Cold baking method for upper tobacco leaves with poor baking resistance after autumn in high-altitude tobacco regions

Abstract

The invention discloses a cold baking method for upper tobacco leaves with poor post-autumn baking resistance in a high-altitude tobacco area, which comprises the steps of timely harvesting fresh tobacco leaves, reasonably weaving the tobacco leaves and loading the tobacco leaves into a kang, and baking by adopting a six-stage cold baking process, and comprises a yellowing starting stage, a low-temperature slow yellowing stage, a yellow-dry coordination stage, a safe color fixing stage, a main vein fading stage and a rapid stem drying stage. The cold baking method has the advantages that the appearance quality of the upper tobacco leaves after autumn can be improved; 2, the post-autumn upper tobacco leaf grade structure can be improved; 3, the activity of polyphenol oxidase in post-autumn upper tobacco leaf baking is reduced; 4, the browning proportion and the baking loss proportion of the upper tobacco leaves after autumn can be reduced; and 5, the aroma substance content and sensory quality of the flue-cured tobacco leaves can be improved.

Description

Technical Field

[0001] The present invention relates to a cold baking method for upper tobacco leaves with poor after - autumn baking tolerance in high - altitude tobacco areas, and belongs to the technical field of tobacco leaf baking. Background Technique

[0002] Guizhou is located on the Yunnan - Guizhou Plateau, with obvious mountain - land stereoscopic climate. With the increase in rainy weather and the increase in temperature difference between day and night after autumn, the average daily temperature is between 10 and 15 °C. For tobacco areas with an altitude above 2000 meters, the average daily temperature is even lower, which easily leads to a relatively thick cuticle, a compact tissue structure, difficult maturity and yellowing, poor baking tolerance, and great baking difficulty for upper tobacco leaves. When the dry - bulb temperature exceeds 44 °C, browning is aggravated, and even some tobacco leaves turn brown between 38 and 43 °C, which is not conducive to improving the quality and usability of upper tobacco leaves after autumn.

[0003] The patent document (authorized announcement number CN106418646B) discloses an upper leaf harvesting and baking process for growing special flue-cured tobacco. When the upper leaves are about 60 days old, the upper leaves are harvested first. During the yellowing period, the yellowing temperature is high, the humidity is high, and the time is long. Fixing color is carried out before 42°C, and the time for synthesizing aroma substances is extended at 52°C. During the stem-drying period, the maximum temperature is about 3°C lower than that of the traditional baking process. The patent document (publication number CN106539117A) discloses a harvesting and baking method for reducing ash and variegation of the upper leaves of Honghuadajinyuan. By continuously irrigating the tobacco field during the ripening period of the upper leaves, 6 upper leaves are harvested at one time after the maturity of the upper 1st-position leaf. A baking method of stable temperature rise and slow moisture discharge, full withering, and gradual color fixing and stem drying is adopted. The patent document (publication number CN117322659) discloses a baking method for upper tobacco leaves in white eel mud tobacco fields. By spraying foliar nutrient solution before harvesting, reducing the harvesting maturity of tobacco leaves, reducing the amount of tobacco stringing, and reducing the loading density of tobacco in the barn, and adopting high-temperature main yellowing, early moisture discharge in the later stage of yellowing and gradually reducing the wet-bulb temperature, low-temperature and low-humidity slow temperature rise for color fixing, and rapid stem drying baking technology, it can effectively reduce the difficulty of color fixing of upper tobacco leaves, reduce ash of upper tobacco leaves, and improve the appearance quality and internal quality of baked tobacco leaves. The patent document (publication number CN119488166A) discloses a method based on nutrient regulation and supporting baking of upper flue-cured tobacco leaves, including spraying foliar regulator I once and spraying foliar regulator II twice, and adopting the baking process of "one low, one high, and one long" during the yellowing period, "one slow, one low, and one long" during the color fixing period, and "one slow, one long, and one low" during the stem-drying period for baking, which can effectively improve the quality of fresh upper tobacco leaves and baking characteristics, reduce the occurrence of diseases of upper tobacco leaves in the field, and improve the quality of baked upper tobacco leaves. The patent document (publication number CN115969070A) discloses a method for harvesting and baking upper tobacco leaves after autumn. Through stem cutting treatment, spraying nutrient solutions of ethephon and potassium dihydrogen phosphate on the leaf surface, harvesting fresh tobacco leaves when they are mature, reasonably classifying and stringing tobacco and loading it into the barn, softening, withering, and yellowing of fresh tobacco leaves, adopting low-temperature and moisture-keeping slow yellowing baking technology in the early stage of yellowing, adopting low-temperature and low-humidity slow yellowing baking technology in the later stage of yellowing, adopting low-temperature and low-humidity slow temperature rise color fixing baking technology during the color fixing period to fix the yellow color of tobacco leaves, and adopting low-temperature and low-humidity stem drying baking technology during the stem-drying period to dry the tobacco stems, the appearance quality and internal quality of baked tobacco leaves are improved.

