Kaneiwa: Soy Sauce Brewed in Cedar Barrels

Q: Is tamari gluten-free?

Tamari is brewed with very little wheat, or none at all, which makes it naturally gluten-free. Always check the label on the bottle.

Q: What is the difference between tamari and regular soy sauce?

Koikuchi contains as much wheat as soy, whereas tamari contains almost none: it is thicker, more powerful and richer in umami.

Q: How long does soy sauce keep?

Several months unopened and away from light; once opened, in the refrigerator and ideally within three months.

Less than 1% of Japanese soy sauce is still brewed in cedar barrels. What happens inside the wood, and how to choose your bottle.

4 min de lecture·24/09/2026·FoodHub édition

Less than 1% of the soy sauce produced in Japan is still brewed in wooden barrels. In the whole country, only three to four thousand kioke remain in use — two-meter-tall cedar vats bound with bamboo hoops, in which the sauce ferments for years. Kaneiwa is one of the houses that still use them.

What a wooden barrel changes

Stainless steel is neutral and can be sterilized. Wood cannot: its fibers harbor a community of yeasts and bacteria unique to each brewery, nurtured over generations. It is this, as much as the recipe, that gives the sauce its flavor.

One house, one barrel, one signature

In a barrel brewery, no one can exactly copy the product next door: you would have to move the microorganisms that live in the wood and in the walls. That is why two soy sauces brewed the same way, in two different houses, never taste alike.

These barrels last more than a century. The coopers who can still make them, however, can now be counted on the fingers of one hand — and that is precisely what would make the loss of this method irreversible if the last houses were to stop.

How soy sauce is born

The soybeans are cooked, the wheat roasted, then the two are mixed together.
Inoculation with koji. This mold, Aspergillus oryzae, is the same one used for sake and miso. It is known to produce nearly 300 aromatic compounds.
The moromi. Salt water is added: the mixture becomes a thick mash that will ferment slowly in the barrel.
Time. Prepared in winter, the moromi comes to life in spring, works through the summer, and matures in the fall. One to three years, depending on the house.
Pressing. The sauce seeps through stacked cloths, first under its own weight and then under the press. Filtration comes last.

Tamari, and why it is gluten-free

Everyday soy sauce, koikuchi, contains as much wheat as soy. Tamari is brewed with very little wheat, often none: that is what makes it naturally gluten-free, and what explains its thicker texture and its intensity on the palate.

It is the sauce richest in umami of the whole family. On roast meat, a wild mushroom or an avocado, it brings a depth that salt alone never can.

From the most delicate to the most powerful

Family	Character	Serve with
White	The most understated, very pale	Vinaigrettes, clear broths
Light	Delicate and subtle	White fish
Koikuchi	The essential, the most widespread	Omelets, stir-fried vegetables
Double-fermented	Brewed with soy sauce instead of water	Tomato braises, duck breast
Tamari	Number one for umami, gluten-free	Ribeye, mushrooms, avocado

Short aging, from three months to a year: the sauce elevates the ingredient. Long aging, from two to four years: it brings a complexity all its own.

The house’s three principles

Nourished by the climate — the koji and the brewery’s microorganisms work to the rhythm of the seasons.
Preserved by hand — the microbial balance of the barrels has been tended, year after year, for more than two centuries.
Refined by time — nothing replaces the years spent in the barrel.

How to use it at home

Never boil it. Add it at the end of cooking: boiling destroys its most delicate aromas.
Instead of salt on roast meat — a few drops are enough.
On an egg, an avocado, a pan-fried mushroom: this is where an aged tamari stands out the most.
Away from light, and in the refrigerator once opened.