Black tea withering treatment process

Abstract

The invention relates to a black tea withering treatment process. Fresh leaves are selected and naturally withered to reduce the water content, then liquid nitrogen freezing treatment is performed, leaf tissue cell sap is frozen at low temperature, cells are burst to change the permeability of cell membranes, polyphenol compounds in unfrozen cells synchronously and rapidly make contact with polyphenol oxidase, an enzymatic oxidation reaction is generated, and then the tea polyphenol content is reduced; the content of theaflavin is increased. Under normal pressure, the temperature of the liquid nitrogen is-196 DEG C, so that cells can be quickly and completely frozen when the tea leaves are frozen by the liquid nitrogen, the cells are damaged more synchronously and efficiently after unfreezing, the cell damage rate of the leaves is increased, and the enzymatic oxidation reaction of polyphenols is promoted. The content of theaflavin in the black tea obtained by the process is obviously increased, and the tea leaves are improved in the aspects of appearance, aroma, liquor color, taste, leaf bottom quality and the like.

Description

Technical Field

[0001] This invention relates to the field of tea processing technology, specifically a withering process for black tea. Background Technology

[0002] Black tea is made from the tender leaves or buds of the tea plant, a member of the Theaceae family. Black tea is not naturally grown but was made from green tea during the late Ming and early Qing dynasties. It is made from suitable new buds and leaves of tea trees through a series of processes including withering, rolling, fermentation, and drying. The fermentation process causes chemical reactions in the tea leaves, resulting in a unique deep red color when brewed with water. Hence, it is called black tea.

[0003] In existing technologies, using fresh leaves from two tea varieties, Taoyuan Daye and Bixiangzao, as raw materials, this study investigated the effects of two freezing treatments—-20℃ freezer freezing and -196℃ liquid nitrogen freezing—on the cell damage rate of fresh and withered tea leaves, and also explored the effect of freezing on theaflavins content of black tea. The results showed that freezing treatment was beneficial for cell damage in both fresh and withered tea leaves. Liquid nitrogen freezing resulted in a higher cell damage rate than freezer freezing, and freezing withered leaves was more effective than freezing fresh leaves. Freezing withered leaves increased the theaflavins content in black tea, thus improving tea quality. Therefore, applying freezing treatment to the withering process of black tea is beneficial for improving tea quality. Summary of the Invention

[0004] In view of the problems existing in the prior art, the present invention discloses a withering process for black tea, including the following steps: Step 1: Select fresh tea leaves and allow them to wither naturally until the moisture content is 60%-70% to obtain the initial tea leaves; Step 2: Freeze the initially processed tea leaves with liquid nitrogen for 10 minutes to obtain frozen leaves; Step 3: After thawing the frozen leaves, remove the surface moisture and knead for 40 minutes to obtain kneaded leaves; Step 4: Allow the kneaded leaves to ferment naturally at room temperature for 4 hours to obtain fermented leaves; Step 5: Dry the fermented leaves at 120℃ until they are 50% dry, then spread them out for 30 minutes to obtain first-dry leaves; Step 6: Dry the once-dried leaves at 75℃ until fully dry to obtain black tea leaves.

[0005] As a preferred embodiment of the present invention, the fresh tea leaves in step one are selected from fresh leaves with one bud and two leaves.

[0006] The beneficial effects of this invention are as follows: Fresh leaves are naturally withered to reduce their moisture content, and then subjected to liquid nitrogen freezing treatment. The low temperature causes the cell sap in the leaf tissue to freeze, rupturing the cells and altering the cell membrane permeability. After thawing, polyphenolic compounds in the cells come into simultaneous and rapid contact with polyphenol oxidase, resulting in an enzymatic oxidation reaction that reduces the content of tea polyphenols and increases the content of theaflavins. At normal pressure, the temperature of liquid nitrogen is -196℃, therefore, liquid nitrogen freezing treatment of tea leaves can more quickly and completely freeze the cells, and after thawing, it can more synchronously and efficiently damage the cells, increasing the cell damage rate of the leaves and promoting the enzymatic oxidation reaction of polyphenols. The theaflavins content of the black tea obtained through this process is significantly increased, and the tea's appearance, aroma, liquor color, taste, and leaf quality are also improved. Detailed Implementation

[0007] Example 1

[0008] The present invention provides a withering process for black tea, comprising the following steps: Step 1: Select fresh tea leaves with one bud and two leaves, and wither them naturally until the moisture content is 60% to obtain the initial tea leaves; Step 2: Freeze the initially processed tea leaves with liquid nitrogen for 10 minutes to obtain frozen leaves; Step 3: After thawing the frozen leaves, remove the surface moisture and knead for 40 minutes to obtain kneaded leaves; Step 4: Allow the kneaded leaves to ferment naturally at room temperature for 4 hours to obtain fermented leaves; Step 5: Dry the fermented leaves at 120℃ until they are 50% dry, then spread them out for 30 minutes to obtain first-dry leaves; Step 6: Dry the once-dried leaves at 75℃ until fully dry to obtain black tea leaves.

