GALWAY, Ireland (Reuters) - A minimum of blood and grit helped Norway unseat Sweden as world oyster-opening champions as contestants from 18 countries vied to prepare the prized shellfish as quickly and neatly as possible.

"It's the classic trade off between speed and quality," explains Terry Brennan as he peers through a magnifying glass.

"Grit in the oyster, that's a penalty right there," the chairman of the panel of seven judges adds.

Damage to the oyster's flesh, failure to detach it from the shell or traces of human blood also mean penalties for the knife-wielding competitors who have come from as far afield as Estonia, the United States, Australia and Japan.

The trick is not to rush things, according to the new world champion who opened his 30 oysters in 2 minutes 39 seconds and incurred just 22 seconds in penalty points.

"Keep your cool, don't stress," advises Ola Nilsson, winner and head chef at a Michelin-star restaurant in Oslo. "You have to find a rhythm and if you just go for speed you lose."

But Gerry Grealish, a three-times title holder turned judge, believes there is more to Scandinavian oyster opening skills.

"The northern Europeans have developed a better technique," says the local dairy farmer. "We use an ordinary single blade knife and they use a double blade which means they can open the shell and release the oyster in the same move."

Sweden's Hans Johannesson was the competition's fastest opener but came in second overall Saturday as judges penalized his presentation. A slower Sam Tamsanguam from the United Kingdom was placed third despite an impressively clean array of oysters.

OYSTER WORSHIP

Thousands have gathered here in Galway to celebrate a new season for oysters which, according to Elizabethan cookbook writer Henry Buttes, are "unseasonable and unwholesome in all months that have not the letter R in their name."

Along with France's Belon oysters, those found along Galway's Atlantic coast are the best and most expensive in the world says Michael Kelly who supplies the delicacy to restaurants in London, Berlin and Canada.

"It's the flavor which comes from the right mix of fresh and salt water," he says. "Water that's so pure you can walk down into the sea and eat them straight from the beds."

Some of the 10,000 visitors at this weekend's festival believe their own varieties are at least as good though.

"Galway's are on a par but you can't beat a Bluff oyster," says Suzanne McKenzie of those from her native New Zealand.

But either way, Michael Kelly's Galway variety sell for 4 euros ($4.92) a piece in top Zurich restaurants.