Narrator: This brown paste is the base
for the world's most expensive soy sauce.
And it won't be ready to sell for another 20 years.
While some popular soy-sauce brands
cost less than bottled water,
Kamebishi's 20-year-aged soy sauce
can reach £99 for only 55 milliliters.
It's because of this thick soybean mash called koji.
It's the key to this soy sauce's flavor.
Here in the city of Higashikagawa, Japan,
Kamebishi dries and ages koji
with a recipe that's more than two centuries old.
Narrator: So, what makes this method worth preserving?
And why is Kamebishi soy sauce so expensive?
Narrator: The complexity of this soy sauce is achieved
by fermenting it for days and aging it for years.
This traditional recipe allows the company
to create flavors that aren't possible
in mass-produced soy sauces.
Narrator: High-quality soy sauce starts
with its most basic ingredient, soybeans.
This never-ending cloud streams from the machine,
steaming soybeans inside.
Narrator: It's a seemingly simple first step
that can make or break the entire product.
Narrator: After 18 hours soaking and steaming,
the beans should be soft and ready.
Narrator: To turn steamed soybeans
into the one-of-a-kind koji,
the beans have to be combined with barley and mold spores.
First, Teppei prepares the barley in a dry room
dusted with finely ground wheat.
Narrator: Unlike other soy-sauce breweries,
Kamebishi grinds it down to fine powder.
Narrator: Teppei mixes koji mold spores
into the ground barley.
Then the steamed soybeans are hand-tossed
with the barley and koji powder.
The mold produces enzymes that break down
the proteins and starches in the beans and barley
into amino acids and sugars.
It's this natural fermentation process
that gives artisanal Japanese soy sauce
its dark color and distinct flavor.
Narrator: Kaori Okada is the current owner of Kamebishi.
She's the 18th generation of her family
to run this business.
Kamebishi is one of the few breweries in the world
that still uses the traditional mushiro koji method.
Narrator: Workers monitor the temperature of the koji
every hour during that time.
Narrator: On the first day,
Teppei heats the room to raise the koji's temperature.
Narrator: The goal in this step
is to heat the koji to stimulate fermentation.
By day two, the fermentation should be so active
that the koji generates its own heat.
Narrator: As it grows, the koji gets so big
it needs to be shaken off the mats,
dumped to the floor, and remixed
to make sure the beans don't stick to each other.
Narrator: The koji ages in these barrels,
where it will transform completely.
Narrator: Moromi is the name of the paste-like mixture
that will age into the finished soy sauce.
It's a mixture of koji, salt, and water.
Adding salt isn't just for flavor.
Salt protects the koji from microorganisms and bacteria
while it ages in cedarwood barrels.
Narrator: But as it ages,
they leave it alone,
except for occasional stirring during the hotter months.
Narrator: Kamebishi ages all of its soy sauces.
The longer they age, the more complex the flavors,
and the more expensive the final product.
Narrator: Kamebishi even has plans
for a 50-year-aged soy sauce,
which won't be ready until around 2032.
Narrator: But before the sauce can be bottled and sold,
it first must be pressed.
Mature moromi aged under 10 years
is spread out on cloth and stacked into layers.
Narrator: Then a machine squeezes the soy sauce
into a bucket below.
Narrator: But anything aged over 10 years
is too dry to press this way.
Narrator: The finished sauce is then heated up
to stop the fermentation
and to pasteurize it for bottling.
Narrator: So when she took over from her sister in 2001,
Kaori started innovating to bolster the historic company.
Narrator: They even make pizza.
Narrator: The company's roots are baked into its name.
Narrator: She felt similarly about
her own foray into the business.