A baking method for reducing ash on upper tobacco leaves

Abstract

The present invention discloses a flue-curing method for reducing ash on upper tobacco leaves. The method shortens the yellowing time at or before 38°C, maintains the same dry-bulb and wet-bulb temperatures at 40°C, stops the circulating fan, reduces the temperature and humidity difference between different tobacco layers in the flue-curing barn, then lowers the wet-bulb temperature. This process is repeated to cause the tobacco leaves to soften, wilt, and turn yellow. The dry-bulb temperature is then raised to 44°C, causing the main ribs to soften. The high temperature is then returned to 42°C, and the wet-bulb temperature is lowered by 1-2°C at 42°C to control the water loss of the tobacco leaves to 40-45%, inhibiting the activity of polyphenol oxidase and promoting yellowing. The dry-bulb and wet-bulb temperatures are then lowered by 1-2°C at the initial color setting stage, slowing the heating rate. A medium temperature, medium humidity, and slow heating are used for color setting in the middle color setting stage. The temperature is then slowly increased in the later color setting stage. The flue-curing time at a steady temperature of 54°C is extended to increase the water loss and dryness of the tobacco leaves. The wet-bulb temperature is increased during the dry rib drying stage. This method can significantly reduce the occurrence of ash on tobacco leaves and improve the appearance quality of the upper tobacco leaves after curing.

Description

Technical Field

[0001] The invention relates to a baking method for reducing ash sticking on upper tobacco leaves, belonging to the technical field of tobacco leaf baking. Background Art

[0002] Tobacco farming is a crucial component of my country's agricultural sector, and tobacco leaf curing is a crucial step in tobacco production, determining whether the leaves can become high-quality agricultural products. Currently, the predominant intensive tobacco leaf curing process in tobacco agricultural production is a three-stage process. However, due to the unique ecological conditions of different tobacco-growing areas and the characteristics of the tobacco growth cycle, this three-stage process can easily lead to the upper leaves becoming soft and withering slowly, yellowing, and losing water unevenly during curing. This also results in heavy ash buildup, a lighter color, and a denser texture after curing, making it difficult to meet the cigarette industry's demand for high-quality tobacco leaf raw materials.

