A method for preparing tobacco leaves by curing and freeze-drying

Abstract

This invention relates to the field of tobacco processing technology, specifically to a method for curing and freeze-drying tobacco leaves; it includes a method for yellowing tobacco leaves and a method for freeze-drying tobacco leaves; the method for yellowing tobacco leaves includes tobacco leaf harvesting, tobacco leaf packaging, and tobacco leaf curing; the method for freeze-drying tobacco leaves includes tobacco leaf pre-freezing, freeze-drying, and post-freeze-drying; the purpose of this invention is to provide a method for curing and freeze-drying tobacco leaves that is suitable for tobacco leaves with certain maturity characteristics, has a precise curing process, can ensure uniform color and stable quality of the cured tobacco leaves, and can maximize the preservation of tobacco leaf tissue and tissue components while reducing the curing loss rate.

Description

Technical Field

[0001] This invention relates to the field of tobacco curing technology, and more specifically to a curing method for curing tobacco leaves by curing and freeze-drying. Background Technology

[0002] Curing tobacco leaves is a crucial step in the process from field growth to the production of finished cigarettes for consumers. Curing allows the potential qualities acquired by fresh tobacco leaves during field growth to be revealed and realized; therefore, it is a key factor determining the post-curing quality and usability of tobacco leaves. Creatively developing various curing techniques (curing, sun-drying, fumigation, freeze-drying, fermentation, etc.) and creatively combining them to enrich the diversity of tobacco raw materials and provide different styles and characteristics for various tobacco products is an important means to address the structural transformation of tobacco product development. Currently, common tobacco curing methods include sun-drying, air-drying, curing, and fumigation, and different curing methods have different effects on the content of internal chemical components in tobacco leaves. To optimize the tobacco curing process, it is essential to scientifically and systematically evaluate the transformation of chemical substances during the curing process.

[0003] Freeze-drying is a method of drying materials by freezing and sublimating the water content using low temperatures and vacuum. It is widely used in the food processing industry. Breaking away from conventional roasting methods, freeze-drying tobacco leaves allows for the production of diverse types of raw materials, which is essential for enriching the variety of tobacco raw materials. However, freeze-drying technology is still in its developmental stage in my country. The mechanism and contribution of freeze-drying to tobacco quality are not fully understood, and the supporting conditioning facilities are not yet well-developed. Basic research on conditioning parameters and degrees of conditioning is relatively scarce. Therefore, improving the freeze-drying technology and quality of tobacco leaves remains a crucial task for enriching the diversity of tobacco raw materials.

[0004] Currently, there is no scientifically sound system for exploring freeze-drying processes for tobacco. The resulting freeze-dried tobacco often suffers from problems such as smooth, stiff, and unsoft leaves, insufficient aroma, and a lack of distinct flavor profile, affecting its industrial usability and value. Therefore, based on the technical principles of freeze-drying and considering the characteristics of tobacco processing, developing a freeze-drying technology that improves the flavor and quality of tobacco leaves and reduces loss is crucial to solving these problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for freeze-drying tobacco leaves after curing, which is suitable for tobacco leaves with certain maturity characteristics, and the curing process is precise, ensuring uniform color and stable quality of the cured tobacco leaves, while maximizing the preservation of tobacco leaf tissue and tissue components and reducing the curing loss rate.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for curing and freeze-drying tobacco leaves includes: a method for curing tobacco leaves to turn yellow and a method for freeze-drying tobacco leaves.

[0008] Furthermore, the method for turning tobacco leaves yellow includes tobacco harvesting, tobacco packaging, and tobacco curing; the specific steps are as follows:

[0009] A. Harvesting: Harvest fresh tobacco leaves that have reached maturity;

[0010] B. Tobacco Leaf Bundling: The harvested fresh tobacco leaves are bundled into poles and loaded into the curing barn.

[0011] C. Yellowing of tobacco leaves: After the tobacco leaves are placed in the curing room, they are dried. After pre-yellowing and yellowing, the tobacco leaves are obtained.

[0012] Furthermore, in step A, the fresh tobacco leaves are any one or more of the following varieties: flue-cured tobacco K326, KRK26, Honghua Dajinyuan (abbreviated as Hongda), Yun series varieties (Yunyan 87, Yunyan 97, Yunyan 99, Yunyan 115), NC series (NC102, NC297) burley tobacco varieties, and aromatic tobacco varieties (Yunxiang Basma).

[0013] The fresh tobacco leaves mentioned are any one or more of the lower, middle, and upper tobacco leaves of the tobacco plant.

[0014] Furthermore, in step A, the tobacco leaves exhibiting maturity characteristics include: early-ripening tobacco leaves, moderately ripening tobacco leaves, slightly overripe tobacco leaves, overripe tobacco leaves, and falsely ripened tobacco leaves. Specifically, this is manifested by more than 50% yellowing of the tobacco leaf surface, a change in leaf color from yellowish-green to pale yellow, slight drooping of leaf tips and edges, and the shedding of a small number to a large amount of pubescence.

[0015] Furthermore, in step B, the principle of weaving the poles is that they should be of the same material and from the same location, with appropriate spacing; the principle of loading the tobacco leaves into the kiln is that they should be of the same material and from the same kiln, and should be evenly and fully loaded.

[0016] The drying room mentioned is a dense drying room.

[0017] Furthermore, in step C, the pre-yellowing process involves placing the tobacco leaves in the curing barn and raising the dry-bulb temperature from room temperature to 30-32°C and the wet-bulb temperature from room temperature to 30-32°C at a rate of 1°C / h, stabilizing the dry-bulb and wet-bulb temperatures for 2-3 hours; then raising the dry-bulb temperature from room temperature to 35°C and the wet-bulb temperature from room temperature to 34-35°C at a rate of 1°C / h, stabilizing the dry-bulb and wet-bulb temperatures for 6-8 hours.

