An airflow alternating tobacco leaf baking method

Abstract

The present invention discloses an air-flow alternating tobacco leaf baking method, which comprises the following steps: S1, select an inner-circulation dehumidifying heat pump enclosed dense baking house, the circulation fan is a two-way axial-flow circulation fan, hot air inlets and air return outlets with the same size are arranged at the top end and the bottom end of the heat insulation wall, and the cold air inlet and the wet discharge louvers are closed; S2, install a set of dry and wet bulb temperature sensors on the bottom shed and the top shed in the tobacco loading chamber respectively, and respectively control the temperature and humidity of the baking house, the heating time and the constant temperature time, and the rotation speed of the circulation fan during the air-flow rising type and the air-flow falling type through an automatic control instrument; S3, freshly harvested tobacco leaves are mature; S4, the freshly harvested tobacco leaves are not classified; S5, tobacco leaves are strung and loaded; S6, during the pre-wilting yellowing period, the yellowing period, the color fixing period and the stem drying period, the circulation fan runs alternately in the positive and negative directions, and the heating speed is slowed down, so as to save energy consumption, reduce labor, increase the content of aroma substances in the tobacco leaves, especially the content of plastid pigment degradation products and brownization reaction products, and make an important contribution to improving the quality, preserving the aroma and increasing the efficiency of the tobacco leaves.

Description

Technical Field

[0001] The present invention relates to an air-flow alternating tobacco leaf baking method, belonging to the technical field of tobacco leaf baking. Background Art

[0002] From the perspective of the development trend of agricultural production in China, agricultural mechanization operation is an inherent requirement and an inevitable choice for the integrated development of agricultural machinery and agronomy. With the continuous development of the commodity economy, the shortage of labor resources is particularly prominent in the process of the transformation from traditional agriculture to modern agriculture in China. Therefore, it is particularly important to solve problems such as the disharmony between agricultural machinery and agronomy and the shortage of labor, promote the deep integration of agricultural machinery and agronomy, and improve the uniformity of the quality of agricultural products.

[0003] At present, tobacco leaf baking is a key problem to be solved in the development of agricultural machinery and agronomy. There is still a long way to go for mechanized mature harvesting, tying (clamping) tobacco leaves, loading tobacco leaves onto the baking bed, and intelligent baking. Currently, the three-stage intensive baking is still the main method for tobacco leaf baking, which has problems such as long baking time, high energy consumption, large labor consumption, large temperature and humidity deviation in the baking house during the baking process, large loss of aroma substances in tobacco leaves, poor uniformity of the appearance quality of the baked tobacco leaves, and large baking losses, which to a certain extent restricts the development of tobacco leaf baking in China.

[0004] The patent document (publication number CN113261694A) discloses a tobacco leaf intensive baking house with a rotatable circulation fan. The baking house includes a tobacco leaf loading chamber and a heating chamber. A partition is provided between the tobacco leaf loading chamber and the heating chamber. Air vents are opened at the top and bottom of the partition. Exhaust windows are provided on both sides of the top and bottom of the baking house. A fan turning mechanism is provided in the heating chamber, and the heating component is arranged below the fan turning mechanism. The present invention controls the air flow direction by using a rotatable axial flow fan, which is not only easy to implement but also reduces the baking cost of tobacco leaves. By controlling the motor to turn the axial flow fan, the alternating operation of the air flow rising mode and the air flow falling mode in the tobacco leaf loading chamber is realized, and it is also avoided that the tobacco leaves at the same position are in the upstream or downstream of the air flow throughout the baking period, so that the dehydration speed and yellowing degree of the upper and lower layer tobacco leaves are relatively consistent, effectively solving the problem that the yellowing and dehydration speeds of the existing tobacco leaves are different and it is difficult to balance the baking quality of the upper and lower layer tobacco leaves.

[0005] Patent document (Publication No. CN109820225A) discloses a control method for a circulating fan in a bulk curing barn to reduce the loss of aroma substances in tobacco leaves. Yellowing stage: From ignition until the dry-bulb temperature in the curing barn reaches 40°C, the forward rotation time is 50 minutes and the reverse rotation time is 10 minutes. Fixing color stage: The reverse rotation function is turned off in this stage, and the fan continuously rotates forward. Dry-leaf stage: After the dry-bulb temperature in the curing barn reaches 57°C, the forward and reverse rotation functions are turned on again, the forward rotation time is 50 minutes, and the reverse rotation time is 10 minutes until the baking is completed. When using this method for tobacco leaf baking, the forward and reverse rotation functions are turned on in the high-temperature section, and more volatile oils and resins, which are substances that produce more smoky fragrance in resins, will be generated. Volatile oils are substances that can emit aromatic odors at room temperature, while resins need to burn or be at a higher temperature to produce substances with smoky fragrance. When the forward and reverse rotation functions are turned on in the low-temperature section, more amino acids will be produced, and amino acids have a dual effect on the color, aroma, and taste of flue-cured tobacco.

