Narrator: 52,000 ceramic jars
hold a Japanese black vinegar known as kurozu
that can only be made in this part of the world.
One batch can take up to five years to age,
and brewmasters like Kenji Tachiwada
keep track of the quality
by checking the taste, sound, and smell.
Narrator: One bottle can cost at least double the price
of a regular, mass-produced rice vinegar.
Chefs across the country seek it out
for its smooth and mellow taste.
Narrator: Sakamoto Kurozu
is one of eight vinegar breweries
in the southern Japanese town of Fukuyama
that still use this 200-year-old fermentation method.
But ramping up production is nearly impossible,
because it's difficult to find more land to lay out jars.
We travel to Fukuyama, Japan, to see how this ancient method
of making black vinegar is still standing.
Kenji starts his work
at the Sakamoto Kurozu facility at 8 a.m.
He's been working here for the past 40 years.
Narrator: Brown rice is one of only three ingredients
in kurozu.
Workers harvest it from nearby fields.
Narrator: They steam the rice and mix it with a mold
that's also used to make sake and soy sauce.
This is called koji,
and it's the first ingredient to go in the jar.
Narrator: Kenji fills up the rest
with plain steamed brown rice.
It makes the vinegar less tangy and acidic.
Then he fills the pot with around 9 gallons
of fresh water from a natural spring.
Narrator: A final layer of koji goes on top.
It will later turn into a thick slab of mold
that protects the vinegar
from other microbes entering the mixture.
Master brewers usually fill the jars up
in the spring and fall,
when the temperatures are just right.
Narrator: This specific region
has the perfect climate to make kurozu
because of its relatively warm weather year-round.
The natural outdoor heat accelerates fermentation.
Over a three-to-six month process,
the mold turns the rice starch into sugar,
then into alcohol.
As the vinegar ages, it turns darker and richer in taste.
It takes at least three years
to reach its signature brownish hue.
Kenji checks all 52,000 pots to keep track of the aging.
Narrator: Each pot ages at its own pace,
but most reach the dark brown color in three years.
Kenji selects a few to ferment for up to five,
and those are the most expensive.
Narrator: The company sells vinegar
at all stages of aging.
These ceramic pots also play
an essential role in the process.
Their dark exterior absorbs heat from the sun,
and the porousness of the clay
allows the mold to keep fermenting.
Sakamoto Kurozu has been buying them
from Chin Jukan pottery for the past 200 years,
and they last for centuries.
The company still has about 1,000 original pots
from two centuries ago.
Narrator: Chin Jukan is a 15th-generation potter
running the 420-year-old family business.
Narrator: People have been making black vinegar
in Fukuyama since the 1800s.
In the early 20th century,
there were about 24 kurozu makers here,
but many closed their doors during World War II,
when the government implemented food rations
and restricted brewers from using rice.
Sakamoto Kurozu managed to stay afloat
by briefly substituting sweet potatoes for rice.
Today, it's one of only eight kurozu businesses left.
It's also one of the largest, covering 35,000 square meters,
the size of more than six American football fields.
Akihiro Sakamoto is the sixth-generation
to run the family business.
Narrator: It also has a restaurant on site,
where visitors can taste the vinegar.
Narrator: Junichi Honda studied the best way
to use vinegar in his dishes.
Like miso and soy sauce,
rice vinegar is one of the basic seasonings used
in Japanese cuisine.
It's usually aged for three months,
and some can be ready in just days with modern technology.
Kurozu's years-long natural process gives it a milder
and less acidic taste than regular rice vinegar.
The restaurant's sweet-and-sour pork
is the most popular item on the menu.
Narrator: A 1,000-milliliter bottle
of kurozu costs around $20.
That's double the price
of standard, mass-produced rice vinegar.
The older it is, the more expensive it becomes.
But Akihiro is not worried about cheaper competitors.
Japan's Ministry of Agriculture, Forestry, and Fisheries
certified kurozu with a geographical indication in 2015.
That means authentic kurozu
can only be made here in this region using these techniques.
Just like Champagne can only be produced
in a certain region of France.
And nowadays, Akihiro has chefs and customers
from across the country seeking his vinegar year-round.
The company expanded its line
to include vinegar-based products like jam,
ponzu sauce, and flavored drinks.
Narrator: Customers buy kurozu
for its supposed health benefits, like weight loss,
lower cholesterol, and increased energy.
Studies suggest people who use it regularly see benefits,
but usually when paired with other healthy lifestyle habits.
But there's no simple way of expanding.
Most of the land in Fukuyama is already taken,
and moving the business somewhere else
would mean losing the geographical indication.
The company also needs a flat area to lay out pots,
and the terrain here is hilly and steep.
And there's no way of accelerating
the natural fermentation process
or changing the size of the pots.
So for now, he's making as much
as the 52,000 pots can produce.
Narrator: And none of that is possible
without veteran brewmasters like Kenji
ensuring that the quality is top-notch.