difference decreases. After the large veins of the lower layer of tobacco leaves turn completely yellow, keep all the leaves of the left and right exhaust windows hanging, maintain high-speed operation of the circulating fan, and program-controlled opening of the cold air inlet door. Place small wooden blocks at the bottom of the cold air inlet door frame to ensure smooth ventilation and prevent the tobacco leaves from darkening. After 9 hours, raise the dry bulb temperature to 54℃ and the wet bulb temperature to 36℃, and maintain this temperature for 6 hours. When there is no fog on the inner wall of the observation window glass, maintain the dry bulb temperature at 54℃ and the wet bulb temperature at 36℃ for 10 hours, until the small veins of the lower layer are completely dry and the color difference between the front and back of the tobacco leaves decreases. Avoid excessive humidity, as this can cause the inner leaves to not dry properly and develop discoloration.

[0076] Step 9: In the early stage of drying the tobacco leaves, increase and stabilize the humidity until the larger ribs shrink and turn half purple. After the smaller ribs in the lower layer are completely dry, close all the blades of the exhaust window, adjust the circulating fan to run at low speed, control the opening of the cold air inlet damper using the program, and remove the small wooden block at the bottom of the cold air inlet damper frame. After 6 hours, raise the dry bulb temperature to 60℃ and the wet bulb temperature to 38℃, and maintain the temperature for 8 hours, until the larger ribs of the lower layer of tobacco leaves shrink and turn half purple. Avoid excessive humidity causing the leaves to turn red, and avoid excessive humidity causing poor oil content.

[0077] Step 10, late drying stage: Stabilize temperature and humidity until all the large ribs of the tobacco leaves shrink and turn purple. After half of the large ribs of the lower layer of tobacco leaves have shrunk and turned purple, control the opening of the cold air inlet and outlet, and keep the circulating fan running at low speed. Raise the dry bulb temperature to 68℃ and the wet bulb temperature to 39℃ for 8 hours, and maintain this temperature for 20 hours until all the large ribs of the lower layer of tobacco leaves have shrunk, turned purple, and hardened. Avoid excessively high temperature and humidity causing the tobacco leaves to turn red, and avoid drastic temperature reduction leading to excessive moisture penetration in the ribs and leaves, or excessively low humidity resulting in poor oil content in the tobacco leaves.

[0078] The following sections evaluate and analyze the tobacco leaves produced by the baking process of this invention and the traditional baking process from the aspects of tobacco leaf output value, appearance quality, and chemical composition.

[0079] Experimental results:

[0080] 1. Impact on tobacco production value

[0081] As shown in Table 4, compared with traditional baking technology, the present invention increases the proportion of high-grade smoke by 5.15 percentage points, decreases the proportion of medium-grade smoke by 3.15 percentage points, increases the average price by 1.5 yuan / kg, and increases the output value by 3375 yuan / hm². 2 .

[0082] Table 4 Comparison of Tobacco Leaf Output Value

[0083] invention 56.78 36.22 26.04 58590.00 Tradition 51.63 39.37 24.54 55215.00

[0084] 2. Impact on the appearance quality of tobacco leaves

[0085] As shown in Table 5, the appearance of the tobacco leaves after curing according to the present invention is superior to that of traditional curing technology in terms of leaf structure, maturity, identity, oil content and color. The yellow tobacco rate is increased by 2.0 percentage points, the mixed color tobacco rate is reduced by 0.9 percentage points, and the green tobacco rate is reduced by 1.1 percentage points.

[0086] Table 5 Comparison of tobacco leaf appearance quality

[0087]

[0088] 3. Effects on the chemical composition of tobacco leaves

[0089] As shown in Table 6, the total sugar and reducing sugar of the flue-cured tobacco leaves of the present invention are higher, while the nicotine content is lower. The total sugar content is 29.4%, and the reducing sugar content is 24.95%, which are 4.19% and 0.89% higher than the traditional content, respectively. The nicotine content is 3.92%, which is 0.41% lower than the traditional content.

