Softness-promoting and aroma-enhancing slow-temperature-adjusting tobacco leaf baking process

Abstract

The invention discloses a tobacco leaf curing process capable of promoting softness, enhancing aroma and slowly adjusting temperature rise, which adopts a'slow temperature rise 'strategy and specifically comprises the following steps: S1, after ignition, slowly raising the temperature to 32-35 DEG C, and stabilizing the temperature for 1 hour; s2, slowly raising the temperature to 40 DEG C of dry pellets and 36-37 DEG C of wet pellets within 36-48 hours, and stabilizing the temperature for 1-2 hours; s3, slowly raising the temperature to 44 DEG C of dry pellets and 35-37 DEG C of wet pellets within 36-48 hours, and stabilizing the temperature for 1-2 hours; s4, slowly raising the temperature to 54 DEG C of dry pellets and 39 DEG C of wet pellets within 28-36 hours, and stabilizing the temperature for 12-14 hours; and S5, raising the temperature to 68 DEG C of a dry bulb and 41 DEG C of a wet bulb in 14-16 hours, and stabilizing the temperature for 20-25 hours until main veins are completely dry. Through long-time temperature stabilization at key nodes such as 40 DEG C and 44 DEG C, sufficient enzymolysis of cell wall substances and conversion of aroma precursors are effectively promoted, the limitation of a single coordination point at 42 DEG C in the prior art is broken through, the problem that yellowing and dehydration are not coordinated is solved, and the softness, aroma quality and chemical component coordination of the baked tobacco leaves are remarkably improved.

Description

Technical Field

[0001] This invention relates to a slow-heating tobacco curing process that promotes mellowing and aroma enhancement, belonging to the field of tobacco curing technology. Background Technology

[0002] Tobacco curing refers to the drying process that controls the temperature and humidity of the tobacco curing room to induce physiological and biochemical changes in harvested fresh tobacco leaves, ultimately resulting in a specific color, aroma, and physical properties such as "bright yellow, soft, and fragrant." Currently, the industry widely uses intensive curing barns for tobacco curing. The core technology lies in the precise control of temperature, humidity, and ventilation parameters to achieve the synergistic process of chlorophyll degradation (yellowing) and moisture evaporation (water loss).

[0003] The curing of tobacco leaves is essentially a regulated process of physiological and biochemical reactions. Yellowing is the result of enzymatic transformation of chlorophyll-protein complexes under specific temperature and humidity conditions, while water loss is a physical process involving the diffusion of water gradients within tobacco leaf cells and stomatal transpiration. These two processes need to be highly synchronized in terms of time window and rate: if yellowing lags behind water loss, "baked green tobacco" is likely to result from insufficient enzymatic decomposition of leaf veins; conversely, if water loss lags behind yellowing, abnormal cell metabolism leads to "ashy tobacco." In traditional curing processes, 42℃ is considered a critical control point for coordination, at which temperature the permeability of tobacco leaf cell membranes changes, and enzyme activity reaches its peak. However, the applicant found in actual curing processes that it is difficult to balance yellowing and water loss at 42℃, resulting in poor softness of the cured tobacco leaves and affecting their quality.

[0004] Existing literature (CN115381125B) discloses a curing method to improve the quality of NC102 tobacco leaves. This method controls the temperature, humidity, and fan status during the yellowing, color-fixing, and stem-drying stages to coordinate yellowing and water loss, thus addressing issues such as ash buildup and a high proportion of green veins and yellow leaves common in NC102 tobacco. However, this method does not fully consider the softness of the leaves and the complete conversion of aroma precursors, particularly limiting the retention of sugars and the regulation of polyphenols in the upper and middle leaves. Existing literature (CN114747783B) discloses a method to increase the soluble sugar content of upper leaves. This method employs strategies such as harvesting with stems, layered loading, and low-temperature slow curing to improve the sugar-to-alkali ratio and sensory quality of the upper leaves. The key to this method is regulating leaf moisture content through stem moisture control and slowing down dehumidification in the later yellowing and early color-fixing stages to promote material conversion. However, the process is still based on the traditional temperature zone division and has not broken through the limitation of the 42℃ coordination point. There is still considerable room for improvement in the softness and aroma coordination of the tobacco leaves after curing.

[0005] In conclusion, existing curing processes still have shortcomings in achieving a balance between yellowing and dehydration of tobacco leaves, as well as improving their softness and aroma quality. Further research and improvement are necessary. Summary of the Invention

[0006] Based on the above, the present invention provides a slow-heating tobacco curing process that promotes tenderness and aroma, which can significantly improve the tenderness, aroma quality and chemical composition of tobacco leaves while ensuring thorough yellowing and coordinated dehydration.