[0018] The yellowing process involves heating the dry bulb to 37-38°C and the wet bulb to 36.0-37°C at a rate of 1°C / 2h when most of the tobacco leaf tips have turned yellow. The dry bulb and wet bulb temperatures are then stabilized and baked for 20-24 hours until 70-80% of the tobacco leaves in the entire kiln have turned yellow.

[0019] Furthermore, the aforementioned tobacco freeze-drying method includes pre-freezing of tobacco leaves, freeze-drying, and post-freeze-drying stages, with the specific steps as follows:

[0020] A. Pre-freezing of tobacco leaves: Wrap the cured tobacco leaves in aluminum foil and place them in liquid nitrogen or a -80°C freezer to freeze them completely.

[0021] B. Main freeze drying: Quickly load the pre-frozen tobacco leaves into the material tray of the freeze dryer and spread them evenly. Set the freeze drying temperature to -80℃ and the vacuum degree to 0.000pa. The freeze drying time is calculated as 5 to 7 days for 1kg of fresh tobacco leaves until the tobacco leaves are completely dry.

[0022] C. Later stage of freeze-drying: After the tobacco leaves are completely dry, set the temperature to 0℃, the vacuum degree to 0.000pa, and the time to 5-6 hours to allow the tobacco leaves to dry fully; restore the temperature to room temperature at a rate of 1℃ / 10min, and after stabilizing for 1-2 hours, the freeze dryer can be turned off. Once the internal and external air pressures are balanced, the completely freeze-dried tobacco leaves can be obtained.

[0023] Furthermore, the specific steps for pre-freezing tobacco leaves using liquid nitrogen as described in step A are as follows: Wrap the roasted tobacco leaves tightly in aluminum foil, place them in liquid nitrogen, and immerse the tobacco leaves completely for 5 to 10 minutes, until no more steam bubbles emerge from the aluminum foil.

[0024] Furthermore, the specific steps for pre-freezing tobacco leaves using a -80℃ refrigerator in step A are as follows: Wrap the cured tobacco leaves tightly in aluminum foil and freeze them in a -80℃ refrigerator for 2-3 days until the tobacco leaves are completely frozen.

[0025] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0026] 1. In the method of the present invention, on the one hand, the "medium temperature and high humidity" yellowing process of baking is used to promote the metabolic transformation of tobacco leaves, including color, structure, morphology, plastid pigments, cell wall substances, proteins, etc., and effectively promote the formation and accumulation of aroma precursor substances; on the other hand, the low temperature and vacuum are used to freeze and sublimate the water in the tobacco leaves, so as to retain the chemical components of the tobacco leaves after yellowing to the maximum extent, thereby improving the aroma quality of the tobacco leaves.

[0027] 2. This invention uses an optimized combination of tobacco curing and freeze-drying to process tobacco leaves. First, the tobacco leaves are cured by curing until they turn yellow, and then they are dried in a freeze dryer. The purpose is to increase the amount and concentration of aroma in the tobacco leaves, reduce their irritation, and thus improve the aroma quality of the tobacco leaves.

[0028] 3. The pre-freezing of tobacco leaves in this invention can quickly freeze the remaining moisture in the tobacco leaves and deactivate the proteins, avoiding the continued degradation of aroma precursors due to slow cooling; it reduces the freezing steps of tobacco leaves in the freeze dryer, and the main drying process can be carried out as soon as the tobacco leaves are put into the freeze dryer, which greatly saves the operation time of the freeze dryer and also saves the consumption of electricity.

[0029] 4. In the later stage of freeze-drying, the temperature of the freeze-drying chamber is restored to room temperature in two stages, which can prevent the dried tobacco leaves from becoming damp due to the sudden increase in external temperature and humidity, which causes small water droplets to condense on the surface; after drying, it is only necessary to store it at room temperature in a self-sealing bag.

[0030] 5. Easy to operate. The freeze-drying program of this invention can run automatically after the program is set, and the freeze-drying process can be completed by a single button operation by a general operator. Attached Figure Description

[0031] Figure 1 is a schematic diagram of the freeze-drying, yellowing freeze-drying, and normal baking processes of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Example 1

[0034] The experiment was conducted in Yanhe Town, Yuxi, using flue-cured tobacco as the type of tobacco and the variety K326.

[0035] Once the middle leaves of the tobacco plant exhibit clear signs of maturity (i.e., the fresh tobacco leaves are those from the middle section of the plant), specifically, the leaves are 80% yellow, the leaf color has turned yellow, the main vein has become white and shiny, the secondary veins are white, the leaf tips and edges droop noticeably, the angle between the stem and leaf is 70°, and most of the pubescence has fallen off, they are ready for harvesting. The harvested fresh tobacco leaves are then bundled into poles and loaded into a densely packed curing barn.

[0036] Three processing methods were set up: control group 1: normally roasted tobacco leaf samples; control group 2: fresh tobacco leaf freeze-dried samples; and experimental group 1: roasted and freeze-dried samples that turned completely yellow, which were then freeze-dried.

[0037] The normal baking process is as follows:

[0038] (1) Yellowing stage: After ignition, the dry bulb temperature is 30℃ and the wet bulb temperature is 30℃. The temperature is maintained for 5 hours. Then, the temperature is increased at a rate of 1.0℃ / h, with the dry bulb temperature slowly increasing to 35℃ and the wet bulb temperature to 34℃. The tobacco leaves are baked for 10 hours until they soften and turn yellow. After the leaf tips turn yellow, the dry bulb temperature is increased to 38℃ at a rate of 1.0℃ / h, and the wet bulb temperature is 35℃. The temperature is maintained for 35 hours until the tobacco leaves are 60% yellow. The temperature is increased at a rate of 1.0℃ / h to 40℃, and the wet bulb temperature is 35.5℃. The temperature is maintained for 15 hours until the tobacco leaves are 80% yellow. The temperature is increased at a rate of 1.0℃ / 2 hours to 42℃, and the wet bulb temperature is 34℃. The temperature is maintained for 20 hours until all the tobacco leaves in the kiln are completely yellow.

