Tokyo: this world-class metropolis is a veritable gourmet wonderland.

Discover the stories behind the ingredients that make this city so delicious - so "oishii."

Our reporter Kailene is about to chomp into... a hot dog!

This time, we're introducing mustard.

It's a common condiment, but Japan has its own special version.

Actually, in Japan, there's a condiment that looks similar to mustard,

but the spiciness and the flavor profile is a bit different.

And the way they eat it is different, too.

Today's theme is "karashi."

Japanese mustard, or karashi, has a unique, spicy kick.

It's an essential condiment in Japanese cuisine.

This mustard is usually served on the edge of a dish.

Just a dash adds a surprising punch that enhances the flavor of many cuisines.

Spicy? Tasty?

So "oishii!"

In the Edo period, mustard was such a staple that it, not wasabi,

was commonly used to flavor "katsuo," or skipjack tuna, sashimi.

Today, we take a deep dive into the beloved Japanese mustard known as karashi.

Trails to Oishii Tokyo.

To learn all about Japanese mustard, Kailene first visits Asakusa in Tokyo.

In Japan, there's one dish in particular that comes to mind when you think of karashi, and that's "oden."

Today we've come to an oden specialty shop in Tokyo.

Let's head inside to learn some more.

This oden restaurant was founded back in 1915.

Oden is a range of seasonal ingredients like veggies and fish paste treats

simmered in a broth of "katsuobushi" shavings and "kombu" kelp.

Mustard is an essential part of oden.

But why is eating oden with mustard a Japanese tradition?

Looks great.

"Itadakimasu."

A little hot.

It's a bit spicy, but whets the appetite.

Yeah. It's not quite a condiment.
Delicious, right?

Oden is thought of as quite simple.

Just the flavor of ingredients and broth.
But mustard adds another layer of flavor.

Yes.

A different spiciness than you find in the US.

"Itadakimasu."

- Perfect match.
- Glad you like it.

A nice balance between the oden
ingredients and the little kick of mustard.

Right.

But why mustard in oden?

Oden was originally sold outdoors
at stalls rather than restaurants.

Mustard was used as an antibacterial agent.
They say that's how it started.

Eating oden at outdoor stalls was once the standard.

It was easy to eat, but cleanliness was a concern.

That's where mustard came into play.

The component that gives it its kick also has an antibacterial function.

Plus, the flavor fits oden perfectly, killing two birds with one spicy stone.

Japanese mustard is created by whisking a powder.

Funadaiku gives Kailene a look at how it's made fresh each day.

First, warm water is added a bit at a time.

Mustard powder itself does not taste spicy.

Spicy components are released as it reacts with water.

When the pungency brings tears to your eyes, it's ready.

Whoa, that's strong. My nose!

What a shock.

Right. The oden business isn't easy.

- Definitely wakes you up.
- Indeed.

Worldwide, mustard is mainly made with these three types of seeds, which come from the Brassica plant.

Western mustard is typically made from white mustard seeds, also called yellow mustard seeds.

It has a mild spiciness and a sourness borne from vinegar, making it perfect for oily foods.

Spicy brown seeds are mixed with white ones to make wholegrain mustard.

The seeds are crushed with their skin intact, giving this mustard a granular texture.

It also has a sour vinegar flavor.

The seeds for Japanese mustard are said to have arrived from China by the 8th century.

The seeds of a plant called "yellow mustard greens," they have a strong spiciness and a yellow-brown color.

Preserved in powdered form, they've long been a popular household seasoning.

To learn a traditional way to use Japanese mustard, Kailene visits another Japanese restaurant.

First up, a dish perfect for the summer heat: egg miso sauce mixed with mustard.

The sweet miso was made by mixing white miso paste, egg yolks, sake and "mirin" sweet sake.

It's then thinned with yuzu vinegar to create mustard and vinegar miso.

Adding mustard creates richness.
The umami becomes richer.

The miso is used to dress in-season eggplant, and the mustard and vinegar miso's sweet richness enhances its flavor.

It's topped with "myoga" and green yuzu zest to create a refreshing salad.

"Itadakimasu."

"Oishii."

Quite mild.

I tasted the miso first, but now I taste the mustard.

It's so easy to eat. A gentle flavor.

With Japanese cuisine, mustard isn't used to
make things spicy, it's used to improve flavor.

I see! I may have been using it wrong.

It's used to bring out umami.

It has those kind of components?

- That kind of effect, I would say.
- Right.

Next, Kanda prepares katsuo, a much-loved fish in Japan.

It's typically eaten with ginger or wasabi, but at this restaurant, it's served with mustard.