[0007] The technical solution of this invention is: a slow-heating tobacco curing process to promote mellowness and enhance aroma, comprising:

[0008] After S1 is ignited, the temperature is slowly increased to the ignition temperature of 32-35℃ / 31-34℃, and then the temperature is kept stable at this point for 1 hour.

[0009] S2 involves slowly heating the tobacco leaves to a dry bulb temperature of 40°C and a wet bulb temperature of 36-37°C over 36-48 hours, and then maintaining a stable temperature of 40°C for 1-2 hours. During this stage, the tobacco leaves turn yellow and dehydrate to the desired state.

[0010] S3 slowly raises the temperature to 44℃ dry bulb temperature and 35-37℃ wet bulb temperature over 36-48 hours, and then bakes at a stable temperature of 44℃ for 1-2 hours. During this stage, the goal of yellowing and dehydration of tobacco leaves is to make the veins of tobacco leaves in the middle greenhouse fade to white and the tips and edges of the tobacco leaves curl.

[0011] S4 is slowly heated to 54°C for dry bulb and 39°C for wet bulb over 28-36 hours, and then baked at a stable temperature of 54°C for 12-14 hours until all the remaining green color of the tobacco leaves turns completely yellow and the leaves of the whole batch are completely dry.

[0012] S5 heats the tobacco leaves to 68°C dry bulb and 41°C wet bulb in 14-16 hours. Once the temperature exceeds 60°C, the air inlet is closed. After the dry bulb temperature reaches 68°C, the tobacco is baked at a stable temperature for 20-28 hours until the main veins of the tobacco leaves are completely dry.

[0013] Preferably, in step S2, for the upper tobacco leaves, the goal of yellowing and dehydration is for the middle-shed tobacco leaves to reach a state where the base of the yellow leaf has green veins; for the middle tobacco leaves, the goal of yellowing and dehydration is for the middle-shed tobacco leaves to reach about 80% yellow; and for the lower tobacco leaves, the goal of yellowing and dehydration is for the middle-shed tobacco leaves to reach 6-7 layers of yellow.

[0014] Preferably, in steps S1, S2, and S4, the speed of the circulating fan is set to 960 rpm, and in step S3, the speed of the circulating fan is set to 1440 rpm.

[0015] The beneficial effects of this invention are:

[0016] 1. This invention employs a "slow-heating" strategy, particularly maintaining a stable temperature for extended periods at two key points: 40℃ and 44℃. This promotes the full enzymatic hydrolysis of tobacco cell wall substances, preventing cell wall hardening caused by excessively rapid heating, thereby significantly enhancing the softness of the cured tobacco leaves. Example data shows that the tobacco leaves treated with this invention exhibit improved appearance indicators such as leaf structure, quality, and oil content. For instance, the leaf structure score of the lower leaves increased from 7.0 to 8.0, the middle leaves from 8.2 to 8.5, and the upper leaves from 5.0 to 7.0. Simultaneously, the weight of individual leaves generally increased, and the stem content decreased, indicating a looser tobacco leaf structure and superior softness.

[0017] 2. The slow heating process of this invention, especially the prolonged residence at 44℃ and 54℃, provides ample conditions for the degradation and transformation of aroma precursors, as well as aroma formation reactions such as the Maillard reaction. Sensory evaluation results show that key indicators such as aroma quality, aroma quantity, and off-odors are superior to conventional processes. For example, the total sensory score of the lower leaves increased from 31.9 to 32.9, the middle leaves from 35.7 to 38.2, and the upper leaves from 35.7 to 37.7, resulting in a more harmonious and pure overall aroma quality.

[0018] 3. This invention utilizes a prolonged, slow heating process up to 40℃ to ensure complete chlorophyll degradation and simultaneous yellowing of coarse fibrous tissues such as leaf veins. This solves the problem of "burnt green" veins caused by incomplete yellowing in traditional processes. Simultaneously, precise control of the wet-bulb temperature at each stage ensures a high degree of matching between the tobacco leaf dehydration rate and the yellowing and color-fixing rates. Particularly at the 44℃ stage, the wet-bulb temperature is controlled at 35-37℃, guaranteeing the necessary moisture for physiological and biochemical reactions while promoting effective water removal, thus preventing browning reactions caused by excessive intracellular water and abnormal metabolism. Example data shows that the maturity and color scores of tobacco leaves in all parts are improved. For example, the maturity of lower leaves increased from 8.5 to 8.8, and the maturity of upper leaves increased from 7.0 to 8.5, indicating more thorough yellowing and effective control of the "burnt green" vein problem.