[0090] Table 6 Comparison of Chemical Components of Tobacco Leaves

[0091] invention 29.40 24.95 3.92 Tradition 25.21 24.06 4.33

[0092] 4. Evaluation of the tobacco curing effect

[0093] In summary, this invention can effectively improve the proportion of high-grade tobacco leaves, appearance quality, and chemical composition of tobacco leaves, thereby improving the industrial usability of tobacco leaves.

[0094] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A process for softening tobacco leaves in the upper part of a descending intensive curing barn, characterized in that, Includes the following steps: First, install the smoke at the top (dense smoke) and the bottom (sparse smoke), close the doors and windows, set the baking process parameters, adjust the baking curve status indicator box to the initial position, turn on the circulating fan at low speed, and start baking. The second step is to maintain the initial target dry and wet bulb temperature of 32℃ and bake for 12-18 hours. After preheating the tobacco leaves, raise the dry bulb temperature to 36℃ and the wet bulb temperature to 35-34℃ for 4 hours and bake for 18-24 hours. The program automatically controls the opening of the cold air inlet door and keeps the circulating fan at a low speed. Bake until the tips of the upper tobacco leaves turn yellow, and there is water mist on the inner wall of the observation window and the tobacco leaves sweat. The third step involves baking the tobacco leaves at 38°C (dry bulb) and 36°C (wet bulb) for 4 hours until the top layer turns 80% yellow and softens. Then, adjust the wet bulb temperature to 35°C and bake the middle layer until it turns 80% yellow and softens. Next, adjust the wet bulb temperature to 34°C and bake the bottom layer until it turns 80% yellow and softens. Maintain the wet bulb temperature at 34°C until the bottom layer is completely yellow and softened. For each 1°C decrease in wet bulb temperature, maintain this temperature for at least 6 hours. Then, bake at a stable 38°C for 24-36 hours. Once the tips of the top layer turn yellow, observe the inner wall of the observation window for water vapor. Hang up two leaves from each of the left and right dehumidification windows, control the opening of the cold air inlet door using the program, and set the circulating fan to high speed. Fourth step: If there is still fog on the inner wall of the observation window, hang up all the blades of the left and right dehumidification windows, keep the circulating fan running at high speed, control the opening of the cold air inlet door according to the program, and place a small wooden block at the bottom of the cold air inlet door frame to prevent the door from closing completely and to keep the ventilation smooth; after 8 hours, raise the dry bulb temperature to 40℃ and the wet bulb temperature to 34℃ for about 6 hours. If there is still fog on the inner wall of the observation window, lower the wet bulb temperature by 1℃ every 6 hours or so until the fog disappears and no further lowering is needed. Bake at a stable temperature of 40℃ for 12-18 hours until the small veins of the lower tobacco leaves are half white and the large veins are completely soft. Step 5: Keep all blades of the left and right exhaust windows hanging, keep the circulating fan running at high speed, control the opening of the cold air inlet door according to the program, and keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation; after 8 hours, raise the dry bulb temperature to 42℃ and the wet bulb temperature to 32℃ for about 6 hours. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃ every 6 hours or so until the wet bulb temperature can be lowered to below 30℃, until the fog disappears and no further lowering is required. Maintain a stable temperature of 42℃ for 12-18 hours, until the small veins of the lower layer of tobacco leaves are completely white and the tips are curled. Step 6: Keep all blades of the left and right exhaust windows hanging, keep the circulating fan running at high speed, control the opening of the cold air inlet door according to the program, and keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure unobstructed ventilation; after 8 hours, raise the dry bulb temperature to 44℃ and the wet bulb temperature to 32℃ and bake for about 6 hours. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃ every 6 hours or so until the wet bulb temperature can be lowered to below 30℃, until the fog disappears and no further lowering is needed. Bake at a stable temperature of 44℃ for 12-18 hours until the large veins of the lower layer of tobacco leaves are completely white and the small veins are half dry. Step 7: Keep all blades of the left and right exhaust windows hanging, keep the circulating fan running at high speed, control the opening of the cold air inlet door according to the program, and keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation; after 8 hours, raise the dry bulb temperature to 48℃ and the wet bulb temperature to 34℃ and bake for about 6 hours. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃. Lower the wet bulb temperature by 1℃ every 6 hours or so until the wet bulb temperature can be lowered to below 32℃, until the fog disappears and no further lowering is needed. Bake at a stable temperature of 48℃ for 10-16 hours until the large veins of the lower layer of tobacco leaves are completely yellow and the base of the small veins is not dry. Step 8: Keep all blades of the left and right exhaust windows hanging, keep the circulating fan running at high speed, control the opening of the cold air inlet door according to the program, and keep a small wooden block placed at the bottom of the cold air inlet door frame to ensure smooth ventilation; after 9 hours, raise the dry bulb temperature to 54℃ and the wet bulb temperature to 36℃ for about 6 hours. If there is fog on the inner wall of the observation window glass, lower the wet bulb temperature by 1℃. Lower the wet bulb temperature by 1℃ every 6 hours or so until the wet bulb temperature can be lowered to below 34℃, until the fog disappears and no further lowering is needed. Maintain a stable temperature of 54℃ for 12-18 hours, until the lower small veins are completely dry and the color difference between the front and back of the tobacco leaves becomes smaller. Step 9: Close all blades of the dehumidification window, adjust the circulating fan to run at low speed, control the opening of the cold air inlet door through the program, and remove the small wooden block at the bottom of the cold air inlet door frame; raise the dry bulb temperature to 60℃ and the wet bulb temperature to 38℃ for 6 hours, and bake at a stable temperature for 8-12 hours until the large veins of the lower layer of tobacco leaves shrink and turn half purple. Step 10: Control the opening of the cold air inlet and the exhaust outlet, and keep the circulating fan running at low speed; raise the dry bulb to 68℃ and the wet bulb to 39℃ in 8 hours, and bake at a stable temperature for 16-24 hours until all the large veins of the lower layer of tobacco leaves shrink, turn purple and harden.