[0004] However, although the above various solutions can solve some problems such as special upper tobacco leaves, poor quality of fresh tobacco leaves, and ash of baked tobacco leaves, due to climate factors such as increased rainy weather, larger temperature difference between day and night, and lower average daily temperature in high-altitude tobacco-growing areas after autumn, the cutin layer of upper tobacco leaves is thicker, the tissue structure is compact, it is difficult to mature and turn yellow, the heat resistance is poor, the baking difficulty is large, and it is easy to brown, and there is no obvious breakthrough in the baking technology level. Summary of the Invention

[0005] Based on the above, the present invention provides a cold baking method for upper tobacco leaves with poor post-autumn baking tolerance in high-altitude tobacco-growing areas. By timely harvesting fresh tobacco leaves, reasonably stringing the tobacco, reasonably loading the tobacco into the baking chamber, and adopting a six-stage cold baking process for baking, it further solves the problems of poor baking tolerance of upper tobacco leaves, difficult baking, and easy browning caused by climate problems in high-altitude tobacco-growing areas, and improves the quality of upper baked tobacco leaves.

[0006] The technical solution of the present invention is: a cold baking method for upper tobacco leaves with poor post-autumn baking tolerance in high-altitude tobacco-growing areas, including:

[0007] S1 Harvesting: When the rainy weather increases, the temperature difference between day and night increases, and the average daily temperature is between 10 and 15 °C after autumn, and when more than 90% of the fresh tobacco leaves in the field have obvious characteristics of chlorophyll degradation and yellowing and maturity, they can be harvested;

[0008] S2 Stringing the tobacco: Classify the tobacco leaves into four categories according to maturity, namely approaching physiological maturity, physiological maturity, technological maturity, and full maturity, and string them on poles by category. The tobacco on the same pole has the same quality. Remove the tobacco leaves without baking value. String 100 - 130 pieces of tobacco on each pole, which is 20% - 30% less than normal stringing;

[0009] S3 Loading the tobacco into the baking chamber: Load the tobacco by classification and layer, and the tobacco of the same layer has the same quality. The fresh tobacco leaves approaching physiological maturity are loaded on the low-temperature layer of the loading chamber of the bulk curing barn, and the fully mature tobacco leaves are loaded on the high-temperature layer of the loading chamber of the bulk curing barn. The remaining positions are loaded with tobacco leaves of physiological maturity and technological maturity. The loading density is 15% - 20% less than the conventional one;

[0010] S4 Baking: Bake according to the six-stage cold baking process, which includes the starting yellowing stage, low-temperature slow yellowing stage, yellowing and drying coordination stage, safe color-fixing stage, main vein fading stage, and rapid stem-drying stage.

[0011] Preferably, in step S2, the approaching physiological maturity is between immature and physiological maturity, and the fresh tobacco leaves already have some maturity characteristics.

[0012] Preferably, the six-stage cold baking process includes:

[0013] The first stage: the starting yellowing stage

[0014] After ignition, raise the dry-bulb temperature to 35 - 36 °C at a heating rate of 1 °C / h, and the wet-bulb temperature is 34 - 35 °C, and keep the temperature stable for baking for 2 - 3 h; then, raise the dry-bulb temperature to 40 - 42 °C at a heating rate of 1 °C / h, and the wet-bulb temperature is 40 - 42 °C, and keep the temperature stable for baking for 3 - 5 h to start the yellowing of the tobacco leaves;

[0015] The second stage: the low-temperature slow yellowing stage

[0016] Reduce the dry bulb temperature to 35 - 36°C at a cooling rate of 1°C / h, control the wet bulb temperature at 34 - 35°C, and bake at a constant temperature for 15 - 25 h until the tobacco leaves turn yellow by 3 - 5 tenths, the leaves become soft, and the water loss is 15% - 25%;

