GB2597585A - A method for processing sweet and mellow black tea - Google Patents

Abstract

A method for processing black tea, comprising the steps: (1) Selecting black tea leaves; (2) Picking leaves; (3) Withering by alternating hot air/red light with cold air/white light; (4) Rocking the green leaves; (5) Secondary withering by alternating red light/hot air with white light/cold air; (6) Ultrasonic crushing; (7) Frequency conversion and short-term cold twisting; (8) Dynamic fermentation at a low temperature and humidity, (9) Initial drying using an electromagnetic roller-hot air coupling drier, (10) Removing broken/yellow leaves using an air separator and cooling; (11) Drying using an electromagnetic chain plate hot air drier at a low temperature; (12) Processing under temperature control, humidity control and far infrared fragrance extraction to obtain sweet and mellow black tea. Preferably the red light is used to wither for 2-2.5 hours at 6000-8000 lux, with hot air at 30-32° C and the white light is used for 1.0-1.5 hours at 3000-5000 lux, the cold air at 22-24℃, the withering steps are repeated with ventilation 2-3 times. Preferably, in step 6, ultrasonic crushing lasts 1.0-1.5 minutes, and the ultrasonic crushing frequency is 40-60KHz.

Description

A Method for Processing Sweet and Mellow Black Tea

Technical Field

The present invention pertains to the technical field of food processing and relates to a tea processing technology, in particular to a method for processing sweet and mellow black tea.

Background Art

Tea, as the second largest beverage in the world after water, is widely favored by consumers because of its good taste and rich phenols, caffeine and amino acids.

The tea can be divided into different tea categories by workmanship, e.g. black tea, green tea, oolong tea, black tea, white tea, yellow tea and so on. The black tea is a tea with maximum consumption in the world, and its yield accounts for more than 60% of the total tea yield.

In China, the black tea is the tea with the second largest production capacity, following the green tea. With recovery of traditional black tea and rapid development of new black tea, the black tea industry develops rapidly, the black tea yield increases rapidly, flavors of the black tea become more and more diversified, and great advances have been made in research on processing technology of black tea products in China. The taste is an important property for evaluating the sensory quality and market value of the black tea and an excellent taste is expressed as sweet and mellow, fresh, sweet and tasty, while a bad taste is expressed as green, astringent, hot, bitter and so on. Unlike the "heavy, strong and fresh" taste standard of the big-leaf the black tea in foreign countries, the taste of the black tea in China is characterized by "sweet, mellow and fresh", e.g. Jiuqu Red Plum, Hunan Black Tea, Ninghong Gongfu Tea, Yihong Gongfu Tea and so on. Production of sweet and mellow taste is significantly pertains to variety of the fresh leaf, quality of the fresh leaf and the processing technology. Quality is based on the fresh leaf with the matching technology as the premise. The traditional black tea is processed by withering, twisting, fermentation, drying and other working procedures, which leads to the strong and astringent taste of the black tea. Generally the black tea is dried, which is easy to cause the taste with stuffy, hot and scorched taste and so on due to poor stability of equipment and improper setting of parameters. In addition, there are still some problems in production of the black tea in China, e.g. different raw materials of fresh leaves, low-level standardization, obsolete processing facilities and so on, which lead to unstable quality and poor taste quality of black tea products in our country, and affect the economic benefits of black tea industry in our country.

At present, few black teas can stably have a taste of "sweet and mellow" on the market, and research on how to obtain high-quality sweet and mellow black tea from the aspects of variety selection, application of new technology, objective evaluation and so on are seldom reported.

Description of the Invention

Purpose: This invention aims to improve the problems in the existing technology, that is, the invention discloses a method for processing sweet and mellow black tea, which meets the concept of consumption and demand of modern tea. Some qualified fresh leaves are selected as raw materials in this invention. By improving the processing technology of the traditional black tea, the new technology is integrated into the black tea process flow. With seamless assembly, integration and improvement of the traditional process and the new technology, a new type of high-quality black tea product with sweet and mellow taste, bright orange-red soup, long-lasting sweet flower fragrance, and high production efficiency, high continuous level and high stability are provided to customers.

The present invention aims to stably obtain excellent sweet and mellow black tea. Based on the qualified fresh leaf as raw materials, by improving and optimizing the traditional process and technology, the high and new technology is integrated into the overall processing flow to improve the inherent flavor and quality stability of black tea, thus providing consumers with a new processing method of high-quality black tea having sweet and mellow taste, bright orange-red soup color and long-lasting sweet flower fragrance.

Technical solution: a method for processing sweet and mellow black tea, which is composed of: (1) The fresh leaves of small and medium-sized tea varieties suitable for black tea as raw materials, wherein: The tea varieties of medium and small leaf species suitable for black tea include Fuding Dabai, Jiukeng, Zhuyeqi and Longjing 43.