2. The tobacco leaf softening process in the upper part of the descending intensive curing barn according to claim 1, characterized in that, In the first step, the tobacco leaves are of the same variety as those used in the kiln, and the maturity of the tobacco leaves in the same layer is consistent. They are then loaded into the upper, middle, and lower layers according to their maturity level (high, medium, and low), with the upper layer being denser and the lower layer sparser, and the filling is complete and even.

3. The tobacco leaf softening process in the upper part of the descending intensive curing barn according to claim 1, characterized in that, In the first step, the baking process parameters are ten target dry-bulb stable temperature points. The first stable temperature point has a dry-bulb temperature of 32℃ and a wet-bulb temperature of 32℃, with a stabilization period of 12-18 hours. The second stable temperature point has a dry-bulb temperature of 36℃ and a wet-bulb temperature of 35-34℃, with a stabilization period of 18-24 hours and a heating time of 4 hours. The third stable temperature point has a dry-bulb temperature of 38℃ and a wet-bulb temperature of 36-34℃, with a stabilization period of 24-36 hours and a heating time of 4 hours. The fourth stable temperature point has a dry-bulb temperature of 40℃ and a wet-bulb temperature of 34-31℃, with a stabilization period of 12-18 hours and a heating time of 8 hours. The fifth stable temperature point has a dry-bulb temperature of 42℃ and a wet-bulb temperature of 32-30℃, with a stabilization period of 12-18 hours and a heating time of 8 hours. 18h, heating time 8h, sixth stable temperature point dry bulb temperature 44℃, wet bulb temperature 32-30℃, stable temperature 12-18h, heating time 8h, seventh stable temperature point dry bulb temperature 48℃, wet bulb temperature 34-32℃, stable temperature 10-16h, heating time 8h, eighth stable temperature point dry bulb temperature 54℃, wet bulb temperature 36-34℃, stable temperature 12-18h, heating time 9h, ninth stable temperature point dry bulb temperature 60℃, wet bulb temperature 38℃, stable temperature 8-12h, heating time 6h, tenth stable temperature point dry bulb temperature 68℃, wet bulb temperature 39℃, stable temperature 16-24h, heating time 8h.

4. The tobacco leaf softening process in the upper part of the descending intensive curing barn according to claim 1, characterized in that, The low-speed setting of the circulating fan corresponds to a speed of 720 r / min, and the high-speed setting corresponds to a speed of 1440 r / min.

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