[0006] However, although the above-mentioned solutions can solve the uniformity of the baking temperature of tobacco leaves at the upper and lower positions in the loading chamber, and reduce the loss of aroma substances such as volatile oils, resins, and amino acids in tobacco leaves, there are still problems such as a large loss of aroma substances in tobacco leaves, the mismatch between the rotation speed and forward and reverse rotation of the circulating fan in each step of the baking operation, high energy consumption, a large amount of labor, poor appearance quality and uniformity of tobacco leaves, the phenomenon of easily burning tobacco leaves due to the large temperature difference between the bottom shed and the top shed during the forward and reverse alternation of the circulating fan during the baking process, and the current situation of tobacco leaf harvesting and baking being unable to meet the needs of the development of the new form and the deep integration of agricultural machinery and agronomy and other technical problems. Summary of the Invention

[0007] Based on the above, the present invention provides an air-flow alternating tobacco leaf baking method, which can further solve technical problems such as the loss of aroma substances on the surface of tobacco leaves and in the loading chamber through the moisture exhaust louvers, a large loss of aroma substances during the dry-leaf period, the mismatch between the rotation speed and forward and reverse rotation of the circulating fan in each step of the baking operation, high energy consumption, a large amount of labor, poor appearance quality and uniformity of tobacco leaves, and the phenomenon of easily burning tobacco leaves due to the large temperature difference between the bottom shed and the top shed during the forward and reverse alternation of the circulating fan during the baking process.

[0008] The technical solution of the present invention is: An air-flow alternating tobacco leaf baking method, comprising the following steps:

[0009] S1, Transformation of the bulk curing barn: The curing barn is an internal circulation dehumidifying heat pump closed-type bulk curing barn, and the circulating fan in its heating chamber is a two-way axial flow circulating fan. At the top and bottom of the heat insulation wall between the heating chamber and the loading chamber, there are hot air inlets or return air inlets with the same size, and the cold air inlet and the moisture exhaust louvers are closed;

[0010] S2, Control by the automatic controller: A set of dry and wet bulb temperature sensors are installed on the bottom shed and the top shed in the loading chamber of the curing barn, and the temperature, humidity, heating time, and stabilizing time of the curing barn as well as the rotation speed of the circulating fan are respectively controlled by the automatic controller during the upward air flow type and the downward air flow type;

[0011] S3, Fresh tobacco leaves are harvested at maturity: The fresh tobacco leaves are harvested at maturity according to the leaf positions and maturity levels.

[0012] S4, The fresh tobacco leaves are not classified.

[0013] S5, Bunching and loading the tobacco leaves: The fresh tobacco leaves should not be bunched too densely, and the loading amount should be appropriate.

[0014] S6, Pre-wilting and yellowing: The fresh tobacco leaves are pre-wilted and yellowed in the curing barn until the leaves are slightly wilted and the tips and edges of the leaves turn yellow.

[0015] S7, Yellowing stage: After ignition, start the circulation fan at a low speed, raise the temperature at a rate of 1°C every 2 hours to 31 - 33°C, with the wet-bulb temperature at 30 - 32°C, and keep the temperature stable for baking for 2 - 3 hours, and the tobacco leaves turn yellow by 1 - 2 tenths; raise the temperature at a rate of 1°C every 2 hours to 35 - 36°C, with the wet-bulb temperature at 34 - 35°C, and keep the temperature stable for baking for 2 - 3 hours, and the tobacco leaves turn yellow by 2 - 3 tenths; raise the temperature at a rate of 1°C every 2 hours to 38°C, with the wet-bulb temperature at 36 - 37°C, and keep the temperature stable for baking for 12 - 18 hours, and the bottom and top layer tobacco leaves turn yellow by 7 - 8 tenths and the leaves become soft; then, raise the temperature at a rate of 1°C every 3 - 4 hours to 40°C, with the wet-bulb temperature at 36 - 37°C, and keep the temperature stable for baking for 4 - 6 hours, and the bottom and top layer tobacco leaves turn yellow by 8 - 9 tenths, and the middle layer tobacco leaves turn yellow by 7 - 8 tenths and the leaves become soft; then, start the circulation fan at a high speed, raise the temperature at a rate of 1°C every 4 - 6 hours to 42°C, with the wet-bulb temperature at 36 - 37°C, and keep the temperature stable for baking for 6 - 8 hours, and the bottom and top layer tobacco leaves have yellow leaves with green veins and the leaf bases are slightly green, and the middle layer tobacco leaves turn yellow by 8 - 9 tenths and are fully wilted and soft; among them, the time interval between the alternating operation of the air flow of the two-way axial flow circulation fan is 1 hour from ignition to 38°C, and 1 - 2 hours from the start of the 38°C temperature stability to the end of the 42°C temperature stability.

[0016] S8, Fixing color stage: Keep the circulation fan running at a high speed, raise the temperature at a rate of 1°C every 4 - 6 hours to 44°C, with the wet-bulb temperature at 37°C, and keep the temperature stable for baking for 4 - 6 hours to remove the remaining green on the leaves, and the bottom and top layer tobacco leaves have hooked tips and curled edges; then, raise the temperature at a rate of 1°C every 4 - 5 hours to 46°C, with the wet-bulb temperature at 37 - 38°C, and keep the temperature stable for baking for 4 - 6 hours, and the bottom and top layer tobacco leaves are half-dry and form small rolls; then, start the circulation fan at a low speed, raise the temperature at a rate of 1°C every 4 - 5 hours to 48 - 50°C, with the wet-bulb temperature at 37 - 38°C, and keep the temperature stable for baking for 4 - 6 hours, and more than 2 / 3 of the bottom and top layer tobacco leaves are dry; then, keep the circulation fan running at a low speed, raise the temperature at a rate of 1°C every 3 - 4 hours to 53 - 54°C, with the wet-bulb temperature at 38 - 39°C, and keep the temperature stable for baking for 6 - 10 hours, and all the tobacco leaves in the whole barn are completely dry and form large rolls; among them, the time interval between the alternating operation of the air flow of the two-way axial flow circulation fan is 2 - 3 hours.

