Comprehensive Review of Tea Standards + Laboratory Services of Marjaan Khatam for Black, Green, Flavored and Tea Bag Teas

At the beginning of this article, the status of the tea industry, particularly its production in the world and in Iran, will be examined. Then, the standards and specialized tests related to different types of tea, including black, green, flavored, and tea bags, will be introduced to ensure product quality and safety, guarantee health against microbial and heavy metal contaminants, verify the absence of unauthorized additives, and more. In addition, the services of Marjaan Khatam Laboratory, as the first and most accredited food laboratory in the country in compliance with the national standards of Iran (NACI 17025) and the Food and Drug Administration, as well as the role of this laboratory in conducting precise tests on tea products, will be described.

The tea industry in the world and iran

Tea, with the scientific name Camellia sinensis, has a history of nearly 5,000 years and is one of the most popular beverages in the world, ranking second after water in consumption. The tea industry is among the largest and oldest beverage industries worldwide. The global tea market, with its significant size and growth trend, indicates increasing demand for tea consumption in different parts of the world. China, the original homeland of tea, remains the largest tea producer in the world. Since its emergence in China, tea has spread through trade routes across centuries and has become one of the major agricultural commodities worldwide. Across Asia, Europe, and the Americas, tea is widely consumed in various types such as black and green tea. According to the latest statistics, global tea consumption in 2022 was about 7.6 billion kilograms. The global tea market in 2024 had a value of USD 80.9 billion and is projected to reach USD 134.96 billion by 2032, with a growth rate of 6.6%. In 2024, global tea production increased by 8.6% compared to the previous year, rising from 6.6 million tons to 7.1 million tons. Among producers, China, with 3.7 million tons of tea (53% of global production), maintained its leading position and further strengthened its dominance with a 12% production increase.

The history of tea consumption in Iran dates back to the 15th century, when this beverage entered the country through trade routes between China and India. The root of the word "chai" in Persian, derived from the Chinese word "cha," itself reflects the cultural and commercial exchanges involved in the spread of this drink. Beyond its high consumption, tea is also significant in terms of production and processing. The use of modern tools and methods in agriculture and factories enhances both the quality and yield of tea. Moreover, decisions by relevant authorities regarding pricing, export, and management can significantly affect production and trade. Agricultural products, including tea, have the potential to play a considerable role in the non-oil exports of the country. However, although Iran is among the top 10 tea-producing countries, it has unfortunately failed to secure a competitive position in the global market, holding less than 5% of the market share. Currently, due to inefficient and unprofessional marketing of agricultural products, including tea, a large portion of profits is absorbed by intermediaries and profiteers. This incorrect approach can, both directly and indirectly, undermine the welfare and economic stability of tea farmers and producers.

Common types of tea in the market

After processing, tea is offered either as whole or broken leaves in different forms such as loose dried leaves for brewing or in tea bag. In both cases, common types of tea such as black, green, and flavored are available in the market.

• Black tea

Black tea is made from fresh buds, leaves, and stems of the tea plant. Its production involves conventional steps such as withering, rolling, oxidation (during which phenolic compounds in the leaves react with oxygen, changing the tea’s color and flavor) and drying. Based on production methods, two main types of tea are known as Orthodox and CTC teas, each with its own distinct physical characteristics.

• Orthodox tea is produced using traditional methods, either manually or with rolling machines. Processing includes withering (reducing moisture and softening the leaves), rolling, oxidation, and drying. In this method, tea leaves remain as whole and intact as possible. The final product is then graded according to size, appearance, aroma, taste, etc.
• CTC tea is made by a fully mechanized method using a CTC machine, where tea leaves are crushed and curled into granules.

• Green Tea

Green tea is also prepared from fresh buds, leaves, and stems of the tea plant. However, unlike black tea, it doesn't undergo an oxidation step during processing. After harvesting, the fresh tea leaves are immediately heated or steamed to deactivate the enzymes responsible for oxidation, such as polyphenol oxidases, which prevents the oxidation reaction from occurring. This process preserves the chlorophyll in the leaves, which is why the tea's green color is maintained.

• Flavored tea

Flavored tea is produced by adding natural flavorings such as dried plant pieces, dried fruits, dried blossoms, spices, or similar natural solid or liquid flavorings to dried tea leaves (such as black or green tea).