[0003] Patent document (publication number CN105146706A) discloses an intensive baking method for reducing ash on the upper leaves of K326, which increases the dry bulb temperature by 40-42°C at the early stage of yellowing to promote 30% early dehydration of the leaves, so that the tobacco leaves wither and collapse, and the branches become soft, and then the temperature is lowered to 36°C, and attention is paid to moisturizing and yellowing, and the difference between dry and wet does not exceed 1°C; Patent document (publication number CN107048459A) discloses an intensive baking method for reducing ash and black residue on Yuyan No. 7 tobacco leaves and its application, focusing on the use of timely dehumidification, dehumidification while yellowing, wet bulb control, and continuous dehumidification; Patent document (publication number CN104489891A) discloses a baking method for reducing ash on the upper tobacco leaves of KRK26, focusing on making the tobacco leaves quickly dry. Yellowing, shortening the yellowing period, dehumidification in advance, ensuring the coordination of yellowing, dehydration and drying, blocking the high temperature and high humidity environment, and inhibiting the browning reaction; Patent document (publication number CN106539117A) discloses a method for reducing the gray and variegated color of the upper leaves of Honghua Dajinyuan, by continuously irrigating the tobacco field during the maturity of the upper leaves, harvesting 6 upper leaves at a time after the upper leaves reach the maturity level, weaving the tobacco into the kang and baking it normally until it turns yellow, steadily raising the temperature and slowly dehumidifying, fully withering, and gradually fixing the color and drying the tendons; Patent document (publication number CN113455689A) discloses a baking method for reducing the graying of Xiangyan No. 6 tobacco, emphasizing that when the leaves are close to 90% yellow during the yellowing period, the dry-wet difference is widened, and the dry-bulb and wet-bulb temperature difference is appropriately increased in the early stage of color fixing, so that the tobacco leaves lose water smoothly , reaching a small roll, and the leaves are more than half dry; the patent document (publication number CN108208904A) discloses a baking method for reducing the ash on the upper tobacco leaves, emphasizing that the dry-bulb temperature of 38°C is raised to 60°C within 1 hour, the wet-bulb temperature is raised to 48-50°C, and the temperature is kept constant for 1 hour, and then the dry-bulb temperature is cooled to 42°C within 4 hours, the wet-bulb temperature is cooled to 36-37°C, and the temperature is kept constant for 3-5 hours; the patent document (publication number CN111657531A) discloses a high-temperature yellowing, cooling and color-fixing baking process for reducing the ash on tobacco leaves, emphasizing the following steps: ① tobacco leaf harvesting and rod weaving, ② germination and yellowing period, ④ high-temperature yellowing period, ⑤ cooling and dehydration period, ⑥ low-temperature color-fixing period, ⑦ high-temperature color-fixing period, ⑧ conventional dry tendon period; the patent The document (publication number CN109259290B) discloses a method for harvesting and curing tobacco leaves to reduce the ash on the upper leaves. The method emphasizes that after topping the tobacco leaves, 2 to 3 axillary buds are retained from the grown axillary buds. The upper tobacco leaves are then harvested at one time after maturity and cured using an optimized curing process for the upper tobacco leaves. The patent document (publication number CN108208905B) discloses a curing process that effectively solves the ash on the upper tobacco leaves. The method emphasizes that the changing state of tobacco leaves during the curing process is divided into 9 stages: 70% to 80% yellowing of the leaves, 90% yellowing of the leaves, yellow leaves and blue veins, complete yellowing of the leaf veins, yellow leaves and yellow veins, and complete dryness of the leaves, the beginning of the drying of the tobacco veins, the beginning of the browning of the base of the tobacco veins, the shrinkage and browning of the tobacco veins and the drying of more than 2 / 3 of the tobacco veins, and the complete dryness of the tobacco veins.Patent document (publication number CN112998301A) discloses a method for stewing, scalding, soft-baking, and bright-baking flue-cured tobacco. It emphasizes closing the air intake door for 15-50 minutes without dehumidification when the wet-bulb temperature reaches 40-41°C or the dry-bulb temperature reaches 42°C, then opening the air intake door for dehumidification for 2-20 minutes. Patent document (publication number CN112042994A) discloses a method for controlling corn pollen-induced flue-cured tobacco ash and a method for curing the tobacco leaves after this control. It emphasizes spraying a protective agent on the upper and middle leaves of the tobacco plants to prevent allergic reactions. The protective agent includes 0.5-1.5 parts cellulase, 0.5-1.5 parts pectinase, 1-3 parts lysozyme, and 200-300 parts water.

[0004] However, while the aforementioned solutions can partially address the issue of ash buildup on upper tobacco leaves, the leaves must begin to yellow before reaching a higher dry-bulb temperature for steady withering. Otherwise, the tobacco can easily become green. Furthermore, stopping the circulating fan for extended periods at medium to high heat and with a dry-bulb temperature exceeding 40°C significantly damages the fan's service life. The upper leaves' main yellowing dry-bulb temperature of around 40°C is the critical dry-bulb temperature for physiological and biochemical transformations and quality development. Furthermore, the upper leaves are thicker, with coarser main veins and a thicker waxy layer on their surface. During the curing process, the leaves and main tendons of the upper tobacco leaves can become soft and difficult to wither, resulting in delayed moisture removal, high polyphenol oxidase activity, and increased ash buildup when heated. When moisture content is high, tobacco leaves in the late yellowing and color-fixing stages exhibit high polyphenol oxidase activity, which can easily lead to ash buildup and browning, hindering the appearance quality of the cured tobacco leaves. Summary of the Invention

[0005] Based on the above, the present invention provides a baking method for reducing ash on the upper tobacco leaves, which can further solve the problem of ash on the upper tobacco leaves and improve the appearance quality of the upper tobacco leaves after baking.

[0006] The technical solution of the present invention is: a baking method for reducing ash on the upper part of tobacco leaves, comprising the following steps:

[0007] S1: After ignition, raise the dry-bulb temperature to 38°C and the wet-bulb temperature to 37°C at a rate of 1°C / hour. Dry-bulb tobacco leaves are then cured at this temperature for 10-20 hours, until they are 30-40% yellow and slightly softened. Compared to conventional processes, this step shortens the yellowing time of the upper tobacco leaves at dry-bulb temperatures of 38°C or below.

