THERE are worse places to be on a weekday afternoon than sitting in a posh hotel sipping Perrier-Jouët Grand Brut from a pleasingly heavy tulip glass, though my bubble-induced sense of wellbeing goes a little flat when I see what my drinking companion is up to: he wants to show me how you can use an iPhone to scythe off the top of a champagne bottle. I gulp when I notice the size and make of the bottle he has grabbed from a nearby counter – a £137 Perrier-Jouët magnum. It's my fault. I did ask.

“There it is,” he says, pointing to the seam which runs up the side of the bottle. “This is the weakest part of the bottle. So basically what you do with the iPhone is manipulate the pressure in the bottle. It's about five or six atmospheric bars of pressure in here, like a tyre on a double decker bus. It's dangerous, but it's also fun. So you run the iPhone along the pressure seam, build up more and more pressure in the neck until you hit the seam just under the top. It just cuts clean off because of the pressure inside, so you don't get any splinters in your glass. It's like a laser.”

He puts the magnum back, to my great relief. But he hasn't quite finished.

“An iPhone Five or Six is better than an iPhone Seven,” he says authoritatively, “because it has the curved edges.”

“And a Samsung Galaxy?”

“You'd be OK with a Samsung Galaxy. Depending if it goes on fire or not.”

My magnum-wielding, iPhone-abusing, esoterica-spouting champagne buddy is 29-year-old Edinburgh boy Davy Zyw, the youngest British sommelier to work at the double Michelin-starred La Gavroche restaurant – he was 22 at the time – and now author of I Love Champagne, a highly readable history of the alcoholic drink which, more than any other, signifies status, luxury, good times, celebrations and (if you're me) the cover of Rod Stewart's A Night On The Town and virtually everything by Roxy Music.

Right now, Zyw is guiding me through an impromptu tasting session which begins with him holding the glass up to the light and observing the bubbles, and ends with a lesson in history and the price of French real estate.

“There's a nucleation point at the bottom of this glass and there's a very steady rise of bubbles,” he says, watching intently. “There will be a minute etching on the bottom of this glass to direct them. This is a very nice glass. Generally the smaller the bubbles, the longer that champagne has spent ageing before release, which essentially means it has had more time to develop more flavour. So you can tell this is going to be a quality champagne … This has spent, I'd say, at least two, two and a half years, ageing in the winery under Perrier-Jouët in the Avenue de Champagne in Épernay, where the head offices are and the champagne is kept.”

Épernay, by the way, is the capital of champagne country, and the Avenue de Champagne is the grand road that runs through it, lined on each side with famous champagne houses. Some look like palaces, others like banks or monasteries. A few look like they could be home to a Bond villain. But it's what's below ground, in the miles of chalk caverns, that's really important.

“They say the Avenue de Champagne is the most expensive road in the world, not because of the buildings but because you have millions and millions of bottles resting in the cellars underneath. Everything from Dom Perignon to Pol Roger to Pommery to Perrier-Jouët. So if anything was to happen to that street, the world would lose an awful lot of champagne. Under that road is gold.”

Anyway, on with the tasting. It's time, says Zyw, “to stick our schnozzes in”.

“I've already done a bit more than that,” I mumble, eyeing my half-finished glass.

He carries on regardless. “And it's a beautiful champagne. It's got lovely white flower, lots of lemon, pineapple, pear, apple character. But underneath is that slightly toasty character: brioche and croissant sitting behind. It's like the sort of burnt, caramelised sweetness you get with Werther's Original sweets. That comes from the secondary fermentation. That's the ageing process.”

Cava and prosecco don't have this, apparently. No, not even the Lidl and Aldi varieties.

“If you open a bottle of cava or prosecco, the bubbles are very large and they travel very fast, which means it has been made pretty quickly,” he explains. “Of course you get amazing types of prosecco, but there is a quality ceiling because it's only one process. It's made in a tank and you can do it on a commercial scale.”

DAVY Zyw has been obsessed with wine since before he was even into his teens. His maternal grandfather had a house in France and he can remember being given a sip from his mother's glass when the family was holidaying there. He was 12 at the time.

