With the opening yesterday by Aldi of its first stores in Ireland, shoppers in Cork and Dublin are not only able to buy a range of goods at rock-bottom prices - they have an opportunity to participate in a ritual that has become an essential part of German life.

An opinion poll last month found that the Aldi brand name means as much to Germans as any religion and one academic has written a thesis comparing the supermarket chain to one of the major Christian churches.

As they manoeuvre their way along narrow aisles, only stopping to reach into large cardboard boxes for products bearing unfamiliar brand names, Irish shoppers may wonder what all the fuss is about. But if the German experience is anything to go by, shopping at Aldi could soon achieve cult status among the next generation of Irish consumers.

Two out of three Germans shop at Aldi at some time each year and one in three admits to being a regular customer at the discount store. Loyal customers need no persuading about the merits of their favourite shop, but market analysts are puzzled by the success of a firm that has trampled over all the rules of modern marketing.

The basic principle is a simple one - a range of less than 750 items, almost all of which are own brand products trading under a variety of sometimes bizarre names and sold at the lowest prices possible. Although there is a minimum of choice, the range of goods is vast - including such items as champagne and computers as well as basic foodstuffs.

The key to Aldi's unrivalled customer loyalty is the fact that low prices are accompanied by consistently high quality so that, for example, Aldi champagne wins high marks in blind tastings and their sunscreen is believed to be the best on the market.

Founded in 1962 by two brothers, Karl and Theodor Albrecht, the company now has more than 3,200 branches in Germany and hundreds more as far away as the US and Australia. As a private company, Aldi (which is short for Albrecht Discount) is not obliged to publish details of its accounts and the Albrecht brothers are notoriously secretive.

We do know, however, that by 1995 Aldi had a turnover of 28 billion deutschmarks (€14.32 billion) in Germany, representing half the country's total discount market - 50 times greater than that of its closest rival, Rewe.

Aldi has achieved this success by ignoring the siren call of retail experts to diversify, to broaden its range of products and to use focus groups, market research and sophisticated advertising. Orders are determined, not by what suppliers are offering at favourable prices at any given time but by what customers want.

But the most striking departure from conventional retailing wisdom is the firm's refusal to centralise - a strategy that not only serves to avoid the obligation to publish accounts but also encourages rivalry between individual branches. The company is divided between Aldi North, run by Theodor and Aldi South, which is Karl's empire. But there are further subdivisions, even within Germany and each store determines which products it chooses to stock.

In Berlin's impoverished Kreuzberg district, for example, basic foodstuffs and toiletries dominate - although Aldi branches in the district stock a number of more exotic items to cater for a large Turkish community. In swanky Grunewald, on the other hand, smoked salmon, olive oil and fine wines are all the rage - even if many well-heeled customers also stock up on such staples as flour and sugar at low prices.

Lean management and low staffing levels help to cut costs, yet Aldi staff are renowned as the friendliest of all German supermarket assistants - perhaps because they are also among the best paid. And the small range of goods in each store means that check-out assistants know the price of each item by heart, with the unnerving result that they can check the goods faster than most customers can place them on the counter.

Aldi has promised to source at least 30 per cent of goods for its Irish stores from local suppliers and competition for contracts is likely to be keen. Renowned for straight dealing and speedy payment, Aldi can also be demanding - insisting on consistently high quality and prompt delivery of goods.

It emerged last year that several international giants, including Nestle and Unilever, have long been supplying no-name products to Aldi - news that came as no surprise to many Aldi regulars who noticed an uncanny similarity between many of their discount favourites and major branded products.

Shopping at Aldi has become such a way of life for many Germans that the Internet boasts a number of fan pages devoted to the store. Dedicated bargain hunters rush to their newsagents each Wednesday morning to scrutinise the company's weekly full-page advertisement, announcing special offers under the sober heading "Aldi informs . . ."

When the store launched its first range of PCs last year, there were all-night queues throughout Germany and one man was arrested after he seized a computer from another customer at gunpoint and walked up to the checkout to pay for it.

Books outlining the Aldi diet and Aldi gourmet cooking underline the appeal of a shop that seems to capture much of the spirit of modern Germany - unassuming, reliable and blind to class divisions. As they preach to dwindling congregations each Sunday, German churchmen may be forgiven for casting a wistful, envious eye at the discount store that has become a way of life for millions.