Three packets stand on a tea shop's shelf. The names on the front read sencha, hojicha and genmaicha. Turn them over and the ingredients on all three come to one word, "green tea", with "brown rice" added to one of them.

What follows traces how three packets part ways from that single word: first the blend, then the roast, then the blending that never reaches the label.

One word on the back, three on the front

Laid side by side face down, the three packets show the same small print in the same places. Only two things can be moved: the roast and the blend.

It is like water from one river taking a new name each time it branches. The industry's labelling rules settle the words a packet may carry. So both the roast and the blend leave a trace on it.

The sources speak only to the words on the packet. The words for the blend come first.

Stems, roasted rice, and a mix

Shake a packet heavy with stems and the thin twigs rattle. The blend is settled clearly, in the words of the name itself.

Under the labelling rules, kukicha and bōcha are teas holding a large share of stems and leaf stalks sorted out in refining. Genmaicha is sencha, bancha or similar tea with roasted rice added. Different kinds of tea combined are called mixed tea.

What the rules give is the name for what went in, and no more. After the blend comes the fire.

A line for finishing, a line for roasting

Standing by a roaster, the dry, toasty air meets the face. What separates hojicha from sencha is not the raw material but the heat added afterwards.

An appendix to the same rules puts the finishing fire and roasting on separate lines, at different temperatures. It names neither the equipment nor where the temperature is taken. What it divides is not kinds of tea but whether a packet may say "manufacturer" or has to say "processor".

Past that heat, the direction depends on where the measuring was done. In a prefectural tea station's figures, the source of astringency fell as the roast deepened, to about a fifth at the darkest. The compounds taken as a marker of roast aroma came out highest at the light end. In another prefecture's trial, roasting stems hotter made the same family of compounds rise with the temperature.

The conditions differ, so these are two separate stories, and the evidence stops there. What this line actually divides is taken up in a later chapter. Last comes a step that never shows on the packet.

Blending, which the label never shows

In a merchant's workroom, several lots of unrefined tea are turned into one heap. Blending, gōgumi (合組), alone never reaches the packet.

Gōgumi is the merchant's step of combining several unrefined teas into the flavour of one bag. Combining moves the figures too. In a government table with the brewing held equal, genmaicha, with its roasted rice, has about half the caffeine of hojicha.

The blending ratio is not in the table, though, and the evidence goes no further. The conditions for roasting and for blending are still to be measured. The figures and conditions are gathered just below.

The numbers in detail

Labelling rules
The Green Tea Labelling Standard (緑茶の表示基準) of the Japan Tea Central Public Interest Incorporated Association. The definitions of kukicha and bōcha, genmaicha and mixed tea come from it.
Temperature lines
In the appendix "Classification of manufacture, processing and sale", the finishing fire at 70–130°C and roasting at 140°C and above sit on separate lines.
Where the line leads
What that line actually divides is taken up in chapter 5.
Catechins
From the Tea Research Station, Kochi Prefectural Agricultural Technology Center. In the 2013 data, the dark roast of first-flush tea held about one fifth of the catechins in aracha.
Pyrazines
In the same report, the two pyrazines used as an index of roast aroma were highest at the light roast, in first-flush tea and karibancha alike.
Stem trial
The Industrial Research Institute of Ishikawa and others roasted stems at drum inner-surface temperatures of 180–220°C. All eight pyrazines rose with the temperature.
Caffeine
In the Ministry of Agriculture, Forestry and Fisheries table, hojicha is 20 mg and genmaicha 10 mg per 100 mL of infusion.
Brewing conditions
Both use 15 g of leaf, water at 90°C, 650 mL and 0.5 minutes. No blending ratio is published.