[0017] The third stage: the stage of coordinating yellowing and drying

[0018] Raise the dry bulb temperature to 37 - 38°C at a heating rate of 1°C / 2 h, with the wet bulb temperature at 36 - 37°C. Reduce the wet bulb temperature by 0.5°C every 6 - 10 h, and bake at a constant temperature until the tobacco leaves turn yellow by 8 - 9 tenths, with a water loss of 30% - 45%, the main vein becomes soft, and the leaves hook at the tip and curl at the edges; then, raise the dry bulb temperature to 39 - 40°C at a heating rate of 1°C / (2 - 3) h, with the wet bulb temperature at 35 - 36°C, and bake at a constant temperature until the tobacco leaves turn yellow by more than 9 tenths, more than half of the leaves are dry, and the water loss is 50% - 65%;

[0019] The fourth stage: the stage of safe color fixation

[0020] Raise the dry bulb temperature to 42°C at a heating rate of 1°C / (2 - 3) h, with the wet bulb temperature at 34.5 - 36°C, and bake at a constant temperature for 6 - 10 h; then raise the dry bulb temperature to 44°C at a heating rate of 1°C / (2 - 3) h, keep the wet bulb temperature unchanged, and bake at a constant temperature until the leaves are basically dry, with a water loss of 70% - 85%;

[0021] The fifth stage: the stage of main vein fading

[0022] Raise the dry bulb temperature to 48 - 50°C at a heating rate of 1°C / (2 - 3) h, with the wet bulb temperature at 37 - 38°C, and bake at a constant temperature for 15 - 20 h until all the main veins of the tobacco leaves turn yellow and are dry by more than 1 / 3;

[0023] The sixth stage: the stage of rapid main vein drying

[0024] Raise the dry bulb temperature to 60 - 65°C at a heating rate of 1°C / h, with the wet bulb temperature at 38 - 39°C, and bake at a constant temperature for 20 - 30 h until all the tobacco leaves in the whole kiln are dry.

[0025] The beneficial effects of the present invention: By timely harvesting fresh tobacco leaves, reasonably stringing and loading the tobacco into the kiln, and adopting a six - stage cold baking process for baking, the present invention can overcome the deficiencies of the existing conventional production management technology and the three - stage baking process, avoid being affected by long - term low temperature and disease stress, reduce the browning of the upper tobacco leaves during the baking process, and improve the quality of the upper tobacco leaves after baking in autumn. The present invention has the following advantages: 1. It is beneficial to improve the appearance quality of the upper tobacco leaves in autumn; 2. It is beneficial to improve the grade structure of the upper tobacco leaves in autumn; 3. It is beneficial to reduce the activity of polyphenol oxidase during the baking of the upper tobacco leaves in autumn; 4. It is beneficial to reduce the browning ratio and baking loss ratio of the upper tobacco leaves in autumn; 5. It is beneficial to increase the content of aroma substances and the sensory quality of the tobacco leaves after baking.

[0026] Specifically, to solve the problems existing in the upper leaves in autumn of the existing tobacco in high-altitude tobacco-growing areas, such as difficult ripening and yellowing, great baking difficulty, and easy browning, the present invention timely harvests fresh tobacco leaves, avoiding the losses caused by climate and diseases of tobacco leaves in the field due to improved maturity; by classifying and stringing tobacco, reducing the stringing amount by 20% - 30%, classifying and layering, loading tobacco with the same quality in the same layer, and reducing the loading amount by 15% - 20%, it can reduce the total moisture content in the curing barn, increase the inter-leaf gap, promote ventilation and moisture discharge in the curing barn, and is conducive to timely moisture discharge and color fixation of tobacco leaves during the baking process; by synchronously raising the dry-bulb temperature and wet-bulb temperature to 40 - 42 °C, it can increase the preheating and yellowing temperature of tobacco leaves, reduce water loss of tobacco leaves, prompt the upper leaves in autumn to sweat, and initiate yellowing of tobacco leaves; by extending the constant-temperature baking time by 10 - 20 h under the low-temperature condition of a dry-bulb temperature of 35 - 36 °C, the degree of water loss and yellowing of the upper leaves in autumn is increased by 1 - 2 degrees, and the activity of polyphenol oxidase is reduced to prevent enzymatic browning after temperature increase, and at the same time, it can promote the accumulation and transformation of aroma precursor substances; by gradually reducing the wet-bulb temperature under the low-temperature condition of a dry-bulb temperature of 37 - 38 °C, the tobacco leaves turn yellow and dehydrate and dry at the same time; by baking at a constant dry-bulb temperature of 39 - 40 °C, the degree of yellowing and water loss of tobacco leaves is further increased, the enzymatic browning reaction of tobacco leaves is reduced, tobacco leaf browning is prevented, and the yellowing and drying of tobacco leaves are coordinated; by baking at a constant temperature under the low-temperature condition of a dry-bulb temperature of 42 - 44 °C, the activity of the browning reaction enzyme of tobacco leaves is reduced, and the tobacco leaves are safely color-fixed; by baking at a relatively high dry-bulb temperature of 48 - 50 °C, the green color of the tobacco leaf veins fades and further water loss and drying occur; under the condition of a relatively high dry-bulb temperature of 60 - 65 °C, the tobacco leaf veins are quickly dried, the volatilization of aroma substances on the surface of tobacco leaves is reduced, and the aroma quality of tobacco leaves is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Changes in the activity of polyphenol oxidase in tobacco leaves during baking under different treatments. DETAILED DESCRIPTION OF THE INVENTION

