CN117137010A - Method for baking tea leaves by vacuum freeze drying - Google Patents
Method for baking tea leaves by vacuum freeze drying Download PDFInfo
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- CN117137010A CN117137010A CN202310928166.9A CN202310928166A CN117137010A CN 117137010 A CN117137010 A CN 117137010A CN 202310928166 A CN202310928166 A CN 202310928166A CN 117137010 A CN117137010 A CN 117137010A
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- 241001122767 Theaceae Species 0.000 title claims abstract description 176
- 238000000034 method Methods 0.000 title claims abstract description 53
- 238000009777 vacuum freeze-drying Methods 0.000 title claims abstract description 45
- 238000004108 freeze drying Methods 0.000 claims abstract description 101
- 238000010438 heat treatment Methods 0.000 claims abstract description 82
- 238000007710 freezing Methods 0.000 claims abstract description 36
- 230000008014 freezing Effects 0.000 claims abstract description 36
- 229910052751 metal Inorganic materials 0.000 claims abstract description 30
- 239000002184 metal Substances 0.000 claims abstract description 30
- 238000001816 cooling Methods 0.000 claims abstract description 14
- 238000009489 vacuum treatment Methods 0.000 claims abstract description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 42
- 238000004519 manufacturing process Methods 0.000 abstract description 2
- 238000001035 drying Methods 0.000 description 16
- 230000000052 comparative effect Effects 0.000 description 15
- 230000000694 effects Effects 0.000 description 11
- 150000001413 amino acids Chemical class 0.000 description 10
- 230000014759 maintenance of location Effects 0.000 description 10
- 238000005086 pumping Methods 0.000 description 10
- 239000003205 fragrance Substances 0.000 description 9
- 230000005496 eutectics Effects 0.000 description 8
- RYYVLZVUVIJVGH-UHFFFAOYSA-N caffeine Chemical compound CN1C(=O)N(C)C(=O)C2=C1N=CN2C RYYVLZVUVIJVGH-UHFFFAOYSA-N 0.000 description 6
- 238000011031 large-scale manufacturing process Methods 0.000 description 5
- 239000007788 liquid Substances 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- DATAGRPVKZEWHA-YFKPBYRVSA-N N(5)-ethyl-L-glutamine Chemical compound CCNC(=O)CC[C@H]([NH3+])C([O-])=O DATAGRPVKZEWHA-YFKPBYRVSA-N 0.000 description 4
- 239000004480 active ingredient Substances 0.000 description 4
- 239000003610 charcoal Substances 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 4
- 238000001291 vacuum drying Methods 0.000 description 4
- LPHGQDQBBGAPDZ-UHFFFAOYSA-N Isocaffeine Natural products CN1C(=O)N(C)C(=O)C2=C1N(C)C=N2 LPHGQDQBBGAPDZ-UHFFFAOYSA-N 0.000 description 3
- 229960001948 caffeine Drugs 0.000 description 3
- VJEONQKOZGKCAK-UHFFFAOYSA-N caffeine Natural products CN1C(=O)N(C)C(=O)C2=C1C=CN2C VJEONQKOZGKCAK-UHFFFAOYSA-N 0.000 description 3
- 238000007603 infrared drying Methods 0.000 description 3
- 150000008442 polyphenolic compounds Chemical class 0.000 description 3
- 235000013824 polyphenols Nutrition 0.000 description 3
- PFTAWBLQPZVEMU-DZGCQCFKSA-N (+)-catechin Chemical compound C1([C@H]2OC3=CC(O)=CC(O)=C3C[C@@H]2O)=CC=C(O)C(O)=C1 PFTAWBLQPZVEMU-DZGCQCFKSA-N 0.000 description 2
- ADRVNXBAWSRFAJ-UHFFFAOYSA-N catechin Natural products OC1Cc2cc(O)cc(O)c2OC1c3ccc(O)c(O)c3 ADRVNXBAWSRFAJ-UHFFFAOYSA-N 0.000 description 2
- 235000005487 catechin Nutrition 0.000 description 2
- 229950001002 cianidanol Drugs 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 229940026510 theanine Drugs 0.000 description 2
- 239000002023 wood Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 125000003118 aryl group Chemical group 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000000796 flavoring agent Substances 0.000 description 1
- 235000019634 flavors Nutrition 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000000447 pesticide residue Substances 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 230000007480 spreading Effects 0.000 description 1
- 230000001954 sterilising effect Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23F—COFFEE; TEA; THEIR SUBSTITUTES; MANUFACTURE, PREPARATION, OR INFUSION THEREOF
- A23F3/00—Tea; Tea substitutes; Preparations thereof
- A23F3/06—Treating tea before extraction; Preparations produced thereby
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L3/00—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs
- A23L3/40—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by drying or kilning; Subsequent reconstitution
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23L—FOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
- A23L3/00—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs
- A23L3/40—Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by drying or kilning; Subsequent reconstitution
- A23L3/44—Freeze-drying
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23V—INDEXING SCHEME RELATING TO FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES AND LACTIC OR PROPIONIC ACID BACTERIA USED IN FOODSTUFFS OR FOOD PREPARATION
- A23V2002/00—Food compositions, function of food ingredients or processes for food or foodstuffs
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- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Polymers & Plastics (AREA)
- Health & Medical Sciences (AREA)
- Nutrition Science (AREA)