Among residents of old Tokyo, it was long said that eating in-season katsuo brought good luck.

Mustard was an indispensable condiment for killing bacteria and bringing out flavor -

plus, it was easy to preserve.

There is even an old haiku that goes,

"the first katsuo of the year without
mustard brings tears."

Kailene prepares to give it a try.

"Itadakimasu."

A bit too much mustard, perhaps.

It's okay?

The mustard brings out the richness.

It enhances umami and sweetness,
making it feel like eating meat.

"Oishii."

This might be better for
Americans who don't like wasabi.

For me, it's got to be mustard on katsuo.

- I picked it up from my grandfather.
- I see.

I never knew about this great
way to eat katsuo. Thank you.

Mustard is a familiar flavoring in Japan.

These days, it's available in paste form, making it even easier to use at home.

It's truly become an essential part of daily dishes in the household.

However, the number of seeds being cultivated in Japan dropped drastically

starting in the 1960s, when imports from abroad increased.

Kailene visits one of the rare farms that still grows seeds domestically.

It's located in Ayabe, a city in northern Kyoto.

Referred to as "Kyoto's forest," it's surrounded by mountains and is rich in nature.

Some beautiful views here that you don't often get to see, especially, like, in Tokyo.

Very luscious very green farmlands in the middle of the mountains.

Here lives a family of farmers who cultivate the seeds used to make Japanese mustard.

- Hello.
- Welcome.

Nice to meet you.

The Takayama family moved here in 2021.

They show Kailene their field.

Oh, different from what I imagined.

We harvested two weeks ago.
Now we're drying.

- Here it is.
- I see.

We cut the plants when they're green,
then age and dry them in here.

The family's mustard is made from yellow mustard greens, which have long been grown in Japan.

In spring, they sprout yellow flowers.

In May, when seeds start to appear, the harvest begins.

Harvesting is done by hand while the pods are still green.

They're then dried in the sun.

Once the seeds ripen and turn yellow, they are threshed.

Threshing is the hardest part.

Let's see how threshing is done.

- Stomp.
- Stomp?

Just stomp.

Nice sound.

The plants are stomped to remove the pods.

Next comes sorting out the seeds.

The small seeds are repeatedly sifted through a fine mesh.

All this work is done by hand.

These tiny, tiny seeds serve as the material for making mustard.

They're 1/5th the size of rice grains.

There aren't machines that can sift them out.

- All by hand.
- Tough work.

It's tough, but the flavor is worth it.

Previously, the Takayamas ran an eatery in Saitama, near Tokyo.

Their desire for delicious mustard led them to try growing their own,

and eventually to moving here and setting up this farm.

These seeds were once grown all over Japan.

But during the economic boom, efficiency
became the keyword, and imports opened up.

Imported seeds were cheap, and growing
in Japan became too much work, cost-wise.

Now there are very few domestic producers.

When we quit our eatery, someone took
our place, but if we quit this, maybe no one will.

We've come this far, and know the greatness
of the seeds, so we want to keep going as long as we can.

Are the seeds spicy when eaten as-is?

The flavor comes out little by little.
It's a gentle spiciness.

They still contain oil.
Once we extract it, they'll get spicier.

I see.

Before processing, mustard seeds are about 40 percent oil.

Powder is made by squeezing out the oil in a press, which creates flakes.

Here are the flakes, minus the oil content.

Here are the flakes. Smell them.

- Kind of a grassy aroma.
- True. Not like mustard.

- Here's the oil.
- Beautiful!

The oil can be used in cooking.

The oil-free flakes are then ground into powder using a millstone, a tool used for milling grains and other materials.

Here it comes.

Like this.

- Want to try it?
- Please! Is it hard?

Oh, yeah, this is a good workout.

Using a millstone means the powder isn't oxidized, so the mustard flavor is preserved.

There's a trick to making this powder into paste.

The Takayamas' powder delivers its best punch with water heated to 80 degrees Celsius.

Moisture brings out spiciness,
so you must spread it all over, like kneading.

Water releases enzymes, which produce spiciness.

- If they don't work right, it leaves bitterness.
- I see.

It's important to let it rest for 15 minutes or more to extract the spiciness.

In the meantime, they start to cook.

Takayama says "tonkatsu" pork cutlet is his favorite dish for appreciating the deliciousness of Japanese mustard.

- "Itadakimasu."
- Dig in.

Spicy? "Oishii?"

- So "oishii!"
- I'm glad.

It's got a proper flavor.
It's not painful. It's a good-feeling spiciness.