(2) The fresh leaves of the above-mentioned small and medium-sized leaf species picked from late March to early May, wherein: The fresh leaves withl bud and 1 leaf -1 bud and 2 leaves or 1 bud and 2 leaves -1 bud and 3 leaves under the initial opening status are selected for proper tenderness; The amino acid content of the fresh leaves is 3.0 -5.0wt%, and the tea polyphenols content is 25wt°/0-30wt%.

(3) The fresh leaves picked in the step (2), which are placed in a continuous withering system and are withered to a leaf moisture content of 68-72%, wherein: The hot air and red light and cold air and white light are used to wither alternately at the ambient temperature of 26-30 °C, the relative humidity of 65-75% and the leaf thickness of 4-8 cm, which fully promotes increase of soluble sugar and amino acid content in leaves.

(4) The withered leaves processed in the step (3) are transferred to a continuous rocking machine for rocking green leaves, which promotes production of substances with sweet flower fragrance and accelerates the enzymatic reaction in the leaves.

(5) The rocked green leaves processed by the step (4) are transferred to a continuous withering system or artificial climate room for secondary withering, and wither to the leaf water content of 60-64%, wherein: The hot air and red light and cold air and white light are used to wither again alternately at the ambient temperature of 26-30 °C and the relative humidity of 60-70%.

(6) The rocked green leaves processed in the step (5) are transferred to ultrasonic crushing equipment for ultrasonic crushing to promote fragmentation of leaf cell membrane and tonoplast and promote the full biochemical reaction between enzymes and substrates in the leaves.

(7) The ultrasonic leaves processed in the step (6) are transferred to the twisting machine with a conveying belt for frequency conversion and cold twisting for a short time, wherein: The frequency conversion and short-time cold rocking is performed at the ambient temperature of 22-25 °C and the relative humidity of 75-85%.

(8) The twisted leaves processed in the step (7) are transferred to a rocking fermenter for dynamic fermentation at low temperature and humidity.

(9) The fermentation leaves processed in the step (8) are transferred to the electromagnetic roller-hot air coupling dryer to carry out primary drying.

(10) The first dried leaves processed in the step (9) are transferred to the spreading and cooling room with a conveying belt, and the broken leaves and yellow leaves are removed by the air separator, wherein: The temperature of the cooling room is controlled at 22-26 °C, the relative humidity is controlled at 55-65%, the leaf thickness is 1-3 cm, and the cooling time is 0.5-1.0 h; (11) The cooling leaves processed in the step (10) are transferred to the electromagnetic chain plate hot air dryer for long-term hot air drying at a low temperature.

(12) The fragrance of the tea samples obtained in the step (11) is extracted by using the far infrared under temperature control, humidity control, and finally sweet and mellow black tea is obtained.

Further, the conditions of the compound withering combination of hot air and red light withering and cold air and white light withering in the step (3) are as follows: The red light is used to wither for 2.0-2.5h at the light intensity of 6000-8000Iux, the hot air temperature of 30-32 °C and the ventilation air volume of 10000-12000m3/h, and then the white light is used to wither for 1.0-1.5h at the cold air temperature of 22-24 °C, the ventilation air volume of 5000-6000m3/h and the light intensity of 3000-5000Iux alternately 2-3 times.

Further, the conditions for rocking green in the step (4) are as follows: The green leaves are rocked for 1.5-2 min at the ambient temperature of 24-28 °C and the relative humidity of 70-800/0 and then are cooled for 3.0.-5.0min on the conveying belt. The above processing steps are repeated alternately 4 times.

Further, the conditions of the compound withering combination of hot air and red light withering and cold air and white light withering in the step (5) are as follows: The red light is used to wither for 2h at the hot air temperature of 30 -32 °C, the hot air volume of 10000-12000m3/h and the light intensity of 6000-8000Iux and then the white light is used to wither for lh at the light intensity of 3000-5000Iux, the cold air temperature of 22 -24 °C and the hot air of 10000-12000m3/h. The above processing steps are repeated alternately 2-3 times.

Furthermore, the ultrasonic processing conditions of the step (6) are as follows: the thickness of the spreading leaf is 6-8 cm, the ultrasonic crushing time is 1.0-1.5 min, and the ultrasonic crushing frequency is 40-60KHz.

Further, the condition of frequency conversion for short-term cold rocking in the step (7) is as follows: first, twist for 25-35min at the frequency of 38-42r/min and a low pressure, and then twist for 15-25min at the frequency of 48-52r/min and a medium pressure until the color of the rolled leaves turns yellow and the rolled twig rate is more than 90%.

Further, the dynamic fermentation conditions of the step (8) are as follows: the temperature is controlled at 24-28°C, the relative humidity is controlled at 75-85%, the rocking speed is 6-8r/min, and the fermentation time is 1.5-2.5h.

Further, the conditions of the initial drying operation in the step (9) are as follows: the roller temperature is 150-160°C, the roller transmission speed is 1000-1100r/min, the roller speed is 20-22r/min, the hot air temperature is 110-120°C, the transmission speed of the hot air fan is 1050-1150 r min, the gross fire time is 2.5-3.0min, and the moisture content of the leaf reaches 20-25%.