[0039] (2) Color-fixing stage: Adjust the heat, raise the dry bulb temperature to 45℃ at a rate of 1℃ / 3h, control the temperature and dehumidify, raise the wet bulb temperature to 36.5℃, and bake for 15h. Raise the dry bulb temperature to 48℃ at a rate of 1℃ / 3h, lower the wet bulb temperature to 35℃, maintain the combined dry and wet bulb temperatures for 18h, and bake until the leaves are 2 / 3 dry. Raise the dry bulb temperature to 52℃ at a rate of 1℃ / h, raise the wet bulb temperature to 38℃, maintain the combined dry and wet bulb temperatures for 10h, and bake until the tobacco leaves are basically color-fixed and the leaf surface is completely dry.

[0040] (3) Drying stage: Adjust the heat and raise the dry bulb temperature to 60℃ and the wet bulb temperature to 38℃ at a heating rate of 1.0℃ / h, and stabilize for 10h. Stabilize the wet bulb temperature at 39℃, and raise the dry bulb temperature to 65℃ at a heating rate of 1.0℃ / h, and stabilize for 24h, until all the main veins of the tobacco leaves are completely dry, and end the tobacco curing.

[0041] Freeze-drying method for tobacco leaves:

[0042] After the tobacco leaves have completely turned yellow, wrap them tightly in aluminum foil and freeze them at -80℃ for 2 days, until they are completely frozen. Quickly load the pre-frozen tobacco leaves into the material tray of the freeze dryer, spreading them evenly. Set the freeze-drying temperature to -80℃, the vacuum degree to 0.000 Pa, and the freeze-drying time to 5 days for 1 kg of fresh tobacco leaves, until the leaves are completely dry. Once the tobacco leaves are completely dry, set the temperature to 0℃, the vacuum degree to 0.000 Pa, and the time to 6 hours to ensure the leaves are thoroughly dried. Reduce the temperature to room temperature at a rate of 1℃ / 10 minutes, and after stabilizing for 2 hours, turn off the freeze dryer. Once the internal and external air pressures are balanced, remove the freeze-dried tobacco leaves.

[0043] The comparison results of the chemical properties of flue-cured tobacco under different curing methods are shown in Tables 1, 2, and 3.

[0044]

[0045] Table 1 shows that the total sugar and reducing sugar contents in the freeze-dried whole-yellow tobacco samples were the highest, increasing by 17.37% and 80.04% respectively compared to normally roasted and fresh freeze-dried tobacco. The total nitrogen, total alkaloids, potassium oxide, and chloride ion contents in the freeze-dried fresh tobacco samples were the lowest, decreasing by 50.78% and 17.19%, 82.05% and 51.79%, 65.08% and 26.19%, and 68.57% and 54.29% respectively compared to normally roasted and freeze-dried whole-yellow samples. The starch and protein contents in the freeze-dried fresh tobacco samples were the highest, increasing by 94.65% and 77.25% respectively compared to normally roasted and freeze-dried whole-yellow samples, and by 17.14% and 23.16% respectively compared to the red soil samples.

[0046]

[0047] Table 2 shows that the freeze-dried fresh tobacco samples had the highest content of plastid pigments, while the normally roasted samples had the lowest content. The freeze-dried fresh tobacco samples had 93.37% and 88.18% higher levels of lutein, chlorophyll a, chlorophyll b, and plastid pigments than the normally roasted and fully yellowed freeze-dried samples, respectively; 64.51% and 62.64% higher levels; 98.44% and 94.33% higher levels; and 98.25% and 91.83% higher levels of plastid pigments than the normally roasted and fully yellowed freeze-dried samples.

[0048]

[0049] As shown in Table 3, the total amounts of chlorogenic acid, rutin, caffeic acid, and polyphenols in the normally roasted samples were the highest, exceeding those in the freeze-dried fresh tobacco leaves by 27.94% and 20.59%, 18.10% and 21.46%, 87.50% and 50.00%, 1.98% and 14.82%, and 10.81% and 18.03%, respectively.

[0050] The comparison of aroma compounds content in flue-cured tobacco under different curing methods is shown in Table 4.

[0051]

[0052] Table 4 shows that the normally roasted samples had the highest contents of furfural, 4-oxoisophorone, nicotine, terpinene, stigmasterone A, stigmasterone B, stigmasterone C, 4-hydroxy-β-dihydrodamascone, stigmasterone D, and neophytadiene, which were 76.38% and 71.84%, 92.96% and 52.11%, 81.90% and 54.77%, 97.58% and 91.79%, 59.36% and 72.73%, 86.98% and 75.69%, 84.94% and 75.68%, 65.98% and 34.02%, 85.56% and 72.43%, and 70.07% and 29.62%, respectively, compared with the freeze-dried fresh tobacco and the fully roasted freeze-dried samples. The contents of 3-chloro-2-methoxy-5-pyridineboronic acid, damascone, and 2,6-di-tert-butyl-p-cresol were the highest in the fully roasted and freeze-dried samples, which were 22.30% and 80.41%, 30.42% and 92.80%, and 57.41% and 62.96% higher than those in the normally roasted and fresh tobacco freeze-dried samples, respectively.