[0028] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following provides a detailed description of the specific embodiments of the present invention. Many specific details are set forth in the following description to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0029] The experiment was carried out in tobacco-growing areas with an altitude of over 2,000 meters in Weining County, Bijie City, Guizhou Province from 2023 to 2024. The flue-cured tobacco variety for the experiment was Yunyan 87, and the tobacco leaves at the 16th upper leaf position were used as the experimental materials. Taking the local conventional harvesting and baking mode and the method of harvesting and baking upper tobacco leaves after autumn (publication number CN115969070A) as the control, and the method of the present invention as the comparative treatment (T), a comparative experiment was carried out.

[0030] Example 1: The cold baking method of the present invention

[0031] S1 Harvesting: When the rainy weather increases, the temperature difference between day and night increases, and the average daily temperature is 10 - 15°C after autumn, harvest when 92% of the fresh tobacco leaves in the field have obvious characteristics of chlorophyll degradation, yellowing, and maturity;

[0032] S2 Bunching: Classify the tobacco leaves into four categories according to maturity, namely, approaching physiological maturity (approaching physiological maturity is between immature and physiological maturity, and some mature characteristics have appeared in the fresh tobacco leaves), physiological maturity, technological maturity, and full maturity, and bunch them on poles. The tobacco leaves on the same pole should have the same quality. Remove the tobacco leaves without baking value. Bunch 120 tobacco leaves on each pole, which is 20% less than the normal bunching;

[0033] S3 Loading into the barn: Load the tobacco leaves according to classification and stratification, with the same quality in the same layer. The fresh tobacco leaves approaching physiological maturity are loaded in the low-temperature layer of the loading chamber of the bulk curing barn, and the fully mature tobacco leaves are loaded in the high-temperature layer of the loading chamber of the bulk curing barn. The remaining positions are loaded with tobacco leaves at physiological maturity and technological maturity. The loading density is 17% less than the conventional one;

[0034] S4 Baking: Bake according to the six-stage cold baking process, specifically as follows:

[0035] The first stage: Starting the yellowing stage

[0036] After ignition, raise the dry-bulb temperature to 35°C at a heating rate of 1°C / h, with the wet-bulb temperature of 34 - 35°C, and bake at a constant temperature for 3h; then, raise the dry-bulb temperature to 42°C at a heating rate of 1°C / h, with the wet-bulb temperature of 42°C, and bake at a constant temperature for 3h to start the yellowing of the tobacco leaves;

[0037] The second stage: Low-temperature slow yellowing stage

[0038] Lower the dry-bulb temperature to 36°C at a cooling rate of 1°C / h, control the wet-bulb temperature at 35°C, and bake at a constant temperature for 20h until the tobacco leaves turn 40% yellow, the leaves become soft, and the water loss is 20%;

[0039] The third stage: Coordination stage of yellowing and drying

[0040] Raise the dry-bulb temperature to 38°C at a heating rate of 1°C every 2 hours, with the wet-bulb temperature at 37°C. Reduce the wet-bulb temperature by 0.5°C every 10 hours, and bake at a constant temperature until the tobacco leaves turn yellow by 80% - 90%, lose 40% of their moisture, the main veins become soft, and the leaf tips curl and the edges roll; then, raise the dry-bulb temperature to 40°C at a heating rate of 1°C every 3 hours, with the wet-bulb temperature at 36°C, and bake at a constant temperature until the tobacco leaves turn yellow by over 90%, more than half of the leaves are dry, and 60% of the moisture is lost.