[0017] S9, during the main vein drying stage, start the circulation fan at high speed and heat up to 58 - 60°C at a rate of 1°C every 2 - 3 hours, with the wet-bulb temperature at 38 - 39°C. Keep the temperature stable for baking for 4 - 6 hours until more than half of the main veins of the bottom and top layer tobacco leaves are dried. Then, start the circulation fan at low speed and heat up to 65 - 68°C at a rate of 1°C every 2 - 3 hours, with the wet-bulb temperature at 38 - 39°C. Keep the temperature stable for baking for 15 - 20 hours until all the tobacco leaves in the whole barn are completely dried. Among them, the time interval for the alternating operation of the air flow of the two-way axial flow circulation fan is 1 - 2 hours at 55 - 60°C and 2 - 3 hours from the start of temperature stabilization at 60°C until the end of baking.

[0018] Preferably, the length and width dimensions of the air return opening of the standard bulk curing barn are respectively modified to 2700 mm and 400 mm.

[0019] Preferably, the two-way axial flow circulation fan is required to have high efficiency and low noise, with the rated power of the motor being 2.2 kW and the air volume being more than 15000 m 3 / h, which can meet the technological requirements of positive and negative alternating ventilation.

[0020] Preferably, when the air flow direction in the bulk curing barn is upward, the temperature and humidity sensor of the bottom layer is used as the main sensor for controlling the curing barn; when the air flow direction is downward, the temperature and humidity sensor of the top layer is used as the main sensor for controlling the curing barn. The control instrument is equipped with automatic and manual modes. When stabilizing the temperature for baking at the key dry-bulb temperature points of 38°C, 40°C, 42°C, 44°C, 46°C, 48 - 50°C, and 54°C, check the temperature and humidity differences between the bottom and top layers through the alarm and query device of the control instrument, and automatically or manually adjust the upward and downward air flow baking modes and related baking parameters to further reduce the temperature and humidity deviation between the bottom and top layers of the curing barn.

[0021] Preferably, the fresh tobacco leaves are harvested when mature. For the middle and lower leaves, 2 - 3 leaves are harvested each time according to the maturity degree and leaf position, and 4 - 6 fully mature upper leaves are harvested at one time.

[0022] Preferably, no classification operation is performed on the fresh tobacco leaves.

[0023] Preferably, the amount of fresh tobacco leaves strung on each pole is 10 ± 1 kg. For a 3-layer standard bulk curing barn, it is appropriate to have 3000 - 4000 kg of lower fresh tobacco leaves and 3500 - 4500 kg of middle and upper fresh tobacco leaves per barn.

[0024] Preferably, after loading the fresh tobacco leaves into the curing barn, start pre-wilting and yellowing, without lighting a fire or dehumidifying. The pre-wilting and yellowing time is 15 - 25 hours. The circulation fan is turned on for 5 - 10 minutes in both forward and reverse directions every 3 - 5 hours. The high-speed rotation of the circulation fan is started 10 hours after the start of pre-wilting and yellowing, and the low-speed rotation of the circulation fan is started 10 hours after pre-wilting and yellowing until the tobacco leaves are slightly wilted and the tips and edges turn yellow.

[0025] Preferably, the two-way axial flow circulation fan adopts variable frequency speed regulation technology. The rotation speed threshold range of the circulation fan during the pre-wilting and yellowing period is 960 - 1450 r / min, where the low-speed range of the circulation fan is 960 - 1200 r / min, and the high-speed range is 1200 - 1450 r / min; the rotation speed threshold range of the circulation fan during the yellowing period is 960 - 1200 r / min, where the low-speed range of the circulation fan is 960 - 1080 r / min, and the high-speed range is 1080 - 1200 r / min; the rotation speed threshold range of the circulation fan during the color-fixing period is 960 - 1450 r / min, where the low-speed range of the circulation fan is 960 - 1200 r / min, and the high-speed range is 1200 - 1450 r / min; the rotation speed threshold range of the circulation fan during the stem-drying period is 720 - 960 r / min, where the low-speed range is 720 - 840 r / min, and the high-speed range is 840 - 960 r / min.

[0026] Preferably, for the bulk curing barn, the fresh tobacco loading amount per flue is based on 3000 kg for the lower leaves and 3500 kg for the middle and upper leaves. When the fresh tobacco loading amount increases by 10%, the corresponding rotation speed of the circulation fan increases by 10% from the critical minimum value within the corresponding threshold range, but the maximum rotation speed of the circulation fan does not exceed the threshold range of each baking period.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] First of all, the present invention reduces the loss of aroma substances in tobacco leaves during baking mainly by adopting an internal circulation dehumidification heat pump closed-type bulk curing barn, setting the forward and reverse rotation of the circulation fan, transforming the ventilation channel of the curing barn, closing the moisture exhaust window, optimizing the temperature, humidity, heating and temperature stabilization time, rotation speed of the circulation fan, and forward and reverse rotation time required for each operation step during the yellowing, color-fixing, and stem-drying periods of baking, extending the baking time in the early stage of stem-drying and the heating time in the stem-drying period, and reducing the temperature stabilization baking time at 65 - 68 °C. Thus, the total content of tobacco aroma substances is improved overall and comprehensively, especially the content of plastid pigment degradation products and brownization reaction products, which makes an important contribution to improving the quality and preserving the aroma of tobacco leaves. This cannot be compared with the traditional bulk baking method and is different from the patent document (publication number CN109820225A) "A control method for the circulation fan of a bulk curing barn to reduce the loss of aroma substances in tobacco leaves", which mainly reduces the loss of volatile oil, resin, and amino acid aroma substances in tobacco leaves by adjusting the forward and reverse rotation time of the circulation fan before 40 °C during the yellowing period and after 57 °C during the stem-drying period.