[0019] 4. The process of this invention can optimize chemical composition, especially in terms of sugar accumulation and polyphenol regulation, which can effectively improve the usability of tobacco leaves. For example, the total sugar and reducing sugar content of the lower leaves increased by 3.47% and 4.16%, respectively, and the ratio of the two sugars in the middle and upper leaves was also better than the control, indicating more coordinated sugar metabolism. Among polyphenols, key components such as chlorogenic acid performed better in the middle and lower leaves, which contributes to aroma balance.

[0020] 5. This invention breaks through the limitation of using 42℃ as a single coordination point in the traditional method. By setting progressive temperature control at 40℃ dry bulb / 36-37℃ wet bulb, 44℃ dry bulb / 35-37℃ wet bulb, 54℃ dry bulb / 39℃ wet bulb, and 68℃ dry bulb / 41℃ wet bulb, it achieves progressive coordination of yellowing, color fixation, and dryness, avoiding the problem of inconsistent yellowing and water loss at the traditional 42℃. Detailed Implementation

[0021] 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.

[0022] Example 1: Baking of lower leaves

[0023] The validation trial was conducted in Jinsha County, Guizhou Province in 2025, using the Yunyan 87 (lower leaves) flue-cured tobacco variety. The tobacco leaves were cultivated and managed according to local standards for high-quality tobacco production, and harvested based on maturity criteria. The curing barn used was a standard, intensive large-scale curing barn.

[0024] 1. Experimental Design

[0025] A comparative experiment was conducted using the local main curing process as a control and the "slow-heating tobacco curing process that promotes mellowness and aroma" as a treatment.

[0026] Conventional baking process (control group):

[0027] After ignition, a low flame is used to slowly raise the temperature of the curing barn to 33℃, maintaining a wet-bulb temperature of 32℃ for 6 hours, during which the tobacco leaves sweat and the leaf tips soften. The dry-bulb temperature is then increased to 38℃ at a rate of 1℃ per hour, while the wet-bulb temperature is controlled at 37℃ for 15 hours, allowing 80% of the tobacco leaves in the high-temperature layer to turn yellow to 60-70%. The dry-bulb temperature is then increased to 40℃ at a rate of 1℃ / 2 hours, with the wet-bulb temperature at 36℃, and the temperature is maintained and humidity is removed for 8 hours, resulting in 8 layers of yellow tobacco leaves and softened leaf tips. The dry-bulb temperature is then raised to 42℃, with the wet-bulb temperature at 36℃, and the temperature is maintained for 12 hours, causing the tobacco leaves in the high-temperature layer to turn yellow, reaching the stage of yellow leaves with green veins.

[0028] The dry bulb temperature was increased to 45℃ at 1℃ / 2h, the wet bulb temperature was 37℃, and the temperature was maintained for 6h. The veins turned white and the leaves fully softened and wilted. The temperature was increased to 48℃ at 1℃ / 2h, the wet bulb temperature was 37℃, and the temperature was maintained for 8h. The leaves with yellow leaves and white veins were semi-dry. The temperature was increased to 51℃ at 1℃ / 3h, the wet bulb temperature was 38℃, and the temperature was maintained for 6h. The midrib faded and turned white. The dry bulb temperature was then increased to 54℃ at 1℃ / 2h, the wet bulb temperature was 39℃, and the temperature was maintained for more than 14h until the leaves were dry.

[0029] Increase the temperature by 1℃ / 1h to 60℃, wet bulb temperature to 40℃, stabilize the temperature for 6h, and balance the tobacco leaves on both sides; increase the temperature by 1℃ / 1h to 68℃, wet bulb temperature to 41℃, stabilize the temperature for 25h, and the tobacco veins will be completely dry.

[0030] Slow-heating tobacco curing process to promote mellowness and aroma (processing group):

[0031] After ignition, slowly raise the temperature to the ignition temperature point, with a dry bulb temperature of 33°C and a wet bulb temperature of 34°C. Maintain the temperature at this point for 1 hour. In this step, the speed of the circulating fan is set to 960 rpm.

[0032] The temperature is slowly increased to 40°C dry bulb temperature and 37°C wet bulb temperature over 38 hours. The tobacco leaves are then baked at a stable temperature of 40°C for 1 hour until they reach 70-80% yellow and become soft. The speed of the circulating fan in this step is set to 960 rpm.

