Goishicha

History

Goishicha (碁石茶, 'Go Stone Tea') is one of only two truly post-fermented teas in Japan - and perhaps the most unusual tea in the entire country. Produced exclusively in the mountain village of Otoyo in Kochi prefecture on the island of Shikoku, Goishicha undergoes both aerobic mold fermentation AND anaerobic lactic acid fermentation - a double fermentation process found in no other tea in the world. The tea gets its name from the small, square-cut pieces that resemble Go game stones (碁石). Goishicha was historically produced as a trade tea - Otoyo villagers would exchange it with coastal communities for salt and fish. By the 1970s, production had nearly died out, with only a single family continuing the tradition. Revitalization efforts since the 2000s have preserved this extraordinary living artifact of Japan's tea history.

Processing

The process is remarkably complex and takes 3–4 weeks. Mature summer leaves are first steamed, then piled in a warm, dark room for 1–2 weeks to undergo aerobic mold fermentation (similar to the initial stage of shou pu-erh). The moldy leaves are then packed tightly into wooden barrels, weighted with heavy stones, and left for 2–3 weeks to undergo anaerobic lactic acid fermentation (similar to making sauerkraut or kimchi). Finally, the fermented mass is cut into small squares and sun-dried. This double fermentation is globally unique.

Tasting Notes

Appearance

Small, dark, flat squares about 3cm across - they genuinely look like Go stones. The surface is dark brown to black with visible mold residue. When brewed, the liquor is a pale golden-yellow with a slight haze - much lighter than you'd expect from the dark appearance of the dry tea.

Aroma

Striking and unusual - sharp lactic acidity (like yogurt), earthy mushroom notes, and a subtle smokiness. The aroma is more reminiscent of fermented foods (miso, pickles) than of tea. It's an acquired scent that fascinates the adventurous.

Taste

Sour, tangy, and earthy - unlike any other tea in the world. The lactic acid fermentation creates a bright, yogurt-like sourness that's the dominant note. Behind it are earthy, mushroom, and subtle woody flavors. The mouthfeel is light and refreshing despite the complex fermentation. There's virtually no bitterness or astringency. The sourness is clean and pleasant, not harsh - similar to kombucha but with more depth.

Brewing Guide

Western Style

• Leaf: 1–2 squares per 300ml
• Water: 90–100°C (194–212°F)
• Time: 2–3 minutes
• Infusions: 2–3 infusions

Step-by-step

1. Use boiling water. Full boiling water is fine - the fermented, mature leaves are extremely robust and won't become bitter. Tip: Unlike delicate green teas, Goishicha wants heat to open up its fermented complexity.
2. Add 1–2 squares. Place 1–2 dried squares in a teapot or large cup. They'll rehydrate and release their unique sour-earthy flavor. Tip: Start with one square if you're new to fermented teas - the sourness can be surprising.
3. Steep 2–3 minutes. Let the squares soften and release their lactic character. The liquor will be a pale golden-yellow. Tip: Longer steeping intensifies the sourness. Adjust to your preference.
4. Re-steep. The squares can be re-steeped 2–3 times. Subsequent steeps are milder and more earthy. Tip: The second steep often has the best balance of sour and earthy notes.
5. Try it cold-brewed. Goishicha makes an excellent cold brew - place 2 squares in 500ml of cold water and refrigerate overnight. Tip: Cold-brewed Goishicha is refreshing, mildly sour, and probiotic-rich - perfect for summer.

Health Benefits

• Rich in lactic acid bacteria - a natural probiotic tea
• The double fermentation creates unique bioactive compounds not found in other teas
• Historically consumed as a digestive aid and general health tonic in Shikoku
• Very low caffeine due to the mature leaf material and extensive fermentation
• Recent Japanese studies suggest potential benefits for gut microbiome health

Food Pairings

• Japanese fermented foods - miso soup, pickled vegetables, natto
• Grilled fish - the acidity cuts through the richness
• Cheese - especially aged or blue varieties
• Rice porridge (okayu) - a traditional Shikoku combination
• As a culinary ingredient - used in salad dressings and marinades in modern Japanese cuisine

Buying Guide

What to look for

• Small, dark, flat squares - the distinctive Go stone shape
• Sour, lactic aroma - not earthy or musty alone
• Otoyo, Kochi prefecture origin - there is no other legitimate source
• Recent production date - while shelf-stable, freshness affects the lactic character

Quality indicators

• Produced in Otoyo village, Kochi - the only genuine production area
• Traditional double fermentation (mold + lactic acid)
• Clean, bright sourness - not musty or off-putting
• Supported by local revitalization programs maintaining traditional methods

Price range: $30–60 for a small package (30–50 squares), $80+ for premium artisan production

Storage: Store in a cool, dry place in an airtight container. Goishicha is very shelf-stable due to its fermentation - it can be kept for several years.

Fun Facts

• Goishicha's double fermentation (aerobic mold + anaerobic lactic acid) is found in no other tea in the world - it's a process more similar to making cheese than making tea.
• By the 1970s, only one family in Otoyo still produced Goishicha - the tradition nearly died out completely before revitalization efforts began.
• The tea's name comes from its resemblance to Go game stones - the small, flat squares are cut by hand from pressed sheets of fermented tea.
• Goishicha is used in Otoyo's traditional 'chagayu' (tea porridge) - rice is cooked in Goishicha broth, creating a mildly sour, probiotic-rich comfort food.
• Recent scientific interest in Goishicha's unique microbiome has brought international attention - researchers have identified lactic acid bacterial strains unique to this tea.

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