Black Tea
What Is Black Tea?
Black Tea is a type of tea that is uniquely produced after acceptable processes, effective oxidation and drying methods by using the leaves, buds and soft branches of Camellia sinensis (Linnaeus) O.Kuntze varieties that are known to be suitable to produce tea that can be consumed as a drink.
The Stages of Black Tea Production
Black tea production consists of: 5 main stages including the withering, curling, oxidation, drying and classification.
What Is Withering?
In this process the warm air is used to vaporize the water of the tea leaf to make it physically ready for the curling process.
The water content of the fresh tea leaves drops from 70-80% to 50-55%.
What are the withering techniques?
The withering can be carried out in two ways; naturally or artificially (forced):
Natural Withering: Tea shoots are withered under natural weather and temperature conditions. During the natural withering process the leaves are placed on the shelves with 10-15 cm intervals (0.5 kg per m2). It provides higher quality values when compared to the forced withering process, although it takes 16-20 hours of time. Low air temperature is the biggest advantage in the natural withering process, in addition to providing plenty of air. The most significant disadvantage of the natural withering is the fact that it completely depends on the weather conditions.
Artificial Withering: The basic purpose of the artificial (forced) withering is to ensure that the tea laves contact with the air with sufficient drying power at suitable temperature to achieve uniform and good withering results.
- Active Withering: In an active system the fresh tea that is going to be provided by the automated fresh tea loading machine to the bunkers is in proportion to the band speed and pouring thickness. These bands are adjusted according to the tea processing conditions to ensure regular feeding with suitable thickness to the withering vessels. The active withering system shall not be stopped during the production other than the compulsory situations.
Temperature used for withering
The temperature of the air that is going to be provided for the withering process may vary depending on:
-The freshness of the fresh tea,
-Wetness,
-Also, depending on the weather and operational conditions, it may vary between the environmental temperature and 38oC.
The ideal artificial withering temperature is 32oC.
The withering process can be shortened by using high temperatures. But quick withering will negatively affect the quality of the black tea.
When tea is excessively withered, the dry tea looks brown while the brew color looks light and greenish.
Withering period : Generally, it is impossible to state a universal withering period to apply. In the natural withering process this takes 16-20 hours and the forced withering process requires a shorter period. In Turkey, the active withering systems are used for a period around 6 hours.
The drying capacity of the air: Increasing the volume and speed of air during the withering process becomes much more efficient than increasing the provided temperature.
Withering technique
The withering can be carried out in two ways; naturally or artificially (forced):
The indicators of a withered leaf
-Floppy, tired and wizened,
-Not lively and bright,
-Stem sections are bendable without breaking.
What is Curling?
This is the process in scope of which the withered tea leaves are crushed, broken into pieces and bent with the help of various tea production machines and the cell juice spreads on the curled leaf surface, with which the oxidation begins.
First Curling (Smooth Curling)
The first curling process is carried out with smooth (leaf) curling machines.
When these curling machines are filled slowly in the long term they can receive at least 300 kg of withered leaves.
A curling machine can be filled and emptied 8 times during a shift and the curling period lasts at least 45 minutes as of the beginning of filling.
After the first curling process the curling machines are slowly emptied.
They are passed through rotorvane in scope of factories with rotorvane; otherwise they are directly passed through fresh tea sieves. But it is recommended to avoid rotorvane usage. Precautions are required to be taken to prevent the need for rotorvane when fresh tea is obtained.
After the tea leaves are aerated at tea sieves, they are sent for second curling process to the press or belly curling machines.
Second Curling
The second curling process is carried out with the help of the press or belly curling machines. Press curling is recommended.
The coarse leaves not broken into pieces during the first curling process are ensured to be broken into pieces under pressure with press or belly curling machines; the cell membrane of the leaves are cracked to leak the cell juice outside and better oxidation conditions are prepared.
The tea emerging from the second curling process (in case of rotorvane, they are passed through rotorvane again) are aerated in scope of the fresh tea sieves and sent to the oxidation unit.
Press Curling
Press curling process takes 40 minutes.