- Drying Of Solid Materials (AREA)
Abstract
The invention relates to the technical field of tea production, in particular to a method for baking tea by vacuum freeze drying. The method comprises the steps of adopting a freeze dryer, wherein the freeze dryer comprises a freeze dryer box, the freeze dryer box is connected with a refrigerator, a vacuum system and a heating system, and the vacuum freeze drying method comprises the following steps: s1, firstly, reducing the temperature of a freeze-drying box to a first temperature, wherein the first temperature is minus or minus ℃, dispersing tea leaves on a metal disc, then, placing the metal disc filled with the tea leaves into the freeze-drying box for pre-freezing for a certain time, and continuously reducing the temperature of the freeze-drying box to a second temperature to freeze the tea leaves for a certain time; s2, cooling the freeze-drying box to a third temperature, enabling the third temperature to be lower than the second temperature, starting a vacuum system, and carrying out vacuum treatment on the freeze-drying box; s3, starting a heating system to heat tea leaves in the freeze-drying box, and baking the tea leaves under the vacuum freezing condition by the method, so that the quality of the tea leaves is improved.
Description
Technical Field
The invention relates to the technical field of tea production, in particular to a method for baking tea by vacuum freeze drying.
Background
The tea leaves need to be baked, the moisture in the tea leaves can be evaporated, the effects of prolonging the shelf life and preventing mildew are achieved, the flavor of the tea leaves can be blended, the foreign odor is eliminated, the fragrance is improved, the taste is fixed, and the effects of reducing pesticide residues and sterilizing can be achieved.
Currently, related tea baking techniques are charcoal baking, electric baking, microwave and far infrared drying. However, these techniques have drawbacks: charcoal baking disadvantages: the control difficulty of the carbon baking mode is high, and the experience and physical requirements on baking staff are high. The requirements on the temperature, time, leaf spreading thickness and turning time of the baking in the processing process are strict, and the quality is easily deteriorated due to uneven heating or stuffy baking. The charcoal baking has higher requirement on wood, high wood consumption and higher material cost. The tea can be obtained after baking for three to four days.
Electric baking disadvantages: lack of far infrared radiation, the tea leaves are thoroughly baked, the technical requirements are extremely high, and the conditions of external dryness and internal humidity or easy turning green are easy to occur. The tea leaves after baking have poorer resistance to soaking.
Microwave and far infrared drying disadvantages: the tea leaves treated in this way at too high a temperature or for a long period of time are bitter and astringent in taste. The water extract content in tea leaves varies greatly with the baking time and is difficult to control. Other tea components are affected by microwaves to vibrate, the temperature is too high or the time is too long, aromatic substances are easy to diffuse and overflow, and tea fragrance is easy to be insufficient.
In addition, the prior art also shows the use of vacuum freeze-drying technology, however, the prior art only uses vacuum freeze technology to dry tea leaves, so that the quality of the tea leaves subjected to vacuum freeze-drying treatment is insufficient.
Disclosure of Invention
The invention aims to avoid the defects in the prior art and provide a method for baking tea leaves by vacuum freeze drying, which can realize the baking of the tea leaves under the vacuum freezing condition and improve the quality of the tea leaves.
In order to achieve the above purpose, the present invention provides the following technical solutions:
there is provided a method of vacuum freeze-drying roasted tea leaves, employing a freeze dryer comprising a freeze dryer tank connected with a refrigerator, a vacuum system and a heating system, the vacuum freeze-drying method comprising the steps of:
s1, firstly, reducing the temperature of a freeze-drying box to a first temperature, wherein the first temperature is minus or minus ℃, dispersing tea leaves on a metal disc, then, placing the metal disc filled with the tea leaves into the freeze-drying box for pre-freezing for a certain time, and continuously reducing the temperature of the freeze-drying box to a second temperature to freeze the tea leaves for a certain time;
s2, cooling the freeze-drying box to a third temperature, enabling the third temperature to be lower than the second temperature, starting a vacuum system, and carrying out vacuum treatment on the freeze-drying box;
s3, starting a heating system to heat tea leaves in the freeze-drying box, wherein the heating step comprises the following steps:
s31, heating for 10-12 hours at the temperature of-15 ℃ to-9 ℃ for the first time until free water in tea leaves is removed;
s32, heating the freeze-drying box to 80-100 ℃ during the second heating, and keeping the heating temperature for 2-3 hours until the bound water in the tea leaves and the water in the freeze-drying box are removed.