[0041] Stage 4: Safe color-fixing stage

[0042] Raise the dry-bulb temperature to 42°C at a heating rate of 1°C every 3 hours, with the wet-bulb temperature at 35°C, and bake at a constant temperature for 8 hours; then raise the dry-bulb temperature to 44°C at a heating rate of 1°C every 2.5 hours, keep the wet-bulb temperature unchanged, and bake at a constant temperature until the leaves are basically dry and 80% of the moisture is lost.

[0043] Stage 5: Main-vein fading stage

[0044] Raise the dry-bulb temperature to 48°C at a heating rate of 1°C every 2 hours, with the wet-bulb temperature at 38°C, and bake at a constant temperature for 20 hours until all the main veins of the tobacco leaves turn yellow and are dry by more than 1 / 3.

[0045] Stage 6: Rapid main-vein drying stage

[0046] Raise the dry-bulb temperature to 65°C at a heating rate of 1°C per hour, with the wet-bulb temperature at 39°C, and bake at a constant temperature for 25 hours until all the tobacco leaves in the whole barn are dry.

[0047] Control Example 1: Conventional harvesting and baking (National Standard GB / T 23219—2008, Technical Regulations for Flue-cured Tobacco Baking)

[0048] S1 Harvesting: Harvest the tobacco leaves when they are mature, with the basic color being yellow, the leaf surface fully yellowed, wrinkled, with obvious maturity spots, the leaf tips drooping, the leaf edges crinkled, the angle between the stem and leaf significantly increased, and the leaf age being 85 days.

[0049] S2 Bunching: Based on the classification of fresh tobacco leaves, bunch the leaves separately, with the same quality on each pole, and the quality of each pole of tobacco being 12 kg.

[0050] S3 Loading: Load the tobacco leaves with consistent cultivation management conditions, positions, and harvesting times into the same barn.

[0051] The tobacco leaves harvested on the same day should be bunched, loaded, and fired for baking on the same day. The center distance between adjacent tobacco poles is 10 cm.

[0052] S4 Baking: Conduct baking according to the conventional three-stage flue-cured tobacco baking process (GB / T 23219—2008).

[0053] S4-1 Yellowing stage: After loading the tobacco leaves, start a small fire to raise the temperature of the curing barn to 36°C, and maintain the wet-bulb temperature at 35°C. After the leaf tips turn yellow, raise the dry-bulb temperature at a rate of 1°C every 2 hours until it reaches 38°C, then keep the temperature stable for an extended period, controlling the wet-bulb temperature at 36°C, so that about 80% of the tobacco leaves on the thermometer shelves in the curing barn reach 70% to 80% yellow, and at the same time the leaves become soft (water loss is about 30%). Then raise the temperature to 40°C, maintain the wet-bulb temperature at 36°C, and bake at a stable temperature for 10 hours. Then raise the temperature to 42°C, maintain the wet-bulb temperature at 37°C, and extend the time to make the tobacco leaves have yellow leaves with slightly green veins, wilt and collapse, and the main veins become soft.

[0054] S4-2 Fixing color stage: First, raise the dry-bulb temperature at an average rate of 1°C every 3 hours until it reaches 44°C and remains stable, control the wet-bulb temperature at 37°C, and bake at a stable temperature until the tobacco leaves hook the tips and curl the edges. Then raise the temperature at an average rate of 1°C every 3 hours until it reaches 48°C and remains stable, control the wet-bulb temperature at 38°C, extend the time to make the tobacco veins turn yellow and the water loss reach small roll-up. Then raise the temperature at a rate of 1°C every 2 hours to 54°C, keep the temperature stable for 12 hours to achieve leaf drying. As the dry-bulb temperature rises, the wet-bulb temperature gradually rises and stabilizes at 39°C.

[0055] S4-3 Stem drying stage: Raise the temperature from 54°C to 65°C at a rate of 1°C per hour and keep it stable until the tobacco leaves are completely dry. Before the dry-bulb temperature reaches 60°C, keep the wet-bulb temperature at 40°C; after 60°C, gradually close the inlet and outlet dampers to reduce the ventilation volume and keep the wet-bulb temperature at 41°C.

[0056] Control Example 2: Harvesting and curing method for upper tobacco leaves after autumn

[0057] S1, Stem cutting: One day after harvesting the middle tobacco leaves, cut the tobacco plant stem at 15 cm below 4 - 6 upper tobacco leaves. The cross-section of the cut tobacco plant stem is 1 / 3 of the stem cross-section to promote the maturity and senescence of the upper tobacco leaves.

