What water should you choose to infuse a speciality tea? (The chemical and sensory guide)
Written by Dian VAULTIER·
In Brief
- To brew a grand cru tea, the ideal water should have a low mineral content, with a dry residue below 50 mg/L, and a neutral or very slightly acidic pH, around 6.5 to…
- A cup of tea is more than 99 % water.
- HOLLIN sommelier expertise: which water to choose for brewing specialty tea, explained by a purist Tea House with no added flavorings, based in Sartrouville (Île-de-France) and shipping its grand crus worldwide.
To brew a grand cru tea, the ideal water should have a low mineral content, with a dry residue below 50 mg/L, and a neutral or very slightly acidic pH, around 6.5 to 7. Hard water, rich in calcium and magnesium, blocks the extraction of aromatic compounds and clouds the liquor. The temperature is then adjusted according to the tea family, between 70 and 95 degrees, never 100 degrees for a delicate tea.
The impact of limescale and minerals on tea leaves
A cup of tea is more than 99 % water. This water is not a neutral solvent: it is a reactant. Dissolved calcium and magnesium, responsible for hardness (measured in French degrees, TH), bind to the leaf's polyphenols upon contact. These ions form insoluble complexes with the tannins, which precipitate instead of remaining in suspension: this is the greyish film that appears on the surface of tea brewed with very hard water.
The consequence is twofold. First, aesthetic: the liquor loses its clarity and coppery brilliance. Then, sensory: the molecules captured by the limescale no longer reach the palate. Extraction becomes partial, the finish collapses, and the tea seems flat despite a very high-quality leaf. The black teas, rich in theaflavins and thearubigins, are affected first: these are precisely the pigments that react most quickly with calcium ions.
The right indicator is not the brand of water but its dry residue at 180 degrees, printed on every label. Below 50 mg/L, the water remains pure enough to let the leaf speak while retaining sufficient mineral structure. Completely demineralized water, by contrast, produces a hollow liquor: extraction needs a minimum amount of ions to occur.
pH: why water that is too acidic or too alkaline destroys umami
pH measures the acidity of water. Above 7.5, alkaline water accelerates the oxidation of catechins in the cup: the liquor turns brown within minutes, bitterness rises and fresh vegetal notes disappear. This phenomenon is most visible on a Japanese green tea, whose jade colour turns bronze almost immediately.
Below 6, water that is too acidic has the opposite effect: it fixes the color but hardens the aromatic profile. Amino acids, first and foremost L-theanine, responsible for the sensation of umami, express themselves poorly in an acidic environment. Yet umami is exactly what one seeks in a Gyokuro, a shade-grown Sencha or a green tea first flush: that velvety roundness, almost like vegetable broth, which distinguishes a carefully cultivated leaf.
The useful range is therefore narrow: 6.5 to 7. Within this range, catechins remain stable, amino acids are fully released and the liquor retains its color. This is also why the same green tea can seem magnificent in your home and disappointing elsewhere: it is not the leaf that changes, but the water supply.
The golden rule of temperature
Pouring water at 100 degrees over a delicate tea is a preparation error, not a shortcut. At boiling point, water has lost much of its dissolved oxygen, which flattens aromatic perception. Above all, excessive heat degrades heat-sensitive amino acids and causes a brutal extraction of tannins: bitterness overwhelms everything else. For a pure tea, whose entire value rests on the leaf's natural finesse, it is subtlety itself that is destroyed.
The guidelines are simple: 70 to 80 degrees for a green tea Japanese, 80 to 85 degrees for a Chinese green tea, 85 to 90 degrees for a white tea or a oolong lightly oxidised, 90 to 95 degrees for a black tea or a roasted oolong. In practice, simply bring the water to a simmer, then let it cool for a few minutes, or add a small amount of temperate water.
The equipment plays a decisive role here. A cast-iron teapot or thick stoneware retains heat and stabilizes extraction throughout the entire duration of thetime, while a thin vessel allows the temperature to drop by several degrees in one minute. Choosing the material of your tea set already means controlling part of its temperature curve.
To explore further how to choose tea according to the time of day, our article Which tea should you choose for the morning? naturally extends this reflection on temperature and intensity.
Adjust your water, then come and taste it in Sartrouville
No theory can replace a comparative tasting: the same tea, brewed with two different waters, side by side. The difference is often more striking than that between two harvests. It is an exercise we regularly practice at the counter.
Come and discuss it and taste our teas pure at Hollin du Goût, our contemporary Asian grocery store in Sartrouville, Île-de-France, from Monday to Saturday, 10h to 20h. We will show you how to adjust your water, temperature and equipment to what you drink each day.
Frequently Asked Questions (FAQ)
- Should you use tap water for tea?
- It depends on your water supply. If your water has little limescale, it is perfectly suitable after resting for a few hours in an open carafe to allow the chlorine to evaporate. If its hardness exceeds 25 French degrees, it will cloud your herbal teas and mask the aromas.
- What is the best bottled water for tea?
- Any spring water with a dry residue below 50 mg/L and a pH close to 7. Read the label rather than the brand: total mineral content is what matters, not the source. Avoid mineral waters with high levels of calcium, magnesium or bicarbonates.
- Can filtered water be used?
- Yes, and it is often the simplest solution for everyday use. A filter carafe or carbon filter reduces chlorine and some of the hardness. Replace the cartridge at the recommended frequency: a saturated filter releases the minerals it had retained.