[0033] The temperature is slowly increased over 36 hours to a dry bulb temperature of 44℃ and a wet bulb temperature of 36.5℃. The tobacco leaves are then baked at a stable temperature of 44℃ for 1 hour. The veins of the tobacco leaves in the middle greenhouse fade and turn white, and the tips and edges of the tobacco leaves curl. The speed of the circulating fan in this step is set to 1440 rpm.

[0034] The temperature is slowly increased to 54°C for dry bulb and 39°C for wet bulb over 28 hours, and then baked at a stable temperature of 54°C for 12 hours. All the remaining green color of the tobacco leaves turns completely yellow and the leaves of the whole batch of tobacco leaves are completely dry. The speed of the circulating fan in this step is set to 960 rpm.

[0035] The temperature was raised to 68°C for dry bulbs and 41°C for wet bulbs over 16 hours, and then maintained at a stable temperature for 22 hours until the main veins of the tobacco leaves were completely dry. The fire was then stopped.

[0036] 2. Results Analysis

[0037] The following section explains the effects of different treatments on the appearance quality, physical characteristics, chemical composition, polyphenol content, and sensory evaluation of cured tobacco leaves.

[0038] 2.1 Quality Analysis of Cured Tobacco Leaves

[0039]

[0040] The scoring results of the appearance evaluation indicators of the first-cured tobacco leaves treated by the two processes (Table 1) show that the first-cured tobacco leaves of the slow-heating process for promoting mellowing and enhancing aroma are superior to those of the conventional curing process in all appearance indicators. The appearance indicators of the first-cured tobacco leaves of the slow-heating process for promoting mellowing and enhancing aroma are color, maturity, leaf structure, identity, oil content and color, respectively, which are 8.0, 8.8, 8.0, 5.5, 5.0 and 5.5 points, respectively, which are 0.5, 0.3, 1.0 and 0.5 points higher than those of the conventional curing process.

[0041]

[0042] The differences in physical characteristics of the first-cured tobacco leaves treated by the two processes are shown in Table 2. The single leaf weight and leaf density of the first-cured tobacco leaves treated by the slow-heating process of promoting mellowing and enhancing aroma are slightly higher than those treated by the conventional curing process, while the stem content is lower. This indicates that the slow-heating process of promoting mellowing and enhancing aroma helps to reduce the loss of tobacco leaf materials and improve the usability of tobacco leaves.

[0043] 2.2 Analysis of routine chemical components of flue-cured tobacco leaves

[0044]

[0045] The differences in conventional chemical indicators of the primary flue-cured tobacco leaves treated by the two processes are shown in Table 3. The content of the two sugars (total sugar and reducing sugar) in the primary flue-cured tobacco leaves treated by the slow-temperature heating process for promoting mellowing and aroma enhancement is significantly higher than that of the conventional curing process, which is 3.47% and 4.16% higher than the control, respectively. This indicates that the slow-temperature heating process for promoting mellowing and aroma enhancement plays an important role in promoting the accumulation of tobacco sugar and reducing the consumption of reducing sugar.

[0046] 2.3 Polyphenolic substances in flue-cured tobacco leaves

[0047]

[0048] The differences in the content of conventional chemical indicators of the primary flue-cured tobacco leaves treated by the two processes are shown in Table 4. The total polyphenol content of the primary flue-cured tobacco leaves treated by the slow-heating process for promoting mellowing and enhancing aroma (31.78 mg / g) is slightly higher than that of the conventional process (30.37 mg / g), mainly reflected in the fact that chlorogenic acid is significantly higher than that of the control. However, the content of neochlorogenic acid, rutin, and campheneol rutin in the primary flue-cured tobacco leaves treated by the slow-heating process for promoting mellowing and enhancing aroma is slightly lower than that of the control process.

[0049] 2.4 Sensory evaluation of quality

[0050]

[0051] Table 5 shows a comparative analysis of the sensory evaluation quality of two different roasting processes. It can be seen that the total sensory evaluation quality score of the tobacco leaves after roasting using the slow-heating process to promote mellowness and aroma is 32.9 points, which is higher than the 31.9 points of the conventional roasting process. This is especially evident in the aroma quality, aroma quantity, and off-flavors of the roasted tobacco leaves.