During the press curling process, the press application is performed 3 times at the least during this period.
Press is applied on the tea for 5-6 minutes with 90-135 kg of pressure.
After 5-6 minutes the press is lifted and the machine runs for 5-6 minutes without press. Therefore the heat of the tea that was increased because of the over-friction during the pressure will be reduced.
Belly Curling
Belly curling machine process takes 15 minutes.
Exceeding this period may make the tea too hot and may cause quality loss.
It must be avoided to place too much curled tea in the belly curling machine, and attention should be paid to leave 25 cm space above, in scope of the curling boiler.
What Is Oxidation?
Oxidation is the process in scope of which the chemical compounds within the cell juice of the curled fresh tea leaf are biologically changed with the effect of the oxidase enzyme, after which the black tea gains the desired color, sourness, brightness, smell and aroma.
After the oxidation process the green color of the tea leaf transforms into copper red, and a pleasant aroma that smells like apple is gained.
Oxidation is the stage, during which the quality of the black tea is created or destroyed.
The factors that affect the oxidation process
Time
The oxidation period is not the time passed for oxidation, but the time that passes between the beginning of the curling process and completion of the oxidation. It shall not exceed 3,5 hours.
The oxidation period is reduced or extended whenever required to correct the mistakes that occur during the curling and withering stages and to bring the color and smell properties to the desired levels.
In orthodox system the oxidation period is 23/4 - 31/2 , otherwise (rotorvane, CTC etc.) it takes 1 hour shorter.
Extended oxidation period reduces the brightness and sourness of the brew.
When the oxidation period is extended the tea brew has more color and less property, and when it is shortened it has less color and more property.
Heat
The oxidation temperature can be between 21-32oC depending on the weather conditions.
Ideal oxidation for tea occurs between 24-26oC.
Oxidation is slower below 21oC.
It gradually slows above 32oC.
It stops at 66oC.
The brightness and liveliness of tea liqueur increases during the low temperature oxidation.
The liveliness is reduced when the temperature is increased; it gives a matt and dull color.
More theaflavin is gained with low temperatures. The brightness, liveliness and hardness depends on TF amount.
Thearubigin formation is accelerated when the temperature is increased. This negatively affects the various properties of the black tea.
The disadvantages of high temperature is more than those of the low temperature.
Humidity
The relative humidity is kept around 90-95% during the oxidation.
The humidity rate must be kept high to avoid discoloration.
Laying Thickness and Density
The temperature of the tea leaves increases depending on the laying thickness.
If the leaves become hotter during the oxidation, the thickness shall be reduced.
Too thin tea layers will cause the temperature to be lost and the oxidation will not happen in a suitable way.
The thickness shall allow the air access.
Laying thick reduces the surface area that is exposed to the drying effect of the air.
Thick laying brings better results against the thin layers that are thought to be suitable.
Oxygen Concentration
Oxidation only occurs thanks to the oxygen in the air.
Oxygen is the basis of the oxidation process. Plenty of oxygen is required for TF formation.
If fresh air is not provided, there might be sections towards the bottom sections of the places where the tea leaves are laid, with higher temperature and insufficient level of oxygen. TR formation will accelerate at such sections and consequently various properties of the black tea will be negatively affected.
During the oxidation process the withered tea leaf particles must contact with air (O2) well. Therefore the catechins can turn into theaflavin and thearubigin.
The extreme air causes lower temperatures and accelerates the cooling through vaporization. This causes unwanted results with the oxidation process.
Oxidation Chamber Conditions
Oxidation chamber shall not be directly affected by the sunlight.
Other factors that affect the oxidation process
The bright colored tea leaves can be oxidized better than the darker ones.
The leaves collected from young tea sources can be oxidized in a shorter time.
The difference between the good leaves and coarse leaves in terms of oxidation is actually the result of easy breakability of the cells of the leaves rather than suitability for oxidization. Therefore the coarse leaves need better curling than the thin leaves.
What Is Drying?
The drying is the process of reducing the humidity rate of curled and fermented tea leaves by being furnaced, to 2-4% levels.