In some embodiments, in step S1, the first temperature is-40 to-20 ℃ and the pre-freezing time is 1 to 2 hours.
In some embodiments, in step S1, the second temperature is-50 to-40 ℃ and the freezing time is 3 to 4 hours.
In some embodiments, in step S2, the third temperature is-55 to-50 ℃.
In some embodiments, in step S2, after the vacuum degree of the freeze-drying box reaches the vacuum threshold, the vacuum is continuously pumped for 1-2 hours.
In some embodiments, the vacuum threshold is 13Pa to 26Pa.
In some embodiments, the lyophilization enclosure is a closed container.
In some embodiments, the vacuum system comprises a vacuum channel connected to the lyophilization tank, a valve in communication with the vacuum channel, the valve connected to a vacuum pump.
In some embodiments, the heating system comprises a heating medium that exchanges heat with the lyophilization tank.
In some embodiments, the heating medium is hot water or hot oil.
The method for baking tea leaves by vacuum freeze drying has the beneficial effects that:
(1) According to the method for vacuum freeze-drying and baking tea leaves, disclosed by the invention, the tea leaves are loaded by using the metal tray, the heat capacity of the metal tray is large, the tea leaves can be frozen or heated more quickly, and the treatment time of the tea leaves is shortened.
(2) According to the method for vacuum freeze-drying and baking tea leaves, the freeze-drying box is cooled, then the tea leaves are placed into the freeze-drying box for pre-freezing, freezing treatment is continued, the freezing treatment step always keeps the tea leaves to be dried at a low temperature, the low temperature enables heat-sensitive substances of the tea leaves not to be easily denatured or lose vitality, the possibility of deterioration of the quality of the tea leaves is reduced, the tea leaves further enable the retention amount of active ingredients in the tea leaves to be more, wherein the retention amount of tea-like amino acid directly freeze-dried after fixation is about 23% higher than that of the tea leaves by the traditional drying method, and fragrance of the tea leaves is fragrant, clear, flower fragrance is obvious and taste is mellow.
(3) According to the method for vacuum freeze-drying and baking tea leaves, when the vacuum is pumped, the third temperature is lower than the second temperature, so that the vacuum pumping is carried out at extremely low temperature, on one hand, water vapor sublimated from the tea leaves is frozen and adsorbed on a metal disc, and on the other hand, the extremely low temperature enables air pressure to be discharged more thoroughly, and the drying effect is promoted.
(4) According to the method for vacuum freeze-drying and baking tea leaves, disclosed by the invention, the heating function of the freeze dryer is utilized, and the heating treatment can be continuously carried out after the vacuum drying, so that the operation convenience is improved. Wherein, the temperature of the first heating is lower, and the temperature of the tea leaves is prevented from exceeding the temperature of the eutectic point or the eutectic point, so that the purpose of removing free water in the tea leaves is achieved. And the second heating is performed at a high temperature, so that bound water in the tea and other water in the freeze-drying box are removed, and the effect of baking and drying is realized.
(5) The method for vacuum freeze-drying and baking the tea leaves, disclosed by the invention, has the advantages of small operation difficulty by using a full-automatic vacuum freeze dryer, no need of excessive manual intervention after setting each operation coefficient, and suitability for large-scale production and application.
Detailed Description
Preferred embodiments of the present invention will be described in more detail below. While the preferred embodiments of the present invention have been illustrated, it should be understood that the invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
Example 1
The embodiment discloses a method for obtaining vacuum freeze-drying baked tea, adopts the freeze dryer, the freeze dryer includes the freeze dryer case, the freeze dryer case is connected with refrigerator, vacuum system and heating system, the vacuum freeze-drying method includes following steps:
s1, firstly, reducing the temperature of a freeze-drying box to a first temperature, wherein the first temperature is minus or minus ℃, dispersing tea leaves on a metal disc, then, placing the metal disc filled with the tea leaves into the freeze-drying box for pre-freezing for a certain time, and continuously reducing the temperature of the freeze-drying box to a second temperature to freeze the tea leaves for a certain time;
s2, cooling the freeze-drying box to a third temperature, enabling the third temperature to be lower than the second temperature, starting a vacuum system, and carrying out vacuum treatment on the freeze-drying box;
s3, starting a heating system to heat tea leaves in the freeze-drying box, wherein the heating step comprises the following steps:
s31, heating for 10 hours at the temperature of 15 ℃ below zero for the first time until free water in tea leaves is removed;
s32, heating the freeze-drying box to 80 ℃ for the second time, and keeping the heating temperature for 2 hours until the bound water in the tea leaves and the water in the freeze-drying box are removed.
