You don't need me to tell you that the consumption of coffee is on the increase in Ireland. The statistics are astounding: coffee sales have been growing at 20% per year for the last four years and the industry is reckoned by some to be worth £30 million a year. We drink it at work, at home and when we go out to eat.

It wasn't always like that. When I first arrived in Ireland in the late sixties I encountered 'Irel', a black liquid that came in a square-sided bottle. There was a similar liquid in the UK called 'Camp Coffee'. You heated a mug of milk and then you flavoured it with a spoonful of the liquid, and voila, you had a cup of coffee. Well, maybe not coffee, but something that was hot, and that was unlike tea. Coming from where I did, the only way I could approach drinks like this was to assume that whatever they might be, coffee was the one thing they were not.

The principles behind a simple thing like a cup of coffee are not really different from those behind tea. You add boiling water to your organic base - leaves for tea and beans for coffee - and drink the infusion. From coffee's beginnings in Ethiopia that was how it was made; boiling water was poured onto the beans and the drink was ready. Roasting the beans first was a later improvement. The descendant of this drink today is what we call Turkish coffee, with the fine grounds remaining in the bottom of the cup. Traditionally coffee was drunk 'long', that's to say with lots of water, and for many people in America and northern Europe that is the standard coffee today. What defines an espresso more than anything else is its shortness. You still use lots of ground coffee, but you concentrate its essences into just a few spoonfuls of water.

How we arrived from the original drink to the espresso of today is a long story. The coffee plant originates from the Horn of Africa, but its international popularity first spread over the sea to the Yemen. In the sixth century A.D. the main port for the coffee trade had a name that is its legacy to the coffee-drinking world: Mocha. From here traders and merchants took coffee all over the Arab world. The first coffee bars were opened in Mecca, then in Aden, Medina and Cairo. Constantinople, the traditional bridge between East and West, got its first coffee house, the Kiva Han, in 1475 and by 1615, thanks to Venetian merchants, coffee made its appearance first in Italy and then in mainland Europe.

It was by no means a runaway success: drinking coffee meant incurring the wrath of the powerful Church of Rome. Perhaps there was something in the fact that people enjoyed it, that made the Church oppose its spread so vigourously. In the protestant countries of northern Europe like England and Holland where Rome's hegemony had little effect, the drink was quickly accepted. The first coffee house opened in England in 1652, where a cup of coffee sold for a penny, and in 1668 Edward Lloyd's coffee house opened in England. It was frequented by merchants and maritime insurance agents at first, but eventually it evolved into Lloyd's of London, the insurance company.

But in Catholic Europe, coffee houses and coffee itself were regarded as 'the work of the devil' and priests threatened coffee drinkers with excommunication because it.

The fact that we have the joy of coffee today - and the fact that the penalty for drinking it is no longer eternal damnation - is thanks to Pope Clement VIII. It would seem that Clement was as wise a man the Danish King Knut, who knew that no man can reverse the tide. He called for a cup of coffee and was served a well-prepared one. He tasted it while his courtiers looked on apprehensively, and then, setting down his cup, pronounced that he would baptise the heathen brew, thus making it fit for true Christians to drink, saying 'coffee is so delicious it would be a pity to let the infidels have exclusive use of it.'

Perhaps because coffee found it's way into Europe through Italy, the Italians and coffee have had a long and symbiotic relationship. Back at the start of the last century the Italians had invented the 'Moka Bialetti', the octagonal cafetiere that unscrews in the middle. Water goes in the bottom half, the grounds are placed in the middle and when it's heated, the boiling water percolates up through the grounds filling the top half with coffee. Whatever else about the percolator, it was a much simpler and more practical way to get a coffee than the powdery Turkish variety. Today these percolators come in all sizes and there's no domestic kitchen in Italy without at least three of them.

But you can think of the percolator as a step on the way to creating the perfect cup of coffee. There's no doubt that it was an improvement of what went before, but compared to what came next, it was like a family car compared to a Formula One racer. Still in Italy, Achille Gaggia began marketing a machine in 1947 which worked with a powerful spring and piston. The barman operated a long lever, which he had to lower with a precise and decisive action - and then release it at exactly the right moment. This lever, spring and piston system pushed hot water at high pressure through the grounds. The coffee fell into the cup drop by drop, and as clients watched it rise gradually in the cup with a creamy froth, they could savour it in anticipation. The espresso was born. In 1956, Cimbali patented a hydraulic system operating with mains water pressure and in 1961 Faema introduced an electric pump. Since then technical innovations have continued, but the espresso remains so much a part of daily life in Italy that its price in a bar is regulated by law.