[0052] Example 2: Baking of the middle leaves

[0053] The validation trial was conducted in Jinsha County, Guizhou Province in 2025, using the Yunyan 87 (middle leaf) flue-cured tobacco variety. The tobacco leaves were cultivated and managed according to local high-quality tobacco production standards and harvested based on maturity criteria. The curing barn used was a standard, intensive large-scale curing barn.

[0054] 1. Experimental Design

[0055] A comparative experiment was conducted using the local main curing process as a control and the "slow-heating tobacco curing process that promotes mellowness and aroma" as a treatment.

[0056] Conventional baking process (control group):

[0057] After ignition, a low flame is used to slowly raise the temperature of the curing barn to 34℃, maintaining a wet-bulb temperature of 33℃ for 8 hours, during which the tobacco leaves sweat and the leaf tips soften. The dry-bulb temperature is then increased to 38℃ at a rate of 1℃ per hour, while the wet-bulb temperature is controlled at 36.5℃, maintaining a stable temperature and humidity for 18 hours, causing 80% of the tobacco leaves in the high-temperature layer to turn yellow to 60-70%. The dry-bulb temperature is then increased to 40℃ at a rate of 1℃ / 2 hours, with a wet-bulb temperature of 36℃, maintaining a stable temperature and removing moisture for 10 hours, resulting in 8 layers of yellow tobacco leaves and softened leaf tips. The dry-bulb temperature is then increased to 42℃, with a wet-bulb temperature of 36℃, maintaining a stable temperature for 16 hours, causing the tobacco leaves in the high-temperature layer to turn yellow, reaching the stage of yellow leaves with green veins.

[0058] The dry bulb temperature was increased to 45℃ at 1℃ / 3h, the wet bulb temperature was 36℃, and the temperature was maintained for 8h. The veins turned white and the leaves fully softened and wilted. The temperature was increased to 48℃ at 1℃ / 3h, the wet bulb temperature was 37℃, and the temperature was maintained for 8h. The leaves with yellow leaves and white veins were semi-dry. The temperature was increased to 51℃ at 1℃ / 2h, the wet bulb temperature was 38℃, and the temperature was maintained for 8h. The midrib faded and turned white. The dry bulb temperature was then increased to 54℃ at 1℃ / 2h, the wet bulb temperature was 39℃, and the temperature was maintained for more than 14h until the leaves were dry.

[0059] Increase the temperature by 1℃ / 1h to 60℃, wet bulb temperature to 40℃, stabilize the temperature for 6h, and balance the tobacco leaves on both sides; increase the temperature by 1℃ / 1h to 68℃, wet bulb temperature to 41℃, stabilize the temperature for 28h, and the tobacco veins will be completely dry.

[0060] Slow-heating tobacco curing process to promote mellowness and aroma (processing group):

[0061] After ignition, slowly raise the temperature to the ignition temperature point, with a dry bulb temperature of 34°C and a wet bulb temperature of 35°C. Maintain the temperature at this point for 1 hour. In this step, the speed of the circulating fan is set to 960 rpm.

[0062] The temperature is slowly increased to 40°C dry bulb temperature and 37°C wet bulb temperature over 42 hours. The tobacco leaves are then baked at a stable temperature of 40°C for 1 hour until they are 80% yellow and soft. The speed of the circulating fan in this step is set to 960 rpm.

[0063] The temperature is slowly increased over 40 hours to a dry bulb temperature of 44℃ and a wet bulb temperature of 36.5℃. The tobacco leaves are then baked at a stable temperature of 44℃ for 1 hour. The veins of the tobacco leaves in the middle rack fade and turn white, and the tips and edges of the tobacco leaves curl. The speed of the circulating fan in this step is set to 1440 rpm.

[0064] The temperature is slowly increased to 54°C for dry bulb and 39°C for wet bulb over 32 hours, and then baked at a stable temperature of 54°C for 14 hours. All the remaining green color of the tobacco leaves turns completely yellow and the leaves of the whole batch of tobacco leaves are completely dry. The speed of the circulating fan in this step is set to 960 rpm.

[0065] The temperature was raised to 68°C for dry bulb and 41°C for wet bulb in 16 hours, and then maintained at a stable temperature for 25 hours until the main veins of the tobacco leaves were completely dry. The fire was then stopped.

[0066] 2. Results Analysis

[0067] The following section explains the effects of different treatments on the appearance quality, physical characteristics, chemical composition, polyphenol content, and sensory evaluation of cured tobacco leaves.