• Tea bag

Tea bag is made from tea dust or fine broken tea particles obtained during the processing of tea leaves (black or green). The particles must be of a size that does not pass through the filter paper of the bag. Tea bag may also be flavored with dried fruits and blossoms, spices and natural/ natural identical food-grade flavorings.

Common tests in different types of tea (black, green, flavored and tea bag) and the necessity of these tests

Different types of tea (black, green, flavored, and tea bags) have specific characteristics, including physical and sensory attributes of brewed tea, additives, chemical properties, heavy metals, microbiological features, and pesticide residues. To evaluate and control the quality of the aforementioned teas, a specific national standard number has been designated for each (black tea: 623, green tea: 10768, flavored tea: 17226 and tea bag: 3119). These standards provide a basis for conducting common and essential tests to ensure the safety, quality, and conformity of the product with the specified characteristics.

1. Physical characteristics of black, green, flavored and tea bag, teas

Physical tests assess the visual quality of tea leaves, aroma and taste, uniformity, amount of impurities, and more. Evaluating the natural aroma and flavor of tea plays a key role in determining the final quality of the product.

The following table presents the common physical characteristics and standard requirements of black, green and flavored teas according to the Iranian National Standards, while the physical characteristics of tea bag comply with those of black and green teas.

• Explanation of some terms used in the table:

 

Dried tea: a product obtained from fresh tea leaves after undergoing processing and drying.

Even: refers to the approximate similarity in the size of tea leaves of a given variety.

Twisted: refers to dried tea leaves that appear curled or twisted.

Clean tea: a type of tea that does not contain any unwanted parts or foreign substances.

Granular: a type of tea in which the particles are spherical or bead-shaped.

Fluff: refers to the tiny fibers found on the back of tender tea leaves, which must be removed.

Stalks: refers to the lignified woody veins of tea leaves, which are considered waste and must be removed.

Flaky: broad, thick, open and light-colored leaves in tea, considered undesirable material.

Unusual stems: light-colored stems introduced into tea due to improper harvesting, which usually cannot be separated by sorting machines.

By weight percentage: refers to the measurement of a certain component (e.g., impurities or unwanted parts) relative to the total weight of the product.

Foreign materials: any material other than tea, such as sand, soil, dust, or similar impurities.

Moldy: tea contamination caused by improper storage, resulting in an unpleasant odor and undesirable taste.

Pest: any living organism, such as insects, mites, or fungi, that damages tea during any stage of growth and reduces product quality and quantity.

Pest infestation: visible signs or injuries caused by pests on tea leaves, observable with the naked eye.

2. Sensory characteristics of black, flavored, green and tea bag, teas

Tea drink is a beverage prepared by infusing tea according to standard methods, and it is used for evaluating the sensory attributes of the product. Sensory tests of brewed tea include examining its color, aroma, taste, flavor, and other sensory qualities. The purpose of these tests is to ensure the desired quality of the product, compliance with relevant standards, consumer satisfaction, and more.

The following table presents the sensory characteristics of black, green and flavored tea drinks according to the requirements of Iranian National Standards and the sensory characteristics of tea bag drink correspond to those of black and green teas.

• Explanation of some terms used in the table:

Copper color of infused leaf: shiny and copper-colored infused leaf, indicating very good quality tea.

Roast: describes a tea drink with a scent similar to that of biscuits.

Grassy: describes a tea drink aroma that is similar to the smell of grass.

Sour (drink taste): refers to an undesirable sour taste and acidic odor in the tea drink.

Musty (drink taste): describes tea with a taste and smell suggestive of moldiness.

Smoky: refers to a tea drink with a smoky taste and aroma, caused by defects in the drying equipment during tea processing, which transfers this characteristic to the brewed tea.

Strength: a tea drink with a rich, dark taste and aroma that is strong and long-lasting.

Astringent: tea drink with astringent taste that causes the mouth to feel slightly dry and puckered.

Brisk: Describes tea drink with a sharp, lingering, and slightly astringent taste, in contrast to mild tea beverages.

Stale: A condition where part or all of the tea’s aroma and taste has diminished due to prolonged storage or storage in a humid environment, which affects the tea drink.

Burnt: Occurs when tea is dried at excessively high temperatures, a characteristic that transfers to the tea drink.

