Patrik Johansson used to be a professional fisherman, once managed a coffee plantation on Madagascar, and made salt from seawater. Now, finally, he has found his true calling. "I am a butter man," he says. Sometimes, the 45-year-old eats butter, with a spoon, right out of the churn (bread ruins the taste). Three times a week Johansson leaves his little wooden house in the forest north-east of Gothenburg and drives to a nearby castle. In one of its chambers, filled with pots and fridges and a small centrifuge, he makes what must be the most prestigious butter in the world. He is known as the Butter Viking.

Folks around there insist the Vikings showed the French how to make butter. Indeed, Sweden was the world's largest butter exporter until 1885. By 1960 the country boasted 6,000 dairies. Then, the dairy company Arla began buying up and subsequently closing down smaller competitors. Today Arla is the world's fourth-largest dairy, and in Sweden only a handful of other companies still sell milk. "A lot of knowledge has been lost with those small dairies," says Johansson.

His butter is served at Noma in Copenhagen, voted best restaurant in the world by Restaurant magazine three years in a row. Multi-Michelin starred chef Joël Robuchon has shown interest in it and Johansson is developing the most buttery butter possible for Heston Blumenthal. The idea is to get solid butter to taste as if it has been heated to its melting point – the high concentration of diacetyl in the melted stuff boosts its buttery taste.

For a year, Johansson experimented with different cows' milk, adjusting times and temperatures. He studied ancient treatments and scientific texts about the art of butter making. He's best known for his so-called "virgin butter". It's creamy and tastes intensely buttery, much more acidic and fresh than standard stuff. Try it once and you'll know why Johansson spoons it out of the churn – it's addictive.

"Everything he makes is unique," says Matt Orlando, Noma's head chef. "He tries so much stuff and never presents it before it is perfect."

The biggest factors in butter's taste are whether it was made from sweet or sour cream, and where it comes from. Sweet cream is easier to process and its butter lasts longer – which is why it's most common. The problem though, is that it lacks diacetyl, one of the principal flavour compounds, and all those acidic or nutty notes, which give sour cream butter its complexity. In addition, the taste is determined by the grass the dairy cows were fed on. Bigger companies source milk from several places for their butter and so the milk's "terroir" gets lost, while small dairies can better preserve it. The butter connoisseur, therefore, should look for butter from small producers.

Buying good butter in the UK can be a challenge. Stephen Harris from the Sportsman in Seasalter makes his own, because he could not find one that met his standards. Neal's Yard Dairy recommends Netherend Farm butter, Keen's, Denhay, and Berkley butter.

After years of decline, artisan butter makers started to reappear all across Europe, and with them, sour-cream butter returned. In the UK, Wardhall Dairy in Cumbria now sells its cultured butter online, as does Ivy House Dairy Farm in Somerset. In France it never disappeared: butter from Normandy and Poitou-Charentes with an AOP symbol has always been cultured. Look out for it on French markets and specialist shops.