Time was when coffee was merely a mixer for Irish whiskey. Most coffee-drinkers were content enough with a cup of instant Maxwell House, while a warm-milked coffee from Bewley's represented sophistication itself, hinting at a hedonism that sat uneasily on our tea-cosied shoulders. Full of beans after sharing 33 shots of espresso with a coffee expert, Fiona McCannis ready to give the lowdown on Dublin cafe society

Those days are gone, and with the Bebo generation ordering skinny decaf frappuccinos with the ease of downtown Manhattanites, it seems a new day has dawned for hot beverages in Ireland. But what does a palate weaned on the tea leaf really know about the coffee bean? What marks a quality espresso, and more importantly, can such a thing be found in a capital city so new to the concept?

To help answer such questions, I elicited the assistance of one of Ireland's foremost coffee enthusiasts, David McKernan, managing director of Java Republic Roasting Company. McKernan, whose passion for coffee is as contagious as his boundless energy, is so enthused about our quest that he brings with him a list of coffee-drinking houses he considers essential on our trail, promising to retain a degree of objectivity by avoiding any establishment which buys his own Java Republic coffee beans.

Our first stop is Dublin's current coffee mecca, the Bald Barista, where we order the first of the 33 espresso-based cups we will eventually down in one heady morning.

Baristas are a breed of professionals who have developed their skills around the preparation of espresso-based coffee drinks. The "Bald" element of this Aungier Street establishment refers to Buzz Fendall, a New Zealand-born barista who has made it his professed mission to "singlehandedly lift the state of coffee in Ireland".

For McKernan, the proof of a good barista is in his espresso. "You know the guy who makes good coffee by the espresso he makes," he says.

So how do you know it's a good espresso? The big giveaway, apparently, is the crema, a golden-coloured froth that's visible on the surface of any well-made espresso and which, according to McKernan, should not only boast depth and a rich colour, but endurance - if it disappears within seconds of the coffee's arrival, you're out of luck.

Fendall's brew gets a definitive thumbs-up, with McKernan particularly impressed by the inclusion of a tiny espresso spoon.

"Once the espresso lands at your table, it should be drunk within 20 to 30 seconds," explains McKernan. "If you decide to put sugar in it, and you use a stainless steel teaspoon, you're dropping the degree of heat by about 11 to 14 per cent." A proper espresso spoon reduces such a risk.

When it comes to the Americano, McKernan really goes to town on describing the desired flavours. Words such as "caramel, hazelnut, vanilla" trip off his tongue, and colours are discussed as if Mark Rothko had created the coffee.

But it's the cappuccino that really impresses, when it arrives with a smiling face drizzled on the surface of the milk. This, McKernan says, is a fine example of "latte art", where baristas get to show off their skills. "It's about the flick of a wrist and the texture of the milk," he explains.

IMPRESSIVE AS THE Bald Barista's latte art collection may be, McKernan, with a coffee-drinker's restless energy, is ready to move on. We head to Fallon & Byrne's, where the espresso is described as "slightly acidic", though this, it turns out, is not a bad thing.

"Acidic can be good when it comes to coffee," says McKernan, who drinks all his coffees without any sweetener. Sugar, he tells me, should not be required in a good espresso, although its addition or otherwise is a matter of taste rather than etiquette. In Ireland, though, there is a problem with the size of the sugar granules.

"Ours generally sink to the bottom, where the Italian fine sugar instantly dissolves with little need for vigorous stirring and less heat loss and disturbance of the all-important crema on top."

Our next port of call is Leon, where McKernan is particularly pleased with the service, a vital component of cafe culture, and with the automatic glass of water served with our coffees. "If you're having espresso, that's the norm in Italy and Spain," he says.

While we are impressed by the "speculoos" - small caramelised biscuits - that accompany the coffees at Leon, it is Butlers, just across the road, that gets our vote when it comes to treats, with delectable complimentary chocolates served with every coffee. McKernan observes that the average coffee-drinker in Ireland spends "about €2,500 a year on coffee", so a free sweet is not to be sniffed at.

As the morning wears on and we move on to Avoca on Suffolk Street, I'm slightly worried that it may be getting too late to continue with the cappuccino element of our order. Won't it be frowned upon by those who insist that such frothy nonsense is only appropriate in the early hours? McKernan is quick to dispel these concerns.

"You can drink cappuccino whenever you want!" he insists. "You've spent too much time with Italians - they think they know everything about coffee, and they don't." He pauses. "They're bloody good at it, but they don't know everything!"

In Avoca, the espresso machine gets the once-over, with McKernan's eagle eye complimenting a "spotless" machine and waxing lyrical about the "tail of the mouse", a term which refers to the shape of the streams of espresso as they leave the portafilter spouts. He also reminds me of the prominent role that tamping plays in good coffee-making.

"It's essential to get it properly packed to make sure the seal is right and make sure you get the flavours of the espresso," he says.

No coffee-tasting exercise would be complete without a trip to Starbucks, but McKernan is considerably underwhelmed by what's on offer.

"They've completely taken away the traditional art of making really good coffee that we've seen all morning, and they're serving 12 ounces of . . ." There's a pause that suggests an expletive on the tip of his tongue, a temptation McKernan politely avoids, instead pointing out the lack of aroma, the poor presentation, and an Americano so bland "it's 12 ounces of liquid water".

Bewley's is the next port of call, the original Dublin cafe where McKernan himself worked for 12 years. Despite the fact that Bewley's and Java Republic are now effectively rivals in the coffee- roasting trade, McKernan pronounces all three of the coffees there "super", emphasising the role the countries of origin have to play when it comes to the varying flavours.

"Every single origin has a distinct taste. If you taste an Ethiopian coffee, a Kenyan, a Brazilian, a Sumatran, a Javan coffee, they're all completely different," he says.

We skip - or at this stage, buzz - through O'Brien's, where the enormous bowl-shaped coffee cups don't impress, and then bounce through Insomnia, where McKernan is pleasantly surprised by a richly flavoured espresso but fears the cappuccino has suffered from time pressures. "The milk is too aerated," he says, a little sadly.

It's the Shelbourne Hotel that really lets him down, however, reinforcing McKernan's belief in the importance of the barista's role when it comes to good coffee.

"They can take all of the technology and put it into the best fully automated machines in the world, but today has proven yet again that it is the manual barista that has the biggest effect on coffee," he says.

It's not, he adds, that the Shelbourne coffee is bad - at €4.50 a pop, one would hope not - but that the preparation is wrong. "They're using good coffee, they're just not presenting it right."

AS WE SETTLE down in Dunne and Crescenzi for our last coffee of the day, a diner at an adjacent table reassures his companion - who turns out to be Swiss - that the coffee here will be infinitely better than the dishwater he has been served all morning.

When our coffees arrive, they're of a quality that would please even the most pernickety of Swiss drinkers: beautifully presented, nicely flavoured - though McKernan detects Robusta coffee in the espresso - but the cappuccino is "superb". The Italians may not know everything about coffee, as McKernan has pointed out, but after a morning with McKernan and 33 brews, I'm pretty sure I do and am happy to approve and bow out of the race before it kills me.