The Chemistry of Brewing Tea: What Water is Best?

Tea brewing is both an art and a science. The ancient practice of preparing tea is rooted in cultures across the world, but beyond the tradition lies an intricate chemistry that can dramatically affect the final brew. From the minerals in the water to the temperature at which it is heated, every element plays a role in the tea's flavor, aroma, and health benefits. While some of these effects have been known intuitively for centuries, recent advances in chemistry have provided more precise answers about how different factors, particularly the properties of water, influence the outcome of tea brewing.

Despite the wealth of knowledge about tea’s chemical composition, a key area often left underexplored is the exact relationship between water quality and the flavors extracted from tea leaves. The purpose of this paper is to address this gap by offering a detailed analysis of water’s role in tea brewing, drawing from scientific literature and presenting evidence to guide tea enthusiasts and professionals alike in selecting the ideal water for their brews.

1. Water Hardness and Its Influence on Tea Brewing

Water hardness is defined by the concentration of dissolved minerals, primarily calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These minerals play a crucial role in the chemical processes during brewing, interacting with compounds like polyphenols and catechins in tea leaves.

• Hard Water: Hard water can have a range of effects on the final cup of tea, including altering its flavor and clarity, particularly in lighter teas such as green and white teas. Research by Bjelica and Vukmirović (2020) confirms that hard water may cause cloudiness in lighter teas such as green and white teas, as calcium salts like calcium carbonate bind with polyphenols, inhibiting their extraction. This results in a duller flavor profile and reduced health benefits. For instance, water with a hardness over 200 mg/L often produces a more astringent and less flavorful cup, with significant cloudiness.
• Soft Water: Water with lower mineral content (less than 100 mg/L) promotes a cleaner, more vibrant tea, as it allows for better extraction of essential compounds like catechins and epicatechins. Green teas such as Sencha or Longjing (Dragon Well) benefit particularly from softer water, resulting in a brighter, fresher, and more antioxidant-rich cup.

Research Result: Researchers found that water with a hardness of 30–60 mg/L produced the best extraction of catechins in Sencha, leading to a more pronounced antioxidant effect.

2. pH Levels and Their Impact on Tea Brewing

The pH of water plays an essential role in tea brewing, influencing the extraction of flavors and aromatic compounds.

Ideal pH Range: The ideal pH for tea brewing falls between 6.5 and 7.0, slightly neutral or slightly acidic. Water that is too alkaline (pH above 7.5) can neutralize key compounds like tannins and catechins, leading to a lack of complexity in flavor.

• Alkaline Water: High pH levels (above 8.0) can break down aromatic compounds, resulting in a dull, flat flavor. This effect is particularly noticeable in green teas, where brightness and complexity are essential.
• Acidic Water: Slightly acidic water preserves volatile compounds responsible for floral and fruity notes, such as methylated catechins. Studies (Smith, 2021) confirm that water with a pH of 6.5–7.0 preserves the complex aroma and delicate flavor profile of teas like Darjeeling and Jasmine.

Research Result: Research by Cao, QQ, et al on oolong tea demonstrated that water with a pH of 6.5 produced the most complex and aromatic infusion, while higher pH levels resulted in a flatter brew.

3. Water Temperature: A Crucial Factor in Extraction

Temperature is one of the most important variables in tea brewing. It determines how efficiently the water extracts compounds such as polyphenols, catechins, and caffeine from the tea leaves.

3.1 Oolong Tea and Its Temperature Requirements

Oolong tea, being a semi-oxidized tea, lies between green and black tea in terms of fermentation. Its brewing temperature generally ranges from 85°C to 95°C (185°F to 203°F). Water that is too cool may fail to extract the full range of oolong tea’s aromatic compounds and flavors, while overly hot water could result in excessive bitterness.

Scientific research highlights the optimal temperature range for oolong tea to release its unique flavor compounds, such as volatile organic compounds (e.g., esters and aldehydes) and non-volatile compounds (e.g., amino acids and polyphenols). These compounds are more efficiently extracted at higher temperatures without overwhelming the tea’s natural sweetness and floral notes.

For instance, studies have shown that volatile aroma compounds such as ethyl acetate and aldehydes are maximized between 85°C and 90°C (185°F to 194°F), which enhances the overall aromatic profile of oolong tea while minimizing bitterness. Proper temperature control ensures the balance of oolong tea’s distinctive floral aroma and rich taste.