Further, the sufficient drying conditions of the step (11) are as follows: the hot air temperature is 90-100 °C, the leaf thickness is 2-4cm, the chain plate drive speed is 400-600 r/min, the hot fan speed is 1000-1100r/min, and the sufficient fire lasts for 20-30min until the leaf moisture content is less than 6%, the leaf is cooled to indoor temperature, is bagged to prevent from light, is cooled, and is stored at a shady and dry place for 15-20 days.

Further, the fragrance extraction conditions of the step (12) are as follows: After the fragrance is extracted for 3-5min at the temperature of 100-110°C and the humidity of 30-400/0, leaves are placed.

Beneficial effect: the method for processing sweet and mellow black tea in the present disclosure is characterized by the following beneficial effects: 1. The hot and cold air is used for alternate withering creatively in the withering process, and the red and white light is added for alternate processing, which promotes activity of polysaccharide hydrolase and proteolytic enzyme in the leaves, then increases the contents of soluble sugars and amino acids in the leaves, and lays a material base for formation of sweet, mellow and refreshing taste.

2. The green leaves are rocked to accelerate transformation of volatile compounds in leaves, promote rapid volatilization of grass-flavored fragrance substances in leaves, and promote the mass production of sweet flower fragrance substances. At the same time, the leaf damage caused by rocking green leaves accelerates enzymatic reaction in the leaves, which contributes to formation of excellent taste and fragrance, and avoids the production of green fragrance and green taste.

3. Ultrasonic crushing processing is creatively added, and frequency conversion short-term low-pressure cold rocking is combined. By crushing cell membrane and tonoplast and setting the twisting frequency from low to high, low-pressure twisting pressure and short-term twisting time, it can ensure that the leaf integrity is maintained, the biochemical reaction between enzymes and substrates in the leaves can also be fully carried out, and production of theaflavins and theaflavins can be accelerated.

4. The new rocking fermentation avoids the uneven fermentation and different degrees caused by the traditional static stacking fermentation, and the stuffy sour taste caused by too high stacking temperature, and the rocking fermentation in low temperature and humidity for a short time promotes uniform fermentation of fermented leaves, improves the high production of theaflavins and theanubins in leaves, and reduces the transformation of theaflavins.

5. The application of new electromagnetic roller-hot air coupling initial drying avoids problems of low and stuffy fragrance and strong stuffy waste taste caused by the slow rise of leaf temperature in traditional hot air initial drying. The combined initial drying of roller and hot air can conduct and convect heat, and promote the rapid loss of leaf moisture and the rapid rise of leaf temperature, which contributes to formation of excellent fragrance and taste. At the same time, short-term operation can improve production efficiency and avoid poor leaf color caused by long-term initial drying. The long-term electromagnetic chain plate hot air sufficient drying operation at low temperature ensures full transformation of flavonoid glycosides, polysaccharides and proteins in the leaves, as well as the mass production of soluble sugars and amino acids. Thus, the black tea has a sweet and fresh taste and sweet and long-lasting fragrance. The far-infrared fragrance extraction under temperature control and humidity control is creatively added to further improve and stabilize the excellent quality of black tea. At the same time, it improves the quality cycle of black tea and stabilize the product quality.

Description of Drawings:

The figure 1 shows a flow chart of a method for processing sweet and mellow black tea in present disclosure.

Embodiments Embodiments of this invention are described in detail below.

Embodiment 1 As shown in the figure 1, a method for processing sweet and mellow black tea includes: (1) The fresh leaves of small and medium-sized tea varieties suitable for black tea are selected as raw materials, wherein: The tea variety of medium and small leaf species suitable for black tea is Fuding Dabai; (2) The fresh leaves of the above-mentioned small and medium-sized leaf species were picked in late March (28 March), wherein: The fresh leaves with 1 bud and 1 leaf -1 bud and 2 leaves under initial opening status are selected for proper tenderness; The amino acid content of the fresh leaves is 3.0wt%, and the content of tea polyphenols is 25wt%.

(3) The fresh leaves picked in the step (2) are placed into a continuous withering system for withering, and the fresh leaves are withered to the leaf water content of 68%, wherein: The hot air and red light and cold air and white light are used to wither alternately at the ambient temperature of 26 °C, the relative humidity of 65%, and the leaf thickness of 4cm, which fully promotes increase of soluble sugar and amino acid content in the leaves. The specific conditions of compound withering combination are as follows: The red light is used to wither for 2.0 h at the hot air temperature of 30 °C, the ventilation air volume of 10000m3/h and the light intensity of 6000Iux, and then the white light is used to wither for 1.0 h at the cold air temperature of 22 °C, ventilation air volume of 5000m3/h, and the light intensity of 3000Iux 2 times alternately.

