It's been called the smelliest food in the world.

The cans swell up after it's packaged -- and that's considered a GOOD thing.

We're here to explain why the Swedes love their surstr ömming, and for that we called in some experts, courtesy of the Swedish embassy here in Washington, DC.

This surstr ömming and this is the actual Swedish Ambassador to the United States.

Surrrrrrrstrrrroming.

"Sour herring," it actually means.

And we can tell you firsthand: It is pretty stinky.

I don't really know how to describe the smell.

It's strong.

It's earthy?

Can you guys smell it over there?

It's not quite what I expected, i'll say that.

I was expecting almost a little bit like poopy diaper from some of the things I read.

But it's not.

Like its Northern European cousins, such as Icelandic hakarl and Norwegian rakfisk, surstr ömming was born out of the need to preserve freshly caught fish.

It's really part of our cultural heritage.

The oldest piece of evidence about surstromming dates back 9000 years.

this is something that is eaten in a lot of cultures, it's a way of preserving food that really took off in the 1500s, because you know we were at war and salt was very expensive, so people needed to find other ways to ferment or to keep food as, you know, there were no refrigerators back then.

So, up until we invented refrigeration, peoples around the world have used a very simple chemical to prevent foods from spoiling: salt.

But for most of human history salt was expensive and there probably wasn't much to go around, particularly in Northern Europe.

So people had to use as little salt as possible.

And that leads to some interesting chemistry..

There is enough salt in surstromming to prevent most bacteria from growing -- the kind that would spoil the food, or make you sick or whatever.

But certain species of bacteria thrive in high-salt, low-pH, low-oxygen environments, and these guys make surstr ömming what it is.

These bacteria also produce lactic acid.

More lactic acid comes from the fish's muscle tissue as it ferments.

Lactic acid makes it even more difficult for other bacteria to grow by dropping the pH to levels they can't stand.

The bacteria also produce propionic acid, butyric acid, and hydrogen sulfide.

Those guys are responsible for the extremely...um, strong smell.

Together they're sharp, pungent, slightly dairy-like, and vinegary.

The hydrogen sulfide might be the worst part, as it's also responsible for the odor of flatulence.

This is a theme we return to whenever we talk about unusual foods like this.

Holding your nose is better than starving, and over time these foods turn into beloved cultural staples.

It's an acquired taste as they say.

I've learned to eat it, I don't like it that much, but it's part of a tradition and it's a fun thing to do because it's very very special.

But there are those who really really love it.

So either you love it or you don't really.

Surstr ömming is fermented for several weeks in its salt and lactic acid brine.

Then it's canned in the same liquid it was fermented in, which means...it doesn't actually stop fermenting.

The bacteria have no source of oxygen, but that doesn't stop them.

They keep doing their thing, producing gases as byproducts.

That's why the cans swell over time.

Swollen cans of green beans or whatever in the supermarket are a sign of botulinum bacteria and are very very bad news don't ever buy swollen cans.

But in surstr ömming it's business as usual.

This can is a little bit swollen.

It really is under pressure, because normally if I was in the grocery store and I saw a swollen can I wouldn't buy it.

But in this case it's OK.

It is OK.

It's been sitting out for a little bit so that's what happens when it expands when it gets the pressure from the outside, so that's what happens They say to open the can under water because that pressure can cause a bit of splatter - - also it smells.

Well let's crack open a can of surstromming Yes.

and as I am the deputy ambassador I ask the executive chef to do that because you really are very professional at opening it.

Yes sir All right here it goes.

Are you ready?

Let's do it.

Oh.

There was a little pop there.

Oh yeah!

A little spray of bubbles that we got.

I can smell it Yep, oh yeah it's pretty strong.

Oh boy yeah.

Here we go, we're in business.

Let's see if we can get a nice, oh yeah it looks like fish fillets.

Once the can is open, there's a right and a wrong way to eat surstr ömming -- not like these boneheads from Buzzfeed did a couple years ago.

Luckily, Frida is here to show us how it should be done.

So we have this wonderful spread in front of us, this is how you would normally serve it.

You wouldn't eat it out of the can, so tell us a little bit about what you got here.

So we got some potatoes, some boiled potatoes, we got some crème fraîche, we got some chives, a little bit of butter, and some red onions.

There's nothing that isn't better with potatoes.

Everything is better with potatoes.

And (if you're of age, of course,) you've got to round it out with some beer.

Or, even better, Akvavit.

So are we going to toast first?

Are we going to take a bite first?

So we take it, here is yours right here, here is mine, we're taking a bite and then we're toasting.

This is how you would do it?

This is how we do it.

This is how we do it.

So welcome to Sweden.

Thank you so much.

Enjoy.

I don't know if I got much of that fish in that bite.

No, I've got it because it's very salty.

Cheers.

Skol.

That's how we say it in Sweden.

So what are you think?

It's good I'm going to go in for another bite.

Do I have to go for another bite?

Yes you do.

Like almost any traditional strong-smelling food, surstr ömming tastes better than it smells, although it's still very strong and salty.

And it's best eaten in late summer, right when the year's catch is done fermenting.

In fact, it used to be the law that you couldn't eat surstromming before the third Thursday in August.

The law was lifted, but the tradition of the surstromming premiere continues.

Is there a reason you eat it in the summer?

You have to be outside.

mistakes have been made.

Opening the can inside, eating it inside.

And then you're going to need to have a total makeover of your home because the smell is really intense.

We attracted a real crowd from around the ambassador's residence, of seasoned surstromming veterans and newbies alike... We'd like to thank Ambassador Olofsdottir and her team because being based in DC is cool sometimes for helping us understand this corner of the world of cuisine.

Like, we got to see the ambassador's residence?

Which was GORGEOUS?

And spend some time and eat cookies with our lovely lovely hosts.

Thanks so much, everybody.