[0008] S2: Raise the dry-bulb temperature to 40°C and the wet-bulb temperature to 40°C at a rate of 1°C / h. Stop the circulating fan to reduce the temperature and humidity differences between different tobacco layers in the flue-curing room. After the wet-bulb temperature stabilizes for 6 to 12 hours, start the circulating fan to lower the wet-bulb temperature to 37 to 38°C. After the wet-bulb temperature stabilizes for 2 to 3 hours, repeat the above steps 1 to 3 times until the tobacco leaves in the high-temperature layer turn 60 to 70% yellow and become soft and withered. By setting both the dry-bulb and wet-bulb temperatures at 40°C, the temperature and humidity are kept constant, which encourages the tobacco leaves to sweat, become soft and withered, and turn yellow.

[0009] S3: Raise the dry-bulb temperature to 44°C at a rate of 1°C / h, with the wet-bulb temperature at 38-39°C, and bake at a steady temperature for 3-5 hours. Then, lower the dry-bulb temperature to 42°C, with the wet-bulb temperature at 36-37°C, and bake at a steady temperature for 6-8 hours, until the high-temperature layer of tobacco leaves turns 80-90% yellow and the main tendons become soft. This step aims to soften the main tendons at high temperatures. This means that the main tendons of tobacco leaves soften faster at a dry-bulb temperature of 44°C.

[0010] S4: Stabilize the dry-bulb temperature at 42°C, lower the wet-bulb temperature to 35-36°C, and bake at this temperature for 8-10 hours until the leaves turn yellow, become fully soft and withered, and curl at the edges, inhibiting polyphenol oxidation activity. By lowering the wet-bulb temperature by 1-2°C in the late color-fixing stage, the water loss of the tobacco leaves is controlled at 40%-45%, inhibiting polyphenol oxidase activity and promoting yellowing of the leaves. This achieves low humidity, which promotes water loss and yellowing of the tobacco leaves and inhibits enzyme activity.

[0011] S5: Raise the dry-bulb temperature to 44°C and the wet-bulb temperature to 35-36°C at a rate of 1°C / 3h. Bake at a steady temperature for 8-12h until more than half of the leaves in the high-temperature layer are dry. Reduce the heating rate by lowering the dry-bulb and wet-bulb temperatures by 1-2°C at the initial color setting stage, achieving low-temperature, low-humidity, and slow temperature rise for initial color setting.

[0012] In step S6, increase the dry-bulb temperature to 48°C and the wet-bulb temperature to 37-38°C at a rate of 1°C / 2h. Bake at a steady temperature for 10-15h until the leaves in the high-temperature layer are more than two-thirds dry and the main tendons are whitish and shrunken. By setting the dry-bulb and wet-bulb temperatures to the intermediate parameters used in conventional operation (i.e., 48°C dry-bulb and 37-38°C wet-bulb) in the middle of the color fixation process, a medium temperature, medium humidity, and medium color fixation can be achieved.

[0013] In step S7, the dry-bulb temperature is raised to 54°C at a rate of 1°C / 2h, with the wet-bulb temperature at 38-39°C. The leaves are then baked at a steady temperature for 15-20h, until the entire kang is dry and the main stems are more than 1 / 3 dry. By setting the dry-bulb temperature increase rate to 1°C / 2h in the late color setting stage and extending the baking time at a steady temperature of 54°C, the water loss and dryness of the tobacco leaves are increased, achieving slow heating and color stability.

[0014] S8: Raise the dry-bulb temperature to 66-68°C and the wet-bulb temperature to 41-42°C at a rate of 1°C / hour. Continue baking at this temperature for 20-30 hours until the entire tobacco leaf is dry. This step aims to improve the appearance quality of the upper tobacco leaves after baking by raising the wet-bulb temperature during the dry-stem period, but not exceeding 42°C.

[0015] Preferably, in steps S1 to S8, there is no special instruction on the operation of the circulating fan during the baking process, and conventional operation can be followed.