“It was a rosé and I know now, because the house is down by Béziers, it was more likely to be a Cote de Provence. But I remember smelling it and tasting it and asking my mum, 'If this is made of grapes, why does it taste of raspberries? It doesn't make sense'. That played with me and stuck with me – how do you metamorphosise those flavours?”

It was a Eureka! moment of sorts. It was certainly the first time he realised he had a discerning palette. And so, from the age of 16 when he left school and took a cookery course at the Edinburgh School of Food and Wine, wine became a passion. He followed that with a part-time evening course in wine. He was still only 17, so not legally able to drink. Nobody seemed to bother.

One fellow student on the wine course, he recalls, was a “super-pretty, very well-spoken English girl”. She and Zyw became friendly and would take the bus back into Edinburgh together. “Then a few years down the line I'm watching the Princess Diana Memorial Concert and I thought, 'Who's that girl sat next to Kate Middleton' – and it was Pippa. I didn't realise I'd done the wine course with her.”

It wasn't Zyw's only brush with the younger Middleton sister. A few years later, now working as a sommelier at the upmarket Bluebird Restaurant on London's King's Road where celebrities and Chelsea footballers were regulars, he met her again – this time with Princes William and Harry “and all the entourage”.

But although Zyw's elder half-brother Danny is the manager of a pub in Leith, the wine business wasn't an obvious choice. In fact the rest of Zyw's immediate family have pursued another line of work entirely. His father, who died when he was 15, was the Edinburgh-based sculptor, poet and architect Adam Zyw. His mother, Adam Zyw's second wife, is noted literary agent Jenny Brown. His uncle, Michael Zyw, is a painter based in Tuscany. His twin brother Tommy is Director of the Scottish Gallery in Edinburgh and his grandfather, who raised Adam and Michael in an extraordinary house perched at the foot of Bell's Brae in the capital's Dean Village, was the celebrated Polish painter Aleksander Zyw, whose work is held in the collection of Tate Britain.

What Zyw does share with his other family members, however, is determination and, perhaps, a mixture of good fortune and good connections. Through a summer job at the Edinburgh International Book Festival he met the restaurateur Martin Wishart – “a huge hero of mine. Edinburgh boy, went down to work for the Roux brothers, got his colours, brought the first Michelin star to Leith. Legend” – and was offered a sommelier job at Wishart's Leith restaurant. He found out about Plumpton College in Brighton, the UK's only undergraduate wine business course, the day before applications closed and still managed to land a place, another stroke of luck. He was helped onto the notoriously steep and slippery London property ladder by none other than Kirsty Allsopp and her Location, Location, Location team (more of that later). And then he went straight from college into one of the most prestigious but highly-pressurised working environments there is – a double Michelin-starred restaurant, in this case Le Gavroche in London, opened in 1967 by French brothers Michel and Albert Roux and now run by Masterchef star Michel Roux Jr. Among the chefs who have cut their teeth there – and probably several fingers – are Gordon Ramsay, Marco Pierre White, Monica Galetti and Marcus Wareing.

“I went from being a bohemian student in Brighton, summer on the beach, to doing 90-hour weeks, working language French, living in a basement in Mayfair and working for Michel Roux Jr. Quite a transition.”

Zyw was the youngest British sommelier the restaurant had ever had and stayed around nine months. It wasn't a bad run: some people who came in for trial shifts lasted only 10 minutes.

“In the kitchen and in the cellar it's chaos,” he says gleefully. “Fast-paced, brilliant, family chaos. On the restaurant floor all you can hear is quiet conversation and the chinking of fine china. But in the kitchen you've got people screaming at each other, slamming plates, things on fire. It was a lot of fun.”

Zyw's modus operandi as a sommelier was to put on his best French accent to tell customers the names of the wines, then drop back into his Edinburgh brogue to explain what they tasted like. It wasn't an approach that endeared him to the restaurant manager, though. Neither was a marked reluctance to tug the forelock.

“In Le Gavroche, there's a lot of money and people are used to having waiting staff and I didn't like the attitudes of some of the customers. So there was a little bit of conflict.”