The combo of the tonkatsu crispiness and
mustard spiciness is perfect.

Good.

They also recommend using mustard mixed into soy sauce, which creates a pungent mustard sauce.

This is great too.

The pork's fat and sweetness, the breading's
crispiness, the saltiness of the sauce...

It really makes you want the mustard's kick.

Mustard has a stronger kick than yellow
or brown mustard. A more "adult" flavor.

I could really get into this.

The children show us a unique way to enjoy mustard.

They break a raw egg on freshly cooked rice and mix it well.

Next, they add in soy sauce, then mustard oil.

According to them, the sweet egg and flavorful oil go great together.

How is it?

Good?

The Takayama family wants more people to learn about Japanese mustard oil.

- This is "oishii."
- It's not spicy at all.

Yet it's so rich.

Amazing that it comes from the same seeds,
yet it's so different.

Next, Kailene visits a restaurant, also located in Ayabe, that uses the Takayamas' mustard in its dishes.

I don't know if I've actually been somewhere in Japan yet where I can hear chickens!

You can hear chickens and there's like a goat down there.

Beautiful, though.

Just what kind of restaurant can be found so deep in this farmland?

Hello. This is quite a location for a restaurant.

In the middle of nowhere, right?

But that's what's great about it.

In the middle of nowhere,
but for some people, it has everything.

Our ingredients for today.

Our base is a chicken farm,
so we've got lots of chickens.

We're farm to table,
combining farm and restaurant.

- The best way to eat fresh.
- Exactly.

Farm to table, which started in the US, is a movement

where food is delivered straight from producers to consumers to ensure safety and freshness.

Watanabe Koki, who owns a Chinese restaurant in central Kyoto,

runs this restaurant where he serves food made with self-grown vegetables and local ingredients.

Today, he features the Takayamas' mustard.

Just grind it like this.

- Me?
- Yes.

I have my customers do it themselves
to better learn what mustard is. It's fun.

At this restaurant, the cooking takes place before your eyes,

helping you learn more about the ingredients being used - and sometimes you even join in!

Once ground to taste, add salt and bring out the spiciness with hot water.

Then add vinegar to give it a sour-and-spicy flavor.

While resting the mustard to let its pungency emerge, Watanabe brings out some mustard oil.

He's going to utilize its unique, non-spicy flavor.

Next comes out some well-pickled "daikon" radish.

Its umami, which comes from fermentation, will add depth to the dish.

It's sauteed in oil.

The mustard oil is used to flavor fragrant cilantro, which is then added to the salty-sour daikon and fresh turnips.

The appetizer is complete.

"Itadakimasu."

So good.

So simple but so complex.

Mustard oil really brings out the
umami of all the ingredients.

Right, not strong, but ties it all together.

So fun.

It goes beyond what most
people think of as Japanese mustard.

The next dish uses an entire "shamo" chicken like the one we just saw.

It's soaked in chicken broth and topped with spices,

then further soaked in lots of Chinese rice wine made with brown rice.

The whole thing is placed in a bamboo steamer to create steamed chicken in soup.

While it's steaming, he visits the adjoining field.

I want to add this.

It's meant to add aroma,
so I'm going to use much more than normal.

He grabs a handful of aromatic "sansho" pepper.

The aroma of the sansho is brought to the fore with oil.

It's placed on the chicken, and the dish is complete.

Here you are.

Beautiful!

It smells so good.

A bold, flavorful chicken meal.

And don't forget the condiment for enhancing its flavor: wholegrain Japanese mustard.

It's the key to the whole dish.

- "Itadakimasu."
- Please.

Complex flavor.

Right, but based around just chicken broth.

And the mustard is just perfect.
Not too spicy. Great texture.

By adding salt and vinegar,
it becomes milder.

It's still a bit spicy, but doesn't sting.
It's more of an accent.

Mix some mustard in here,
then drink a bit of the soup.

Wow!

The oil and mustard bring the flavors together.
They're less about adding flavor...

- ...than binding everything together?
- Right.

It's hard to preserve truly delicious things.

Japan's population is shrinking,
and there are fewer young people.

Fewer people want to be farmers.

But without great ingredients,
we can't create great dishes.

Making everything domestically is important
for every kind of ingredient.

I've never eaten at an outdoor restaurant
like this one. I was really moved.

It makes me want to learn more about where
the food I love comes from and how to make it well.

Japanese mustard seeds may be small, but they lead to a giant number of "oishii" possibilities.

In the world of this Japanese mustard, there's even more to discover.

In Tokyo - and Kyoto - every ingredient has its own story.