3.2 White Tea and Its Temperature Requirements

White tea is unique for its minimal processing, which preserves its delicate flavors and fresh character. The brewing temperature for white tea varies depending on the specific type. Baihao Yinzhen (Silver Needle), known for its fine buds, requires a lower brewing temperature, typically between 75°C and 85°C (167°F to 185°F), to preserve its subtle sweetness and floral notes. Higher temperatures can lead to an over-extraction of tannins and polyphenols, introducing bitterness that overwhelms the tea’s naturally sweet and mellow profile.

However, other varieties such as Bai Mudan (White Peony) and Gongmei (Long Brow), which contain more mature leaves, benefit from slightly higher temperatures, generally between 85°C and 90°C (185°F to 194°F). The higher heat helps to extract a fuller spectrum of flavors, enhancing the tea's body and richness without compromising its delicate nature.

As white tea ages, the ideal brewing temperature increases. Aged white tea, such as well-preserved old Bai Mudan or Gongmei, can be brewed with boiling water (100°C/212°F), or even boiled directly in a pot. The aging process enhances the tea’s complexity, making it more robust and capable of withstanding higher temperatures, which extract deeper, richer flavors that reveal earthy, woody, and sometimes even honey-like notes.

Studies confirm that these temperature adjustments allow for optimal flavor extraction, ensuring the preservation of delicate aromatic compounds in young teas, while fully developing the deeper characteristics in aged varieties.

3.3 Pu-erh Tea and Its Temperature Requirements

Pu-erh tea, which is either raw (sheng) or fermented (shou), requires higher brewing temperatures to unlock its complex flavors. Recommended water temperatures are typically 95°C to 100°C (203°F to 212°F). The fermentation process in Pu-erh tea produces stable compounds that necessitate high heat for proper extraction, ensuring the tea’s robust and layered profile.

Studies reveal that higher brewing temperatures efficiently extract polyphenols, caffeine, and amino acids, which contribute to Pu-erh tea’s rich and smooth texture. Additionally, volatile compounds such as aromatic alcohols and phenolic compounds are more fully released under these conditions, intensifying the tea’s signature earthy and woody notes.

In particular, higher water temperatures accelerate the oxidation and hydrolysis of tea’s internal components, a process critical for Pu-erh tea’s unique aged and mellow characteristics. For shou Pu-erh, brewed at near-boiling temperatures, the resulting tea liquor exhibits an enhanced depth of flavor and a silky mouthfeel.

4. Contaminants in Water: The Role of Chlorine and Other Chemicals

Water quality plays a crucial role in the tea brewing process, as contaminants such as chlorine, fluoride, and heavy metals can significantly affect the extraction of flavor compounds and the overall sensory profile of tea. These chemicals not only alter the taste of the tea but may also have long-term health implications, making water purification an important consideration for tea enthusiasts and professionals alike.

4.1 Chlorine: A Common Water Contaminant

Chlorine is commonly used in municipal water systems as a disinfectant to kill harmful microorganisms. However, its presence in water can negatively impact the taste and quality of tea. Chlorine can create undesirable odors and alter the delicate balance of flavors, masking the natural aromas of the tea. When chlorine is present in high concentrations, it may produce a harsh, medicinal taste, which is particularly noticeable in delicate teas such as green and white tea.

The presence of chlorine in water can also interfere with the extraction of certain compounds in tea. Studies have shown that chlorine reacts with polyphenolic compounds, such as catechins in green tea and theaflavins in black tea, reducing the tea’s antioxidant properties and diminishing its flavor complexity. For instance, a study found that water chlorination significantly reduced the concentration of catechins in green tea infusions, which directly impacted the tea’s taste and health benefits.

To mitigate the adverse effects of chlorine, many tea professionals recommend using filtered or dechlorinated water. Activated carbon filters are particularly effective at removing chlorine, as they adsorb chlorine molecules, preventing them from interfering with the brewing process.

4.2 Fluoride and Heavy Metals: Impacts on Tea Flavor and Health

Fluoride is another common contaminant that may be present in municipal water supplies. While fluoride is beneficial for dental health at low concentrations, excessive amounts can alter the flavor of tea, giving it an unpleasant, astringent aftertaste. High fluoride concentrations may also lead to the formation of insoluble salts with minerals present in tea leaves, potentially decreasing the extraction of important flavor compounds and altering the tea's color and clarity.

A study  found that the fluoride content in tea, especially in low-quality or poorly processed teas, can accumulate to significant levels. Excessive fluoride levels in drinking water can lead to the accumulation of fluoride in the tea leaves, which may be harmful to human health over time, potentially causing fluorosis .

Heavy metals such as lead, arsenic, and cadmium may also be present in water, especially in regions with pollution or older plumbing systems. These contaminants can accumulate in tea leaves during the brewing process, impacting both the health benefits and the taste of the tea. Studies have shown that heavy metals may affect the polyphenol content of tea, reducing its antioxidant efficacy.  Research reported that lead contamination in water significantly lowered the total polyphenol content in tea infusions, resulting in a duller and less flavorful brew.