[0029] Secondly, starting from agricultural machinery and agronomy, the present invention focuses on solving technical problems such as the current tobacco leaf harvesting and baking situation being unable to meet the needs of the new form of development and the deep integration of agricultural machinery and agronomy, prepares for mechanized harvesting and baking, and highlights the purpose of energy conservation and labor saving. The technical means adopted by the present invention is to conduct mature harvesting according to the leaf position based on the maturity of fresh tobacco leaves in the field, preparing for the mechanized harvesting of tobacco leaves; in addition, no classification of fresh tobacco leaves is carried out to save labor, providing an important prerequisite for the future integration of agricultural machinery and agronomy and mechanized operation, which is significantly different from the traditional production method; furthermore, the density of strung (clamped) tobacco and the loading amount of tobacco are scientifically and reasonably quantified, and the fresh tobacco leaves in the curing barn are pre-withered and yellowed before ignition, not only quantifying the pre-withered and yellowed time and target state of tobacco leaves, but also quantifying the rotation speed of the circulation fan at different pre-withered and yellowed stages, and further promoting the full conversion of the internal substances of tobacco leaves through the forward and reverse rotation of the circulation fan, thereby shortening the time for the conversion of tobacco leaf substances during the baking process, saving energy consumption, and all these are different from conventional baking and the disclosed patent documents.

[0030] Thirdly, the present invention solves the problems of large temperature differences between the top and bottom canopies caused by long-term temperature stabilization during the baking process and the phenomenon of tobacco leaves being damaged by rapid temperature increase by slowing down the temperature increase speed during the baking process (about half of the conventional baking temperature increase speed), extending the temperature increase time, and reducing the temperature stabilization time; and matching the corresponding fan rotation speed at each baking stage can not only improve the appearance quality and uniformity of tobacco leaves, avoid red baking, rigid baking, and ash hanging, but also solve the problems of high energy consumption and a large amount of labor.

[0031] Finally, the three-stage baking process adopted by the present invention has corresponding dry and wet bulb temperatures, temperature increase time, temperature stabilization time, corresponding fan rotation speed thresholds, and tobacco leaf change states in each period, fully reflecting the coordination and synchronization of tobacco leaf yellowing, appearance morphological changes, material conversion, and environmental conditions. It not only reduces the temperature and humidity deviation between different layers and within the same layer of the curing barn, but also makes the appearance morphological changes of tobacco leaves during the baking process uniform, reduces the baking loss of tobacco leaves, especially reduces the generation of moldy, rigid, and ash-hanging tobacco leaves to a certain extent. The new air flow alternating tobacco leaf baking method can promote the full withering and softening of harvested and baked tobacco leaves and the uniformity and consistency of tobacco leaf changes during the baking process through creative, systematic, scientific, holistic, and qualitative and quantitative descriptions and operations, thereby improving the uniformity of the quality of baked tobacco leaves. Detailed implementation manners

[0032] 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 implementation manners of the present invention. Many specific details are set forth in the following description to facilitate a full understanding of 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 implementations disclosed below.

[0033] The experiment was conducted in Fuquan City, Guizhou Province in 2022. The flue-cured tobacco variety for the experiment was Yunyan 87, and the tobacco leaves at the 10th leaf position in the middle part were used as the experimental materials. The tested tobacco leaves were cultivated and managed according to the local standardized cultivation of high-quality tobacco leaves, and were harvested at maturity according to the tobacco leaf maturity standard and process. The tested curing barns were a conventional upward-flow heat pump bulk curing barn (control group 1), an internal circulation dehumidifying heat pump airtight bulk curing barn (control group 2), and a modified internal circulation dehumidifying heat pump airtight bulk curing barn (treatment group). Taking the local conventional three-stage baking process as the control and the baking process of the present invention as the comparative treatment, a comparative experiment was carried out.

[0034] 1. The baking process of the present invention

[0035] Reconstruction of the bulk curing barn: Taking the conventional bulk curing barn and the internal circulation dehumidifying heat pump airtight bulk curing barn as the control, the internal circulation dehumidifying heat pump airtight bulk curing barn was reconstructed. The circulation fan in the heating chamber was a two-way axial flow circulation fan. The two-way axial flow circulation fan was required to have high efficiency and low noise, the rated power of the motor was 2.2 kW, and the air volume was above 15000 m 3 / h, which could meet the process requirements of positive and negative alternating ventilation. Hot air inlet or return air outlets with the same size were opened at the top and bottom of the heat insulation wall between the heating chamber and the loading chamber. The length and width dimensions of the return air outlet of the standard bulk curing barn were respectively reconstructed to 2700 mm and 400 mm, and the cold air inlet and the dehumidifying louver were closed; A set of dry and wet bulb temperature sensors were installed on the bottom shed and the ceiling in the loading chamber respectively, and the temperature, humidity, heating-up time, constant-temperature time and the rotation speed of the circulation fan of the upward-flow and downward-flow bulk curing barns were respectively controlled by an automatic control instrument. When the air flow direction in the bulk curing barn was upward, the temperature and humidity sensor on the bottom shed was used as the main sensor of the curing barn for control. When the air flow direction was downward, the temperature and humidity sensor on the ceiling was used as the main sensor of the curing barn for control; The control instrument was equipped with automatic and manual modes. When baking at a constant temperature at the key dry bulb temperature points of 38 °C, 40 °C, 42 °C, 44 °C, 46 °C, 48 - 50 °C, and 54 °C, by controlling the alarm of the control instrument and querying the temperature and humidity difference between the bottom shed and the ceiling, the upward-flow and downward-flow baking modes and related baking parameters were automatically or manually adjusted to further reduce the temperature and humidity deviation between the bottom shed and the ceiling of the curing barn.