According to the method for vacuum freeze-drying and baking the tea leaves, the tea leaves are loaded by using the metal tray, the heat capacity of the metal tray is large, the tea leaves can be frozen or heated more quickly, and the treatment time of the tea leaves is shortened. Firstly cooling the freeze-drying box, then putting tea leaves into the freeze-drying box for pre-freezing, and continuing to perform freezing treatment, wherein the freezing treatment step always keeps the tea leaves to be dried at a low temperature, the low temperature ensures that heat-sensitive substances of the tea leaves are not easy to denature or lose vitality, the possibility of deterioration of the quality of the tea leaves is reduced, and the tea leaves further ensure that the retention amount of tea polyphenol and amino acid active ingredients in the tea leaves is more, wherein the retention amount of tea-like amino acid directly freeze-dried after fixation is about 23 percent higher than that of the conventional drying method, so that the aroma of the tea leaves is fragrant, clear and rich in fragrance and taste. When the vacuum pumping device is used for vacuum pumping, the third temperature is lower than the second temperature, so that vacuum pumping is guaranteed at extremely low temperature, on one hand, vapor sublimated from tea is frozen and adsorbed on the metal disc, and on the other hand, the extremely low temperature enables the air pressure to be discharged more thoroughly, and the drying effect is promoted. The freeze dryer has the advantages that the heating function of the freeze dryer is utilized, and the vacuum drying can be carried out for continuous heating treatment, so that the operation convenience is improved. Wherein, the temperature of the first heating is lower, and the temperature of the tea leaves is prevented from exceeding the temperature of the eutectic point or the eutectic point, so that the purpose of removing free water in the tea leaves is achieved. And the second heating is performed at a high temperature, so that bound water in the tea and other water in the freeze-drying box are removed, and the effect of baking and drying is realized. The full-automatic vacuum freeze dryer is used, the operation difficulty is low, excessive manual intervention is not needed after each operation coefficient is set, and the full-automatic vacuum freeze dryer is suitable for large-scale production and application.
In this embodiment, in step S1, the first temperature is-20 ℃, and the pre-freezing time is 1h. The value of the first temperature can be selected according to actual requirements, and is not limited herein.
In this embodiment, in step S1, the second temperature is-40 ℃, and the freezing time is 3 hours. The value of the second temperature can be selected according to the actual requirement, and is not limited herein.
In this embodiment, in step S2, the third temperature is-50 ℃. The value of the third temperature can be selected according to the actual requirement, and is not limited herein.
In this embodiment, in step S2, after the vacuum degree of the freeze-drying box reaches the vacuum threshold, the vacuum is continuously pumped for 1h. The cooling time is convenient to shorten. The vacuum threshold is 13Pa. The value of the vacuum can be selected according to the actual requirements, and is not limited herein.
In this embodiment, the freeze-drying box is a closed container. The freeze-drying box is a closed container, so that vacuumizing and heating are conveniently realized.
In this embodiment, the vacuum system includes a vacuum channel connected to the freeze-drying box, a valve connected to the vacuum channel, and a vacuum pump connected to the valve. The embodiment also comprises various control switches, indication adjusting instruments, automatic devices and the like. The control system is used for controlling the freeze dryer manually or automatically, and operating the machine normally so that the freeze dryer produces the desirable tea leaves.
In this embodiment, the heating system includes a heating medium that exchanges heat with the lyophilization tank.
In this embodiment, the heating medium is hot water or hot oil.
Example 2
The method for vacuum freeze-drying and baking tea leaves disclosed in the embodiment adopts a freeze dryer, wherein the freeze dryer comprises a freeze dryer box, the freeze dryer box is connected with a refrigerator, a vacuum system and a heating system, and the vacuum freeze-drying method comprises the following steps:
s1, firstly, reducing the temperature of a freeze-drying box to a first temperature, wherein the first temperature is minus or minus ℃, dispersing tea leaves on a metal disc, then, placing the metal disc filled with the tea leaves into the freeze-drying box for pre-freezing for a certain time, and continuously reducing the temperature of the freeze-drying box to a second temperature to freeze the tea leaves for a certain time;
s2, cooling the freeze-drying box to a third temperature, enabling the third temperature to be lower than the second temperature, starting a vacuum system, and carrying out vacuum treatment on the freeze-drying box;
s3, starting a heating system to heat tea leaves in the freeze-drying box, wherein the heating step comprises the following steps:
s31, heating for 12 hours at the temperature of-9 ℃ for the first time until free water in tea leaves is removed;
s32, heating the freeze-drying box to 100 ℃ for the second time, and keeping the heating temperature for 3 hours until the bound water in the tea leaves and the water in the freeze-drying box are removed.