[0058] S2, Spraying foliar nutrient solution for promoting ripening: Dilute 40% ethephon solution with 500 times water and potassium dihydrogen phosphate solution with 300 times water, mix the above two diluted solutions in a ratio of 1:1 and spray on the leaves. The spraying amount per mu is 20 kg to further coordinate the nutrient balance of the upper tobacco leaves, improve the quality of the tobacco leaves, and promote the maturity and senescence of the tobacco leaves.

[0059] S3, Harvesting of fresh tobacco leaves at maturity: 93% of the harvested fresh tobacco leaves are physiologically mature and technologically mature. The leaves are mainly green-yellow and light-yellow, the leaf tips turn yellow and wither, the leaf edges turn yellow, most of the trichomes fall off, the main veins are basically all white, and most of the branch veins are white.

[0060] S4, Classification and stringing of fresh tobacco leaves: Roughly classify the fresh tobacco leaves into three categories: under-ripe, ripe, and fully ripe according to the maturity degree, and string them separately. Each string has 130 tobacco leaves.

[0061] S5, Loading fresh tobacco leaves into the curing barn: Classify and layer the tobacco leaves, and load the tobacco leaves of the same quality in the same layer. Under-ripe tobacco leaves are loaded in the low-temperature layer, fully ripe tobacco leaves are loaded in the high-temperature layer, and mature tobacco leaves are loaded in other layers. The loading density is increased by 10% compared with the conventional method;

[0062] S6, Softening, withering and yellowing of fresh tobacco leaves: After loading the fresh tobacco leaves into the curing barn, close the cold air inlet and the moisture exhaust window, start the circulation fan for 2 h, and then turn off the circulation fan to keep warm and moisturize for 20 h until the fresh tobacco leaves are slightly softened and withered, and the tobacco leaves turn yellow by 10%-20%;

[0063] S7, Curing: In the early stage of yellowing, adopt the low-temperature and humidity-keeping slow yellowing curing technology; in the later stage of yellowing, adopt the low-temperature and low-humidity slow yellowing curing technology to promote the tobacco leaves to fully soften, wither and turn yellow. In the color-fixing stage, adopt the low-temperature and low-humidity slow temperature-rising color-fixing curing technology to fix the yellow color of the tobacco leaves. In the stem-drying stage, adopt the low-temperature and low-humidity stem-drying curing technology to dry the tobacco stems.

[0064] Adopt the low-temperature and humidity-keeping slow yellowing curing technology in the early stage of yellowing: After ignition, raise the dry-bulb temperature to 32 °C at a heating rate of 1 °C / h, with the wet-bulb temperature of 31 °C, and keep the temperature stable for baking for 15 h, and the tobacco leaves turn yellow by 40%. Then, raise the dry-bulb temperature to 36 °C at a heating rate of 1 °C / 2 h, with the wet-bulb temperature of 35 °C, and keep the temperature stable for baking for 35 h, and the tobacco leaves turn yellow by 70%, and more than 1 / 2 of the leaves are softened.

[0065] Adopt the low-temperature and low-humidity slow yellowing curing technology in the later stage of yellowing: Raise the dry-bulb temperature to 38 °C at a heating rate of 1 °C / 3 h, with the wet-bulb temperature of 35 °C, and keep the temperature stable for baking for 30 h, and the tobacco leaves turn yellow by 90% and wither and soften; then, raise the dry-bulb temperature to 40 °C at a heating rate of 1 °C / 3 h, with the wet-bulb temperature of 35 °C, and keep the temperature stable for baking for 10 h, and the tobacco leaves have yellow leaves and green veins, are fully softened, withered and yellowed, and prevent the tobacco leaves from turning green during curing.

[0066] Adopt the low-temperature and low-humidity slow temperature-rising color-fixing curing technology in the color-fixing stage: Raise the dry-bulb temperature to 42 °C at a heating rate of 1 °C / 3 h, with the wet-bulb temperature of 35 °C, and keep the temperature stable for baking for 15 h, and the tobacco leaves hook the tips and curl the edges, and the water loss is more than 45%; then, raise the dry-bulb temperature to 44 °C at a heating rate of 1 °C / 3 h, with the wet-bulb temperature of 35 °C, and keep the temperature stable for baking for 15 h, and the main veins of the tobacco leaves in the high-temperature layer are basically yellowed, and more than 1 / 2 of the tobacco leaves are dried; then, raise the dry-bulb temperature to 48 °C at a heating rate of 1 °C / 2 h, with the wet-bulb temperature of 36 °C, and keep the temperature stable for baking for 15 h, and the main veins of all the tobacco leaves in the whole barn are fully yellowed and the leaves are fully dried.