[0036] Harvesting of fresh tobacco leaves at maturity: The fresh tobacco leaves were harvested at maturity according to the leaf position of the field maturity of the fresh tobacco leaves, and 2 - 3 leaves were harvested each time.

[0037] Classification and loading of fresh tobacco leaves: The fresh tobacco leaves were not classified, and the amount of fresh tobacco loaded on each pole was about 10 kg. Each curing batch in a three-layer standard bulk curing barn was about 4000 kg of fresh tobacco leaves.

[0038] Pre-wilting and yellowing: After loading fresh tobacco leaves into the curing barn, start pre-wilting and yellowing without lighting a fire or dehumidifying. The pre-wilting and yellowing time is 20h. The circulation fan is turned on for 10 minutes in each direction every 4h. The high-speed rotation of the circulation fan is started from the beginning of pre-wilting and yellowing until 10h. After 10h of pre-wilting and yellowing, the low-speed rotation of the circulation fan is started until the tobacco leaves are slightly wilted and the tips and edges of the leaves turn yellow.

[0039] Yellowing stage: After lighting a fire, start the low-speed rotation of the circulation fan and heat up at a speed of 1℃ / 2h to 32℃ with a wet-bulb temperature of 31℃, and keep the temperature stable for baking for 3h, and the tobacco leaves turn yellow by 10%; heat up at a speed of 1℃ / 2h to 35℃ with a wet-bulb temperature of 34℃, and keep the temperature stable for baking for 3h, and the tobacco leaves turn yellow by 20%; heat up at a speed of 1℃ / 2h to 38℃ with a wet-bulb temperature of 37℃, and keep the temperature stable for baking for 16h, and the bottom and top layer tobacco leaves turn yellow by 70% and the leaves become soft; then, heat up at a speed of 1℃ / 4h to 40℃ with a wet-bulb temperature of 37℃, and keep the temperature stable for baking for 6h, and the bottom and top layer tobacco leaves turn yellow by 80 - 90%, the tobacco leaves in the middle layer turn yellow by 80%, and the leaves become soft; then, start the high-speed rotation of the circulation fan and heat up at a speed of 1℃ / 6h to 42℃ with a wet-bulb temperature of 36℃, and keep the temperature stable for baking for 8h, and the bottom and top layer tobacco leaves have yellow leaves with green veins and the leaf bases are slightly green, and the tobacco leaves in the middle layer turn yellow by 80 - 90% and are fully wilted and soft; among them, the time interval for the alternating operation of the air flow of the two-way axial flow circulation fan is 1h from ignition to 38℃ and 2h from the start of temperature stabilization at 38℃ to the end of temperature stabilization at 42℃;

[0040] S8, Fixing color stage: Keep the high-speed rotation of the circulation fan running, heat up at a speed of 1℃ / 6h to 44℃ with a wet-bulb temperature of 37℃, and keep the temperature stable for baking for 6h to remove the remaining green on the leaves, and the bottom and top layer tobacco leaves hook the tips and curl the edges; then, heat up at a speed of 1℃ / 5h to 46℃ with a wet-bulb temperature of 38℃, and keep the temperature stable for baking for 6h, and the bottom and top layer tobacco leaves are half-dry and small in roll; then, start the low-speed rotation of the circulation fan and heat up at a speed of 1℃ / 5h to 50℃ with a wet-bulb temperature of 38℃, and keep the temperature stable for baking for 6h, and more than 2 / 3 of the bottom and top layer tobacco leaves are dry; then, keep the low-speed rotation of the circulation fan running, heat up at a speed of 1℃ / 4h to 53℃ with a wet-bulb temperature of 39℃, and keep the temperature stable for baking for 8h, and all the tobacco leaves in the whole barn are completely dry and large in roll; among them, the time interval for the alternating operation of the air flow of the two-way axial flow circulation fan is 2.5h;

[0041] S9, Stem-drying stage: Start the high-speed rotation of the circulation fan and heat up at a speed of 1℃ / 2h to 60℃ with a wet-bulb temperature of 39℃, and keep the temperature stable for baking for 5h, and more than 1 / 2 of the main veins of the bottom and top layer tobacco leaves are dry; then, start the low-speed rotation of the circulation fan and heat up at a speed of 1℃ / 2h to 65℃ with a wet-bulb temperature of 39℃, and keep the temperature stable for baking for 20h, and all the tobacco leaves in the whole barn are completely dry; among them, the time interval for the alternating operation of the air flow of the two-way axial flow circulation fan is 1h from 54℃ to 60℃ and 2h from the start of temperature stabilization at 60℃ to the end of baking.