[0016] The beneficial effects of the present invention are as follows: in order to solve the problem that the upper tobacco leaves of the existing baking process are prone to dusting, the present invention shortens the yellowing time at a dry-bulb temperature of 38°C and before, keeps the dry-bulb temperature and wet-bulb temperature at the same temperature and humidity at 40°C, stops the circulating fan, reduces the temperature and humidity difference between different tobacco layers in the baking room, then lowers the wet-bulb temperature, and repeats the operation to cause the tobacco leaves to soften, wither and turn yellow; then the dry-bulb temperature is raised to 44°C, the high temperature causes the main tendons to soften, and then returns to 42°C, the wet-bulb temperature is lowered by 1-2°C at 42°C, the water loss of the tobacco leaves is controlled to 40%-45%, the activity of polyphenol oxidase is inhibited, and the yellowing of the tobacco leaves is promoted at the same time; then the dry-bulb temperature and wet-bulb temperature are lowered by 1-2°C in the initial stage of color fixing, the heating speed is slowed down, medium temperature and medium humidity are adopted for color fixing in the middle stage of color fixing, the temperature is slowly raised in the late stage of color fixing, and the baking time at a steady temperature of 54°C is extended to increase the water loss and dryness of the tobacco leaves, and the wet-bulb temperature is increased in the dry tendon stage. The new upper tobacco leaf baking method of the present invention can overcome the shortcomings of the existing upper tobacco leaf baking process, can promote the tobacco leaves to fully soften and wither, coordinate yellowing and water loss, inhibit the activity of polyphenol oxidase, greatly reduce the production of tobacco leaves with ash, and improve the quality of the upper tobacco leaves after baking. Although there are patent documents reporting on reducing the ash of upper tobacco leaves, the main yellowing dry bulb temperature of the upper leaves is around 40°C, which is most suitable for its physiological and biochemical transformation and quality formation. Too high a dry bulb temperature is prone to the phenomenon of baking green tobacco; raising the dry bulb temperature to 44°C is conducive to the softening and water loss of the main tendons, thereby promoting the yellowing and drying of tobacco leaves in a coordinated manner. The present invention focuses on regulating the dry-bulb and wet-bulb temperatures, circulating fans and other operations between 40 and 44°C, which can promote the tobacco leaves to fully soften and wither, coordinate yellowing and water loss, inhibit the activity of polyphenol oxidase, thereby reducing the ash of the upper tobacco leaves and improving the quality of tobacco leaves after baking. DETAILED DESCRIPTION

[0017] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, specific embodiments of the present invention are described in detail below. The following description sets forth numerous specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0018] The experiment was conducted in Fuquan and Anshun cities in Guizhou Province from 2020 to 2022. The flue-cured tobacco variety tested was Yunyan 87, and leaves from the upper 16th leaf position were used as test material. The test tobacco leaves were cultivated and managed according to local standardized practices for high-quality tobacco production and harvested at maturity according to tobacco leaf maturity standards. The test flue-curing barn was a conventional airflow-upstream intensive flue-curing barn. Comparative experiments were conducted using a local conventional three-stage flue-curing process as a control and the flue-curing process of the present invention as a comparative treatment. Aside from the process conditions, other factors, such as the flue-curing barn structure, tobacco leaf variety, quantity, and tobacco packing density, remained the same.

[0019] 1. Baking process of the present invention

[0020] S1: After ignition, raise the dry-bulb temperature to 38°C and the wet-bulb temperature to 37°C at a heating rate of 1°C / h. Bake at a steady temperature for 15 hours until the tobacco leaves in the high-temperature layer turn 30% yellow and become slightly soft.

[0021] S2: Raise the dry-bulb temperature to 40°C and the wet-bulb temperature to 40°C at a heating rate of 1°C / h. Stop the circulating fan to reduce the temperature and humidity difference between different tobacco layers in the flue-curing room. After the wet-bulb temperature stabilizes for 8 hours, start the circulating fan to lower the wet-bulb temperature to 38°C. After the wet-bulb temperature stabilizes for 3 hours, repeat the above operation twice until the tobacco leaves in the high-temperature layer turn 70% yellow and become soft and withered.

