Water is the basis for the preparation of tea, it is one of the essential criteria for a good tea. From tap water to purified water, the choice of water has never been greater. Many preconceived ideas about the composition of water and the recommendations of various health agencies make the choice even more difficult. So what is the best water for making tea ?
Amateurs and specialists of original teas have noticed differences in taste between tap water, mineral water, spring water and pure water. They recommend spring or pure water for the detection of the most subtle aromatic notes. But are they the best waters for extracting antioxidants? caffeine? amino acids?
Water, a question of mineral salts and pH
Most naturally occurring waters contain varying amounts of mineral salts. Mineral salts (1) are divided into two classes: macrominerals (calcium, sulphates, sodium, magnesium, potassium, bicarbonates, chlorides) present in the human body and microminerals (iron, silica, cobalt, iodine, etc.), present in trace amounts but important for certain biological functions.
These mineral salts are in fact atoms that carry electrical charges: they are called ions. For example, the calcium ion in water has two positive charges and will be called cation Ca2+. The chloride ion in water has a negative charge and will be called a Cl- anion.
The presence of hydroxonium and hydroxide ions and the quantity of mineral salts are important because they will dictate whether the water is acidic or alkaline: this is the hydrogen potential or pH. In general, drinking water is close to neutral pH at 7: between 6 (slightly acidic) and 8.5 (rather alkaline). The cations will decrease this pH value while the anions will increase the pH value (2)
The amount of mineral salts and the pH value affect the taste of the water. If you drink tap water that is rather chlorinated (Cl-) and very mineral, the water will tend to be harder and alkaline, while water that is very low in minerals will be rather soft and acidic.
What are the differences between the waters?
Tap water is mineral water that has been cleaned of contaminants such as nitrates and treated with chlorine to prevent bacterial growth. It is a water that is perfectly compatible for daily consumption but can tend to be calcareous and alkaline depending on the department. You can consult the water map of France here. It is possible to filter chlorine and certain pollutants with a tap filter or a filter jug, which softens and slightly acidifies the water.
Mineral water is a natural and underground water with a stable composition. Spring water can come from different underground sources and has a variable mineral salt composition. (3). The levels of mineral salts and the pH of these two waters are very variable, you can get the information on the label of the bottles. A very low mineral content water will be at < 50 mg/L of dry residue at 180°C.
Pure water is water that has undergone special filtration to remove all pollutants and virtually all mineral salts. This is the case with osmosis water and distilled water, for example. These waters are generally very soft and rather acidic, with a pH between 6 and 7.
What are the impacts of the quantity of mineral salts and the pH on tea infusion?
First of all the appearance of the liquor and EGCG (antioxidant)
The publication of Franks (4) is one of the most recent studies to answer this question. This research team tested the impact of tap water, low mineral content and pure water on the infusion of Zhejiang green tea and Mao Feng black tea in Taiwan (2.5g tea, 125 mL water. 3min at 80°C for green tea, 5min at 100°C for black tea).
First, the team measured the turbidity of each infusion, i.e. the colour and opacity of each infusion. They showed that infusions in tap water (Tap) are much more opaque than low mineral (Bottled) and pure (deionized) water.
This is due to the presence of minerals in large quantities such as calcium and magnesium.
The team then measured the amount of antioxidants extracted in each infusion, in this case the most antioxidant catechin: EGCG. Although the team found no difference for black tea (EGCG is much less present in black tea compared to green tea), they observed that low mineral content and pure water extracts twice as much EGCG as tap water. An organoleptic test among 103 people found that people found green tea more bitter with low mineral content and pure water than with tap water. The EGCG gives the tea bitterness which is a sign of its presence in the infusion.
A water rich in mineral salts would therefore reduce the diffusion of the tea's antioxidants and modify the appearance of the liquor.
What about the others? Caffeine? Theanine? The taste?
Zhang's team (5) was interested in the diffusion of caffeine, polyphenols, amino acids and the organoleptic value of Bai Hao Yin Zhen white tea brewed with tap water, spring water and pure water. Like Franks et al, they were interested in the quantity of mineral salts (calcium, potassium, magnesium and sodium) but also in the pH of each water. Pure water has a pH of 6.6 and almost no mineral salts, spring water has a pH of 7.3 and a mineral salt concentration of < 5 mg/L, and tap water has a pH of 7.4 and mineral salt levels ten times higher. After infusion of white tea (3g, 150mL of water at 100°C for 5min, a scandal for tea lovers!).
They observed the following rates :
- EGCG levels (antioxidant that gives bitterness to tea): Pure water > Spring water > Tap water. A rather acid pH and a low level of mineral salts allows more EGCG to be diffused.
- Caffeine content (gives character to tea): Spring water > Pure water > Tap water. An acid pH with few mineral salts or an alkaline pH with a high level of mineral salts allows less caffeine to be released.
- Theanine level (amino acid that gives the umami flavour to tea): Spring water > Tap water > Pure water. An alkaline pH makes it possible to diffuse more theanine.
An organoleptic test was carried out within the team and the university and found a more pleasant taste, colour and aroma for pure water and spring water. This observation had also been noted in a previous study (6) for calcium-enriched distilled water. The higher the calcium level, the less appreciated the green tea obtained. For a calcium level close to that of tap water (40 mg/L), tea is less bitter with less EGCG and is more astringent, less umami and less sweet than distilled water.
So who's winning the water battle?
According to science, the water with the most benefits and better tea would be pure water. Then comes water with a low mineral content (< 50mg/L of dry residue at 180°C). A rather acid pH would allow a better infusion. Tap water would be the least efficient of all waters for brewing tea.
However, in practice, no water is perfect. For tea drinking, the use of filters to remove limescale and chlorine is often recommended. Chlorine in water limits bacterial growth, so the filter should be changed regularly.
Bottled water poses a problem in particular because of the possible diffusion of endocrine disruptors (plastic molecules such as phthalates and bisphenol that bind to our hormone receptors. They mimic the action of hormones and disrupt normal hormonal functioning) and the recycling of plastic bottles.
As for pure water, it is demineralised and the risks of mineral deficiencies through its exclusive and long-term consumption has not been studied in humans (although this also depends on diet). Purification techniques can be non-ecological as they sometimes require the use of more water before obtaining osmosis water for example.
Test and alternate between different types of water for your drink and for tea.
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