The purpose is to stop the enzyme oxidation and to create an environment to prevent the loss of gained properties and formed substances and to make tea suitable for storage, packaging and transportation.
Furnace Settings
Furnaces have two main settings.
First one is the thickness (palette) setting which lays the tea as thin and thick layers.
The second one is the cycle (belt-pulley or variator) setting that defines the period during which the tea will be kept in the furnace.
The duration for removing the tea from the furnaces
For Marshall type furnaces, the oxidized tea leaves put into the furnace are removed from the
furnace according to these durations: 1st belt: 32 min, 2nd belt: 27 minutes, 3rd belt: 21 minutes, 4th belt: 17 minutes, 5th belt: 12 minutes.
The furnaces are generally run during the 1st and 2nd belts.
The factors that affect the drying process
The temperature of the air supplied to the furnace, the flow rate, the thickness of the leaves on the palette, the duration of stay within the furnace are the factors that affect the drying process.
Drying temperatures
The entrance temperature for drying is kept between 90-1000C, while the exit temperature is kept between 45-650C depending on the fume hood shape of the drying furnaces.
What is Sorting?
Sorting is the process of separating the tea by using sieves according to the determined standards in terms of thinness, thickness and quality levels.
They can be sorted well with the 2-4% humidity amount after the tea leaves are furnaced.
The humidity rates of the tea which are waited and not stored well increase; they gain elastic properties and they cannot be sorted well, they become moldy and harmful for health in a short time.
Sorting the tea varieties
The produced tea varieties are generally categorized into 2 classes as main grade tea and broken tea.
The tea leaves that emerge from the drying process towards the sorting, which are eliminated without any breaking process are called the main grade tea varieties.
These are (OF), (BOP) and (OP) tea varieties.
When the tea that remains above 8 and 10 no. Middleton sieves are mechanically broken and re-eliminated, the obtained tea varieties are called the broken tea varieties.
These are (F) and (BP) tea varieties.
The tea below 30 sorting mesh value is called the dust tea (D).
Black Tea is a type of tea that is uniquely produced after acceptable processes, effective oxidation and drying methods by using the leaves, buds and soft branches of Camellia sinensis (Linnaeus) O.Kuntze varieties that are known to be suitable to produce tea that can be consumed as a drink.
The Stages of Black Tea Production
Black tea production consists of: 5 main stages including the withering, curling, oxidation, drying and classification.
What Is Withering?
In this process the warm air is used to vaporize the water of the tea leaf to make it physically ready for the curling process.
The water content of the fresh tea leaves drops from 70-80% to 50-55%.
What are the withering techniques?
The withering can be carried out in two ways; naturally or artificially (forced):
Natural Withering: Tea shoots are withered under natural weather and temperature conditions. During the natural withering process the leaves are placed on the shelves with 10-15 cm intervals (0.5 kg per m2). It provides higher quality values when compared to the forced withering process, although it takes 16-20 hours of time. Low air temperature is the biggest advantage in the natural withering process, in addition to providing plenty of air. The most significant disadvantage of the natural withering is the fact that it completely depends on the weather conditions.
Artificial Withering: The basic purpose of the artificial (forced) withering is to ensure that the tea laves contact with the air with sufficient drying power at suitable temperature to achieve uniform and good withering results.
- Active Withering: In an active system the fresh tea that is going to be provided by the automated fresh tea loading machine to the bunkers is in proportion to the band speed and pouring thickness. These bands are adjusted according to the tea processing conditions to ensure regular feeding with suitable thickness to the withering vessels. The active withering system shall not be stopped during the production other than the compulsory situations.
Temperature used for withering
The temperature of the air that is going to be provided for the withering process may vary depending on:
-The freshness of the fresh tea,
-Wetness,
-Also, depending on the weather and operational conditions, it may vary between the environmental temperature and 38oC.
The ideal artificial withering temperature is 32oC.
The withering process can be shortened by using high temperatures. But quick withering will negatively affect the quality of the black tea.
When tea is excessively withered, the dry tea looks brown while the brew color looks light and greenish.