[0022] S3: Raise the dry-bulb temperature to 44°C and the wet-bulb temperature to 38-39°C at a heating rate of 1°C / h, and bake at a steady temperature for 4 hours; then lower the dry-bulb temperature to 42°C and the wet-bulb temperature to 37°C, and bake at a steady temperature for 7 hours, until the high-temperature layer of tobacco leaves turns 90% yellow and the main tendons become soft;

[0023] S4: Stabilize the dry-bulb temperature at 42°C, lower the wet-bulb temperature to 36°C, and bake at this temperature for 9 hours until the high-temperature layer of tobacco leaves turns yellow, veins turn green, soften and wilt, and curl at the edges, inhibiting the oxidation activity of polyphenols.

[0024] S5, raise the dry-bulb temperature to 44°C and the wet-bulb temperature to 36°C at a heating rate of 1°C / 3h, and bake at a steady temperature for 10h until more than 1 / 2 of the leaves in the high-temperature layer are dry;

[0025] S6, raise the dry-bulb temperature to 48°C and the wet-bulb temperature to 38°C at a rate of 1°C / 2h, and bake at a steady temperature for 12h until the leaves in the high-temperature layer are more than 2 / 3 dry and the main tendons are white and shrunk;

[0026] S7, raise the dry-bulb temperature to 54°C and the wet-bulb temperature to 39°C at a heating rate of 1°C / 2h, and bake at a steady temperature for 17h until the entire tobacco leaf is dry and the main ribs are more than 1 / 3 dry;

[0027] S8, raise the dry-bulb temperature to 67°C and the wet-bulb temperature to 41°C at a heating rate of 1°C / h, and bake at a steady temperature for 25 hours until the tobacco leaves are completely dry.

[0028] 2. Conventional three-stage baking process

[0029] The local flue-curing operation is carried out according to the three-stage curing process for conventional flue-cured tobacco varieties (GB / T 23219-2008).

[0030] Yellowing stage: After loading tobacco, use a low fire to raise the temperature of the flue-curing room to 35°C, maintain the wet-bulb temperature at 34°C, and after the leaf tips turn yellow, increase the dry-bulb temperature by 1°C every 2 hours to 38°C. Keep the temperature steady for a longer time and control the wet-bulb temperature at 36°C until about 80% of the tobacco leaves in the flue-curing room with thermometers reach 70% to 80% yellow and the leaves become soft (water loss of about 30%). Then raise the temperature to 42°C, maintain the wet-bulb temperature at 37°C, and extend the time until the tobacco leaves reach yellow leaves with slightly green veins, with withered frames and softened main veins.

[0031] Color Fixation Period: The dry-bulb temperature is first raised to 46°C at an average rate of 1°C every 3 hours and held steady for a prolonged period until the tobacco leaves turn yellow and lose water, reaching the point of small reels. The temperature is then raised to 54°C at an average rate of 1°C every 2 hours and held steady for 10 hours to achieve leaf drying. As the dry-bulb temperature rises, the wet-bulb temperature gradually rises and stabilizes at 39°C.

[0032] During the dry-stem stage, increase the temperature from 54°C to 68°C at a rate of 1°C per hour and maintain a stable temperature until the tobacco leaves are completely dry. Before the dry-bulb temperature reaches 60°C, maintain the wet-bulb temperature at 40°C. After 60°C, gradually close the moisture inlet and outlet ports, reduce ventilation, and maintain the wet-bulb temperature at 40°C.

[0033] The following is an evaluation and analysis of tobacco leaves cured by the curing method of the present invention and conventional three-stage curing from the aspects of polyphenol oxidase activity during curing, quality of the upper tobacco leaves after curing, and economic properties.

[0034] 1. Effects of different treatments on polyphenol oxidase activity in tobacco leaves during baking

[0035] Two high-temperature layer tobacco leaf samples (2 tobacco rods away from the door of the tobacco loading chamber) were taken at 0 h before baking and 24 h, 48 h, 72 h, and 96 h during baking to measure the polyphenol oxidase activity. The results are shown in Table 1. As can be seen from Table 1, the polyphenol oxidase activity of the baking process of the present invention is relatively high at 24 h during the baking process, gradually decreases after 48 h, and is significantly less than that of the conventional baking process after 72 h.

[0036] Table 1 Effects of different treatments on polyphenol oxidase activity in tobacco leaves during baking (U / L)

[0037]

[0038] Note: Different lowercase letters indicate significant differences at the 5% level, with 3 biological replicates.

