Folk singer Rachel Sermanni on Mumford & Sons and her debut album

The setting was incongruous for folk singer Rachel Sermanni’s big rock‘n’ roll blow-out. “The thing about Zurich is that everyone works in finance,” says the 21-year-old from the shadows of the Cairngorms, who decided that as this was the last night of the tour, she’d dispense with her no-booze rule. Several whiskies later, she had a Cairngorms-sized hangover.

I’d been planning to ask Sermanni about a gig earlier in the tour, this one in London, where she stopped mid-song, started to cry and urged her manager to fetch some amber liquid that definitely wasn’t Irn-Bru.

“You think there’s a trend developing here?” she says with a chuckle. “Well, sometimes you need some fire in your belly and whisky is such lovely, pure juice. But that was a gig which could have gone badly wrong. I wasn’t very happy and felt I should tell the audience. I was tired, hadn’t written a new song in months and felt my worth dwindling. I was on this treadmill, just playing and playing and playing, giving all the time … ”

It should be said that Sermanni recovered that night, her whisky wobble being no impediment to a rave review. It should also be said that in Glasgow today, layered-up against the cold and with a Hermann Hesse book by her side, she’s drinking camomile tea and looking happy. Finally, she’s heading home.

Home for Sermanni is Carrbridge in Badenoch and Strathspey. “I miss my family and friends and it’s the only place I can write,” she explains in her lovely Highland lilt. The population of Carrbridge is about 700. Sermanni is too close to it to say, but some reckon you can hear the spectacular landscape in her songs. Earlier in her life, though, the village seemed like the teeming metropolis. “I used to live in Farr, which was just six cottages and a wee school. I look on that time as my true childhood. It was so innocent, so perfect, so magical. And then aged ten in my new classroom in Carrbridge I heard swearwords for the first time!”

Sermanni has just released her debut album, Under Mountains, and to the earlier patronage of Mumford & Sons, comparisons with Laura Marling and support slots with Elvis Costello and Rumer, she was able to add the approbation of Elbow’s Guy Garvey, who enthused about her “astonishing” voice on his 6 Music radio show. But perhaps some will be wondering if she’s too sweet for the music biz.

She’s shown a fair bit of courage thus far, having forsaken university and mildly alarmed her parents – police dog-handler Dom, and Grace, who helps children with mental health issues – with her decision to leave her tiny, tight-knit community at the age of 17 and head down to Glasgow to busk.

And she’s not afraid of hard work, having racked up a huge number of gigs already. “In 2011 I did more than 200 shows. The Performing Rights Society compiles a list of the biggest giggers and I was there at No 8 next to Ed Sheeran and Olly Murs. This year I’m sure I did even more shows and 2013 will see plenty more in support of the album. I’m not daunted by that, but I need to know I’m headed somewhere. I’d had a wee chat with my manager and I’m a lot happier now.”

Sermanni’s exotic name comes from Barga in Italy, which is also where fellow Italo-Scots Paolo Nutini and Nicola Benedetti have their roots. “I’ve discussed the connection with both of them. Paolo told me it was good for the soul to go back. I visited when I was very young but not since and now I’m keen to find some cousins.” Growing up with a younger brother and sister, Simon & Garfunkel, Bob Dylan and Fairport Convention were the soundtrack to long car journeys. “And my friends were the weird kids rather than the cool ones.”

The Mumfords connection began on a beach. After seeing the nu-folk movement’s leading lights perform at Ullapool’s Loopallu festival she was confident enough to ask if she could jam with them. “That was a fateful meeting. They took me under their wing, on tour and down to London. That was when I realised how huge the music business is. It was unnerving but I also realised that if I was going to make it then I had to stop twinkling about on the guitar, only singing sweet songs. The Mumfords taught me that I could be louder and a bit darker.”

Although grateful for their support, Sermanni wants to go her own way. The comparisons with Laura Marling, whom she greatly admires, made her hesitate about using artist Sophie Milner for the sleeve of Under Mountains because of the latter’s work with Marling. Ultimately, though, she liked Milner’s illustration too much. “She understands my appreciation for symbolism, a desire to lean towards darker things and great intrigue in dreams.” Sermanni likes to dream – it’s where she gets lots of her ideas. “Most of the songs on the album came from dreams. Breathe Easy is about a lovely idyll, swimming with friends in a river, being under the water with a boy I liked. Waltz is similar: another protected space, this time in a dance, and another boy.”

These tracks and others were written when she was 16. Black Current is more recent, with teenage fun being supplanted by the realisation that life just got more serious. “That one came from a dream in which I was a bird with long, thin wings flying too high. The situation was precarious. I guess that was me worrying too much about the pressure, the investment that’s been made in me, the belief.”

For Sermanni, like so many singer-songwriters, affairs of the heart dominate. But, given her tender years and sheltered upbringing, she surely can’t have had her heart broken too many times. “I really haven’t and I can be thankful for that. Back home, I stayed very innocent until a very late stage.” Glasgow, though, seems to be fast-tracking her into young adulthood. “I’m becoming aware of different emotions, like losing yourself. Another newer song, Bones, didn’t come from a dream. For the first time in my life I didn’t listen to myself at all. I was trying to be cool for someone.”

Sermanni is attempting to strike a balance between innocence and experience, aware that the latter is just as useful in her work. When she gets back to Carrbridge for Christmas – to run up mountains and hopefully write some new songs – she’ll be reunited with younger siblings who appear to be more grown-up. “My sister and brother seem much older than me and I admit I’ve tried to retain feelings of being a child as long as I possibly can. But isn’t that what all musicians do?”

• Under Mountains is out now on Middle of Nowhere. Rachel Sermanni performs on the Hogmanay Live show on BBC1 on 31 December, then live in a secret location in Edinburgh on 1 January, as part of Your Lucky Day (see panel, right).