Evening, the kettle on, and a search for the caffeine in hojicha. The government page and a tea merchant's page give slightly different figures. In the sencha row sits the same figure as hojicha. The kettle starts to sing, and steam clouds the kitchen window.

What follows traces why the figures move and why they overlap: the brewing conditions first, then the national table, a shop's page, and the editions of the table.

Leaf, water, heat and time

Leaf goes into the pot, water over it, and then a short wait. The caffeine figure moves from source to source because this way of brewing differs from figure to figure.

Every published value is a weight per set volume of tea brewed one particular way. Amount of leaf, amount of water, water temperature, steeping time. Only when those four are fixed does a single figure exist.

Those conditions are set separately for each kind of tea. What the sources support is this much: every figure comes with its own way of brewing. After the conditions comes one line of the national table.

Hojicha and sencha, side by side

Run a finger down the national food table and hojicha and sencha carry the same value. They look alike because two separate ways of brewing happened to land in the same place.

Hojicha is brewed with more leaf and more water, for a short time. Sencha uses less of both, and twice as long. The values do not match because the contents resemble each other.

A government Q&A citing another edition of the table keeps the pair level as well. The sources go no further than this: on the table, the two look the same. After the table comes a tea merchant's page.

Two figures, side by side in a shop

Open a packet of bōcha and the dry, toasty smell of stems rises. On a shop's page, a value taken from the table and a value the shop measured itself sit next to each other.

One merchant gives ordinary hojicha the national table's value. Beside it sits its own bōcha, measured by a prefectural research institute, a little lower. Its brewing uses the same ratio of leaf to water as the table; only the water temperature differs.

The page gives its own reason for the lower figure: the main raw material is stem, not leaf. The sources support the shop's stated reason, and no more. After the shop come the table's own editions.

A new line in a new edition

Take an old food table off the shelf and it smells of dry paper. Some figures did move with the editions, and the one that moved is the line for the leaf itself.

A recent supplement added a new row for hojicha leaf. Most explanations in circulation still cite the edition before it. Under the same words, hojicha caffeine, the value for the leaf and the value for the brewed tea are different things.

Where an explanation does not say which edition it cites, the difference cannot be checked. After the editions comes the question of when things were measured.

A gap in the dates

A finger traces the notes beneath the table, slowly. The values for brewed bancha, hojicha and the rest were set from new analysis and from an old edition together.

That old edition came out a long time ago. Which components were carried over from it is written nowhere in the text.

Lining the figures up by when they were measured is not something the current table allows. The figures and conditions are gathered just below. By the time the steam thins over the cup, the usual brew is ready.

The numbers in detail

Hojicha in the national table: On MAFF's page about excessive caffeine intake, hojicha infusion is 20 mg per 100 mL. The composition table prints 0.02 g per 100 mL, under 15 g of leaf, 650 mL of water at 90°C, 0.5 minutes.
Sencha in the national table: Sencha in the same table is also 20 mg. Its conditions are 10 g of leaf, 430 mL of water at 90°C, 1 minute.
Government Q&A
The table in the MHLW's caffeine Q&A cites the 2015 (seventh revised) edition. There too sencha is 20 mg and hojicha 20 mg, with the same brewing conditions.
A shop's bōcha
The tea merchant cites the seventh revised edition for general hojicha at 20 mg. Its own bōcha beside it is 16 mg, measured in 2016 by the Industrial Research Institute of Ishikawa.
The shop's brewing
The same page brews 6 g of tea with 260 mL of boiling water. Per 100 mL of water that is 2.3 g of leaf, the composition table's ratio [calculated]. The table's water is 90°C; the shop's is boiling.
Editions
The 2023 supplement added a row for hojicha leaf, at 1.5 g per 100 g (chapter column). Most explanations in circulation cite the earlier 2020 (eighth revised) edition.
Timing of measurement
For the infusions of bancha, hojicha, genmaicha and oolong tea, the tables say the values were set from analytical values and those in the fourth revised edition. That edition was published in 1982.