Withering period : Generally, it is impossible to state a universal withering period to apply. In the natural withering process this takes 16-20 hours and the forced withering process requires a shorter period. In Turkey, the active withering systems are used for a period around 6 hours.
The drying capacity of the air: Increasing the volume and speed of air during the withering process becomes much more efficient than increasing the provided temperature.
Withering technique
The withering can be carried out in two ways; naturally or artificially (forced):
The indicators of a withered leaf
-Floppy, tired and wizened,
-Not lively and bright,
-Stem sections are bendable without breaking.
What is Curling?
This is the process in scope of which the withered tea leaves are crushed, broken into pieces and bent with the help of various tea production machines and the cell juice spreads on the curled leaf surface, with which the oxidation begins.
First Curling (Smooth Curling)
The first curling process is carried out with smooth (leaf) curling machines.
When these curling machines are filled slowly in the long term they can receive at least 300 kg of withered leaves.
A curling machine can be filled and emptied 8 times during a shift and the curling period lasts at least 45 minutes as of the beginning of filling.
After the first curling process the curling machines are slowly emptied.
They are passed through rotorvane in scope of factories with rotorvane; otherwise they are directly passed through fresh tea sieves. But it is recommended to avoid rotorvane usage. Precautions are required to be taken to prevent the need for rotorvane when fresh tea is obtained.
After the tea leaves are aerated at tea sieves, they are sent for second curling process to the press or belly curling machines.
Second Curling
The second curling process is carried out with the help of the press or belly curling machines. Press curling is recommended.
The coarse leaves not broken into pieces during the first curling process are ensured to be broken into pieces under pressure with press or belly curling machines; the cell membrane of the leaves are cracked to leak the cell juice outside and better oxidation conditions are prepared.
The tea emerging from the second curling process (in case of rotorvane, they are passed through rotorvane again) are aerated in scope of the fresh tea sieves and sent to the oxidation unit.
Press Curling
Press curling process takes 40 minutes.
During the press curling process, the press application is performed 3 times at the least during this period.
Press is applied on the tea for 5-6 minutes with 90-135 kg of pressure.
After 5-6 minutes the press is lifted and the machine runs for 5-6 minutes without press. Therefore the heat of the tea that was increased because of the over-friction during the pressure will be reduced.
Belly Curling
Belly curling machine process takes 15 minutes.
Exceeding this period may make the tea too hot and may cause quality loss.
It must be avoided to place too much curled tea in the belly curling machine, and attention should be paid to leave 25 cm space above, in scope of the curling boiler.
What Is Oxidation?
Oxidation is the process in scope of which the chemical compounds within the cell juice of the curled fresh tea leaf are biologically changed with the effect of the oxidase enzyme, after which the black tea gains the desired color, sourness, brightness, smell and aroma.
After the oxidation process the green color of the tea leaf transforms into copper red, and a pleasant aroma that smells like apple is gained.
Oxidation is the stage, during which the quality of the black tea is created or destroyed.
The factors that affect the oxidation process
- Time
- Heat
- Humidity Laying Thickness and Density
- Oxygen Concentration
- Oxidation Chamber Conditions
- Other Factors (leaf type, picking standard, freshness and oldness of the leaf, the growing conditions)
Time
The oxidation period is not the time passed for oxidation, but the time that passes between the beginning of the curling process and completion of the oxidation. It shall not exceed 3,5 hours.
The oxidation period is reduced or extended whenever required to correct the mistakes that occur during the curling and withering stages and to bring the color and smell properties to the desired levels.
In orthodox system the oxidation period is 23/4 - 31/2 , otherwise (rotorvane, CTC etc.) it takes 1 hour shorter.
Extended oxidation period reduces the brightness and sourness of the brew.
When the oxidation period is extended the tea brew has more color and less property, and when it is shortened it has less color and more property.
Heat
The oxidation temperature can be between 21-32oC depending on the weather conditions.
Ideal oxidation for tea occurs between 24-26oC.
Oxidation is slower below 21oC.
It gradually slows above 32oC.
It stops at 66oC.
The brightness and liveliness of tea liqueur increases during the low temperature oxidation.