[0053] The appearance of the obtained tobacco leaves is as follows Figure 1 As shown, sensory evaluations of flue-cured tobacco under different processing methods revealed the following: Normally cured tobacco samples exhibited higher smoke concentration and a slightly stronger flavor, but the aroma was relatively thin and lacked richness, with a slightly bitter aftertaste. Freeze-dried tobacco samples, compared to normally cured samples, showed increased aroma, with more pronounced roasting, sweet, and fresh aromas at moderate concentrations, and the smoke was slightly dry. Fully yellow freeze-dried tobacco samples, compared to normally cured samples, had a more prominent fresh aroma, a looser smoke, and better taste comfort, but a slightly stronger raw, grassy aroma and slightly lower maturity. In conclusion, tobacco obtained by freeze-drying after the leaves have fully turned yellow has a slightly lower sensory quality than fresh tobacco directly freeze-dried, possibly due to the excessively long yellowing time leading to excessive consumption of substances in the tobacco leaves.

[0054] Example 2

[0055] A method for processing flue-dried tobacco leaves after curing and freezing, tested in Yanhe Town, Yuxi, using flue-cured tobacco, includes the following steps:

[0056] 1) Methods for turning tobacco leaves yellow: including tobacco harvesting, tobacco packaging, and tobacco curing.

[0057] A. Harvesting: Harvest fresh tobacco leaves with mature characteristics; the type of fresh tobacco leaves is flue-cured tobacco, and the variety is [specific variety]. The fresh tobacco leaves are the lower leaves of the tobacco plant; the specific characteristics of mature tobacco leaves are as follows: the leaf surface turns 80% yellow, the leaf color turns yellow, the main vein turns white and shiny, the branch veins are white, the leaf tip and leaf edge droops obviously, the angle between the stem and leaf is 70°, and most of the hairs have fallen off.

[0058] B. Tobacco Leaf Bundling: The harvested fresh flue-cured tobacco leaves are bundled into poles and then loaded into the curing barn. The principle of pole bundling is that the same pole should be of the same material and from the same part of the plant, with appropriate spacing. The principle of loading the tobacco leaves into the barn is that the same tobacco leaves should be of the same material and should be evenly and completely filled. The curing barn is a dense curing barn.

[0059] C. Yellowing of Tobacco Leaves: After the tobacco leaves are placed in the curing barn, they are cured. Through the early, middle, and late stages of yellowing, fully yellowed tobacco leaves are obtained. Among these stages:

[0060] The pre-yellowing process involves placing the tobacco leaves in the curing barn and raising the dry-bulb temperature from room temperature to 30℃-32℃ and the wet-bulb temperature from room temperature to 32℃ at a rate of 1℃ / h, stabilizing the dry-bulb and wet-bulb temperatures for 3 hours; then raising the dry-bulb temperature from room temperature to 35℃ and the wet-bulb temperature from room temperature to 35℃ at a rate of 1℃ / h, stabilizing the dry-bulb and wet-bulb temperatures for 8 hours.

[0061] The yellowing process involves heating the dry bulb to 38°C and the wet bulb to 37°C at a rate of 1°C / 2h until most of the tobacco leaf tips turn yellow. The dry bulb and wet bulb temperatures are then stabilized and baked for 24 hours until 80% of the tobacco leaves in the kiln turn yellow.

[0062] 2) Tobacco leaf freeze-drying method: including pre-freezing of tobacco leaves, freeze-drying, and post-freeze-drying.

[0063] A. Pre-freezing of tobacco leaves: Wrap the cured tobacco leaves tightly in aluminum foil and freeze them in a -80℃ freezer for 2 days until the tobacco leaves are completely frozen.

[0064] B. Main freeze drying: Quickly load the pre-frozen tobacco leaves into the material tray of the freeze dryer and spread them evenly. Set the freeze drying temperature to -80℃, the vacuum degree to 0.000pa, and calculate the freeze drying time as 5 days for 1kg of fresh tobacco leaves, until the tobacco leaves are completely dry.

[0065] C. Post-freeze-drying stage: After the tobacco leaves are completely dry, set the temperature to 0℃, the vacuum degree to 0.000pa, and the time to 6h to allow the tobacco leaves to dry fully; restore the temperature to room temperature at a rate of 1℃ / 10min, and after stabilizing for 2h, turn off the freeze dryer. After the internal and external air pressures become balanced, take out the freeze-dried tobacco leaves.

[0066] Experimental Group 2: The flue-cured tobacco variety K326 was tested according to Example 2, resulting in Experimental Group 2;

[0067] Experimental Group 3: The flue-cured tobacco variety Hongda was tested according to Example 2, resulting in Experimental Group 3;

[0068] Experimental Group 4: The flue-cured tobacco variety Yun 87 was tested according to Example 2, resulting in Experimental Group 4;

[0069] Experimental group 5: The flue-cured tobacco variety NC102 was tested according to Example 2, resulting in experimental group 5;

[0070] Control group 3: Fresh tobacco leaves of flue-cured tobacco variety K326 were directly freeze-dried to obtain control group 3;

[0071] Control group 4: Fresh leaves of the flue-cured tobacco variety Hongda were directly freeze-dried to obtain control group 4;

[0072] Control group 5: Fresh tobacco leaves of the flue-cured tobacco variety Yun 87 were directly freeze-dried to obtain control group 5;

[0073] Control group 6: Fresh tobacco leaves of flue-cured tobacco variety NC102 were directly freeze-dried to obtain control group 6;

[0074] Control group 7: Fresh tobacco leaves of flue-cured tobacco variety K326 were harvested and freeze-dried using the method of complete transformation as described in Experiment 1, resulting in control group 7;

[0075] Control group 8: The fresh leaves of the flue-cured tobacco variety Hongda were freeze-dried after complete transformation as described in Experiment 1, resulting in control group 8;

[0076] Control group 9: Fresh tobacco leaves of the Yun 87 flue-cured tobacco variety were harvested and freeze-dried using the method described in Experiment 1 after complete transformation, thus obtaining control group 9;

[0077] Control group 10: Fresh tobacco leaves of the NC102 flue-cured tobacco variety were harvested and freeze-dried using the method described in Experiment 1 after complete transformation, resulting in control group 10.