Of course serving up £1000 bottles of wine means dealing with very wealthy customers, just as writing a book about champagne means hymning a drink which, although associated with celebration, can also symbolise the worst sort of excess. Think of those braying City fat cats quaffing magnums to celebrate another million-pound bonus. Does that side of the champagne world leave a bitter taste in his mouth?

“Because it's a desirable luxury item, some people are buying it for the price tag or the kudos it gives them among the other people in the room,” he admits. “But it also polarises people too, particularly us Scots. We don't like the fact that people are dropping 100 grand on something that's gone in an instant, and there's a lot of people who do that.”

One story of such excess sticks out from his days at Le Gavroche. It involves “a banker type – fat, pinstripe suit” who “dropped five grand” on a bottle of 1996 Vintage Krug champagne and a 1982 Chateau Mouton Rothschild. Zyw told the man he had made an excellent choice and asked if he wanted both wines decanted. He did.

“I'm just on my way out and he says, 'Oh sorry, can I get a carafe of orange juice and a carafe of Coca-Cola as well please?' I looked at the girl [his companion] and thought, 'Maybe she's not the red wine type'. So I brought them down – and he poured the orange juice into the carafe of champagne. He basically had a Krug 1996 Buck's Fizz.”

The Chateau Mouton Rothschild, a red, was then poured into the Coca-Cola.

“I had friends in Spain who used to drink that [red wine and coke] to get pissed when they were 14,” Zyw says, still disbelieving. “Anyway, I went to David Galetti [head sommelier and husband of Monica] and said 'I'm not serving that table, get someone else to do it'. Of course he has every single right to spend his money how he wants, but there are all these desirable bottles in the world and so many people who'd like to drink them and appreciate them for what they are – and he's diluting them at the last minute. He was disrespecting the product.”

TODAY, Zyw is a wine buyer for Laithwaite's, an online retailer. Prior to that he worked as a wine buyer for Tesco. You've probably drunk something he sourced in Chile, California, Australia or South Africa. And home is that flat in West London, the one Kirsty Allsopp helped him buy. Do tell me more, I say, as I empty my glass.

“I'd been looking to buy a flat in London for about 18 months,” he explains. “But if it's online it's gone already. You'd go and look at a flat and it was like a house party – full of people my age with their parents in tow. It became ridiculous. It was almost pointless searching. I just kept getting priced out.”

Then a family friend who was addicted to the Channel 4 property show Location, Location, Location suggested he apply to go on it. So he did.

“Tommy was on Bargain Hunt,” he laughs. “He applied when he was at university. It was like a cult thing for them to watch during the day. But it was five years before he got a call up.” Twin brother Davy did it a little quicker. A week after applying he was sitting hunched over his iPad, “super hungover from the night before”, having a Skype interview with a member of the production company. She told him to book a week off work – filming started on the Monday. In all the production company saw 40 flats, and “cut away all the crap”.

“I saved myself two years of weekends,” he laughs. He's now the proud owner of a bijou flat on the fringes of Notting Hill, a purchase I'm sure he celebrated with a glass or two of bubbly – and possibly from a bottle he opened with his iPhone.

I Love Champagne: Fall In Love With 50 Of The World's Best Champagnes by Davy Zyw is out now (Freight Books, £12.99). He will be talking about the book at: 

Waterstones Sauchiehall Street, Glasgow on Wednesday, 27 September at 6pm

http://www.waterstones.com/events/search/shop/glasgow-sauchiehall

Waterstones George Street, Edinburgh on Thursday 28 September at 6pm www.waterstones.com/events/search/shop/edinburgh-west-end

Wigtown Book Festival on Saturday 30 September at 7pm Tickets £7 from www.wigtownbookfestival.com at 7pm

Friday 1st December 6.30m at the Mitchell Library, Glasgow tickets £6 from www.ayewrite.com

Davy Zyw and Barry Didcock were guests of the Peacock Alley Lobby Lounge in the Waldorf Astoria Edinburgh: The Caledonian