According to the method for vacuum freeze-drying and baking the tea leaves, the tea leaves are loaded by using the metal tray, the heat capacity of the metal tray is large, the tea leaves can be frozen or heated more quickly, and the treatment time of the tea leaves is shortened. Firstly cooling the freeze-drying box, then putting tea leaves into the freeze-drying box for pre-freezing, and continuing to perform freezing treatment, wherein the freezing treatment step always keeps the tea leaves to be dried at a low temperature, the low temperature ensures that heat-sensitive substances of the tea leaves are not easy to denature or lose vitality, the possibility of deterioration of the quality of the tea leaves is reduced, and the tea leaves further ensure that the retention amount of tea polyphenol and amino acid active ingredients in the tea leaves is more, wherein the retention amount of tea-like amino acid directly freeze-dried after fixation is about 23 percent higher than that of the conventional drying method, so that the aroma of the tea leaves is fragrant, clear and rich in fragrance and taste. When the vacuum pumping device is used for vacuum pumping, the third temperature is lower than the second temperature, so that vacuum pumping is guaranteed at extremely low temperature, on one hand, vapor sublimated from tea is frozen and adsorbed on the metal disc, and on the other hand, the extremely low temperature enables the air pressure to be discharged more thoroughly, and the drying effect is promoted. The freeze dryer has the advantages that the heating function of the freeze dryer is utilized, and the vacuum drying can be carried out for continuous heating treatment, so that the operation convenience is improved. Wherein, the temperature of the first heating is lower, and the temperature of the tea leaves is prevented from exceeding the temperature of the eutectic point or the eutectic point, so that the purpose of removing free water in the tea leaves is achieved. And the second heating is performed at a high temperature, so that bound water in the tea and other water in the freeze-drying box are removed, and the effect of baking and drying is realized. The full-automatic vacuum freeze dryer is used, the operation difficulty is low, excessive manual intervention is not needed after each operation coefficient is set, and the full-automatic vacuum freeze dryer is suitable for large-scale production and application.
In this embodiment, in step S1, the first temperature is-40 ℃, and the pre-freezing time is 2 hours. The value of the first temperature can be selected according to actual requirements, and is not limited herein.
In this embodiment, in step S1, the second temperature is-50 ℃, and the freezing time is 4 hours. The value of the second temperature can be selected according to the actual requirement, and is not limited herein.
In this embodiment, in step S2, the third temperature is-55 ℃. The value of the third temperature can be selected according to the actual requirement, and is not limited herein.
In this embodiment, in step S2, after the vacuum degree of the freeze-drying box reaches the vacuum threshold, the vacuum is continuously pumped for 2 hours. The cooling time is convenient to shorten. The vacuum threshold is 26Pa. The value of the vacuum can be selected according to the actual requirements, and is not limited herein.
Example 3
The method for vacuum freeze-drying and baking tea leaves disclosed in the embodiment adopts a freeze dryer, wherein the freeze dryer comprises a freeze dryer box, the freeze dryer box is connected with a refrigerator, a vacuum system and a heating system, and the vacuum freeze-drying method comprises the following steps:
s1, firstly, reducing the temperature of a freeze-drying box to a first temperature, wherein the first temperature is minus or minus ℃, dispersing tea leaves on a metal disc, then, placing the metal disc filled with the tea leaves into the freeze-drying box for pre-freezing for a certain time, and continuously reducing the temperature of the freeze-drying box to a second temperature to freeze the tea leaves for a certain time;
s2, cooling the freeze-drying box to a third temperature, enabling the third temperature to be lower than the second temperature, starting a vacuum system, and carrying out vacuum treatment on the freeze-drying box;
s3, starting a heating system to heat tea leaves in the freeze-drying box, wherein the heating step comprises the following steps:
s31, heating at the temperature of-12 ℃ for 11 hours for the first time until free water in tea leaves is removed;
s32, heating the freeze-drying box to 90 ℃ for the second time, and keeping the heating temperature for 2.5 hours until the bound water in the tea leaves and the water in the freeze-drying box are removed.