[0078] The sensory evaluation of flue-cured tobacco under different modulation methods was compared, and the test results are shown in Table 5.

[0079]

[0080] Table 5 shows that the style characteristics of the products using Example 2 of the present invention (Experimental Groups 2 to 5) were 25% to 52.08% higher than those of the control groups (3 to 6), the concentration score was 14.91% to 48% higher, the aroma score was 30.51% to 39.34% higher, the irritation score was 7.61% to 33.96% higher, the aftertaste score was 10.78% to 28.04% higher, and the total score was 23.88% higher than those of the control groups (3 to 6). The style characteristic score of the experimental group (experimental group 2 to experimental group 5) of Example 2 of the present invention was 38.30% to 58.33% higher than that of the control group (7 to 10), the concentration score was 39.13% to 56.21% higher than that of the control group (7 to 10), the aroma score was 36.90% to 48.30% higher than that of the control group (7 to 10), the strength score was 41.54% to 69.71% higher than that of the control group (7 to 10), the irritation score was 28.26% to 36.79% higher than that of the control group (7 to 10), the aftertaste score was 28.43% to 35.58% higher than that of the control group (7 to 10), and the total score was 36.54% to 38.52% higher than that of the control group (7 to 10).

[0081] Example 3

[0082] A method for processing flue-dried tobacco leaves after curing and freezing, tested in Yanhe Town, Yuxi, using flue-cured tobacco, includes the following steps:

[0083] 1) Methods for turning tobacco leaves yellow: including tobacco harvesting, tobacco packaging, and tobacco curing.

[0084] A. Harvesting: Harvest fresh tobacco leaves with mature characteristics; the variety of fresh tobacco leaves is; the fresh tobacco leaves are the middle and upper leaves of the tobacco plant; the specific characteristics of mature tobacco leaves are that the leaf surface turns 50% yellow, the leaf color turns yellowish-green, the leaf tip and edge droop slightly, the angle between the stem and leaf is 35°, and a few hairs fall off.

[0085] B. Tobacco Leaf Bundling: The harvested fresh flue-cured tobacco leaves are bundled into poles and then loaded into the curing barn. The principle of pole bundling is that the same pole should be of the same material and from the same part of the plant, with appropriate spacing. The principle of loading the tobacco leaves into the barn is that the same tobacco leaves should be of the same material and should be evenly and completely filled. The curing barn is a dense curing barn.

[0086] C. Yellowing of Tobacco Leaves: After the tobacco leaves are placed in the curing barn, they are cured. Through the early, middle, and late stages of yellowing, fully yellowed tobacco leaves are obtained. Among these stages:

[0087] The pre-yellowing process involves placing the tobacco leaves in the curing barn and raising the dry-bulb temperature from room temperature to 31°C and the wet-bulb temperature from room temperature to 31°C at a rate of 1°C / h, stabilizing the dry-bulb and wet-bulb temperatures for 2.5 hours; then raising the dry-bulb temperature from room temperature to 35°C and the wet-bulb temperature from room temperature to 35°C at a rate of 1°C / h, stabilizing the dry-bulb and wet-bulb temperatures for 7 hours.

[0088] The yellowing process involves raising the dry bulb temperature to 38°C and the wet bulb temperature to 37°C at a rate of 1°C / 2h, and then stabilizing the dry and wet bulb temperatures for 22 hours until about 70% of the tobacco leaves in the kiln turn yellow.

[0089] 2) Tobacco leaf freeze-drying method: including pre-freezing of tobacco leaves, freeze-drying, and post-freeze-drying.

[0090] A. Pre-freezing of tobacco leaves: Wrap the cured tobacco leaves tightly in aluminum foil and freeze them in a -80℃ freezer for 2 days until the tobacco leaves are completely frozen.

[0091] B. Main freeze drying: Quickly load the pre-frozen tobacco leaves into the material tray of the freeze dryer and spread them evenly. Set the freeze drying temperature to -80℃, the vacuum degree to 0.000pa, and calculate the freeze drying time as 6 days for 1kg of fresh tobacco leaves until the tobacco leaves are completely dry.

[0092] C. Post-freeze-drying stage: After the tobacco leaves are completely dry, set the temperature to 0℃, the vacuum degree to 0.000pa, and the time to 6h to allow the tobacco leaves to dry fully; restore the temperature to room temperature at a rate of 1℃ / 10min, and after stabilizing for 2h, turn off the freeze dryer. After the internal and external air pressures become balanced, take out the freeze-dried tobacco leaves.

[0093] Experimental Group 6: The flue-cured tobacco variety K326 was tested according to Example 3, resulting in Experimental Group 6;

[0094] Experimental Group 7: The flue-cured tobacco variety Hongda was tested according to Example 3, resulting in Experimental Group 7;

[0095] Experimental Group 8: The flue-cured tobacco variety Yun 87 was tested according to Example 3, resulting in Experimental Group 8;

[0096] Experimental group 9: The flue-cured tobacco variety NC102 was tested according to Example 3, resulting in experimental group 9;

[0097] Control group 11: Fresh tobacco leaves of flue-cured tobacco variety K326 were directly freeze-dried to obtain control group 11;

[0098] Control group 12: Fresh leaves of the flue-cured tobacco variety Hongda were directly freeze-dried to obtain control group 12;

[0099] Control group 13: Fresh tobacco leaves of flue-cured tobacco variety Yun 87 were directly freeze-dried to obtain control group 13;

[0100] Control group 14: Fresh tobacco leaves of flue-cured tobacco variety NC102 were directly freeze-dried to obtain control group 14;

[0101] Control group 15: Fresh tobacco leaves of the K326 flue-cured tobacco variety were cured using conventional curing techniques to obtain control group 15;

[0102] Control group 16: The harvested flue-cured tobacco leaves of the Hongda Fresh variety were cured using conventional curing techniques to obtain control group 16;

[0103] Control group 17: Fresh tobacco leaves of the Yun 87 variety were harvested and cured using conventional curing techniques to obtain control group 17;

[0104] Control group 18: Fresh tobacco leaves of the NC102 flue-cured tobacco variety were cured using conventional curing techniques to obtain control group 18.