Musty: A condition caused by poor transport and storage of fresh tea leaves before processing, reducing the quality of aroma and taste, which then transfers to the tea drink.

Taint: A condition where foreign substances cause a change in the true aroma and flavor of the tea, and this characteristic is transferred to the tea drink.

3. Characteristics of additives in black, flavoredand tea bag:

Testing for natural and artificial additives, including colors, flavorings, and sweeteners, is essential for ensuring the safety and quality of tea. These tests help confirm that any additives used are permitted and within safe levels, thereby preventing potential health risks. For black tea, the use of any additives, whether natural or artificial, including colors, flavorings, or sweeteners, is prohibited at all stages of production and packaging. In flavored tea, the addition of any colorants, sweeteners (natural or artificial), or artificial flavorings is prohibited. However, natural or nature-identical flavorings, in the form of solids, liquids, or dried plant parts such as fruits, blossoms, and spices, may be used as long as they do not alter the chemical properties of the tea. 

The addition of any essential oils or natural flavorings to tea bag must comply with the Iranian National Standard No. 10242. The use of any artificial flavorings or colorants is strictly prohibited.

4. Chemical characteristics of black, green, flavored and tea bag:

Chemical tests assess tea quality by examining properties such as moisture content, total ash, water extract and more, including:

• Moisture

Determining the moisture content of tea leaves is crucial, as it directly affects product quality and shelf life. Balanced moisture provides optimal conditions for processing fresh tea leaves through steps like withering and rolling, without causing mold or leaf brittleness. In addition, balanced moisture activates the natural chemical compounds (such as aromatic compounds) present in the tea leaves that are responsible for the tea's aroma and fragrance. This allows the pleasant scent of the tea to be released during the withering and oxidation stages. Furthermore, balanced moisture provides the proper conditions for the oxidation of polyphenols, creating the desired flavor and... of the tea.

• Total ash

Tea ash is the residue obtained after burning tea at a temperature of approximately 550°C. Its main composition is minerals, most of which are considered nutrients. The amount of total ash normally varies between 4% and 7.5% and at least half of it must be soluble in water. This chemical indicator is a primary standard for evaluating tea types, as it reflects the total mineral content and presence of impurities. Excessive ash may indicate foreign materials such as soil or sand.

• Water-soluble ash

The portion of total ash that dissolves in water.

• Acid-insoluble ash

The portion of total ash insoluble in acid.

• Alkalinity of watersoluble ash (as KOH)

Measures alkaline compounds remaining in the ash after dissolution in water, typically assessed using potassium hydroxide (KOH).

• Water extract

A test to assess tea quality (including taste intensity, color, and aroma) by measuring soluble solids extracted from leaves in hot water. Younger leaves have higher water extract, indicating superior quality.

• Crude fiber

The crude fiber test in tea is a key indicator of quality, measuring indigestible substances like cellulose, lignin, and hemicellulose. Young tea leaves are lower in fiber, indicating freshness and higher quality. Conversely, a high crude fiber content typically points to the presence of older leaves or stems in the tea blend, which can negatively affect its taste and aroma. Therefore, measuring crude fiber is an effective way to detect tea adulteration and determine its true quality, as a high fiber content indicates the use of older leaves and lower-quality raw materials. Furthermore, older leaves generally contain fewer beneficial compounds and antioxidants, such as polyphenols and catechins. Thus, a higher crude fiber content correlates with a lower nutritional value and fewer potential health benefits.

• Caffeine

Measuring caffeine content is important as it influences tea quality. Caffeine interacts with catechins and other phenolic compounds to create a stable structure, providing a pleasant and balanced taste while moderating bitterness and astringency. It also stimulates the nervous system, temporarily reducing drowsiness and improving alertness and focus.

• Total polyphenols

Polyphenols are key secondary metabolites, including flavanols, flavonols, and phenolic acids. Unlike primary metabolites (carbohydrates, proteins, and fats) essential for growth, secondary metabolites are produced in response to environmental stressors (e.g., sunlight, drought, nutrient deficiency, pest attack) and provide protective functions. In tea, polyphenols contribute to bitterness and astringency, shaping the sensory characteristics of the infusion. Over three-quarters of polyphenols in tea leaves are catechins, a type of flavanol responsible for the bitter and astringent taste, especially in green tea. Measuring polyphenols also helps evaluate antioxidant properties and potential health benefits, including cardiovascular protection and inhibition of cancer cell growth.