[0068] 2.1 Quality Analysis of Cured Tobacco Leaves

[0069]

[0070] The scoring results of the appearance evaluation indicators of the first-cured tobacco leaves treated by the two processes (Table 6) show that the first-cured tobacco leaves of the slow-heating process for promoting mellowing and enhancing aroma are superior to those of the conventional curing process in all aspects of appearance indicators. The appearance indicators of the first-cured tobacco leaves of the slow-heating process for promoting mellowing and enhancing aroma are color, maturity, leaf structure, identity, oil content and color, respectively, which are 8.5, 9.0, 8.5, 8.5, 7.5 and 7.0, respectively, which are 0.5, 0.5, 0.3, 0.3, 0.5 and 1.0 points higher than those of the conventional curing process.

[0071]

[0072] The differences in physical characteristics of the primary flue-cured tobacco leaves treated by the two processes are shown in Table 7. The primary flue-cured tobacco leaves treated by the slow-heating process of promoting mellowing and enhancing aroma have a higher single leaf weight than those treated by the conventional process, while the leaf density and stem content are lower. This indicates that the slow-heating process of promoting mellowing and enhancing aroma helps to improve the looseness of the tobacco leaf structure, improve the overall quality of the tobacco leaf, and increase the usability of the tobacco leaf.

[0073] 2.2 Analysis of routine chemical components of flue-cured tobacco leaves

[0074]

[0075] Table 8 shows the differences in the content of conventional chemical indicators of the primary flue-cured tobacco leaves treated by the two processes. The content of the two sugars (total sugar and reducing sugar) in the primary flue-cured tobacco leaves treated by the slow-heating process for promoting mellowing and aroma enhancement was not significantly different from that of the conventional process, and the total sugar content of the treated process was even slightly lower than that of the control. The ratios of the two sugars in the treated process and the control process were 0.81 and 0.76, respectively. The ratio of the two sugars in the treated tobacco leaves was slightly higher than that in the control, indicating that the slow-heating process for promoting mellowing and aroma enhancement plays an important role in reducing the consumption of reducing sugars.

[0076] 2.3 Polyphenolic substances in flue-cured tobacco leaves

[0077]

[0078] The differences in the content of conventional chemical indicators of the primary flue-cured tobacco leaves treated by the two processes are shown in Table 9. The total polyphenol content of the primary flue-cured tobacco leaves treated by the slow-heating process for promoting mellowing and enhancing aroma (32.93 mg / g) was slightly lower than that of the conventional process (34.42 mg / g). The levels of neochlorogenic acid, chlorogenic acid, rutin, and campheneol rutin in the primary flue-cured tobacco leaves treated by the slow-heating process for promoting mellowing and enhancing aroma were also slightly lower than those in the control process. This indicates that the slow-heating process for promoting mellowing and enhancing aroma plays an important role in regulating polyphenol content and balancing the aroma quality of tobacco leaves.

[0079] 2.4 Sensory evaluation of absorption quality

[0080]

[0081] Table 10 shows a comparative analysis of the sensory evaluation quality of two different roasting processes. It can be seen that the total sensory evaluation quality score of the tobacco leaves after roasting using the slow-heating process that promotes mellowing and aroma enhancement reaches 38.2 points, which is higher than the sensory evaluation quality score of 35.7 points for the tobacco leaves after roasting using the conventional roasting process. This is especially evident in the aroma quality, aroma quantity, off-flavors, and irritation of the roasted tobacco leaves.

[0082] Example 3: Baking of the upper leaves

[0083] The validation trial was conducted in Jinsha County, Guizhou Province in 2025, using the Yunyan 87 (lower leaves) flue-cured tobacco variety. The tobacco leaves were cultivated and managed according to local standards for high-quality tobacco production, and harvested based on maturity criteria. The curing barn used was a standard, intensive large-scale curing barn.

[0084] 1. Experimental Design

[0085] A comparative experiment was conducted using the local main curing process as a control and the "slow-heating tobacco curing process that promotes mellowness and aroma" as a treatment.

[0086] Conventional baking process (comparison):

[0087] After ignition, a low flame is used to slowly raise the temperature of the curing barn to 34℃, maintaining the wet-bulb temperature at 34℃ for 6 hours, causing the tobacco leaves to sweat and the leaf tips to soften. The dry-bulb temperature is then increased to 38℃ at a rate of 1℃ per hour, while the wet-bulb temperature is controlled at 36℃ for 20 hours, allowing 80% of the tobacco leaves in the high-temperature layer to turn yellow to 60-70%. The dry-bulb temperature is then increased to 40℃ at a rate of 1℃ / 2 hours, with the wet-bulb temperature at 36℃, and the temperature is maintained and moisture removed for 12 hours, resulting in 8 layers of yellow tobacco leaves and softened leaf tips. The dry-bulb temperature is then increased to 42℃, with the wet-bulb temperature at 36℃, and the temperature is maintained for 18 hours, causing the tobacco leaves in the high-temperature layer to turn yellow, reaching the stage of yellow leaves with green veins.