[0067] During the dry vein stage, a low-temperature and low-humidity dry vein baking technique is adopted: with a heating rate of 1 °C / h, the dry bulb temperature is raised to 54 °C, the wet bulb temperature is 36 °C, and baking is carried out at a constant temperature for 5 h, with the tobacco veins being dried by half; then, with a heating rate of 1 °C / h, the dry bulb temperature is raised to 65 °C, the wet bulb temperature is 38 °C, and baking is carried out at a constant temperature for 25 h until all the tobacco leaves in the whole barn are completely dry.

[0068] Taking conventional harvesting and baking as control 1 (CK1), the method of harvesting and baking the upper tobacco leaves after autumn as control 2 (CK2), and the method of the present invention as the comparative treatment (T), the following will illustrate the effects of different treatments on the polyphenol oxidase activity of tobacco leaves during baking, the appearance quality, grade structure, browning and baking loss ratio, aroma substance content and sensory quality of the upper tobacco leaves after baking, etc.

[0069] 1. Polyphenol oxidase activity of tobacco leaves

[0070] It can be seen from Figure 1 that compared with conventional harvesting and baking (CK1) and the method of harvesting and baking the upper tobacco leaves after autumn (CK2), the polyphenol oxidase activity of tobacco leaves during baking by the method of the present invention is generally lower. Except that there is no significant difference in the polyphenol oxidase activity between fresh tobacco leaves and at 38 °C, the activity at other sampling temperature points is lower, indicating that the method of the present invention can significantly reduce the polyphenol oxidase activity of tobacco leaves during baking, which is beneficial to reducing the risk of enzymatic browning of the upper tobacco leaves after autumn.

[0071] 2. Appearance quality of the upper tobacco leaves after baking

[0072] Table 1 Effects of different treatments on the appearance quality of tobacco leaves after baking (%)

[0073]

[0074] It can be seen from Table 1 that compared with conventional harvesting and baking (CK1) and the method of harvesting and baking the upper tobacco leaves after autumn (CK2), the leaf structure, identity, oil content and chroma of B2F tobacco leaves after baking by the method of the present invention have been significantly improved, and there is no obvious difference in color and maturity. It shows that the method of the present invention is beneficial to improving the appearance quality of the upper tobacco leaves after autumn.

[0075] 3. Grade structure, browning and baking loss ratio of the upper tobacco leaves after baking

[0076] Table 2 Effects of different treatments on the grade structure, browning and baking loss ratio of tobacco leaves after baking

[0077]

[0078] Note: Different lowercase letters in the same column indicate significant differences at the 0.05% level. The same below

[0079] As can be seen from Table 2, compared with conventional harvesting and baking (CK1) and the method of harvesting and baking upper tobacco leaves after autumn (CK2), the proportion of orange tobacco leaves, the proportion of upper and medium-grade tobacco, and the average price of the tobacco leaves baked by the method of the present invention are significantly increased, while the proportion of browned tobacco leaves and the proportion of baking losses after baking are significantly lower. It shows that the method of the present invention is beneficial to improving the grade structure of the tobacco leaves after baking, reducing the proportion of browned tobacco leaves and the proportion of baking losses, thereby improving the economic benefits of the tobacco leaves.

[0080] 4. Aroma components of tobacco leaves after baking

[0081] Table 3 Effects of different treatments on the content of aroma components in tobacco leaves after baking (μg / g)

[0082]

[0083] As can be seen from Table 3, compared with conventional harvesting and baking (CK1) and the method of harvesting and baking upper tobacco leaves after autumn (CK2), the contents of Maillard reaction products, degradation products of aromatic amino acids, degradation products of cembranoid-like compounds, and fatty acid substances in B2F tobacco leaves after baking by the method of the present invention are significantly increased. It shows that the method of the present invention is beneficial to increasing the content of aroma components in tobacco leaves after baking.

[0084] 5. Sensory quality of tobacco leaves after baking

[0085] Table 4 Effects of different treatments on the sensory quality of tobacco leaves after baking

[0086]

[0087] Note: The sensory quality evaluation is the sum of the scores of 6 items: aroma quality, aroma quantity, taste, off-flavor, irritation, and body, and each item is 9 points.

[0088] As can be seen from Table 4, compared with conventional harvesting and baking (CK1) and the method of harvesting and baking upper tobacco leaves after autumn (CK2), the aroma quality, aroma quantity, taste, off-flavor, and irritation of B2F tobacco leaves after baking by the method of the present invention are significantly improved, and the total scores are increased by 1.5 points and 0.7 points respectively. It shows that the method of the present invention is beneficial to improving the sensory quality of tobacco leaves after baking.

