My Round: Robert Parker revolutionised wine tasting with his 100-point system, says Richard Ehrlich

But did things change for the better?

Robert M Parker Jr will go down in the history of wine as the man who introduced us to buying by numbers. Mostly by his numbers, to be precise.

When he started publishing his newsletter The Wine Advocate in 1978, he instituted a 100-point marking system to serve as an accessory to his long, detailed tasting notes. Nearly a quarter of a century later, those numbers are the most influential marketing tool in the wine world.

Indeed, they have made Parker the most influential wine writer in history. He can make or break a wine's commercial prospects, and lead winemakers to change fundamentally the products they make.

Some start-up wineries, especially in the USA, tailor everything they do to the aim of pleasing Mr Parker. He has even seen his name used as the basis of a French verb: parkeriser is to remake a wine in the mould of the big, high-alcohol "fruit bombs" that he likes so much.

Parker would never have predicted all this when he first caught the wine bug in the early 1970s. He wanted to make a good living from writing about wine, and he wanted to be a big shot, but I don't think his numerical ratings were conceived as the path to worldwide supremacy.

That's the clear impression conveyed by a surprisingly enjoyable book: Elin McCoy's The Emperor of Wine: The Remarkable Story of the Rise and Reign of Robert Parker (Grub Street, £20). This unlikely page-turner is in part a biography, though the biographical elements are the least interesting. Where it really enthrals is in chronicling changes that have taken place in the wine world since the 1970s. Apart from certain minor lapses, it is a well-written, engaging book that should interest anyone who cares about the shaping of the modern wine world.

It was common, at the end of the last century, to call those 100 years "The American Century". In wine, the century began late - in the 1960s, when a combination of factors (including a strong dollar and increasing international travel) made Americans more interested in French wine - especially in claret, which was to become Parker's greatest passion.

As interest increased, and as the choice of wines increased, the market was ripe for independent shopping advice. A few took up the challenge, but no one did it as successfully as Parker.

"The true genius of the 100-point system," writes McCoy, "was that it was universally understood by average Americans and seemed completely straightforward. At the time, seeing a wine slapped with a number was new and fascinating."

In fact, the numerical system was anything but straightforward: sensory evaluation of wine is not science, even when the taster is as gifted as Parker. But Parker meant well when he set up his system. As a young lawyer, he admired Ralph Nader, the crusading consumer-rights lawyer who stood up to entrenched business interests without fear or compromise.

Parker's stance in wine was similar: believing that many wines were priced too high because of the name on the label, he cared only about what was inside the bottle.

And he wanted to make those contents comprehensible in the way that a car or a lawn mower could be made comprehensible. And readers love him for it, even if wine merchants know it's misleading. One New York wine merchant told me: "As a drinker, I pay no attention to Parker; as a seller, I pay a lot of attention to him."

As Parker's power has grown, so has his list of enemies - and he sometimes goes to quite extraordinary lengths to counter their attacks. If there's one unpleasant character trait that emerges most clearly from The Emperor of Wine, it's a refusal to admit to fallibility - and a readiness to accuse detractors of professional envy. That too is a distinctly American trait, similar to what we see right now in the higher echelons of the US government. All part of a fascinating story, very well told. If you want to see how wine got Parkerised and Americanised, read this book.

Three possibly Parkery clarets

Château Segonzac 2002, Premières Côtes de Blaye (£7.99, Waitrose) Easy-drinking at an easy price.

2003 La Violette, Côtes de Castillon (£111.60 a case, Seckford Wines,tel: 01394 446 622) Mostly Merlot, and all loveliness in the mouth.

Château Sissan 2003, Premières Côtes de Bordeaux (£9, Co-op) Cabernet Sauvignon, Merlot and a little Cabernet Franc. Quietly impressive.