Pour water over tea and, in a few seconds, everything begins to change. The leaves rehydrate, their structure opens, molecules pass into the water and the liquor gradually acquires color, fragrance, sweetness, bitterness, astringency and body. This phenomenon seems simple. Yet, brewing tea is above all an extraction, and this extraction is much more complex than the idea of a simple "taste coming out of the leaves".

Understanding this mechanism allows us to grasp something essential: a brew that is steeped too long is not necessarily the same cup, just "stronger". By changing the time or temperature, we also change the balance between the extracted substances.

1. Water Does Not Carry Away the Tea: It Selects What It Can Extract

A dry tea leaf contains an extremely complex set of constituents: polyphenols, amino acids, caffeine, carbohydrates, minerals, pigments and aromatic molecules, to which are added the compounds formed or transformed during the production of the tea.

When hot water reaches the leaf, it begins by penetrating its tissues. The leaf rehydrates. Some soluble substances then gradually pass from the plant matrix into the water.

This transfer relies notably on phenomena of dissolution and diffusion. A molecule present inside the leaf does not instantly find itself in the cup: it must be able to be put into solution and then migrate through a plant structure that offers a certain resistance.

2. The First Seconds: The Leaf Comes Back to Life

A rolled, twisted or compressed leaf does not immediately offer all its surface to the water. At the beginning of the brewing, it absorbs water and begins to regain volume.

This rehydration is particularly visible with certain rolled oolongs, compressed Pu-erhs or large whole leaves. They may require several successive infusions to open completely.

The geometry of the leaf matters a great deal. A broken leaf, a fanning, or a powder offers a much larger contact surface relative to its volume than an intact large leaf.

This is one of the reasons why a highly fragmented tea can give an intense liquor very quickly.

3. Amino Acids: Part of the Sweetness and Umami

Among the important constituents of the cup are free amino acids, including L-theanine, which is particularly well known in tea. They contribute notably to the sensations of sweetness and umami and participate in the flavor balance of certain green teas.

They are soluble in water and therefore begin to join the liquor during brewing. However, it would be incorrect to state that they are systematically "all extracted before the other compounds".

Studies carried out on different teas show that their extraction also depends on the temperature, the duration and especially the plant material studied. An increase in time or temperature can increase their concentration in the cup, but the precise behavior varies depending on the teas.

This is where a fundamental rule of brewing appears: the initial composition of the leaf matters as much as the recipe used.

4. Caffeine: Fast, But Not Instant

Caffeine — traditionally called theine when talking about tea — is also soluble in water.

It begins to be extracted quickly, but its release is not instantaneous. Studies on the kinetics of brewing have shown that the diffusion of caffeine through the leaf matrix is strongly hindered compared to its diffusion in free water.

Temperature accelerates this transfer. All other things being equal, warmer water generally promotes a greater and faster extraction of caffeine.

This also allows us to correct a very widespread idea: systematically throwing away the first seconds of brewing does not reliably turn a classic tea into a "decaffeinated" drink. A part of the caffeine can indeed pass quickly into the water, but a significant amount still remains available for the following infusions.

To delve deeper into this subject, also consult the Tsuru No. 025 Dedicated to Theine.

5. Polyphenols: Where the Balance Can Tip

Polyphenols constitute a very large family. In green teas, catechins represent an important component. In black teas, the oxidation carried out during production transforms part of these molecules and produces notably theaflavins and other phenolic compounds.

These substances play a major role in the flavor structure of tea. They contribute to the bitterness, astringency, color and body of the liquor.

The extraction of catechins generally increases when temperature and time increase. But once again, the relationship is not infinitely linear: some molecules can also undergo transformations during very long or high-temperature extractions.

This is why a prolonged brew does not only give "more flavor". It can shift the relationship between sweetness, umami, bitterness, astringency and mouthfeel.

This mechanism directly joins the Tsuru Dedicated to Bitterness and the one Dedicated to Astringency.

6. So, What Comes Out First?

The scientific answer is less spectacular than a chronological chart, but much more interesting: several families of molecules begin to be extracted simultaneously.