[0042] In this baking process, the two-way axial flow circulation fan adopts variable frequency speed regulation technology. The speed threshold range of the circulation fan during the pre-wilting and yellowing period is 960 - 1450 r / min, among which the low-speed range of the circulation fan is 960 - 1200 r / min, and the high-speed range is 1200 - 1450 r / min; the speed threshold range of the circulation fan during the yellowing period is 960 - 1200 r / min, among which the low-speed range of the circulation fan is 960 - 1080 r / min, and the high-speed range is 1080 - 1200 r / min; the speed threshold range of the circulation fan during the color fixing period is 960 - 1450 r / min, among which the low-speed range of the circulation fan is 960 - 1200 r / min, and the high-speed range is 1200 - 1450 r / min; the speed threshold range of the circulation fan during the stem drying period is 720 - 960 r / min, among which the low-speed range is 720 - 840 r / min, and the high-speed range is 840 - 960 r / min.

[0043] 2. Conventional three-stage baking process

[0044] Carry out baking operations according to the conventional three-stage baking process for flue-cured tobacco varieties (GB / T 23219—2008), and do not transform the conventional bulk curing barn and the closed bulk curing barn with internal circulation dehumidification heat pump.

[0045] Harvest fresh tobacco leaves when ripe: Harvest fresh tobacco leaves when they are ripe according to the maturity degree of fresh tobacco leaves, and harvest 2 - 3 middle leaves each time.

[0046] Classification and loading of fresh tobacco leaves: Classify and string fresh tobacco leaves according to the conventional baking operation, and there is no significant difference in the amount of fresh tobacco leaves strung on each pole and the amount of tobacco loaded in the curing barn compared with the treatment.

[0047] Yellowing period: After loading the tobacco, light a small fire to raise the temperature of the curing barn to 35°C, keep the wet-bulb temperature at 34°C. After the tips of the leaves turn yellow, raise the dry-bulb temperature at a rate of 1°C every 2 hours until it reaches 38°C, and keep the temperature stable for an extended time, controlling the wet-bulb temperature at 36°C, so that about 80% of the tobacco leaves at the thermometer hanging positions in the curing barn reach 70% - 80% yellow, and at the same time the leaves become soft (water loss is about 30%). Then raise the temperature to 42°C, keep the wet-bulb temperature at 37°C, and extend the time to make the tobacco leaves turn yellow with yellow leaves and green veins slightly tinged with green, wilt and collapse, and the main veins become soft.

[0048] Color fixing period: First, raise the dry-bulb temperature at an average rate of 1°C every 3 hours until it reaches 46°C and remains stable. Extend the time to make the tobacco veins turn yellow and the water loss reach the small roll state. Then raise the temperature at a rate of 1°C every 2 hours until it reaches 54°C, and keep the temperature stable for 10 hours to achieve dry leaves. As the dry-bulb temperature rises, the wet-bulb temperature gradually rises and stabilizes at 39°C.

[0049] Drying period: Raise the temperature from 54℃ to 65℃ at a rate of 1℃ per hour and keep it stable until the tobacco leaves are completely dry. Before the dry-bulb temperature reaches 60℃, keep the wet-bulb temperature at 40℃; after 60℃, gradually close the moisture inlet and outlet, reduce the ventilation volume, and keep the wet-bulb temperature at 41℃.

[0050] The tobacco leaves of the baking method of the present invention (treatment group) and the conventional three-stage baking (control group 1 and control group 2) were evaluated and analyzed from the aspects of temperature and humidity deviation in the baking room, baking time, energy consumption and labor, appearance quality of tobacco leaves, main chemical components, aroma substances, sensory quality and economic traits.

[0051] 1. Effects of different treatments on temperature and humidity deviations of the bottom and ceiling of intensive baking rooms

[0052] Table 1 Effects of different treatments on temperature and humidity deviations in the bottom and ceiling of the intensive baking room

[0053]

[0054]

[0055] Note: Control group 1 is a conventional airflow uplift intensive baking room using a three-stage baking process for baking operation; control group 2 is an internal circulation dehumidification heat pump closed intensive baking room using a three-stage baking process for baking operation; different lowercase letters indicate significant differences at the 5% level, 3 biological replicates. Same below

[0056] As shown in Table 1, after stabilizing the temperature for 2 hours at 42°C (late yellowing stage), 54°C (late color fixing stage) and 65°C (late steel drying stage), the temperature and humidity difference between the bottom shed and the top shed of the baking room was recorded every 30 minutes for 3 consecutive times, and the average value was taken. The results show that the temperature deviation and humidity deviation of the baking (treatment group) of the present invention at 42°C (late yellowing stage), 54°C (late color fixing stage) and 65°C (late steel drying stage) during the baking process are better than those of the control group.

[0057] 2. Effects of different treatments on the appearance of different layers of tobacco leaves during the baking process

[0058] Table 2 Effects of different treatments on the appearance of different layers of tobacco leaves during the baking process

[0059]

[0060] 3. Effects of different treatments on baking time and energy consumption

[0061] Table 3 Effects of different treatments on baking time, energy consumption and labor

[0062]

[0063] Note: The electricity cost is 0.50 yuan per degree; the labor cost is 150 yuan per worker, and the working hours are 8 hours per day.