The liveliness is reduced when the temperature is increased; it gives a matt and dull color.
More theaflavin is gained with low temperatures. The brightness, liveliness and hardness depends on TF amount.
Thearubigin formation is accelerated when the temperature is increased. This negatively affects the various properties of the black tea.
The disadvantages of high temperature is more than those of the low temperature.
Humidity
The relative humidity is kept around 90-95% during the oxidation.
The humidity rate must be kept high to avoid discoloration.
Laying Thickness and Density
The temperature of the tea leaves increases depending on the laying thickness.
If the leaves become hotter during the oxidation, the thickness shall be reduced.
Too thin tea layers will cause the temperature to be lost and the oxidation will not happen in a suitable way.
The thickness shall allow the air access.
Laying thick reduces the surface area that is exposed to the drying effect of the air.
Thick laying brings better results against the thin layers that are thought to be suitable.
Oxygen Concentration
Oxidation only occurs thanks to the oxygen in the air.
Oxygen is the basis of the oxidation process. Plenty of oxygen is required for TF formation.
If fresh air is not provided, there might be sections towards the bottom sections of the places where the tea leaves are laid, with higher temperature and insufficient level of oxygen. TR formation will accelerate at such sections and consequently various properties of the black tea will be negatively affected.
During the oxidation process the withered tea leaf particles must contact with air (O2) well. Therefore the catechins can turn into theaflavin and thearubigin.
The extreme air causes lower temperatures and accelerates the cooling through vaporization. This causes unwanted results with the oxidation process.
Oxidation Chamber Conditions
Oxidation chamber shall not be directly affected by the sunlight.
Other factors that affect the oxidation process
The bright colored tea leaves can be oxidized better than the darker ones.
The leaves collected from young tea sources can be oxidized in a shorter time.
The difference between the good leaves and coarse leaves in terms of oxidation is actually the result of easy breakability of the cells of the leaves rather than suitability for oxidization. Therefore the coarse leaves need better curling than the thin leaves.
What Is Drying?
The drying is the process of reducing the humidity rate of curled and fermented tea leaves by being furnaced, to 2-4% levels.
The purpose is to stop the enzyme oxidation and to create an environment to prevent the loss of gained properties and formed substances and to make tea suitable for storage, packaging and transportation.
Furnace Settings
Furnaces have two main settings.
First one is the thickness (palette) setting which lays the tea as thin and thick layers.
The second one is the cycle (belt-pulley or variator) setting that defines the period during which the tea will be kept in the furnace.
The duration for removing the tea from the furnaces
For Marshall type furnaces, the oxidized tea leaves put into the furnace are removed from the
furnace according to these durations: 1st belt: 32 min, 2nd belt: 27 minutes, 3rd belt: 21 minutes, 4th belt: 17 minutes, 5th belt: 12 minutes.
The furnaces are generally run during the 1st and 2nd belts.
The factors that affect the drying process
The temperature of the air supplied to the furnace, the flow rate, the thickness of the leaves on the palette, the duration of stay within the furnace are the factors that affect the drying process.
Drying temperatures
The entrance temperature for drying is kept between 90-1000C, while the exit temperature is kept between 45-650C depending on the fume hood shape of the drying furnaces.
What is Sorting?
Sorting is the process of separating the tea by using sieves according to the determined standards in terms of thinness, thickness and quality levels.
They can be sorted well with the 2-4% humidity amount after the tea leaves are furnaced.
The humidity rates of the tea which are waited and not stored well increase; they gain elastic properties and they cannot be sorted well, they become moldy and harmful for health in a short time.
Sorting the tea varieties
The produced tea varieties are generally categorized into 2 classes as main grade tea and broken tea.
The tea leaves that emerge from the drying process towards the sorting, which are eliminated without any breaking process are called the main grade tea varieties.
These are (OF), (BOP) and (OP) tea varieties.
When the tea that remains above 8 and 10 no. Middleton sieves are mechanically broken and re-eliminated, the obtained tea varieties are called the broken tea varieties.
These are (F) and (BP) tea varieties.
The tea below 30 sorting mesh value is called the dust tea (D).