[0088] The dry bulb temperature was increased to 45℃ at 1℃ / 3h, the wet bulb temperature was 37℃, and the temperature was maintained for 10h. The veins turned white and the leaves softened and wilted completely. The temperature was increased to 48℃ at 1℃ / 3h, the wet bulb temperature was 37℃, and the temperature was maintained for 8h. The leaves with yellow leaves and white veins were semi-dry. The temperature was increased to 51℃ at 1℃ / 3h, the wet bulb temperature was 38℃, and the temperature was maintained for 8h. The midrib faded and turned white. The dry bulb temperature was then increased to 54℃ at 1℃ / 2h, the wet bulb temperature was 39℃, and the temperature was maintained for more than 16h until the leaves were dry.

[0089] Increase the temperature by 1℃ / 1h to 60℃, wet bulb temperature to 40℃, stabilize the temperature for 6h, and balance the tobacco leaves on both sides; increase the temperature by 1℃ / 1h to 68℃, wet bulb temperature to 41℃, stabilize the temperature for 28h, and the tobacco veins will be completely dry.

[0090] Slow-heating tobacco curing process to promote mellowness and aroma (treatment)

[0091] After ignition, slowly raise the temperature to the ignition temperature point, with a dry bulb temperature of 34°C and a wet bulb temperature of 36°C. Maintain the temperature at this point for 1 hour. In this step, the speed of the circulating fan is set to 960 rpm.

[0092] The temperature is slowly increased to 40°C dry bulb temperature and 37°C wet bulb temperature over 46 hours. The tobacco leaves are then baked at a stable temperature of 40°C for 1 hour until they turn yellow with green veins and green base, and the leaves become soft. The speed of the circulating fan in this step is set to 960 rpm.

[0093] The temperature is slowly increased over 46 hours to a dry bulb temperature of 44℃ and a wet bulb temperature of 35.5℃. The tobacco leaves are then baked at a stable temperature of 44℃ for 1 hour. The veins of the tobacco leaves in the middle greenhouse fade and turn white, and the tips and edges of the tobacco leaves curl. The speed of the circulating fan in this step is set to 1440 rpm.

[0094] The temperature is slowly increased to 54°C for dry bulb and 39°C for wet bulb over 36 hours, and then baked at a stable temperature of 54°C for 14 hours. All the remaining green color of the tobacco leaves turns completely yellow and the leaves of the whole batch of tobacco leaves are completely dry. The speed of the circulating fan in this step is set to 960 rpm.

[0095] The temperature was raised to 68°C for dry bulb and 41°C for wet bulb in 16 hours, and then maintained at a stable temperature for 25 hours until the main veins of the tobacco leaves were completely dry. The fire was then stopped.

[0096] 2. Results Analysis

[0097] The following section explains the effects of different treatments on the appearance quality, physical characteristics, chemical composition, polyphenol content, and sensory evaluation of cured tobacco leaves.

[0098] 2.1 Quality Analysis of Cured Tobacco Leaves

[0099]

[0100] The scoring results of the appearance evaluation indicators of the first-cured tobacco leaves treated by the two processes (Table 11) show that the first-cured tobacco leaves of the slow-heating process for promoting mellowing and enhancing aroma are superior to those of the conventional curing process in terms of appearance indicators. The appearance indicators of the first-cured tobacco leaves of the slow-heating process for promoting mellowing and enhancing aroma are color, maturity, leaf structure, identity, oil content and color, respectively, which are 8.0, 8.5, 7.0, 7.0, 8.0 and 7.0 points, respectively, which are 0.5, 0.5, 2.0 and 0.5 points, and 1.0 and 1.0 points higher than those of the conventional curing process.

[0101]

[0102] The differences in physical characteristics of the primary flue-cured tobacco leaves treated by the two processes are shown in Table 12. The single leaf weight, stem content, and leaf density of the primary flue-cured tobacco leaves treated by the slow-heating process of promoting mellowing and enhancing aroma are slightly lower than those of the conventional curing process. This indicates that the slow-heating process of promoting mellowing and enhancing aroma helps to improve the material transformation of the upper tobacco leaves, enhance the tissue structure of the tobacco leaves, and improve the usability of the tobacco leaves.