[0064] 4. Effects of Different Treatments on the Appearance Quality of Flue-cured Tobacco Leaves after Baking

[0065] Table 4 Effects of Different Treatments on the Appearance Quality of Flue-cured Tobacco Leaves after Baking

[0066]

[0067] 5. Effects of Different Treatments on the Grade and Economic Characters of Flue-cured Tobacco Leaves after Baking

[0068] Table 5 Effects of Different Treatments on the Grade and Economic Characters of Flue-cured Tobacco Leaves after Baking

[0069]

[0070] 6. Effects of Different Treatments on the Coordination of Chemical Components, the Content of Aroma Substances and the Sensory Quality of Flue-cured Tobacco Leaves after Baking

[0071] Table 6 Effects of Different Treatments on the Inner Quality of Flue-cured Tobacco Leaves after Baking

[0072]

[0073] Note: The sensory quality evaluation is the sum of the scores of 6 items: aroma quality, aroma quantity, taste, off-flavor, irritation, and strength, and each item is 10 points. The ratio of two sugars (the ratio of reducing sugar to total sugar), greater than 0.9 is more coordinated; the ratio of sugar to alkali (the ratio of water-soluble sugar to nicotine), generally considered to be about 10 is better.

[0074] As can be seen from Table 2 to Table 6, compared with Control Group 1 and Control Group 2, in the baking process of the baking method of the present invention (treatment group), the changes in the appearance morphology of different layers of tobacco leaves are more uniform and consistent, the temperature and humidity deviation in the baking room is relatively small, the baking time is shortened, the energy consumption and labor are reduced, the appearance quality and economic characters of the flue-cured tobacco leaves after baking are improved, the chemical components are more coordinated, the aroma-producing substances (especially the degradation products of plastid pigments and the products of browning reaction) are significantly increased, and the sensory evaluation quality is better.

[0075] The above-described embodiments only represent several implementation manners of the present invention, and the description is relatively specific and detailed, but it should not be construed as a limitation to 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 deformations 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. An air-flow alternating tobacco leaf baking method, characterized in that, it includes the following steps: S1, Dense curing barn transformation: The curing barn is an internal circulation dehumidification heat pump closed dense curing barn. The circulation fan in its heating chamber is a two-way axial flow circulation fan. At the top and bottom of the heat insulation wall between the heating chamber and the loading chamber, there are hot air inlets or return air outlets with the same size, and the cold air inlet and the dehumidification louver are closed; S2, Automatic control instrument control: One set of dry and wet bulb temperature sensors is installed on the bottom shed and the top shed in the loading chamber of the curing barn. The temperature, humidity, heating time, constant temperature time and circulation fan speed of the curing barn during the air-flow rising type and the air-flow falling type are respectively controlled by the automatic control instrument; S3, Fresh tobacco leaf mature harvesting: Mature harvesting is carried out according to the maturity of fresh tobacco leaves by leaf position; S4, Fresh tobacco leaves are not classified; S5, Bunching and loading tobacco: The fresh tobacco leaves should not be bunched too densely and the loading amount should be appropriate; S6, Pre-wilting and yellowing: Pre-wilt and yellow the fresh tobacco leaves in the curing barn until the tobacco leaves are slightly wilted and the tips and edges of the leaves turn yellow; S7, Yellowing stage: After ignition, start the circulation fan at low speed, heat up to 31 - 33 °C at a speed of 1 °C / 2 h, with the wet bulb temperature of 30 - 32 °C, keep the temperature constant for baking for 2 - 3 h, and the tobacco leaves turn yellow by 1 - 2 degrees; heat up to 35 - 36 °C at a speed of 1 °C / 2 h, with the wet bulb temperature of 34 - 35 °C, keep the temperature constant for baking for 2 - 3 h, and the tobacco leaves turn yellow by 2 - 3 degrees; heat up to 38 °C at a speed of 1 °C / 2 h, with the wet bulb temperature of 36 - 37 °C, keep the temperature constant for baking for 12 - 18 h, and the tobacco leaves on the bottom shed and the top shed turn yellow by 7 - 8 degrees and the leaves become soft; then, heat up to 40 °C at a speed of 1 °C / 3 - 4 h, with the wet bulb temperature of 36 - 37 °C, keep the temperature constant for baking for 4 - 6 h, and the tobacco leaves on the bottom shed and the top shed turn yellow by 8 - 9 degrees, and the tobacco leaves on the middle shed turn yellow by 7 - 8 degrees and the leaves become soft; After that, start the circulation fan at high speed, heat up to 42 °C at a speed of 1 °C / 4 - 6 h, with the wet bulb temperature of 36 - 37 °C, keep the temperature constant for baking for 6 - 8 h, and the tobacco leaves on the bottom shed and the top shed have yellow leaves with green veins and the leaf bases are slightly green, and the tobacco leaves on the middle shed turn yellow by 8 - 9 degrees and are fully wilted and soft; among them, the time interval of the air-flow alternating operation of the two-way axial flow circulation fan is 1 h from ignition to 38 °C, and 1 - 2 h from the start of the 38 °C constant temperature to the end of the 42 °C constant temperature; S8, Fixing Color Stage: Keep the circulating fan running at high speed, heat up to 44°C at a rate of 1°C every 4 - 6 hours, with a wet-bulb temperature of 37°C, and bake at a stable temperature for 4 - 6 hours to remove the remaining green color of the leaves, and the leaves at the bottom and top tiers of the tobacco leaves are hooked at the tips and curled at the edges; then, heat up to 46°C at a rate of 1°C every 4 - 5 hours, with a wet-bulb temperature of 37 - 38°C, and bake at a stable temperature for 4 - 6 hours, and the leaves at the bottom and top tiers of the tobacco leaves are semi-dry and slightly curled; then, start the circulating fan at low speed, heat up to 48 - 50°C at a rate of 1°C every 4 - 5 hours, with a wet-bulb temperature of 37 - 38°C, and bake at a stable temperature for 4 - 6 hours, and more than 2 / 3 of the leaves at the bottom and top tiers of the tobacco leaves are dry; then, keep the circulating fan running at low speed, heat up to 53 - 54°C at a rate of 1°C every 3 - 4 hours, with a wet-bulb temperature of 38 - 39°C, and bake at a stable temperature for 6 - 10 hours, and all the leaves in the whole barn are completely dry and greatly curled; among them, the time interval between the alternating operation of the air flow of the two-way axial flow circulating fan is 2 - 3 hours; S9, Stem Drying Stage: Start the circulating fan at high speed, heat up to 58 - 60°C at a rate of 1°C every 2 - 3 hours, with a wet-bulb temperature of 38 - 39°C, and bake at a stable temperature for 4 - 6 hours, and more than 1 / 2 of the main veins of the leaves at the bottom and top tiers of the tobacco leaves are dry; then, start the circulating fan at low speed and run, heat up to 65 - 68°C at a rate of 1°C every 2 - 3 hours, with a wet-bulb temperature of 38 - 39°C, and bake at a stable temperature for 15 - 20 hours, and all the tobacco leaves in the whole barn are completely dry; among them, the time interval between the alternating operation of the air flow of the two-way axial flow circulating fan is 1 - 2 hours at 55 - 60°C and 2 - 3 hours from the start of stable temperature at 60°C to the end of baking.