[0089] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A method for cold-baking upper tobacco leaves with poor baking resistance in high-altitude tobacco-growing areas after autumn, characterized in that: include: S1 Harvesting: After autumn, when the rainy weather increases, the temperature difference between day and night increases, and the average daily temperature is between 10 and 15 degrees Celsius, when more than 90% of the fresh tobacco leaves in the field have obvious signs of fading green and yellowing, they can be harvested; S2 tobacco braiding: the tobacco leaves are divided into four categories according to maturity: nearly physiologically mature, physiologically mature, technologically mature and fully mature, and then braided into rods according to the categories. The same rods are of the same quality, and tobacco leaves without baking value are removed. Each rod has 100 to 130 leaves, which is 20% to 30% less than normal braiding. S3 loading: Load tobacco by classification and layering, with the same layer and quality. Fresh tobacco leaves close to physiological maturity are loaded in the low-temperature layer of the loading room of the intensive flue-curing room, fully mature tobacco leaves are loaded in the high-temperature layer of the loading room of the intensive flue-curing room, and the remaining positions are loaded with physiologically mature and technologically mature tobacco leaves. The loading density is reduced by 15% to 20% compared with the conventional method. S4 baking: Baking is carried out according to the six-stage cold baking process, which includes the starting yellowing stage, the low-temperature slow yellowing stage, the yellow-drying coordination stage, the safe color fixing stage, the main vein fading stage, and the rapid drying stage.

2. The cold baking method for upper tobacco leaves with poor baking resistance in high-altitude tobacco-growing areas after autumn according to claim 1, characterized in that: In step S2, the "close to physiological maturity" is between unripe and physiological maturity, and the fresh tobacco leaves already have some mature characteristics.

3. The cold baking method for upper tobacco leaves with poor baking resistance in high-altitude tobacco areas after autumn according to claim 1, characterized in that: The six-stage cold baking process includes: Stage 1: Start the yellowing stage After ignition, the dry bulb temperature is raised to 35-36°C and the wet bulb temperature is 34-35°C at a heating rate of 1°C / h, and the temperature is kept at a steady temperature for 2-3 hours; then, the dry bulb temperature is raised to 40-42°C and the wet bulb temperature is 40-42°C at a heating rate of 1°C / h, and the temperature is kept at a steady temperature for 3-5 hours to start the yellowing of tobacco leaves; The second stage: low temperature and slow yellowing stage Lower the dry bulb temperature to 35-36°C at a cooling rate of 1°C / h, control the wet bulb temperature to 34-35°C, and bake at a steady temperature for 15-25 hours until the tobacco leaves turn 30% to 50% yellow, become soft, and lose 15% to 25% of their water. The third stage: Huanggan coordination stage Raise the dry-bulb temperature to 37-38°C and the wet-bulb temperature to 36-37°C at a rate of 1°C / 2h, lower the wet-bulb temperature by 0.5°C every 6-10h, and bake at a steady temperature until the tobacco leaves turn 80%-90% yellow, lose 30%-45% of water, soften the main veins, and curl the edges of the leaves; then, raise the dry-bulb temperature to 39-40°C and the wet-bulb temperature to 35-36°C at a rate of 1°C / 2-3h, and bake at a steady temperature until the tobacco leaves turn more than 90% yellow, dry more than half of the leaves, and lose 50%-65% of water; Stage 4: Safe color setting stage Raise the dry-bulb temperature to 42°C at a rate of 1°C / 2-3h, and the wet-bulb temperature to 34.5-36°C, and bake at a steady temperature for 6-10h; then raise the dry-bulb temperature to 44°C at a rate of 1°C / 2-3h, keep the wet-bulb temperature constant, and bake at a steady temperature until the leaves are basically dry and have lost 70%-85% of their water; Stage 5: Main vein fading stage Raise the dry-bulb temperature to 48-50°C and the wet-bulb temperature to 37-38°C at a rate of 1°C / 2-3h, and bake at a steady temperature for 15-20h until the main veins of the tobacco leaves turn yellow and are more than 1 / 3 dry; Stage 6: Rapid Drying Stage Raise the dry-bulb temperature to 60-65°C at a rate of 1°C / h, and the wet-bulb temperature to 38-39°C. Bake at a steady temperature for 20-30 hours until the entire tobacco leaf is dry.

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