(4) The withered leaves processed in the step (3) are transferred to a continuous rocking machine for rocking green leaves, which promotes production of substances with sweet flower fragrance and accelerates the enzymatic reaction in the leaves. The specific conditions of rocking green leaves are as follows: rock green leaves for 1.5 minutes at the ambient temperature of 24 °C and the relative humidity of 70%, then spread out and cool rocked green leaves for 3 minutes on the conveying belt, and next rock green leaves and cool them alternately 4 times.

(5) The rocked green leaves processed in the step (4) are transferred to a continuous withering system or artificial climate room for secondary withering, and wither to the leaf water content of 60%, wherein: The hot air red light and cold air white light are used to wither again alternately at the ambient temperature of 26 °C and the relative humidity of 60%. The specific conditions are as follows: the red light is used to wither for 2h at the hot air temperature of 30 °C, the hot air volume of 10000m3/h and the light intensity of 6000Iux, then the white light is used to wither for th at the light intensity of 3000Iux, the cold air temperature of 22 °C and the hot air volume of 10000m3/h, and next repeat the above processing steps 2 times alternately.

(6) The rocked green leaves processed in the step (5) are transferred to ultrasonic crushing equipment for ultrasonic crushing, which promotes fragmentation of leaf cell membrane and tonoplast, and promotes the full biochemical reaction between enzymes and substrates in the leaves. The ultrasonic processing conditions are as follows: The thickness of the spreading leaf is 6 cm, the ultrasonic crushing time is 1 minute, and the ultrasonic crushing frequency is 40KHz.

(7) The ultrasonic leaves processed in the step (6) are transferred to the twisting machine with a conveying belt for frequency conversion and cold twisting for a short time, wherein: The specific conditions of frequency conversion short-term cold twisting are as follows: the temperature is controlled at 25°C and the relative humidity is controlled at 85%; First, the leaves are twisted at the frequency of 38r/min and a low pressure for 25 minutes, then are twisted at the frequency of 48 r/min and a medium pressure for 15 minutes until the leaves turn yellow and the rolled twig rate is more than 90%.

(8) The twisted leaves processed in the step (7) are transferred to a rocking fermenter with a conveying belt to carry out dynamic fermentation at a low temperature and humidity. The specific conditions are as follows: the temperature is controlled at 24 °C, the relative humidity is controlled at 75%, the rocking speed is 6r / min, and the fermentation time is 1.5h.

(9) The fermented leaves processed in the step (8) are transferred to the electromagnetic roller-hot air coupling dryer with a conveying belt to carry out initial drying. The specific conditions are as follows: The roller temperature is 150 °C, the roller transmission speed is 1000r/min, the roller speed is 20r/min, the hot air temperature is 110 °C, the transmission speed of the hot air fan is 1050r/min, the gross fire time is 2.5min, and the water content of the leaf is 25%.

(10) The first dried leaves processed in the step (9) are transferred to the cooling room with a conveying belt, and the broken leaves and yellow leaves are removed by using the air separator, wherein: The temperature of the cooling room is controlled at 22 °C, the relative humidity is controlled at 55%, the thickness of spreading leaves is 1cm, and the cooling time is 0.5h; (11) The cooling leaves processed in the step (10) are transmitted to the electromagnetic chain plate hot air dryer with a conveying belt to carry out sufficient drying. The specific conditions are as follows: the hot air temperature is 90°C, the leaf thickness is 2cm, the chain plate drive speed is 400 rpm min, and the hot air fan speed is 1000 rpm min. The sufficient fire lasts for 20 minutes until the leaf moisture content is less than 6%. The leaves are spread out to the indoor temperature, are bagged to prevent from light, and are stored at a shadowy and dry place for 15 days.

(12) The fragrance of the tea samples obtained in the step (11) is extracted by using the far infrared under temperature control, humidity control and finally sweet and mellow black tea is obtained. The conditions of fragrance extraction are as follows: After the fragrance is extracted for 3min at the temperature of 100°C and the humidity of 35%, leaves are placed.

Embodiment 2 A method for processing sweet and mellow black tea, which is composed of: (1) The fresh leaves of small and medium-sized tea varieties suitable for black tea as raw materials, wherein: The tea variety of medium and small leaf species suitable for black tea is Jiukeng.

(2) The fresh leaves of the above-mentioned small and medium-sized leaf species picked in the first ten days of May, wherein: The fresh leaves withl bud and 2 leaf -1 bud and 3 leaves under initial opening status are selected for proper tenderness; The amino acid content of the fresh leaves is 5.0wt%, and the tea polyphenols content is 30wt%.

