Hello. This is 6 Minute English from BBC Learning English. I'm Phil. And I'm Beth.

Most people have eaten some unusual food at least once in their life. What's the most unusual thing you've ever eaten, Beth?

Oh, I ate camel in Australia, and I really didn't like it, to be honest. What about you?

I ate caiman in Northern Argentina, and it was delicious! Oh, OK. Good!

Well, in this programme we'll be discussing some very unusual food known as 'forever food' – dishes, like stews and soups, which can be kept going day after day, year after year.

We'll also be learning some useful new vocabulary, all of which you can download, along with a worksheet for this programme, at our website, bbclearningenglish.com.

But let's get back to forever food, and a Bangkok restaurant called, Wattana Panich, that's famous for a soup which has been cooking for over 50 years!

Here's radio listener, David Shirley, who called BBC World Service programme, The Food Chain, after tasting the soup himself:

I had never heard of a perpetual stew before, but the first time I'd ever heard about it was when I was in Bangkok. I found a stew that had been simmering for fifty years.

David tasted perpetual stew, a pot into which ingredients are placed and cooked continuously. The pot is never completely emptied.

Instead, new ingredients and water are added when necessary and left simmering – cooking at a temperature just below boiling so that the food bubbles gently.

A 50-year-old soup might not be to everyone's taste, but forever foods are surprisingly common.

And, Phil, I have a question for you about Wattana Panich's 50-year-old soup. What do you think is the main ingredient? Is it: a) beef? b) chicken? or, c) vegetables?

Oh, I think vegetables. I think that's probably safer. OK. Well, we'll find out the correct answer later in the programme.

It's not just Bangkok where people cook forever foods. Fuchsia Dunlop is a writer and cook specialising in Chinese food.

Here, she tells BBC World Service programme, 'The Food Chain', about a Chinese stew that is rumoured to be 100 years old:

In China they sometimes, you know, professionals talk about having a bǎinián laolu which means, like, a 100-year-old-broth.

So, I don't know if this is strictly true, but theoretically as long as you have a good practice of hygiene -

which is to say that you always skim it, and boil it every day, and also replenish it as needed with more water, more salt, more spices, and you know, you keep tasting - then it just gets richer and richer.

Cooks need to replenish a forever stew, to fill it up again with fresh ingredients before it's completely eaten. By being regularly replenished, some dishes are rumoured to last 100 years.

Wow, that is a long time! Fuchsia doesn't know if it's strictly true, or completely true, that the same stew has really lasted 100 years, but she thinks it's possible in theory, as long as it's kept safe and hygienic through boiling.

Professor Martha Carlin is a historian with a special interest in medieval cookery.

Here, she explains to BBC World Service programme, 'The Food Chain', why long-lasting foods could have been familiar to people in the Middle Ages:

In theory, it would make sense to think that people who didn't have matches or fire starters, for whom starting a fire from scratch was quite a cumbersome process,

would naturally want to keep a stew pot bubbling if they had the means to do that, and to avoid the labour of constantly restarting the fire, and also to make sure that they had a hot meal waiting at any time.

Having hot food bubbling away on the fire means there' is always something ready to eat, and avoids having to start a fire from scratch.

When you do something, like cook food or make a fire, from scratch, you do it from the beginning, without the help of anything that has already been made.

Starting a fire is also cumbersome, an adjective meaning difficult to do, taking time and effort.

But Professor Carlin says only rich families were able to afford enough wood to keep a fire going all day.

Anyway, all this talk of food has made me hungry, Beth, so what was the answer to your question?

Ah, I asked you what the main ingredient is in the Bangkok stew, and you said vegetables. And I'm afraid that's wrong. It was, in fact, beef.

OK, let's recap the vocabulary we've learned in this programme about forever foods such as perpetual stew, a pot of stew into which new ingredients are regularly added, allowing the dish to be eaten over a long time.

When food is simmering, it's cooking at a temperature slightly below boiling so that it bubbles gently.

The verb replenish means to fill something up again. If something is not strictly true, it's not completely or entirely true.

When you do an activity such as cooking, from scratch, you do it from the beginning, without using anything that has already been made.

And finally, if an activity is cumbersome, it's difficult to do and takes a lot of time and effort. Once again, our six minutes are up.

Remember to visit our website, bbclearningenglish.com, where you'll find a worksheet and a quiz related to this programme, and we'll see you again soon for more trending topics and useful vocabulary, here at 6 Minute English. Goodbye for now! Bye!