4.3 Other Contaminants: Pesticides and Industrial Pollutants

In addition to common chemicals like chlorine and fluoride, tea water may also be contaminated with pesticides and industrial pollutants, especially in areas with intensive agricultural practices. Residues from pesticides can leach into water sources and impact the flavor of the tea, often introducing bitter or chemical notes. While the risk of pesticide contamination in drinking water may be lower in comparison to direct contamination in the tea leaves themselves, it remains an important concern for health-conscious consumers.

Moreover, water from industrial areas may contain pollutants such as volatile organic compounds (VOCs) or polychlorinated biphenyls (PCBs), which can disrupt the delicate balance of compounds in tea. Research by Zhang et al. (2015) found that VOCs present in contaminated water reduced the levels of key aromatic compounds in tea, resulting in a less fragrant and more flat infusion.

4.4 Recommendations for Clean Water and Optimal Tea Brewing

Given the significant impact of water contaminants on tea quality, many tea experts recommend using water that is both clean and free from harmful chemicals. The following strategies are commonly suggested:

• Use filtered or bottled water: Water filtration systems, such as activated carbon filters, reverse osmosis, or distillation, can effectively remove chlorine, fluoride, and heavy metals from tap water.
• Pre-boil water and let it cool: If chlorine or other volatile chemicals are present in tap water, boiling and then letting the water cool allows the chlorine to evaporate, improving the water's taste and reducing its impact on tea flavor.
• Monitor water quality: Using a water quality testing kit can help detect the presence of harmful chemicals or minerals in water, allowing consumers to adjust their water treatment accordingly.

5. Total Dissolved Solids (TDS) and Its Role in Tea Brewing

TDS refers to the total concentration of dissolved substances in water, including minerals, salts, and organic matter. The ideal TDS level for brewing tea ranges between 30–90 mg/L, as this provides enough minerals to facilitate proper extraction without overwhelming the tea.

• Low TDS (Below 30 mg/L): Water with very low TDS, such as distilled or deionized water, may extract flavors poorly, leading to a bland and underwhelming brew. While such water allows the tea to release its essence, it lacks the minerals necessary for the proper interaction with the tea's polyphenols, amino acids, and aromatic compounds. Tea brewed with low-TDS water may taste flat and lack the depth of flavor.
• High TDS (Above 100 mg/L): Water with a higher TDS level can be excessively mineralized, leading to a more pronounced flavor but also a less desirable taste. When the TDS exceeds 100 mg/L, particularly with an abundance of calcium and magnesium, the extraction of tannins and polyphenols can become too strong, resulting in a bitter, astringent brew. For instance, brewing delicate teas like Dragon Well or White Peony with water that has high TDS may result in a harsh, overly tannic taste.

Research confirms that water with a TDS between 30 and 90 mg/L strikes the optimal balance, promoting a rich flavor extraction without overpowering the subtlety of the tea. At this TDS range, the water can interact effectively with the chemical compounds in the leaves, enhancing both flavor complexity and smoothness.

6. The Ideal Water Composition for Brewing Tea

To achieve the perfect brew, water should meet certain criteria:

• TDS: Between 30–90 mg/L, ensuring enough minerals for extraction without overpowering the tea’s delicate flavors.
• Calcium (Ca²⁺): Around 30–50 mg/L, contributing to smoothness and body, while avoiding cloudiness.
• Magnesium (Mg²⁺): Also around 30–50 mg/L, enhancing flavor extraction and mouthfeel, especially for black and oolong teas.
• Sodium and Chlorine: These should be minimal or nonexistent, as they negatively affect the flavor and aroma.
• pH: A neutral to slightly acidic range (6.5–7.0) is ideal for maintaining flavor balance and enhancing the extraction of aromatic compounds.

With these ideal properties, water will facilitate the best extraction from tea leaves, enhancing the natural flavors and aromas of the tea, whether delicate green tea or robust black tea.

6. Conclusion

The composition of the water used in tea brewing is just as important as the quality of the tea leaves themselves. By understanding and controlling key factors such as TDS, mineral content, and pH, tea drinkers can significantly improve their brewing outcomes. The ideal water for tea should have balanced mineral content (especially calcium and magnesium), a neutral or slightly acidic pH, and low levels of contaminants like chlorine or sodium. By optimizing water composition, tea enthusiasts can enjoy a more flavorful, aromatic, and enjoyable tea experience—whether they are brewing delicate green tea or robust black tea.

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