(3) The fresh leaves picked in the step (2), which are placed into a continuous withering system for withering till the leaf water content of 72%, wherein: The hot air and red light and cold air and white light are used to wither alternately at the ambient temperature of 30 °C, the relative humidity of 75%, and the leaf thickness of 6 cm, which fully promotes the increase of soluble sugar and amino acid content in the leaves. The conditions of compound withering combination are as follows: The red light is used to wither for 2.5h at the hot air temperature of 32 °C, the ventilation air volume of 12000m3/h, the light intensity of 8000Iux, then the white light is used to wither for 1.5h at the cold air temperature of 24 °C, the ventilation air volume of 6000m3/h and the light intensity of 5000Iux, and the above processing steps are repeated alternatively 3 times.

(4) The withered leaves processed in the step (3) are transferred to a continuous rocking machine for rocking green leaves, which promotes the production of sweet flower fragrance substances and accelerates the enzymatic reaction in the leaves. The specific conditions of rocking green are as follows: rock green leaves for 2 minutes at the ambient temperature of 28 °C and the relative humidity of 800/0, spread out the rocked green leaves for cooling, return to the water for 5.0 minutes on the conveying belt, and rock green and spread and cool alternately 6 times.

(5) The rocked green leaves processed in the step (4) are transferred to a continuous withering system or artificial climate room for secondary withering until the leaf water content of 640/0, wherein: The hot air and red light and cold air and white light are used to wither alternatively at the ambient temperature of 30 °C and the relative humidity of 700/o. The specific conditions of compound withering combination are as follows: the red light is used to wither for 2h at the hot air temperature of 32 °C, the hot air volume of 12000m3/h and the light intensity of 8000Iux, then the white light is used to wither for lh at the cold air temperature of 24 °C, the hot air volume of 12000m3/h and the light intensity of 5000Iux, and the above processing steps are repeated 3 times.

(6) The rocked green leaves processed in the step (5) are transmitted to ultrasonic crushing equipment for ultrasonic crushing, which promotes the fragmentation of leaf cell membrane and tonoplast, and promotes the full biochemical reaction between enzymes and substrates in the leaves. The ultrasonic processing conditions are as follows: the thickness of the spreading leaf is 8cm, the ultrasonic crushing time is 1.5min, and the ultrasonic crushing frequency is 60KHz.

(7) The ultrasonic leaves processed in the step (6) is transferred to the twisting machine with a conveying belt for frequency conversion and cold twisting for a short time, wherein: The specific conditions of frequency conversion short-term cold rocking are as follows: the temperature is controlled at 25 °C and the relative humidity is controlled at 85%; First, it is twisted at 42r/min frequency and low pressure for 35 minutes, then at 52 r/min frequency and medium pressure for 25 minutes until the leaves turn yellow and the rolled twig rate is more than 90%.

(8) The twisted leaves processed in the step (7) are transferred to a rocking fermenter with a conveying belt to carry out dynamic fermentation at low temperature and medium humidity. The specific conditions are as follows: the temperature is controlled at 28 °C, the relative humidity is controlled at 85%, the rocking speed is 8r/ min, and the fermentation time is 2.5h.

(9) The fermented leaves processed in the step (8) are transferred to the electromagnetic roller-hot air coupling dryer with a conveying belt to carry out the initial drying operation. The specific conditions are as follows: the roller temperature is 160 °C, the roller transmission speed is 1100r/min, the roller speed is 22r/min, the hot air temperature is 120 °C, the hot air fan transmission speed is 1150r/min, the gross fire time is 3.0 minutes, and the water content of the leaf is 20%.

(10) The first dried leaves processed in the step (9) are transferred to the cooling room with a conveying belt, and the broken leaves and yellow leaves are removed by the air separator, wherein: The temperature of the spreading and cooling room is controlled at 26°C, the relative humidity is controlled at 65%, the thickness of the leaves is 3cm, and the spreading and cooling time is 1.0h; (11) The spreading cooling leaves processed in the step (10) are transmitted to the electromagnetic chain plate hot air dryer with a conveying belt to carry out foot drying operation. The specific conditions are as follows: the hot air temperature is 100 °C, the leaf thickness is 4cm, the chain plate drive speed is 600r/min, the hot air fan speed is 1100r/min, and the sufficient fire lasts for 30min until the leaf moisture content is less than 6%. Spread leaves out and cool to room temperature, bag them to avoid light, and store them at a shady and dry place for 20 days; (12) The fragrance of the tea samples obtained in the step (11) is extracted by using the far infrared under temperature control, humidity control, and finally sweet and mellow black tea is obtained after. The conditions of fragrance extraction are as follows: the temperature is 110°C and the humidity is 40%. After the fragrance is extracted for 4min, leaves are placed.

Embodiment 3 A method for processing sweet and mellow black tea, which is composed of: (1) The fresh leaves of small and medium-sized tea varieties suitable for black tea as raw materials, wherein: The tea variety of medium and small leaf species suitable for black tea is Longjing 43.

(2) The fresh leaves of the above-mentioned small and medium-sized leaf species picked in the first ten days of April, wherein: The fresh leaves withl 1 bud and 1 leaf -1 bud and 2 leaves under initial opening status are selected for proper tenderness; The amino acid content of the fresh leaves is 4wt%, and the content of tea polyphenols is 27wt%.

