Its unmistakable smell permeates Seoul subway carriages during the rush hour, and aficionados claim it is the healthiest food on the planet.

Once valued as a source of vitamin C before the arrival of refrigerators, kimchi now crops up on menus far from its birthplace on the Korean peninsula. The spicy, garlicky cabbage dish is to be found as a pizza topping and taco filling in the UK, Australia and the US, where the Obamas are said to be converts. Kimjang, the traditionally communal act of making kimchi, was recently awarded world cultural heritage status by Unesco.

But despite its growing popularity in restaurants from Los Angeles to London, South Korea's national dish is in crisis in its country of origin. To kimchi's basic ingredients of napa cabbage, garlic, seasoning and copious amounts of chilli power, we can now add a trade war with China and fears of lasting damage to Korean cultural identity.

According to the World Institute of Kimchi, South Korea's kimchi exports were worth $89.2m (£54m) in 2013, down 16% on the previous year. But imports – almost all of which come from China – rose almost 6% to $117.4m. That left the South Koreans with a kimchi deficit of more than $28m – and a wound to their national pride that has festered since the trade imbalance first appeared in 2006.

"It's a shame that so much of our kimchi comes from China," said Kwon Seung-hee, who teaches tourists how to make the dish at her guesthouse in Seoul. "It's cheap, but it doesn't taste as good as ours. I can tell straight away if I'm eating imported kimchi."

The kimchi deficit should have been foreseen, perhaps, when the dish made the transition from luxury food to popular staple in the late 18th century. To keep up with demand, Korea began importing cabbages from China.

Kimchi is an indispensable part of the Korean diet, with South Koreans eating almost 2m tonnes every year. Though it often appears in stews and soups, no meal is considered complete without a side dish of cabbage kimchi, along with variations made from daikon radish, cucumber, perilla leaf or a host of other seasonal vegetables.

"The making of kimchi … is a culture that continues to be shared by virtually all Koreans and is a significant part of their lives," Park Hei-woong, a cultural heritage administration official, said when the Unesco status was announced at the end of last year, adding that kimchi-making maintained the "cohesiveness of Korean communities … and is an essential part of the Korean cultural identity".

There are an estimated 100 varieties from the fresh, crunchy dish preferred in the north to the more pungent version commonly eaten further south. According to the cultural heritage administration in Seoul, about 95 percent of Koreans eat kimchi more than once a day; more than 60 percent have it for breakfast, lunch and dinner.

According to Jia Choi, president of O'ngo Food Communications, a cookery school in Seoul, kimchi forms the basis of a perfectly balanced meal: several dishes made with seasonal vegetables, with a smaller quantity of rice or noodle dishes providing the carbohydrate.

Traditionally, meat was never considered part of the Korean culinary jigsaw, and the famed barbecue restaurants that line Seoul's streets today only took off after the city hosted the summer Olympics in 1988.

"The Unesco award certainly gave us an added sense of pride," said Choi, who hopes kimchi's international recognition will boost consumption among her young compatriots. "Interest in traditional Korean traditional cuisine is waning. Kids today eat a more varied diet that includes a lot more western food, and that's why kimchi consumption is declining year after year."

A stall selling kimchi in South Korea. Photograph: Justin McCurry for the Guardian

If children develop a kimchi habit while dining out, they will almost certainly be served the Chinese version. Chinese kimchi is cheaper and, for most diners, impossible to identify as a "fraud". The trade deficit, coupled with declining consumption at home, has been described by one politician as an ordeal "as harsh as a Korean winter". But South Koreans are now looking beyond their own borders to secure kimchi's long-term future.

Korean cuisine has been part of the trendy food scene in parts of California for several years and was among Forbes magazine's top 10 food trends of 2013.

Kimchi and other staples such as bulgogi [], japchae [] and samgyeopsal are also finding their way on to menus in parts of the areas of the UK outside the Korean expat enclave of New Malden.

Many Britons had their first taste of kimchi, along with more than 100 other Korean foods during a two-week Tesco promotion at the end of last year, when overall imports of Korean food products to the UK rose 135 percent compared with 2012.

And after years of being overlooked, Korean cuisine has joined other Asian cuisines on the UK celebrity chef beat, as demonstrated by the Hairy Bikers in a programme from South Korea that aired this week.

"We need to keep pushing Korean-made kimchi as authentic, in the same way that European countries promote their cheese and wine," said Choi. "We're a tiny country compared to China, so although we can't compete in terms of volume, we can remind people around the world that our kimchi is authentic and safe."

Kimchi is usually made from napa cabbage, garlic, seasoning and chilli powder. Photograph: Brian Yarvin / Alamy/Alamy

How to make kimchi

A quarter of a head of napa cabbage, soaked in brine overnight

A quarter of a cup of coarse sea salt for the brine

100g daikon radish

30g spring onion

5 tbsp chilli powder

20g shrimp sauce

2 tsp minced garlic

1 tsp minced ginger

1 tbsp sugar

1. Julienne the daikon radish and cut the spring onion into 3cm slivers.

2. Colour the radish with the chilli powder then add the spring onion and all of the other ingredients except the cabbage to make the paste. Give it a thorough mixing. Rubber or plastic gloves recommended.

3. Place the cabbage in a shallow tray and along with the paste. Starting with the outer leaves and working in, smear generous amounts of the paste on each leaf until the entire cabbage is covered.

4. Tightly press the leaves together to create a bundle, and transfer the cabbage to an airtight container and place it in the fridge.

You can eat the kimchi after a few days; for a more pungent dish, leave it to ferment for a month to several weeks.

Courtesy of O'ngo Food Communications

• This article was amended on 21 March 2014. The recipe mistakenly omitted 1/4 cup coarse sea salt for the brine and the 30g spring onion was wrongly changed to 3g in the editing process. These have been corrected.