The table below presents the chemical characteristics of black, green, and tea bag teas according to Iranian national standards. The chemical characteristics of flavored tea correspond to those of black and green teas.

5. Characteristics of heavy metals in black, green, flavored and tea bag teas

Heavy metals such as arsenic (As), copper (Cu), mercury (Hg), lead (Pb), and cadmium (Cd) are among the most significant contaminants in tea. The main sources of these contaminants include soil, fertilizers, nutrients, pesticides used during cultivation, and other factors. Tea plant contamination with these metals can occur at various stages of growth in the field or during industrial processing and packaging in factories.

The tea plant can absorb these elements from its surrounding environment and store them in different parts of the plant. Initially, these elements are absorbed by the roots, where their concentration is highest, and then they are translocated to the stems. The accumulation of metals in the leaves also depends on leaf age; older leaves accumulate more metals than younger leaves because they have been exposed to metals for a longer period. Additionally, soil pH plays a crucial role in the plant's uptake of these elements. For example, in acidic soils, metals such as cadmium and lead become more soluble, making their absorption by the plant easier and higher.

Tea plantations in provinces such as Gilan, particularly those located along busy roads with heavy traffic during tourist seasons, are exposed to heavy metal accumulation due to traffic-related pollution. Metals such as lead, cadmium, copper, and zinc can transfer to fresh tea leaves, affecting the quality of agricultural products. Therefore, the presence of tea plantations near high-traffic roads in provinces like Gilan is considered a significant factor in increasing the concentration of heavy metals in fresh tea leaves. These metals can also be transferred to the tea infusion and enter the human body.

The transfer of heavy metals in food chains occurs due to characteristics such as stability, non-degradability and .... Heavy metals can cause serious health issues, including cancer, kidney failure, liver damage, cardiovascular diseases, neurological disorders, and more.

The table below presents the characteristics of metallic contaminants in black, green, and flavored teas according to the requirements of Iranian national standards.

6. Microbial characteristics of black, green, flavored and tea bag teas

The microbial characteristics of tea vary depending on the type of tea and its processing methods. Microbial contamination of tea can occur at different stages of processing, with one of the main sources being the microorganisms present on the surface of tea leaves. However, the drying process of tea leaves (such as moisture reduction and related steps) during processing can reduce contamination. Nevertheless, if post-harvest stages such as grading, packaging, and storage are not carried out properly, tea may still become microbially contaminated. Using hot water to prepare tea infusion can reduce microbial risks. However, using water at temperatures below boiling may not eliminate all pathogens, including bacterial spores (the resistant form).

Microbiological tests of tea, which are used to identify potential contamination by bacteria, molds, and other microorganisms, are essential for ensuring its safety and quality. The presence of microorganisms, besides posing a health risk to consumers, can alter the taste, aroma, color, and other characteristics of tea. For example, bacteria such as Escherichia coli (E. coli) can contaminate tea, reducing sensory quality, increasing the likelihood of spoilage, altering product characteristics, and shortening shelf life.

By analyzing tea for microbial contamination, tea producers and sellers can ensure that their products are safe, hygienic, and compliant with relevant standards.

The microbiological characteristics of black, green, flavored, and tea bag teas must comply with Iranian National Standard No. 17070. The microbial characteristics of different types of tea are presented in the table below:

7. Characteristics of pesticide residues in black, green and flavored teas

Pesticide residues are small amounts of chemical compounds that remain on or within agricultural products after pesticide application. Tea, due to frequent harvesting (continuous production of young leaves), growth in warm and humid regions, and the lack of natural protective layers on its leaves, is highly exposed to pests, which leads to the extensive use of pesticides. Unlike plants with protective waxy layers or thick skins, tea leaves lack a similar defense. This allows certain pesticides to easily penetrate the leaf tissue. These types of pesticides are not easily removed by washing and can negatively impact the final quality of the tea, altering its natural flavor and aroma or creating unpleasant tastes.