[0105] The sensory evaluation of flue-cured tobacco under different modulation methods was compared, and the test results are shown in Table 6:

[0106]

[0107] As shown in Table 6, the style characteristics of the products using Example 3 of the present invention (experimental groups 6-9) were 35.71%-72.09% higher than those of the control group (11-14), the aroma score was 42.86%-59.91% higher, the strength score was 44.57%-56.99% higher, the irritation score was 25.00%-36.44% higher, the aftertaste score was 15.18%-32.09% higher, and the total score was 28.07%-34.57% higher than those of the control group (11-14). The aroma score of the products using Example 3 of the present invention (experimental groups 6-9) was 20.41%-20.41% higher than those of the control group (15-18). The score for enthusiasm was 33.49%, which was 1.10% to 9.87% higher than that of the control group (15-18), and the score for stimulation was 6.78% to 14.73% higher than that of the control group (15-18). The total score was 8.34% to 15.76% higher than that of the control group (15-18).

[0108] Example 4

[0109] A method for curing and freeze-drying tobacco leaves, tested in Yanhe Town, Yuxi City, using Burley tobacco, includes the following steps:

[0110] 1) Methods for turning tobacco leaves yellow: including tobacco harvesting, tobacco packaging, and tobacco curing.

[0111] A. Harvesting: Harvest fresh tobacco leaves with mature characteristics; the type of fresh tobacco leaves is Burley tobacco, and the specific characteristics of mature tobacco leaves are as follows: the leaf surface turns 70% yellow, the leaf color turns light yellow, the main vein turns white, the branch veins are white, the leaf tip and leaf edge droop, the angle between the stem and leaf is 70°, and the pubescence is lost.

[0112] B. Tobacco Leaf Bundling: The harvested fresh tobacco leaves are bundled into poles and then loaded into the curing barn. The principle of pole bundling is that the same pole should be of the same material and from the same part of the plant, with appropriate spacing. The principle of loading the tobacco leaves into the barn is that the same tobacco leaves should be of the same material and should be evenly and completely filled. The curing barn is a dense curing barn.

[0113] C. Yellowing of Tobacco Leaves: After the tobacco leaves are placed in the curing barn, they are cured. Through the early, middle, and late stages of yellowing, fully yellowed tobacco leaves are obtained. Among these stages:

[0114] The pre-yellowing process involves placing the tobacco leaves in the curing barn and raising the dry-bulb temperature from room temperature to 30℃-32℃ and the wet-bulb temperature from room temperature to 32℃ at a rate of 1℃ / h, stabilizing the dry-bulb and wet-bulb temperatures for 2.5 hours; then raising the dry-bulb temperature from room temperature to 35℃ and the wet-bulb temperature from room temperature to 35℃ at a rate of 1℃ / h, stabilizing the dry-bulb and wet-bulb temperatures for 8 hours.

[0115] The yellowing process involves heating the dry bulb to 38°C and the wet bulb to 37°C at a rate of 1°C / 2h until most of the tobacco leaf tips turn yellow. The dry bulb and wet bulb temperatures are then stabilized and baked for 22 hours until 80% of the tobacco leaves in the kiln turn yellow.

[0116] 2) Tobacco leaf freeze-drying method: including pre-freezing of tobacco leaves, freeze-drying, and post-freeze-drying.

[0117] A. Pre-freezing of tobacco leaves: Wrap the roasted tobacco leaves tightly in aluminum foil and freeze them in a -80℃ freezer for 3 days until the tobacco leaves are completely frozen.

[0118] B. Main freeze drying: Quickly load the pre-frozen tobacco leaves into the material tray of the freeze dryer and spread them evenly. Set the freeze drying temperature to -80℃, the vacuum degree to 0.000pa, and calculate the freeze drying time as 6 days for 1kg of fresh tobacco leaves until the tobacco leaves are completely dry.

[0119] C. Post-freeze-drying stage: After the tobacco leaves are completely dry, set the temperature to 0℃, the vacuum degree to 0.000pa, and the time to 6h to allow the tobacco leaves to dry fully; restore the temperature to room temperature at a rate of 1℃ / 10min, and after stabilizing for 2h, turn off the freeze dryer. After the internal and external air pressures become balanced, take out the freeze-dried tobacco leaves.

