The Theory and Target of Temomi-Tea

The ultimate goal in rolling tea leaf is to draw the water out of it properly. What matters here is getting out not only the water sitting on the surface but the water remaining inside the leaf — the core moisture.

The tea plant is an evergreen of subtropical and temperate regions, and freshly picked leaf is saturated with water throughout. That water has to be driven off thoroughly, from the outside and from the core alike.

So is drying without rolling not enough?

The answer depends on the kind of tea. White tea, for example, is traditionally made by withering and drying, without rolling. Sencha and most green teas, by contrast, are rolled after a heating step — though there are exceptions even within green tea, such as tencha, the material for matcha, which is dried without rolling.

What can be said in every case is that simply leaving freshly picked leaf exposed to the air without management invites unintended oxidation and variability in quality. Processing carried out with intent is the key to drawing out and stabilising the quality of the leaf.

Rolling also has a secondary benefit. Leaf gathered into a small tight form has a far smaller surface area than it did originally, so it is less affected by the air during storage, and the flavour on brewing is both more stable and better.

So by what procedure, and at what pace, should the water be drawn out?

Practice varies greatly between tea cultures, but there is a rule of thumb spoken of across schools: when you look at the strength of the action applied during the process along a time axis, it should trace a smooth S-curve. Enter quietly, strengthen through the middle, and ease off quietly towards the end.

This principle applies not only to how pressure is applied but equally to how heat and drying are applied. Blasting leaf still full of water with strong, high-temperature air in order to dry it all at once is not effective: the surface dries first while the core moisture fails to come out, and colour, lustre and aroma suffer. Heat, like pressure, should be handled gently at both ends and allowed to work fully in the middle.

The S-curve, then, is best understood not simply as a matter of harder and softer rolling, but as a principle common to the temporal profile of every action in the rolling process — pressure, heat and drying alike.

Note that the heating step preceding the rolling — steaming or pan-firing — has the purpose of halting enzyme activity quickly, so the S-curve principle does not apply to it. Steaming and pan-firing are a different kind of step, in which heat of the required strength must be applied promptly. Take the S-curve as a principle for the rolling and drying that follow.

Pressure

The more abruptly you move, the greater the instantaneous impact.

Applying strong pressure suddenly to leaf still holding its original form breaks it all at once. Physical damage to cells and tissue is a common cause of poor colour and lustre and of harsh, unpleasant notes.

So at the start of hand-rolling, keep the pressure on the leaf to a minimum. Watch how it responds and raise the pressure gradually, or change the manner of rolling itself, moving to whatever way of applying force is right at that moment.

Suddenly releasing pressure from leaf that has been under it is just as likely to lower quality. Leaf that has been held together and is then abruptly exposed to the air releases its moisture all at once. Towards the end of the process too, pressure needs to be eased off by degrees.

Heat and drying

The same thinking applies directly to the drying that proceeds alongside rolling. Rather than applying strong heat from the outset, begin moving the moisture gently at a lower temperature, let the heat work fully through the middle while watching the state of the leaf, and bring it down gently again at the end. Tracing this S-curve is what lets you draw out the core moisture while protecting colour and aroma.

Trying to finish in one go with high heat over a short time produces the surface-drying discussed below: the outside dries while water remains at the core, and the aromatics you have worked for are driven off. With heat as with pressure, the care taken entering and leaving decides the result.

Surface-drying

To manage all of the above, the thing to keep constantly in mind is preventing the surface of the leaf from drying ahead of the interior — what is called surface-drying.

Roll leaf whose surface alone has dried and the dry outside breaks and cracks first, and the colour and lustre lose their brightness. The leaf takes damage and the quality falls.

The ideal is to carry the work through from beginning to end with the lustre and the colour still beautiful.