You might think that using one of these modern machines means that a perfect espresso is the result every time. Alas, not so. Recently I was asked to be a judge at the Robert Roberts and Brasilia 'Barista of the Year' Irish finals. A barista is, of course, the person who operates the espresso machine. Two identical machines were set up for the contest, the same coffee grounds were used by all the contestants, the water supply was common to all - and yet each of the six contestants produced espressos of differing quality, something that came as a surprise to me. The winner on the night was Yvonne Gamble from Northrn Ireland, who went on the represent Ireland in the European finals in London. What makes me agree to doing jobs like judging barista competitions is that competitions like these enhance awareness, not just of baristas, but also of good coffee. When people become passionate enough about it to enter competitions, you know we've come a long way from the coffee-flavoured essence in the square bottle.

It's plain enough that a significant variable in the equation that produces a good coffee is the barista. When this became clear to me, I realised why espressos can vary so much from place to place: not only can the barista be good or bad, but different places use different grounds and different machines. Sometimes the water temperature isn't properly controlled, sometimes the grounds are too coarse or too fine, sometimes they're not properly tamped down to the required pressure of 10 pounds per square inch, sometimes it's simply an inferior blend of coffee. These variables all combine in determining the final product, an espresso that can be sublime or simply hot and wet. This variability in a drink that Italians pride themselves on having given the world, prompted The National Institute of Italian Espresso Coffee, with head offices in Brescia, to define the authentic Italian espresso. By setting a standard they hope not only to promote the real thing, but also to discourage the poor imitations that pass themselves off as espressos.

The formula that the Institute came up with does perhaps take a little of the alchemy and mystery away, but at least it's precise. 'Espresso coffee is made by passing 25 ml of water at 90 C (plus or minus 2 C) at a pressure of 9 atmospheres through a wad of 6.5 grammes (plus or minus 0.5 gr) of ground coffee so that the required volume (25 ml including the crema) is served in 25 seconds with a tolerance of plus or minus 2.5 seconds'.

You'll notice that it's precise on the time as well; 25 seconds. It may be called 'espresso', but that's got nothing to do with speed - the name means 'pressed or squeezed out', like expressing the juice from an orange. If a barista serves an espresso coffee which is far too quick, around l5 seconds, then the drink will be thin, bitter and will have a faint aroma. If, on the other hand, preparation time goes beyond 30 seconds, the cup of coffee will contain unpleasant and astringent woody substances. These extremes may even appeal to some, but they can't really be considered to be fine ltalian espressos. The simplest test of all for a well-made espresso is to sprinkle sugar lightly onto the 'crema', the light brown foam of coffee-bean oils that sits on the top of an espresso. If this crema can support the sugar for a moment or two before it sinks down into the coffee, you have a good espresso in front of you. Needless to say, if it has no 'crema' at all, it's a badly made one - about as much use as a pint of Guinness with no head.

Like all things, it's a matter of taste. There are two main coffee-bean varieties, the Arabica and the Robusta. Of the two, Arabica is considered much the finer, but even this bean is sold on the international coffee markets in many grades. So just to complicate things, you could maintain that a first grade Robusta might be better than a low-grade Arabica. Although we call them 'beans' strictly speaking they're not. The coffee tree produces a fruit about the size of a large grape. It ripens from green to red, to black and for coffee they're picked at the red stage. Inside each fruit are two seeds, and these are the beans from which the coffee comes.

The roast of the bean is crucial, too, to the final flavour of the coffee. In Italy a dark roast is the norm, other markets prefer a lighter roast. Whereas once there was little choice in Ireland, now the choices are many more. Supermarket shelves carry Dutch and Italian commercial blends as well as products from the two main Irish roasters, Bewleys and Robert Roberts. In Europe there are over 2,000 micro-roasters, that's to say small roasting plants serving small, and often local, markets. Ireland now has one of these as well, in the shape of the speciality coffees from Java Republic, whose informative consumer handbook is worth reading.