[0120] Experimental Group 10: The lower leaves of Burley tobacco were treated according to the method in Example 4 to obtain Experimental Group 10;

[0121] Experimental Group 11: The middle tobacco leaves of Burley tobacco were treated according to the method of Example 4 to obtain Experimental Group 11;

[0122] Experimental Group 12: The upper tobacco leaves of Burley tobacco were treated according to the method in Example 4 to obtain Experimental Group 12;

[0123] Control group 19: The lower leaves of Burley tobacco were processed by freeze drying to obtain control group 19;

[0124] Control group 20: The middle part of Burley tobacco leaves was processed by freeze drying to obtain control group 20;

[0125] Control group 21: The upper leaves of Burley tobacco were treated by freeze drying to obtain control group 21;

[0126] Control group 22: The lower leaves of Burley tobacco were cured using conventional curing techniques to obtain control group 22;

[0127] Control group 23: The middle tobacco leaves of Burley tobacco were cured using conventional curing process to obtain control group 23;

[0128] Control group 24: The upper tobacco leaves of Burley tobacco were cured using conventional curing process to obtain control group 24;

[0129] The sensory evaluation of flue-cured tobacco under different modulation methods is compared, and the test results are shown in Table 7:

[0130]

[0131] Table 7 shows that the style characteristics of the products using Example 4 of the present invention (experimental groups 10-12) were 12.50%-78.72% higher than those of the control groups (19-21), the concentration score was 7.51%-27.16% higher, the aroma score was 35.85%-58.33% higher, the strength score was 25.37%-34.44% higher, the irritation score was 13.04%-34.75% higher, and the aftertaste score was 9.52%-4% higher. The concentration score of the experimental group (experimental group 10-12) was 3.48%, and the total score was 22.38%-35.52% higher than that of the control group (19-21). The concentration score of the experimental group (experimental group 10-12) was 11.56%-14.12% higher than that of the control group (22-24), the concentration score was 26.89%-27.78% higher than that of the control group (22-24), the aroma score was 36.90%-48.30% higher than that of the control group (22-24), the aftertaste score was 2.86%-17.70% higher than that of the control group (22-24), and the total score was 9.13%-10.24% higher than that of the control group (22-24).

[0132] Example 5

[0133] A method for freeze-drying and curing tobacco leaves to achieve yellowing is described. The experiment was conducted in Yanhe Town, Yuxi City, using aromatic tobacco leaves. The method includes the following steps:

[0134] 1) Methods for turning tobacco leaves yellow: including tobacco harvesting, tobacco packaging, and tobacco curing.

[0135] A. Harvesting: Harvest fresh tobacco leaves with mature characteristics; the type of fresh tobacco leaves is aromatic tobacco, and the variety is; the specific manifestations of mature tobacco leaves are that the leaf surface turns yellow by 60%, the leaf color turns yellowish-green, the main vein is white, the leaf tip and leaf edge droops obviously, the stem-leaf angle is 40°, and the pubescence is slightly lost.

[0136] B. Tobacco Leaf Bundling: The harvested fresh tobacco leaves are bundled into poles and then loaded into the curing barn. The principle of pole bundling is that the same pole should be of the same material and from the same part of the plant, with appropriate spacing. The principle of loading the tobacco leaves into the barn is that the same tobacco leaves should be of the same material and should be evenly and completely filled. The curing barn is a dense curing barn.

[0137] C. Yellowing of Tobacco Leaves: After the tobacco leaves are placed in the curing barn, they are cured. Through the early, middle, and late stages of yellowing, fully yellowed tobacco leaves are obtained. Among these stages:

[0138] The pre-yellowing process involves placing the tobacco leaves in the curing barn and raising the dry-bulb temperature from room temperature to 30°C and the wet-bulb temperature from room temperature to 30°C at a rate of 1°C / h, stabilizing the dry-bulb and wet-bulb temperatures for 2 hours; then raising the dry-bulb temperature from room temperature to 35°C and the wet-bulb temperature from room temperature to 34°C at a rate of 1°C / h, stabilizing the dry-bulb and wet-bulb temperatures for 7 hours.

[0139] The yellowing process involves heating the dry bulb to 37°C and the wet bulb to 36.0°C at a rate of 1°C / 2h, and then stabilizing both the dry and wet bulb temperatures for 22 hours until 80% of the tobacco leaves in the kiln have turned yellow.

[0140] 2) Tobacco leaf freeze-drying method: including pre-freezing of tobacco leaves, freeze-drying, and post-freeze-drying.

[0141] A. Pre-freezing of tobacco leaves: Wrap the roasted tobacco leaves tightly in aluminum foil and place them in liquid nitrogen, immersing them completely for 8 minutes until no more steam escapes from the aluminum foil.

[0142] B. Main freeze drying: Quickly load the pre-frozen tobacco leaves into the material tray of the freeze dryer and spread them evenly. Set the freeze drying temperature to -80℃, the vacuum degree to 0.000pa, and the freeze drying time to 7 days for 1kg of fresh tobacco leaves, until the tobacco leaves are completely dry.

[0143] C. Post-freeze-drying stage: After the tobacco leaves are completely dry, set the temperature to 0℃, the vacuum degree to 0.000pa, and the time to 5h to allow the tobacco leaves to dry fully; restore the temperature to room temperature at a rate of 1℃ / 10min, and after stabilizing for 2h, turn off the freeze dryer. After the internal and external air pressures become balanced, take out the freeze-dried tobacco leaves.

[0144] Experimental Group 13: The lower tobacco leaves of the aromatic tobacco were treated according to the method in Example 5 to obtain Experimental Group 13;

[0145] Experimental Group 14: The middle tobacco leaves of the aromatic tobacco were treated according to the method of Example 5 to obtain Experimental Group 14;

[0146] Experimental Group 15: The upper tobacco leaves of the aromatic tobacco were treated according to the method of Example 5 to obtain Experimental Group 15;

[0147] Control group 25: The lower tobacco leaves of aromatic tobacco were treated by freeze drying to obtain control group 25;

[0148] Control group 26: The middle part of the aromatic tobacco leaves was processed by freeze drying to obtain control group 26;

[0149] Control group 27: The upper tobacco leaves of aromatic tobacco were treated by freeze drying to obtain control group 27;

[0150] Control group 28: The lower tobacco leaves of the aromatic tobacco were roasted using a conventional roasting process to obtain control group 28;