(3) The fresh leaves picked in the step (2) are placed into a continuous withering system for withering processing, and the fresh leaves are withered to the leaf water content of 70%, wherein: The hot air and red light and cold air and white light are used to wither alternatively at the ambient temperature of 28 °C, the relative humidity of 70%, and the leaf thickness of 8 cm, which fully promotes the increase of soluble sugar and amino acid content in the leaves. The specific conditions of compound withering combination are as follows: The red light is used to wither for 2.2h at the hot air temperature of 31 °C, the ventilation air volume of 11000m3/h, and the light intensity of 7000Iux, then the white light is used to wither for 1.2h at the cold air temperature of 23 °C, the ventilation air volume of 5500m3/h and the light intensity of 4000Iux, and the above processing steps are repeated alternately 2 times.

(4) The withered leaves processed in the step (3) are transported to a continuous rocking machine for green processing, which promotes the production of sweet flower fragrance substances and accelerates the enzymatic reaction in the leaves. The specific conditions of rocking green are as follows: Rock green leaves for 1.6 minutes at the ambient temperature of 26 °C and the relative humidity of 75%., spread out rocked green leaves to cool and return water for 4 min on the conveying belt, and then rock green, spread and cool alternately for 5 times.

(5) The rocked green leaves processed in the step (4) are transferred to a continuous withering system or artificial climate room for secondary withering and wither to the leaf water content of 62%, wherein: The hot air and red light and cold air and white light are used to wither alternately at the ambient temperature of 28 °C and the relative humidity of 65%. The specific conditions are as follows: carry out red light withering for 2h at the hot air temperature of 31 °C, the hot air volume of 11000m3/h and the light intensity of 7000Iux, then carry out the white light withering for lh 3 times alternately at the cold air temperature of 23 °C, the hot air volume of 11000m3/h and the light intensity of 4000Iux.

(6) The rocked green leaves processed in the step (5) are transferred to ultrasonic crushing equipment for ultrasonic crushing, which promotes the fragmentation of leaf cell membrane and tonoplast, and promotes the full biochemical reaction between enzymes and substrates in the leaves. The specific conditions of ultrasonic processing are as follows: the thickness of spreading leaf is 7cm, the ultrasonic crushing time is 1.2min, and the ultrasonic crushing frequency is 50KHz.

(7) The ultrasonic leaves processed in the step (6) are transferred to the twisting machine with a conveying belt for frequency conversion and cold twisting for a short time, wherein: The specific conditions of frequency conversion short-term cold rocking are as follows: the temperature is controlled at 23 °C and the relative humidity is controlled at 80%; First, it is twisted at 40r/min frequency and low pressure for 30 minutes, and then at the frequency of 50 r/min and medium pressure for 20 minutes until the leaves turn yellow and the rolled twig rate is more than 90%.

(8) The twisted leaves processed in the step (7) are transferred to a rocking fermenter with a conveying belt to carry out dynamic fermentation at low temperature and humidity. The specific conditions are as follows: the temperature is controlled at 26 °C, the relative humidity is controlled at 80°k, the rocking speed is 7r/min, and the fermentation time is 2h.

(9) The fermented leaves processed in the step (8) are transferred to the electromagnetic roller-hot air coupling dryer with a conveying belt to carry out the initial drying operation. The specific conditions are as follows: the roller temperature is 155°C, the roller transmission speed is 1050r/min, the roller speed is 21r/min, the hot air temperature is 115°C, the hot air fan transmission speed is 1100 r/min, the gross fire time is 2.75min, and the water content of the leaf is 23%.

(10) The first dried leaves processed in the step (9) are transferred to the cooling room with a conveying belt, and the broken leaves and yellow leaves are removed by the air separator, wherein: The temperature of the cooling room is controlled at 24 °C, the relative humidity is controlled at 60%, the leaf thickness is 2cm, and the cooling time is 0.7h.

(11) The cooling leaves processed in the step (10) are transmitted to the electromagnetic chain plate hot air dryer with a conveying belt to carry out sufficient drying. The specific conditions are as follows: the hot air temperature is 95°C, the leaf thickness is 3cm, the chain plate drive speed is 500r/min, the hot air fan speed is 1050r/min, and the sufficient fire is 25min until the leaf moisture content is less than 60/0, spread leaves out and cool to room temperature, bag them to avoid light, and store them at a shady and dry for 18 days.

(12) Fragrance of the tea samples obtained in the step (11) is extracted by using the far infrared under temperature control, humidity control, and finally sweet and mellow black tea is obtained. The conditions of fragrance extraction are as follows: the temperature is 105°C and the humidity is 30%. After fragrance is extracted for 5min, the leaves are placed.

Contrast embodiment 4 Taking the tea products made by the traditional process as the contrast sample together with the tea products processed by the above two processes for sensory evaluation, the results are shown in the table 1. It can be seen from the table 1 that the black tea sample made by the whole set of technology has a sweet and fresh taste, bright orange-red soup, obvious and long-lasting fragrance of sweet flowers, which is significantly better than that of the traditional black tea sample.

