One corner of the shelf holds packets of tea that look like fine twigs. Kukicha, bōcha, karigane, shiraore: the names vary. Inside, all of them are the stems of the tea plant, and what they point to overlaps almost entirely. The names part because regions and shops keep different habits.
This piece looks behind the names at what differs inside, before roasting and after.
Leaf and stem, before roasting
Pinched between the fingers, a dry stem is lighter than leaf, with a faint green smell. Before roasting, stems carry more savouriness and less astringency.
Stems hold more amino acids, and less of the catechins and caffeine behind astringency, than leaves. A long-standing tea body lists several other names for stem tea and notes that shops use them differently.
How many times more is not fixed at one figure, and the gap need not survive roasting. The sources go as far as raw material before roasting. Next, the moment stem and leaf part.
Parting before the fire
Leaf from the field is steamed, rolled and dried into aracha, the unrefined tea. Stem and leaf part before any roasting.
The industry's rules define stem tea as tea rich in stems and leaf stalks, sorted out by machine and the like during finishing. That sorting happens after the tea has become aracha. The contents have already divided before the fire.
The sources show that the difference arises before roasting. How large it is after the parting depends on the study.
How many times more, study by study
Line up the papers and the multiples for stem savouriness are scattered. The figure changes from one study to the next.
One puts stems at about half the leaf; another finds a far larger gap in young stems. What was compared, the cultivar and the season all differ.
In one set of measurements under shared conditions, stem tea's caffeine came close to eight-tenths of first-flush tea's. But that was a row of stem tea added to a line-up of seasonal aracha. It was not a comparison of the same shoots split into leaf and stem, and the sources go no further. Why the stems differ is explained from another field.
Figure 7-1-1Five studies comparing leaves and stems: samples, conditions, before or after roasting
| Source | Samples (what was compared with what) | Measurement and extraction conditions | Before or after roasting | Result |
|---|---|---|---|---|
| Miwa et al. (1978) | Tea leaves by leaf position (leaves and stems) | — | Before roasting | Stems about twice the amino acids, about 1/2 the tannin and caffeine (these expressions come from the summary in Hara et al. 1993; the original is qualitative) |
| Sasaki et al. (2015) | Stems and leaves taken from the same tea plant | — | Before roasting | About 1.5 times the amino acids in stems |
| Zhang et al. (2025) | Stems and leaves of the new shoots of 11 Chinese cultivars | — | Before roasting | Stem／leaf theanine 3.8 to 8.8 times (differences between stems under twofold, between leaves up to 3.4-fold) |
| Kochi (Table 3, 2014) | One line for kukicha added to a line-up of aracha by picking season (not a paired comparison of leaf and stem) | 1 g of ground leaf, about 80 mL of hot water, extracted at 80°C for 30 minutes, made up to 100 mL (not the strength of tea as drunk) | Before roasting | Caffeine in kukicha 77% of first-flush tea |
| Hara et al. (1993) | One commercial kukicha and one medium-grade sencha (1991) | — | Before roasting | Kukicha lower in catechins, caffeine and sucrose, higher in theanine and potassium quinate |
Before stem or leaf: when it was picked
In a spring tea field, the new shoots shine soft and pale. Before stem or leaf comes another axis: when the tea was picked.
Within young shoots, the source of savouriness tends to gather in the stem. Plant research on the system that carries amino acids has shown this. An older survey found more of it the earlier the picking, with wide swings by season.
The sources show that stem differences are tangled with picking time. Everything so far has been before roasting.
What is left after roasting
Roasted leaf no longer smells green; a toasty smell fills the room instead. After roasting, little of the source of savouriness remains.
When a prefectural station measured it at each roast depth, it fell sharply at the light roast. At the medium and dark roasts it was not found. That trial roasted seasonal aracha, and no roasted-stem figures appear in the same table.
The sources show that stems are rich in savouriness only as far as aracha. The study names and figures come together at the end.
The numbers in detail
- Other names
- The Kyoto Prefectural Tea Industry Council lists ore, shiraore, bō, hone and karigane as other names for stem tea, noting that some shops use karigane for gyokuro stems. A tea merchant in Yame calls it shiraore.
- Labelling rules
- The Japan Tea Central Association's standard defines kukicha or bōcha as tea rich in stems and leaf stalks, selected with stem-separating machines and the like during the finishing of aracha.
- Range of multiples
- From about half the leaf to more than eight times in young stems. Studies include Miwa et al. (1978), Sasaki et al. (2015), Zhang et al. (2025) and Hara et al. (1993).
- Caffeine
- In Table 3 of the Kochi Agricultural Technology Center tea station report, stem tea was 77% of first-flush tea. The liquid was 1 g of ground leaf extracted at 80°C for 30 minutes, made up to 100 mL (2014).
- The stem tea row
- The report does not say whether its stem tea was stems only or mixed.
- Shoot research
- A 2025 plant physiology paper identified an amino acid transporter in new shoots of 11 cultivars and found young stems to be the main site of theanine accumulation.
- Picking time
- A 1962 survey in Shizuoka found more theanine the earlier the plucking, with wide seasonal variation.
- After roasting
- In the same station's Table 2 (2013), first-flush theanine was 21.12 mg in the aracha and 1.27 mg at the light roast. It was not detected at the medium or dark roast.
- Extraction
- Per 100 mL of infusion from 1.9 g of leaf in 200 mL of boiling water for 5 minutes. The trial roasted first-flush, kariban and second-flush aracha.