According to the method for vacuum freeze-drying and baking the tea leaves, the tea leaves are loaded by using the metal tray, the heat capacity of the metal tray is large, the tea leaves can be frozen or heated more quickly, and the treatment time of the tea leaves is shortened. Firstly cooling the freeze-drying box, then putting tea leaves into the freeze-drying box for pre-freezing, and continuing to perform freezing treatment, wherein the freezing treatment step always keeps the tea leaves to be dried at a low temperature, the low temperature ensures that heat-sensitive substances of the tea leaves are not easy to denature or lose vitality, the possibility of deterioration of the quality of the tea leaves is reduced, and the tea leaves further ensure that the retention amount of tea polyphenol and amino acid active ingredients in the tea leaves is more, wherein the retention amount of tea-like amino acid directly freeze-dried after fixation is about 23 percent higher than that of the conventional drying method, so that the aroma of the tea leaves is fragrant, clear and rich in fragrance and taste. When the vacuum pumping device is used for vacuum pumping, the third temperature is lower than the second temperature, so that vacuum pumping is guaranteed at extremely low temperature, on one hand, vapor sublimated from tea is frozen and adsorbed on the metal disc, and on the other hand, the extremely low temperature enables the air pressure to be discharged more thoroughly, and the drying effect is promoted. The freeze dryer has the advantages that the heating function of the freeze dryer is utilized, and the vacuum drying can be carried out for continuous heating treatment, so that the operation convenience is improved. Wherein, the temperature of the first heating is lower, and the temperature of the tea leaves is prevented from exceeding the temperature of the eutectic point or the eutectic point, so that the purpose of removing free water in the tea leaves is achieved. And the second heating is performed at a high temperature, so that bound water in the tea and other water in the freeze-drying box are removed, and the effect of baking and drying is realized. The full-automatic vacuum freeze dryer is used, the operation difficulty is low, excessive manual intervention is not needed after each operation coefficient is set, and the full-automatic vacuum freeze dryer is suitable for large-scale production and application.
In this embodiment, in step S1, the first temperature is-35 ℃, and the pre-freezing time is 1.5h. The value of the first temperature can be selected according to actual requirements, and is not limited herein.
In this embodiment, in step S1, the second temperature is-45 ℃, and the freezing time is 3.5h. The value of the second temperature can be selected according to the actual requirement, and is not limited herein.
In this embodiment, in step S2, the third temperature is-50 ℃. The value of the third temperature can be selected according to the actual requirement, and is not limited herein.
In this embodiment, in step S2, after the vacuum degree of the freeze-drying box reaches the vacuum threshold, the vacuum is continuously pumped for 1.5 hours. The cooling time is convenient to shorten. The vacuum threshold is 20Pa. The value of the vacuum can be selected according to the actual requirements, and is not limited herein.
Example 4
The method for vacuum freeze-drying and baking tea leaves disclosed in the embodiment adopts a freeze dryer, wherein the freeze dryer comprises a freeze dryer box, the freeze dryer box is connected with a refrigerator, a vacuum system and a heating system, and the vacuum freeze-drying method comprises the following steps:
s1, firstly, reducing the temperature of a freeze-drying box to a first temperature, wherein the first temperature is minus or minus ℃, dispersing tea leaves on a metal disc, then, placing the metal disc filled with the tea leaves into the freeze-drying box for pre-freezing for a certain time, and continuously reducing the temperature of the freeze-drying box to a second temperature to freeze the tea leaves for a certain time;
s2, cooling the freeze-drying box to a third temperature, enabling the third temperature to be lower than the second temperature, starting a vacuum system, and carrying out vacuum treatment on the freeze-drying box;
s3, starting a heating system to heat tea leaves in the freeze-drying box, wherein the heating step comprises the following steps:
s31, heating at the temperature of-12 ℃ for 11 hours for the first time until free water in tea leaves is removed;
s32, heating the freeze-drying box to 95 ℃ for the second time, and keeping the heating temperature for 2.7 hours until the bound water in the tea leaves and the water in the freeze-drying box are removed.
In this embodiment, in step S1, the first temperature is-30 ℃, and the pre-freezing time is 1.8h.
In this embodiment, in step S1, the second temperature is-48 ℃, and the freezing time is 3.2h.
In this embodiment, in step S2, the third temperature is-56 ℃.
In this embodiment, in step S2, after the vacuum degree of the freeze-drying box reaches the vacuum threshold, the vacuum is continuously pumped for 1.8 hours.
In this embodiment, the vacuum threshold is 20Pa.
In this embodiment, the freeze-drying box is a closed container.
In this embodiment, the vacuum system includes a vacuum channel connected to the freeze-drying box, a valve connected to the vacuum channel, and a vacuum pump connected to the valve.
