The origins of the Kendal mint cake date to prehistoric times, when unique geological conditions created sweet, marble-like deposits in the caverns of England’s Lake District. Local miners armed with pickaxes risk their lives to carve out this valuable foodstuff.

Of course, that’s the fictional, tongue-in-cheek version related by Colin Bowden. Along with his wife Margot, he runs a shop called The Mintcake Mine in Bowness-on-Windermere, a picturesque Lake District town. As well as selling the delicacy, the shop houses a tiny exhibition on the mint-cake myth – complete with pickaxes and a helmet belonging to the so-called mint-cake miners.

The real story of Kendal mint cake is no less interesting.

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The treat was created by accident in 1869 in the nearby market town of Kendal. Confectioner Joseph Wiper was in the process of making mints. During a bout of inattention, the sugary mixture started to solidify and turn cloudy. The Kendal mint cake – more of a bar than a floury cake, eaten more frequently by hikers looking for a glucose boost than diners in the mood for dessert – was born.

Today, the product remains simple, made of sugar, glucose syrup, water and peppermint oil. The oldest existing manufacturer of Kendal mint cake, Quiggins, adds salt.

Simple or not, the mint cake has played an outsized role in mountaineering history. In 1953, Edmund Hillary and Tenzing Norgay ate it on their attempt to be the first team to ascend Mt Everest.

The expedition manager responsible for their provisions had read about Kendal mint cake in a climbing magazine. In 1952 he wrote to Romney’s, one of the bar’s main manufacturers to this day, to request 38lb (17kg) of brown mint cake, a version made with brown sugar. He had never tried the product himself, but as his letter says, "Experience thas [sic] shown this to be an excellent High Altitude food".

This was seven years after the end of World War II, when the UK was still subject to food rationing. As a result, Romney’s had to make a special request for additional sugar, which was granted.

Hillary and Norgay became the first confirmed people to summit Mt Everest. As for the mint cake, one member of the expedition wrote, "It was easily the most popular item on our high altitude ration – our only criticism was that we did not have enough of it."

Kendal mint cake continues to be popular with climbers, cyclists and runners as a portable, durable source of energy. Emma Stevenson, a professor of sport and exercise science at Newcastle University, explained, “It is high in glucose and therefore is rapidly digested when consumed, and so is a quick source of energy. This is why it is popular on walks etc.”

Kendal mint cake has been called the world’s first energy bar. The sugar content is particularly useful at high altitudes, where the body craves sugar and finds other types of food hard to digest. The strong mint flavour is also appropriate, as high altitudes dull taste buds.

More than 60 years after the summiting of Everest, the making of Kendal mint cake remains largely unchanged.

For one thing, it’s still a family affair in at least one mint cake-producing company. John Barron, the current managing director of Romney’s, is the fourth generation of the family to run the business. As a child, he worked in the factory on school holidays. He operates Romney’s with his wife, Paula, and her brother. The Barrons hope that their two sons will take over the business someday. Regardless, they won’t entertain ideas about selling it. “It’s security for our family and future generations,” Paula said.

Founded in 1914, Romney’s has also retained much of the original production process. The factory happens to be located on Mintsfeet Road North, near the foot of the River Mint. (Amazingly, there’s no connection between these names and the treat.)

Arriving at Romney’s, a minty smell wafts over the unassuming industrial estate that surrounds it. Once inside, the scent is powerful. The factory is smaller than you might expect: just three small rooms. The Barrons are nervous about expanding: getting too big “wouldn’t give us that quality of life and that enjoyment,” said Paula.

The actual production is confined to one room. First, a large vat heats up and mixes the sugar with glucose and water. The next steps are done by hand. The sugar mixture is poured into copper pans nearly a century old. Factory workers add essence of peppermint and mix this in a process known as ‘graining’, which helps the compound achieve its distinctive cloudy appearance. Employees then ladle the concoction into silicone moulds in a variety of sizes and shapes. These moulds have perforations for easy splitting of the sheets.

It takes up to 30 minutes for the cake to turn solid; the staff can tell at a glance, by the texture and colour, whether it’s ready. They break the cake into bars and weigh them. The bars then go to the other rooms of the factory, where they’re wrapped, packed and stacked for distribution.

Kendal mint cake isn’t for everyone. It’s intensely minty – to the point that you’ll continue to taste the herb well after you’ve swallowed the cake. (The chocolate-covered version helps to temper the mintiness.) For intrepid souls only, there’s even an extra-strong version. This is one cake that’s less dessert than fuel, functional rather than gourmet.

Outdoorsy pursuits like climbing are a good fit for the Lake District, a scenic part of north-west England, in the county of Cumbria, known for its 16 main lakes, mountainous terrain and literary heritage (it inspired the likes of William Wordsworth and Beatrix Potter). In July 2017, Unesco named the Lake District a World Heritage Site, a status bound to increase tourism to the already much-visited region.

The Lake District remains proud of its home-grown product, and Kendal mint cake can be found just about everywhere in Kendal. It retains an old-fashioned reputation, but that’s key to its appeal to tourists and locals alike. “It’s not changed,” said Paula. “It’s still made by hand.”

Whatever the future of tourism for the Lake District, and for Kendal in particular, it’s clear that a mint-flavoured bar beloved of mountaineers will long continue to be associated with it.

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