Table 1 -Results of sensory evaluation of black tea samples processed by different processing techniques.

Processing sample Taste Soup color Fragrance Embodiment 1 Sweet, mellow and fresh Orange, Sweet flower red and fragrance and long-lasting brig ht Embodiment 2 Sweet and mellow with fresh Orange, Sweet flower red and fragrance, strong bright and long-lasting Embodiment 3 Sweet and mellow with freshness Orange, Sweet flower red and fragrance, strong brig ht and long-lasting Traditional black Sweet and mellow Red and Sweet, fragrant and long-lasting tea sample 1 brighter Traditional black Sweet and mellow Red and With a hint of tea sample 2 brig ht sweetness and fragrance Note: 1. Traditional black tea process: Wither: wither in a natural bamboo form inside the workshop under the leaf thickness of 2cm and moisture content of 61% for 15h; Twist: twist in a indoor natural form, carry out "empty twisting for 20min, light twisting for 20min, heavy twisting for 10min, light twisting for 15min, and empty twisting for 5min" with total 70min; Ferment: ferment inside the static stacking fermentation basket under 28°C, cover with wet cloth under the leaf thickness of 10cm for 3.5h; Dry: carry out initial drying with a box-type fragrance extractor under 110°C and leaf thickness of 2cm till moisture content of 23%, dry it again under 95 °C and leaf thickness of 3cm for sufficient drying; 2. Traditional black tea technology 2: Wither, wither at the withering trough inside the workshop under the leaf thickness of 6cm, temperature of 28°C, blow the air for 2h and wither for 12h till the moisture content of 60%; Twisting: carry out indoor natural twisting, twist in the way of "empty twisting for 20min, light twisting for 20min, heavy twisting for 10min, light twisting 15min and empty twisting 5min" with total 70min. Ferment: Ferment inside the static stacking fermentation basket under 28°C, cover with wet cloth under the leaf thickness of 10 cm for 4.0h; Dry: Carry out initial drying inside the box type incense extractor under 110 °C and the leaf thickness of 2cm till moisture content 22%, re-dry under the 95 °C and the leaf thickness for 3cm till sufficient drying. 3. From the results of sensory evaluation, it can be seen that the products processed by the new technology of the invention are better than the traditional process in taste, fragrance and soup color, and the new process can obtain stable and obvious sweet and mellow taste.

Embodiments of the invention are described in detail above. However, the invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by ordinary technicians in the technical field without deviating from the purpose of the invention.

Claims (10)