[0009] Example 2

[0010] The present invention provides a withering process for black tea, comprising the following steps: Step 1: Select fresh tea leaves with one bud and two leaves, and wither them naturally until the moisture content is 70% to obtain the initial tea leaves; Step 2: Freeze the initially processed tea leaves with liquid nitrogen for 10 minutes to obtain frozen leaves; Step 3: After thawing the frozen leaves, remove the surface moisture and knead for 40 minutes to obtain kneaded leaves; Step 4: Allow the kneaded leaves to ferment naturally at room temperature for 4 hours to obtain fermented leaves; Step 5: Dry the fermented leaves at 120℃ until they are 50% dry, then spread them out for 30 minutes to obtain first-dry leaves; Step 6: Dry the once-dried leaves at 75℃ until fully dry to obtain black tea leaves.

[0011] Example 3

[0012] The present invention provides a withering process for black tea, comprising the following steps: Step 1: Select fresh tea leaves with one bud and two leaves, and wither them naturally until the moisture content is 64% to obtain the initial tea leaves; Step 2: Freeze the initially processed tea leaves with liquid nitrogen for 10 minutes to obtain frozen leaves; Step 3: After thawing the frozen leaves, remove the surface moisture and knead for 40 minutes to obtain kneaded leaves; Step 4: Allow the kneaded leaves to ferment naturally at room temperature for 4 hours to obtain fermented leaves; Step 5: Dry the fermented leaves at 120℃ until they are 50% dry, then spread them out for 30 minutes to obtain first-dry leaves; Step 6: Dry the once-dried leaves at 75℃ until fully dry to obtain black tea leaves.

[0013] As shown in the table below, a control experiment was set up: A. Traditional process black tea (control) treatment requirements: A) Withering fresh leaves to a moisture content of approximately 64%, kneading for 70 minutes, natural fermentation indoors for 4 hours, initial drying at 120℃ to about 50% dryness, spreading out for 30 minutes, and drying at 75℃ until fully dry; B) Fresh leaf freeze-drying treatment requirements: Place fresh leaves in a -20℃ freezer for 12 hours, remove and thaw to the appropriate level, knead for 40 minutes, and then proceed with the same treatment as in A; C) Withered leaf freeze-drying treatment requirements: After withering fresh leaves to a moisture content of approximately 64%, place them in a -20℃ freezer for 12 hours, remove and thaw to remove surface water, knead for 40 minutes, and then proceed with the same treatment as in A; D) Fresh leaf liquid nitrogen freezing treatment requirements: Place fresh leaves in a stainless steel container, add liquid nitrogen to fully contact the fresh leaves, freeze for 10 minutes, and then proceed with the same treatment as in B; E) This is the process in Example 3 of the present invention. The Effects of Different Freezing Methods on the Sensory Quality of Gongfu Black Tea Table3 Effects of different freezing methods on sensory quality of Congou black tea Note: A. Traditional process (control), B. Fresh leaves frozen in refrigerator, C. Wilted leaves frozen in refrigerator, D. Fresh leaves frozen in liquid nitrogen, E. Wilted leaves frozen in liquid nitrogen, the same below.

[0014] The theaflavin content of black tea processed using the process of this invention is 0.65% ± 0.02%, while the theaflavin content of black tea obtained by the control process is 0.51% ± 0.00%, representing an increase of 27.5%. The black tea processed using the process of this invention has improved in terms of appearance, aroma, liquor color, taste, and leaf quality.

[0015] Components not described in detail in this article are existing technologies.

[0016] While the specific embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and modifications or variations without creative effort are still within the protection scope of the present invention.

Claims

1. A withering process for black tea, characterized in that, The steps include the following: Step 1: Select fresh tea leaves and allow them to wither naturally until the moisture content is 60%-70% to obtain the initial tea leaves; Step 2: Freeze the initially processed tea leaves with liquid nitrogen for 10 minutes to obtain frozen leaves; Step 3: After thawing the frozen leaves, remove the surface moisture and knead for 40 minutes to obtain kneaded leaves; Step 4: Allow the kneaded leaves to ferment naturally at room temperature for 4 hours to obtain fermented leaves; Step 5: Dry the fermented leaves at 120℃ until they are 50% dry, then spread them out for 30 minutes to obtain first-dry leaves; Step 6: Dry the once-dried leaves at 75℃ until fully dry to obtain black tea leaves.

2. The withering process for black tea according to claim 1, characterized in that: The tea leaves mentioned in step one are fresh leaves with one bud and two leaves.

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