In this embodiment, the heating system includes a heating medium that exchanges heat with the lyophilization tank.
In this embodiment, the heating medium is hot water or hot oil.
Example 5
The method for vacuum freeze-drying and baking tea leaves disclosed in the embodiment adopts a freeze dryer, wherein the freeze dryer comprises a freeze dryer box, the freeze dryer box is connected with a refrigerator, a vacuum system and a heating system, and the vacuum freeze-drying method comprises the following steps:
s1, firstly, reducing the temperature of a freeze-drying box to a first temperature, wherein the first temperature is minus or minus ℃, dispersing tea leaves on a metal disc, then, placing the metal disc filled with the tea leaves into the freeze-drying box for pre-freezing for a certain time, and continuously reducing the temperature of the freeze-drying box to a second temperature to freeze the tea leaves for a certain time;
s2, cooling the freeze-drying box to a third temperature, enabling the third temperature to be lower than the second temperature, starting a vacuum system, and carrying out vacuum treatment on the freeze-drying box;
s3, starting a heating system to heat tea leaves in the freeze-drying box, wherein the heating step comprises the following steps:
s31, heating for 11 hours at the temperature of-10 ℃ for the first time until free water in tea leaves is removed;
s32, heating the freeze-drying box to 90 ℃ for the second time, and keeping the heating temperature for 2-3 hours until the bound water in the tea leaves and the water in the freeze-drying box are removed.
In this embodiment, in step S1, the first temperature is-25 ℃, and the pre-freezing time is 1.5h.
In this embodiment, in step S1, the second temperature is-45 ℃, and the freezing time is 3.5h.
In this embodiment, in step S2, the third temperature is-52 ℃.
In this embodiment, in step S2, after the vacuum degree of the freeze-drying box reaches the vacuum threshold, the vacuum is continuously pumped for 1.5 hours.
In this embodiment, the vacuum threshold is 15Pa.
In this embodiment, the freeze-drying box is a closed container.
In this embodiment, the vacuum system includes a vacuum channel connected to the freeze-drying box, a valve connected to the vacuum channel, and a vacuum pump connected to the valve.
In this embodiment, the heating system includes a heating medium that exchanges heat with the lyophilization tank.
In this embodiment, the heating medium is hot water or hot oil.
Performance testing
To verify the effect of the method for vacuum freeze-drying baked tea leaves of the present invention, the following experiment was taken as an example,
example 1:
the method comprises the following steps:
step 1: before drying, 20g of fresh She Shancong tea to be dried was evenly distributed on a suitable metal tray with the evaporation surface as large as possible and the thickness as thin as possible.
Step 2: placing the metal disc filled with the single tea into a groove position which is matched with the size of the freeze-drying box; before being put into a freeze-drying box, the freeze-drying box is firstly cooled to reduce the temperature in the box to minus 30 ℃, then tea leaves are put into the freeze-drying box for prefreezing, and the temperature in the box reaches minus 40 ℃.
Step 3: and (3) reducing the temperature of the condenser to below minus 40 ℃ before vacuumizing, and starting a vacuum pump to perform vacuumizing operation.
Step 4: and (5) continuously vacuumizing for more than 1-2 hours when the vacuum degree reaches 26Pa, so that the tea leaves in the box can be heated.
Step 5: the heating is carried out in two steps: heating to-10deg.C, removing water from tea leaves, heating to 100deg.C, maintaining at 100deg.C for more than 2 hr, and removing water adsorbed in the drying layer to obtain tea leaves.
Comparative example 1The charcoal baking method comprises the following steps: 25g of fresh She Shancong tea was placed on a charcoal-fired container and baked for 80s, thereby producing an electric baking-treated sample.
Comparative example 2Electric baking method: 25g of fresh She Shancong tea was placed in an [ Stoer K35FK602 electric oven ], 1000W, baked at 180℃for 80s, whereby an electric baking-treated sample was prepared.
Comparative example 3Microwave method comprises placing 25g of fresh She Shancong tea into microwave oven (M1-211A/M1-L213B microwave oven)]400W (medium fire grade) microwaves 80s, dried to a sufficient dryness at 80 ℃, thereby preparing a microwave-treated sample.
Comparative example 4Far infrared drying method: a far infrared treated sample was prepared by placing 25g of fresh She Shancong tea in a temperature of 300W,40℃for 48 hours.
Comparative example 5Vacuum freeze drying method: 25g of fresh She Shancong tea was placed on aluminum foil sample paper and placed in a liquid nitrogen tank. After the sample is soaked in liquid nitrogen to be completely vitrified, the sample is transferred to a refrigerator at the temperature of minus 40 ℃ for preservation, and then the sample is put into a vacuum freeze dryer for vacuum freeze drying for 24 hours, so that the vacuum freeze-dried sample is prepared.