1. CLAIMS1. A method for preparing sweet and mellow black tea, which is characterized as follows: (1) fresh leaves of small and medium-sized tea varieties suitable for black tea are selected as raw materials, wherein: the tea varieties of medium and small leaf species suitable for black tea include Fuding Dabai, lukeng, Zhuyeqi and Longjing 43; (2) the fresh leaves of the above-mentioned small and medium-sized leaf species are picked from late March to early May, wherein: the fresh leaves with 1 bud and 1 leaf to 1 bud and 2 leaves or 1 bud and 2 leaves to 1 bud and 3 leaves under initial opening status are selected for proper tenderness; the amino acid content of the above fresh leaves is 3.0-5.0wt%, and the tea polyphenols content is 25wt°/0-30wt%; (3) the fresh leaves picked in step (2) are placed into a continuous withering system for withering, and the fresh leaves are withered to a leaf moisture content of about 68 to about 72%, wherein: hot air and red light and cold air and white light are used for withering alternately at the ambient temperature of about 26 to about 30°C, the relative humidity of about 65 to about 75%, and the leaf thickness of about 4 to about 8 cm, which fully promotes growth of soluble sugar and amino acid content in leaves; (4) the withered leaves processed in step (3) are transferred to a continuous rocking machine for rocking green leaves, which promotes production of sweet flower fragrance substances and accelerates enzymatic reaction in the leaves; (5) the rocked green leaves processed in step (4) are transferred to a continuous withering system or artificial climate room for secondary withering, and wither to leaves with a water content of about 60 to about 64%, wherein: the hot air and red light and cold air and white light are used for second withering alternatively at the ambient temperature of about 26 to about 30 °C, the relative humidity of about 60 to about 70%; (6) the rocked green leaves processed in step (5) are transferred to ultrasonic crushing equipment for ultrasonic crushing, which can promote fragmentation of leaf cell membrane and tonoplast and promote full biochemical reaction between enzymes and substrates in the leaves; (7) the ultrasonic leaves processed in step (6) are transferred to a twisting machine by using a conveying belt for frequency conversion and cold twisting for a short time, wherein: the frequency conversion short-time cold twisting is carried out at the ambient temperature of about 22 to about 25°C and the relative humidity of about 75 to about 85%; (8) the twisted leaves processed in step (7) are transferred to a rolling fermenter for dynamic fermentation at a low temperature and humidity.(9) the fermentation leaves processed in step (8) are transferred to an electromagnetic roller-hot air coupling dryer to carry out a roller-hot air coupling primary drying operation; (10) the first dried leaves processed in step (9) are transferred to the cooling room with a conveying belt, which can remove the broken leaves and yellow leaves by using an air separator, wherein: the leaves are spread and cooled for about 0.5 to about 1.0 h at a temperature of about 22 to about 26°C, the relative humidity of about 55 to about 65%, the spreading leave thickness of about 1 to about 3 cm; (11) the spread and cooling leaves processed in step (10) are transferred to an electromagnetic chain plate hot air dryer for long-term hot air drying at a low temperature; (12) the tea samples obtained in step (11) are processed at a controlled temperature and humidity by using far infrared fragrance extraction, and finally sweet and mellow black tea is obtained.
2. 2. A method according to claim 1, characterized by the following compound withering conditions of hot air red and light withering and cold air and white light withering in step (3): the red light is used to wither for about 2.0 to about 2.5 hours at the light intensity of about 6000 to about 8000 lux, the hot air temperature of about 30 to about 32° C and the ventilation air volume of about 10000 to about 12000 m3/h, and then the white light is used to wither for about 1.0 to about 1.5 hours at the light intensity of about 3000 to about 5000 lux, the cold air temperature of about 22 to about 24°C, the ventilation air volume of about 5000 to about 6000 m3/h, and the above processing steps are repeated alternatively about 2 to about 3 times.
3. 3. A method according to claim 1 or claim 2, which is characterized by the following rocking conditions of step (4): the green leaves are rocked for about 1.5 to about 2 min at an ambient temperature of about 24 to about 28°C and a relative humidity of about 70 to about 80%, and the rocked leaves are spread, cooled and returned to water for about 3.0 to about 5.0 min on the conveying belt, and then rocked and cooled alternately for about 4 to about 6 times.
4. 4. A method according to any one of the preceding claims, which is characterized by the following compound withering conditions of hot air and red light withering and cold air and white light withering in step (5): the red light is used to wither for 2 hours at the light intensity of about 6000 to about 8000 lux, a hot air temperature of about 30 to about 32°C, a ventilation air volume of about 10000 to about 12000 m3/h, then the white light is used to wither for lh at a light intensity of about 3000 to about 5000 lux, a cold air temperature of about 22 to about 24°C and a ventilation air volume of about 10000 to about 12000 m3/h, and the above processing steps are repeated alternatively about 2 to about 3 times.
5. 5. A method according to any one of the preceding claims, which is characterized by the following ultrasonic processing conditions of step (6): the thickness of the spreading leaves is about 6 to about 8 cm, ultrasonic crushing lasts for about 1.0 to about 1.5 min, and the ultrasonic crushing frequency is about 40 to about 60KHz.
6. 6. A method according to any one of the preceding claims, which is characterized by the following frequency conversion short-term cold twisting condition in step (7): first twist at the frequency of about 38 to about 42 r/min for about 25 to about 35 min at a low pressure, and then twist at the frequency of about 48 to about 52 r/min for about 15 to about 25 min at a medium pressure until the leaves turn yellow and the rolled twig rate is more than 90%.
7. 7. A method according to any one of the preceding claims, which is characterized by the following dynamic fermentation conditions of step (8): the temperature is controlled at about 24 to about 28°C, the relative humidity is controlled at about 75 to about 85%, the rolling speed is about 6 to about 8 r/min, and the fermentation time is about 1.5 to about 2.5 hours.
8. 8. A method according to any one of the preceding claims, which is characterized by the following initial drying conditions of step (9): the roller temperature is about 150 to about 160°C, the roller transmission speed is about 1000 to about 1100 r/min, the roller speed is about 20 to about 22 r/min, the hot air temperature is about 110 to about 120°C, the transmission speed of the hot air fan is about 1050 to about 1150 r/min, the gross fire time is about 2.5 to about 3.0 mins, and the moisture content of the leaf is about 20 to about 25%.
9. 9. A method according to any one of the preceding claims, which is characterized by the following sufficient drying conditions of step (11): the sufficient fire lasts for about 20 to 30 mins at the hot air temperature of about 90 to about 100°C, the leaf thickness of about 2 to about 4 cm, the chain plate transmission speed of about 400 to about 600 r/min and the hot fan speed of about 1000 to about 1100 r/min rpm until the moisture content of the leaf is less than 6%, the leaves are cooled to room temperature, are bagged to prevent from light, and are stored at cool and dry conditions for 15 days.
10. 10. A method according to any one of the preceding claims, which is characterized by the following fragrance extraction conditions of step (12): after fragrance is extracted for about 3 to about 5 mins at a temperature of about 100 to about 110°C and a humidity of about 30 to about 40%, leaves are placed.