Furthermore, pesticide residues can be harmful to consumers and pose health risks, including hormonal disorders, fertility issues, cancer, and more. Ensuring that tea products comply with the maximum residue limits (MRLs) helps protect consumers from potential hazards associated with pesticide exposure. Therefore, in food laboratories, the analysis of pesticide residues, including their identification and precise quantification, is performed. Accurate measurement and detection of pesticide residues in tea are of particular importance and are carefully examined in food testing laboratories.

For reference and evaluation of the Maximum Residue Limits (MRLs) of pesticides in different types of tea, please refer to Iranian National Standard No. 13118.

Iranian National Standard No. 13118

8. Characteristics of mycotoxins in flavored tea

Mycotoxins, or fungal toxins, are stable chemical compounds produced by certain fungi (molds) such as Aspergillus spp.Various factors, including improper agricultural practices, unprincipled processing and drying, as well as unsuitable packaging and storage conditions, can facilitate mold growth in tea leaves and increase the risk of mycotoxin contamination. Moreover, the warm and humid climate favorable for tea cultivation also provides ideal conditions for the growth of mycotoxin-producing fungi, ultimately raising the likelihood of tea leaf contamination.

Assessment of mycotoxins in tea is highly important, as consuming contaminated tea can pose serious health risks. Aflatoxins are among the most significant mycotoxins found in flavored tea and are mainly produced by Aspergillus flavus and A. parasiticus. Among them, aflatoxin B1 exhibits the highest level of contamination and the greatest toxicity. Aflatoxins have been classified by the International Agency for Research on Cancer (IARC) as Group 1 carcinogens.

The levels of mycotoxins in flavored tea containing dried plant pieces must comply with the values presented in the table below:

Marjaan Khatam Laboratory

Organization for Standardization of Iran, the Iranian Food and Drug Administration, and the Veterinary Organization of the country. This laboratory provides its services through four domestic branches located in Tehran, Khorramshahr, Bandar Imam Khomeini and Kerman, as well as one international branch in Russia. With extensive experience in food quality control and by employing qualified experts and advanced laboratory equipment, the laboratory has successfully obtained ISO/IEC 17025 accreditation from the National Accreditation Center of Iran (NACI).

Marjaan Khatam Laboratory is capable of delivering accurate and specialized testing services for various types of tea, including black tea, green tea, flavored tea, and tea bags, in compliance with Iranian National Standards and the requirements of the Iranian Food and Drug Administration.

Specialized testing of various types of tea at Marjaan Khatam Laboratory

• The tests conducted by Marjaan Khatam Laboratory are performed in accordance with Iran’s national standards (NACI 17025) for various types of tea and include the following:

• The tests performed by Marjaan Khatam Laboratory are carried out in accordance with the requirements of the Food and Drug Administration during the process of issuing health permits and monitoring the safety of various types of tea, and include the following:

• Attention: At Marjaan Khatam Laboratory, advanced Gas Chromatography–Mass Spectrometry (GC-MS) and Liquid Chromatography–Tandem Mass Spectrometry (LC-MS/MS) methods are extensively employed as two key and highly sensitive analytical techniques for the accurate measurement and identification of pesticide residues in various types of tea. Owing to their exceptional accuracy and capability to detect very low and trace-level concentrations of pesticides, these instruments play a crucial role in ensuring the quality and safety of tea products and provide highly reliable traceability of potential contaminations.

LOQ values (ppb) in tea determined by GC-MS

LOQ values (ppb) in tea determined by LC-MS/MS

• Attention: At Marjaan Khatam Laboratory, caffeine testing in black tea is performed using HPLC.

Conclusion

To enhance the quality, safety, and competitiveness of Iranian tea, conducting regular specialized tests in accredited laboratories plays a crucial role in ensuring the health, authenticity, and market acceptance of the product. Proper management of production processes, drying, storage, and packaging, along with adherence to labeling requirements and provision of technical information on product labels, can increase consumer trust, reduce waste, enhance added value, and promote the export of Iranian tea. Accurate implementation of these tests gives producers confidence that the final product meets national and international standards and is free from any contamination or harmful substances. Accredited laboratories such as Marjaan Khatam Laboratory, equipped with advanced instruments and expert personnel, can provide extensive services in quality control and authentication of tea. Collaborating with such specialized centers not only enhances product safety but also strengthens consumer confidence and the position of Iranian tea in both domestic and foreign markets.

For submitting samples or obtaining more information, please visit the following link:

https://marjaangroup.com/en/contact-us