[0151] Control group 29: The middle tobacco leaves of the aromatic tobacco were roasted using a conventional roasting process to obtain control group 29;

[0152] Control group 30: The upper tobacco leaves of the aromatic tobacco were roasted using a conventional roasting process to obtain control group 30;

[0153] The sensory evaluation of flue-cured tobacco under different modulation methods was compared, and the test results are shown in Table 8:

[0154]

[0155] Table 8 shows that the style characteristics of the products using Example 5 of the present invention (experimental groups 13-15) were 23.26%-87.18% higher than those of the control group (25-27), the concentration score was 35.58%-55.95% higher, the aroma score was 38.46%-66.51% higher, the strength score was 23.08%-51.81% higher, the off-flavor score was 21.92%-36.62% higher, and the irritation score was higher than those of the control group (25-27). The aroma score of the control group (25-27) increased by 28.45%-38.60%, the aftertaste score increased by 22.0%-41.44% compared with the control group (25-27), and the total score increased by 35.15%-49.30% compared with the control group (25-27); the aroma score of the control group (28-30) using Example 5 of the present invention (Experimental Group 13-Experimental Group 15) was 23.56%-29.33% higher than that of the control group (28-30), the strength score increased by 1.20%-10.99% compared with the control group (28-30), and the total score increased by 5.84%-13.06% compared with the control group (28-30).

[0156] Although the invention has been described herein with reference to several illustrative embodiments, it should be understood that many other modifications and implementations can be devised by those skilled in the art, which will fall within the scope and spirit of the principles disclosed herein. More specifically, various variations and modifications can be made to the components and / or layout of the subject matter arrangement within the scope of the disclosure, drawings, and claims. Besides variations and modifications to the components and / or layout, other uses will be apparent to those skilled in the art.

Claims

1. A method of curing tobacco by flue-curing and freeze-drying, characterized in that: The application relates to a tobacco leaf yellowing method and a tobacco leaf freeze-drying method. A, harvesting: harvesting fresh tobacco leaves with mature characteristics; B, tobacco leaf packing: packing the harvested fresh tobacco leaves into a pole and into a curing room; C, tobacco leaf yellowing: after the tobacco leaves are packed into the curing room, the tobacco leaves are baked to obtain yellowed tobacco leaves; In step C, the pre-yellowing is as follows: after the tobacco leaves are put into the curing room, the dry ball temperature is increased to 30-32 DEG C at a temperature increasing speed of 1 DEG C / h, the wet ball temperature is adjusted to 30-32 DEG C, the dry ball temperature and the wet ball temperature are stabilized for 2-3 hours; then the dry ball temperature is increased to 35 DEG C at a temperature increasing speed of 1 DEG C / h, the wet ball temperature is adjusted to 34-35 DEG C, the dry ball temperature and the wet ball temperature are stabilized for 6-8 hours; The yellowing is as follows: when most of the tobacco leaf tips are yellow, the dry ball temperature is increased to 37-38 DEG C at a temperature increasing speed of 1 DEG C / 2h, the wet ball temperature is adjusted to 36.0-37 DEG C, the dry ball temperature and the wet ball temperature are stabilized for 20-24 hours until 70-80 percent of the tobacco leaves in the whole furnace are yellow; The tobacco leaf freeze-drying method comprises the following steps of: A, tobacco leaf pre-freezing: wrapping the yellowed tobacco leaves with tin foil paper, and placing the tobacco leaves into liquid nitrogen or a -80 DEG C refrigerator to completely freeze the tobacco leaves; B, main freeze-drying: quickly packing the pre-frozen tobacco leaves into a material disc in a freeze-drying machine, evenly spreading the tobacco leaves, setting the freeze-drying temperature to -80 DEG C, setting the vacuum degree to 0.000 pa, and calculating the freeze-drying time according to 5-7 days for 1 kg of fresh tobacco leaves to completely dry the tobacco leaves; C, post-freeze-drying: after the tobacco leaves are completely dried, the temperature is set to 0 DEG C, the vacuum degree is set to 0.000 pa, and the time is set to 5-6 hours to completely dry the tobacco leaves; the temperature is restored to room temperature at a speed of 1 DEG C / 10 min, the freeze-drying machine is closed after the temperature is stabilized for 1-2 hours, and the completely freeze-dried tobacco leaves are obtained when the inner and outer air is balanced. In step A, the fresh tobacco leaves are any one or more of lower tobacco leaves, middle tobacco leaves and upper tobacco leaves.

2. A method of curing tobacco leaves by curing and freeze drying as claimed in claim 1, wherein: In step A, the fresh tobacco leaves with mature characteristics are characterized by the following: the tobacco leaf surface is yellowed by more than 50 percent, the tobacco leaf color is yellowish green to light yellow, the leaf tip and leaf edge are slightly drooping, and the fuzz is partially or completely fallen off.

3. A method of curing tobacco leaves by curing and freeze drying as claimed in claim 1, wherein: In step A, the pre-freezing of the tobacco leaves by liquid nitrogen is specifically as follows: wrapping the yellowed tobacco leaves with tin foil paper, placing the tobacco leaves into liquid nitrogen, completely immersing the tobacco leaves for 5-10 minutes, and stopping until no bubbles are generated from the tin foil paper.

4. The method as claimed in claim 1, wherein the tobacco leaves are cured by yellowing and freeze-dried. In step A, the pre-freezing of the tobacco leaves by a -80 DEG C refrigerator is specifically as follows: wrapping the yellowed tobacco leaves with tin foil paper, placing the tobacco leaves into the -80 DEG C refrigerator, and freezing the tobacco leaves for 2-3 days until the tobacco leaves are completely frozen.

5. The method as claimed in claim 1, wherein the tobacco leaves are cured by yellowing and freeze-dried. ​

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