[0039] 2. Effects of different treatments on the softening, withering and yellowing of tobacco leaves during the baking process

[0040] Table 2 Effects of different treatments on the softening, withering and yellowing of tobacco leaves during the baking process

[0041]

[0042] Tobacco leaf samples from the high-temperature layer of two treatment flue-curing processes (two tobacco rods from the flue-curing chamber door) were taken, and the degree of yellowing, leaf softening, main vein softening and yellowing, and water loss of the tobacco leaves were measured and statistically analyzed. The results are shown in Table 2. As can be seen from Table 2, compared with the conventional flue-curing process, the flue-curing process of the present invention achieves more complete softening and wilting of the tobacco leaves during the flue-curing process, and the yellowing and water loss and drying are more coordinated, which is beneficial for inhibiting the activity of tobacco polyphenol oxidase during the flue-curing process and improving the appearance quality of the flue-cured tobacco leaves.

[0043] 3. Effects of different treatments on the grade and economic traits of flue-cured tobacco leaves

[0044] Two flue-cured tobacco leaves were taken from each treatment, and statistics were collected on the orange tobacco, upper-medium tobacco, stiff tobacco, ash-containing tobacco, and average purchase price. The results are shown in Table 3. As can be seen from Table 3, compared with the conventional flue-curing process, the flue-curing process of the present invention has a higher proportion of orange tobacco, upper-medium tobacco, and average price, and a lower proportion of ash-containing tobacco and stiff tobacco. In particular, the flue-curing process of the present invention is more effective in reducing the amount of ash-containing tobacco after flue-curing.

[0045] Table 3 Effects of different treatments on grade and economic traits of flue-cured tobacco leaves

[0046]

[0047] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for reducing ash on upper tobacco leaves, characterized in that: The following steps are involved: S1: After ignition, raise the dry-bulb temperature to 38°C and the wet-bulb temperature to 37°C at a heating rate of 1°C / h. Bake at a steady temperature for 10-20 hours until the tobacco leaves in the high-temperature layer turn 30% to 40% yellow and become slightly soft. S2: Raise the dry-bulb temperature to 40°C at a rate of 1°C / h and the wet-bulb temperature to 40°C. Stop the circulating fan to reduce the temperature and humidity differences between different tobacco layers in the flue-curing room. After the wet-bulb temperature stabilizes for 6-12 hours, start the circulating fan to lower the wet-bulb temperature to 37-38°C. After the wet-bulb temperature stabilizes for 2-3 hours, repeat the above operation 1-3 times until the tobacco leaves in the high-temperature layer turn 60-70% yellow and become soft and withered. S3: Raise the dry-bulb temperature to 44°C and the wet-bulb temperature to 38-39°C at a heating rate of 1°C / h, and bake at a steady temperature for 3-5 hours. Then, lower the dry-bulb temperature to 42°C and the wet-bulb temperature to 36-37°C, and bake at a steady temperature for 6-8 hours, until the high-temperature layer of tobacco leaves turns 80% to 90% yellow and the main tendons become soft. S4: Stabilize the dry-bulb temperature at 42°C, lower the wet-bulb temperature to 35-36°C, and bake at this temperature for 8-10 hours until the leaves in the high-temperature layer turn yellow and have blue veins, become fully soft and withered, and curl at the edges, thus inhibiting the oxidation activity of polyphenols. S5: Raise the dry-bulb temperature to 44°C at a rate of 1°C / 3h and the wet-bulb temperature to 35-36°C. Bake at a steady temperature for 8-12h until the leaves in the high-temperature layer are more than 1 / 2 dry. S6: Raise the dry-bulb temperature to 48°C at a rate of 1°C / 2h and the wet-bulb temperature to 37-38°C. Bake at a steady temperature for 10-15h until the leaves in the high-temperature layer are more than 2 / 3 dry and the main tendons are white and shrunk. S7, raise the dry-bulb temperature to 54°C and the wet-bulb temperature to 38-39°C at a heating rate of 1°C / 2h, and bake at a steady temperature for 15-20h until the entire tobacco leaf is dry and the main ribs are more than 1 / 3 dry; S8, raise the dry-bulb temperature to 66~68℃ and the wet-bulb temperature to 41~42℃ at a heating rate of 1℃ / h, and bake at a steady temperature for 20~30h until the whole tobacco leaves are dry.

Images