[0103] 2.2 Analysis of routine chemical components of flue-cured tobacco leaves

[0104]

[0105] Table 13 shows the differences in the content of conventional chemical indicators of the primary flue-cured tobacco leaves treated by the two processes. The content of the two sugars (total sugar and reducing sugar) in the primary flue-cured tobacco leaves treated by the slow-heating process for promoting mellowing and aroma enhancement was not significantly different from that of the conventional process, and the total sugar content of the treated process was even slightly lower than that of the control. The ratios of the two sugars in the treated process and the control process were 0.84 and 0.76, respectively. The ratio of the two sugars in the treated tobacco leaves was higher than that in the control, indicating that the slow-heating process for promoting mellowing and aroma enhancement plays an important role in reducing the consumption of reducing sugars.

[0106] 2.3 Polyphenolic substances in flue-cured tobacco leaves

[0107]

[0108] The differences in the content of conventional chemical indicators of the primary flue-cured tobacco leaves treated by the two processes are shown in Table 14. The total polyphenol content of the primary flue-cured tobacco leaves treated by the slow-heating process for promoting mellowing and enhancing aroma (28.903 mg / g) was slightly lower than that of the conventional process (49.24 mg / g). The levels of neochlorogenic acid, chlorogenic acid, rutin, and campheneol rutin in the primary flue-cured tobacco leaves treated by the slow-heating process for promoting mellowing and enhancing aroma were significantly lower than those in the control process. This indicates that the slow-heating process for promoting mellowing and enhancing aroma plays an important role in regulating polyphenol content and balancing the aroma quality of tobacco leaves.

[0109] 2.4 Sensory evaluation of absorption quality

[0110]

[0111] Table 15 shows a comparative analysis of the sensory evaluation quality of two different roasting processes. It can be seen that the total sensory evaluation quality score of the tobacco leaves after roasting using the slow-heating process that promotes mellowing and aroma enhancement reaches 37.7 points, which is higher than the 35.7 points of the conventional roasting process. This is especially evident in the aroma quality, aroma quantity, off-flavors, and irritation of the roasted tobacco leaves.

[0112] 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 slow-heating tobacco curing process to promote mellowness and aroma, characterized in that, include: After S1 is ignited, the temperature is slowly increased to the ignition temperature of 32-35℃ / 33-36℃, and then the temperature is kept stable at this point for 1 hour. S2 involves slowly heating the tobacco leaves to a dry bulb temperature of 40°C and a wet bulb temperature of 36-37°C over 36-48 hours, and then maintaining a stable temperature of 40°C for 1-2 hours. During this stage, the tobacco leaves turn yellow and dehydrate to the desired state. S3 slowly raises the temperature to 44℃ dry bulb temperature and 35-37℃ wet bulb temperature over 36-48 hours, and then bakes at a stable temperature of 44℃ for 1-2 hours. During this stage, the goal of yellowing and dehydration of tobacco leaves is to make the veins of tobacco leaves in the middle greenhouse fade to white and the tips and edges of the tobacco leaves curl. S4 is slowly heated to 54°C for dry bulb and 39°C for wet bulb over 28-36 hours, and then baked at a stable temperature of 54°C for 12-14 hours until all the remaining green color of the tobacco leaves turns completely yellow and the leaves of the whole batch are completely dry. S5 heats the tobacco leaves to 68°C dry bulb and 41°C wet bulb in 14-16 hours. Once the temperature exceeds 60°C, the air inlet is closed. After the dry bulb temperature reaches 68°C, the tobacco is baked at a stable temperature for 20-28 hours until the main veins of the tobacco leaves are completely dry.

2. The slow-heating tobacco curing process for promoting mellowness and aroma according to claim 1, characterized in that, In step S2, for the upper tobacco leaves, the goal of yellowing and dehydration is for the middle-shed tobacco leaves to reach a state where the base of the yellow leaf has green veins and the leaf is soft; for the middle tobacco leaves, the goal of yellowing and dehydration is for the middle-shed tobacco leaves to reach about 80% yellow and the leaf is soft; for the lower tobacco leaves, the goal of yellowing and dehydration is for the middle-shed tobacco leaves to reach a state where 7-8 layers of yellow are present and the leaf is soft.

3. The slow-heating tobacco curing process for promoting mellowness and aroma according to claim 1, characterized in that, In steps S1, S2, and S4, the speed of the circulating fan is set to 960 rpm, and in step S3, the speed of the circulating fan is set to 1440 rpm.

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