home to the world's largest concentration

of frozen-custard shops.

Now, frozen custard is not the same thing as ice cream,

and by law it has to have at least 10% butterfat

and a lot more egg yolk.

And because Wisconsin is home to dairy,

lots of dairy,

it is the perfect fit for frozen-custard shops.

Now, what are we waiting for?

Let's go see how frozen custard is made.

Scott Borkin: Custard's more dense.

Ice cream has a lot of air in it,

and this has less amount of air.

So when you're eating it,

custard goes on your palate

and it's gonna stay there longer,

where ice cream, it's gonna melt quicker.

Medha: But before you even taste

that rich frozen custard,

it starts as this liquid dairy mix.

Kopp's mix is top secret,

but we do know that it is at least 10% butterfat

and more than 1.4% egg yolk.

And these aren't just arbitrary measurements.

To officially be considered frozen custard,

the US Food and Drug Administration

actually mandates these percentages.

While your premium ice creams

may have that same amount of butterfat,

your average ice cream probably isn't going to,

and it's even more unlikely

for ice cream to have that much egg yolk,

instead consisting of more air, like Scott said.

Kopp's gets its secret mix

from Galloway, a dairy processor

that actually introduced frozen custard to the Midwest

during the 1933 Chicago World's Fair.

The dessert found a home in Wisconsin.

Its more than 100,000 dairy farms meant easy access

to fresh cream and butterfat milk.

Scott: We pour it up in the hopper,

and then they'll start the machine up.

[machine whirring]

These machines are running at about 16 degrees.

Ice cream is about,

temperature's obviously got to be under 32,

but not much under 32,

so custard is running at a colder temperature.

Medha: This machine is what really does the work

of turning the mix into custard.

As the machine freezes the custard,

it adds in as little air as possible.

While regular soft-serve ice cream

might be about 40% air,

frozen custard can range anywhere from 15% to 30% air,

giving it a thicker texture than ice cream.

As it thickens,

the machine slowly pushes the custard forward.

Once the custard gets to the right consistency,

it pushes its way through the front of the machine.

How old are they?

Scott: These two machines were made probably

in the mid to late '40s.

Medha: OK.

Kopp's has a pretty unique way

of keeping such old machines running.

If something goes wrong, they actually call up Leon's,

a competing frozen-custard stand

that also works on maintaining old custard machines.

Scott: 'Cause he also has a business, a machine shop.

He builds all the parts for us

for all the custard stands.

So if we need something, we call him,

and they make parts that we need

for our machines to keep them going.

Employee: 138!

For you.

Medha: Is it plain, or is it vanilla?

Scott: We call it plain.

Most people would say it's vanilla,

'cause vanilla is a plain.

Until we add the vanilla extract, to us,

it's not a vanilla custard.

That vanilla extract is what makes it

the vanilla custard.

Right now, we're probably spending

close to $500 a gallon.

Medha: Oh, wow.

Scott: It's the premiere vanilla extract.

It's like comparing it to a Volkswagen to a Mercedes.

We're using a Mercedes.

You can taste that expensive vanilla in this custard.

This vanilla tastes so good.

It has a very creamy consistency.

There's so much more of the treat in one bite,

or one lick, I should say.

This is definitely better than ice cream.

Scott: Beer isn't what made Milwaukee.

It's the custard.