Their extraction speed and their final concentration are simply not identical.

7. Aroma Follows a Different Logic

When we bring our nose close to a freshly prepared cup, part of the molecules responsible for the fragrance already leaves the liquor to join the air.

The aroma therefore does not depend only on what was extracted in the water: it also depends on the volatility of the molecules, their concentration, the temperature of the cup and their interaction with the other constituents.

Very hot water can promote the extraction of certain substances while simultaneously accelerating the volatilization of certain aromatic molecules.

This is also the reason why a tea can seem extremely fragrant in the first seconds and then present a different expression when it cools.

The aromatic perception continues even after swallowing thanks to retronasal olfaction, a subject studied in the Tsuru No. 033 — Retronasal Olfaction of Tea.

8. Why Does Hot Water Accelerate Brewing So Much?

Increasing the temperature changes several phenomena simultaneously: diffusion becomes faster, the solubility of many compounds increases and water penetrates more effectively into the structure of the leaf.

Experiments carried out on different types of tea thus generally show more caffeine and catechins in brews made at high temperature or for a longer duration.

This does not mean, however, that "hotter = better".

The goal of a preparation intended for tasting is not to extract the maximum possible quantity of all molecules. If that were the case, it would suffice to boil each tea for a long time.

The real objective consists in obtaining a pleasant sensory relationship between the different extracted constituents.

This is exactly the reason for the joint adjustment of temperature and time studied in the Tsuru No. 006.

9. Time Therefore Does Not Just Strengthen the Cup

Imagine two brews of the same tea.

The first lasts two minutes. The second six minutes.

The second will generally contain more extracted matter. But the relationship between the families of substances can also have changed. It can become more astringent, more bitter, denser or present a more persistent finish.

Saying that it is simply "three times stronger" would therefore be inaccurate.

The notion of strength itself mixes several perceptions: aromatic intensity, bitterness, astringency, concentration, color and body. Yet these characteristics do not necessarily all progress at the same pace.

10. Leaf Size Changes the Speed of the Cup

Take a whole leaf and reduce it to very fine particles. Its overall chemical composition has not suddenly changed, but its way of interacting with water, yes.

Significant fragmentation increases the available surface and reduces the distances that certain molecules must travel before reaching the water.

This is why teas made of fine particles can brew extremely quickly.

Conversely, large intact leaves or a compressed tea can present a much more gradual evolution.

11. Production Leaves Its Mark Even in the Teapot

Rolling, grinding, oxidation, roasting, drying, compression: the production steps modify the tissues of the leaf and its composition.

They therefore also influence the way water accesses the soluble substances.

Research dedicated to caffeine has thus shown that the production method could modify its extraction kinetics.

This explains why it is risky to seek a universal brewing curve applicable to all teas.

A finely shaped Sencha, a large-leaf Darjeeling, a CTC black tea, a rolled oolong and a Pu-erh cake do not make their composition available to the water in the same way.

12. And During Successive Brews?

When the same leaves are brewed several times, each pass modifies what remains available for the next.

A first brew extracts a part of the soluble constituents. The second therefore works with a leaf already rehydrated, often more open, but also already partially depleted.

This combination explains why the second brew can sometimes seem more expressive than the first: the leaves are more open while they still contain a lot of soluble matter.

Then, gradually, the extractable reserves decrease.

Once again, there is no single rule. Depending on the temperature used, the shape of the leaves and the tea studied, the distribution between the first, second and third brew varies.

13. The True Art of Brewing: Deciding Where to Stop the Extraction

A successful brew is therefore not the one that extracts everything.

It is the one that is interrupted at the moment when the desired balance is reached.

For certain green teas, we will seek a fresh, sweet and umami cup, with contained astringency. For a robust black tea, a more energetic extraction may be desired. For an oolong or a Pu-erh, several short infusions can allow us to observe the progressive evolution of the leaf.

The right recipe is therefore never simply a temperature written on a box.

It constitutes a compromise between the tea, the water, the quantity of leaves, the temperature, the time and the desired sensory result.

This is where chemistry directly joins the Tsuru No. 034 Dedicated to the Balance of Tea.