TABLE 1
| Treatment of | Catechin (liquid chromatogram peak area) | Theanine (liquid chromatogram peak area) |
| Example 1 | 9010633 | 642122 |
| Comparative example 1 | 7803230 | 522759 |
| Comparative example 2 | 7393117 | 472390 |
| Comparative example 3 | 7314963 | 415324 |
| Comparative example 4 | 7448219 | 449687 |
| Comparative example 5 | 8671140 | 550772 |
| Treatment of | Caffeine (liquid chromatogram peak area) | Free amino acids (mg/mL) |
| Example 1 | 6872909 | 0.0864 |
| Comparative example 1 | 6618625 | 0.0672 |
| Comparative example 2 | 6415929 | 0.0623 |
| Comparative example 3 | 6431870 | 0.0641 |
| Comparative example 4 | 6433242 | 0.0712 |
| Comparative example 5 | 6503500 | 0.0706 |
As can be seen from Table 1, the retention amount of catechin and theanine in the tea sample prepared by the method for vacuum freeze-drying and baking tea leaves is higher than that of the tea sample prepared by the traditional drying method, so that the tea leaves have strong fragrance, clear and high fragrance, and mellow taste, and are suitable for large-scale production and application. In addition, the caffeine and the free amino acid are carried out simultaneously, so that the caffeine and the free amino acid in the tea sample prepared by the method for vacuum freeze-drying and baking the tea leaves disclosed by the invention have higher retention than those in the tea sample prepared by the traditional drying method, and the taste, the color and the quality of the tea sample prepared by the method disclosed by the invention are more advantageous.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method for vacuum freeze drying baked tea leaves, which is characterized in that: the freeze dryer is adopted, the freeze dryer comprises a freeze dryer box, the freeze dryer box is connected with a refrigerator, a vacuum system and a heating system, and the vacuum freeze drying method comprises the following steps:
s1, firstly, reducing the temperature of a freeze-drying box to a first temperature, wherein the first temperature is minus or minus ℃, dispersing tea leaves on a metal disc, then, placing the metal disc filled with the tea leaves into the freeze-drying box for pre-freezing for a certain time, and continuously reducing the temperature of the freeze-drying box to a second temperature to freeze the tea leaves for a certain time;
s2, cooling the freeze-drying box to a third temperature, enabling the third temperature to be lower than the second temperature, starting a vacuum system, and carrying out vacuum treatment on the freeze-drying box;
s3, starting a heating system to heat tea leaves in the freeze-drying box, wherein the heating step comprises the following steps:
s31, heating for 10-12 hours at the temperature of-15 ℃ to-9 ℃ for the first time until free water in tea leaves is removed;
s32, heating the freeze-drying box to 80-100 ℃ during the second heating, and keeping the heating temperature for 2-3 hours until the bound water in the tea leaves and the water in the freeze-drying box are removed.
2. A method of vacuum freeze drying baked tea leaves as claimed in claim 1, wherein: in the step S1, the first temperature is-40 to-20 ℃, and the pre-freezing time is 1-2 h.
3. A method of vacuum freeze drying baked tea leaves as claimed in claim 2, wherein: in the step S1, the second temperature is-50 to-40 ℃, and the freezing time is 3-4 hours.
4. A method of vacuum freeze drying baked tea leaves as claimed in claim 1, wherein: in the step S2, the third temperature is-55 to-50 ℃.
5. A method of vacuum freeze-drying baked tea leaves as claimed in claim 4, wherein: in the step S2, after the vacuum degree of the freeze-drying box reaches a vacuum threshold value, the vacuum is continuously pumped for 1 to 2 hours.
6. A method of vacuum freeze-drying baked tea leaves as claimed in claim 5, wherein: the vacuum threshold is 13 Pa-26 Pa.
7. A method of vacuum freeze drying baked tea leaves as claimed in claim 1, wherein: the freeze-drying box is a closed container.
8. A method of vacuum freeze drying baked tea leaves as claimed in claim 1, wherein: the vacuum system comprises a vacuum channel connected with the freeze-drying box and a valve communicated with the vacuum channel, and the valve is connected with a vacuum pump.
9. A method of vacuum freeze drying baked tea leaves as claimed in claim 1, wherein: the heating system comprises a heating medium which exchanges heat with the freeze-drying box.
10. A method of vacuum freeze drying baked tea leaves as claimed in claim 9, wherein: the heating medium is hot water or hot oil.
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