2. The air flow alternating type tobacco leaf baking method according to claim 1, characterized in that, the length and width dimensions of the air return opening of the bulk curing barn are respectively modified to 2700 mm and 400 mm.

3. The air flow alternating type tobacco leaf baking method according to claim 1, characterized in that, The two-way axial flow circulation fan is required to have high efficiency and low noise. The rated power of the motor is 2.2 kW, and the air volume is above 15000 m 3 / h, which can meet the technological requirements of positive and negative alternating ventilation.

4. The air flow alternating type tobacco leaf baking method according to claim 1, characterized in that, When the air flow movement direction in the bulk curing barn is upward, the temperature and humidity sensor at the bottom tier is used as the main sensor for controlling the baking of the barn, and when the air flow movement direction is downward, the temperature and humidity sensor at the top tier is used as the main sensor for controlling the baking of the barn; there are automatic and manual modes on the controller. When baking at a stable temperature at the key dry-bulb temperature points of 38°C, 40°C, 42°C, 44°C, 46°C, 48 - 50°C, and 54°C, the temperature and humidity differences between the bottom and top tiers are queried through the alarm and query device on the controller, and the air flow upward and downward baking modes and related baking parameters are automatically or manually adjusted to further reduce the temperature and humidity deviation between the bottom and top tiers of the barn.

5. The air flow alternating type tobacco leaf baking method according to claim 1, characterized in that, The fresh tobacco leaves are harvested when mature. For the middle and lower leaves, 2 - 3 leaves are harvested each time according to the maturity degree and leaf position, and 4 - 6 fully mature upper leaves are harvested at one time.

6. The air flow alternating type tobacco leaf baking method according to claim 1, characterized in that, The fresh tobacco leaves are not classified.

7. The air flow alternating type tobacco leaf baking method according to claim 1, characterized in that, The fresh tobacco quantity per pole is 10±1 kg. For a 3-layer standard bulk curing barn, it is appropriate to load 3000 - 4000 kg of lower fresh tobacco leaves per batch, and 3500 - 4500 kg of middle and upper fresh tobacco leaves per batch.

8. The air-flow alternating tobacco leaf baking method according to claim 1, characterized in that, after loading the fresh tobacco leaves into the curing barn, start pre-wilting and yellowing, without ignition and dehumidification. The pre-wilting and yellowing time is 15 - 25 h. The circulation fan is turned on in both forward and reverse directions for 5 - 10 min every 3 - 5 h. The high-speed rotation of the circulation fan is started 10 h after the start of pre-wilting and yellowing, and the low-speed rotation of the circulation fan is started 10 h after pre-wilting and yellowing, until the tobacco leaves are slightly wilted and the tips and edges of the leaves turn yellow.

9. The air-flow alternating tobacco leaf baking method according to claim 1, characterized in that, the two-way axial-flow circulation fan adopts variable frequency speed regulation technology. The rotation speed threshold range of the circulation fan during the pre-wilting and yellowing period is 960 - 1450 r / min, of which the low-speed rotation range of the circulation fan is 960 - 1200 r / min, and the high-speed rotation range is 1200 - 1450 r / min; the rotation speed threshold range of the circulation fan during the yellowing period is 960 - 1200 r / min, of which the low-speed rotation range of the circulation fan is 960 - 1080 r / min, and the high-speed rotation range is 1080 - 1200 r / min; the rotation speed threshold range of the circulation fan during the color-fixing period is 960 - 1450 r / min, of which the low-speed rotation range of the circulation fan is 960 - 1200 r / min, and the high-speed rotation range is 1200 - 1450 r / min; the rotation speed threshold range of the circulation fan during the stem-drying period is 720 - 960 r / min, of which the low-speed rotation range is 720 - 840 r / min, and the high-speed rotation range is 840 - 960 r / min.

10. The air-flow alternating tobacco leaf baking method according to claim 1, characterized in that, for the bulk curing barn, based on 3000 kg of lower fresh tobacco leaves and 3500 kg of middle and upper fresh tobacco leaves per batch, when the fresh tobacco loading quantity increases by 10%, the corresponding rotation speed of the circulation fan is increased by 10% from the critical minimum value within the corresponding threshold range, but the maximum rotation speed of the circulation fan does not exceed the threshold range of each baking period.

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