Not many people can taste something their grandfather made 90 years ago.
Jamie Callister can - and likes it. Barack Obama disagrees. When the US president visited Australia in 2011he said Cyril Callister's invention tasted "horrible".
In 1923 Cyril cooked up a salty black paste made from a by-product of beer-making. About 22 million jars of it are sold every year. Travelling Aussies reverently hand jars to expatriates in far-flung corners of the globe.
It is, of course, Vegemite - and its status in Australia is iconic, ironic, historic.
Jamie Callister is the grandson of Cyril Percy Callister, the man who invented Vegemite. Jamie's late father Bill was "one of the original Vegemite kids". He and his siblings Jean and Ian got to taste the experimental pastes that Cyril brought home from Fred Walker & Company lab in Melbourne.
As a child, Jamie had no particular interest in family history but remembers a chest of old papers, and the way his father would slather Vegemite on toast ("and just about everything") and say: "You either love it or hate it.
But you should never forget that the old man invented it."
Jamie didn't forget. In the 1990s Bill, who'd been the family member who would speak to the media whenever there was a Vegemite anniversary, handed that baton to Jamie.
"So that's when I went back to the letters, back to the chest," Jamie says. "I was hooked."
He was given access to Kraft's archives and spoke to old family members about Cyril, who died in 1949. "I just kept on finding the most incredible information," he says.
He gradually built up an image of the grandfather he never met, of Cyril's professionalism - and of his heartbreak when his "golden boy" Ian died in a wartime Spitfire accident.
Now Jamie has turned his research into a book, The Man Who Invented Vegemite.
Cyril, born into a humble family in rural Victoria in 1893, studied science at university and worked as a munitions chemist in Britain during World War I.
He returned to Melbourne with his new wife Kit and worked as an industrial chemist making soap, shoe polish and sheep dip. An encounter with an entrepreneur called Fred Walker transformed him into a food technologist.
Food preservation was an obsession of the pre-refrigeration era when meat, milk and cheese were all doomed to go off within days. Fred Walker & Company had already developed a more resilient cheese and Bonox, a beef tea.
In the early 1920s Walker's sights were set on producing a challenger to Britain's Marmite, then used mostly for flavouring stews and soups. Marmite was in short supply after the war and Walker spotted an opportunity.
He lined up supplies of spent brewer's yeast from Carlton & United Breweries for a bargain price. Trouble was, he hadn't a clue how to make something palatable from the bitter, smelly mess.
So he asked Cyril Callister to come on board. The recipe remains secret, but Cyril's deeply chemical process involved the autolysis of yeast - the breakdown of cells caused when the enzymes and proteins attack each other.
Cyril, a department of one, slaved over vacuum pans and sieves, bringing home samples that "at best resembled axle grease and, at worst, tar" for his family to taste-test.
By spring 1923 he had come up with something he and Walker thought was palatable. It was packed up into little glass jars with yellow and red labels identifying its contents as "Vegemite". (The name was the result of a competition.)
Callister, who went on to become a director of the company, was convinced that success would come from Vegemite's vitamin B content (the word "vitamin" had been invented a few years earlier). He was right - but for almost 15 years Vegemite languished on the shelves, supported by profits from another of Walker's products.
Walker had made a deal with the US company Kraft to gain access to the patent for the ultimate long-life cheese. The Kraft Walker Cheese Company was born, and for years Vegemite was Kraft cheese's poor cousin.
Vegemite's success came in small steps. Putting it in a jar that could have a second life as a drinking glass helped. So did scientific reports Cyril obtained confirming the spread's nutritional value, which encouraged women to feed it to their children.
"But the watershed, I think, was when Professor Cedric Stanton Hicks (a member of the government's food advisory panel) wrote it into the army ration book for World War II," Jamie says.
Vegemite went to war in every soldier's rations, and came back a winner. "Somewhere along the way people embraced it," Jamie says.
Why has it worked the way into Australia's psyche when almost no foreigner appreciates the taste?
"There's just something about it," Jamie says. "I think people enjoy the fact that, by liking it, it's something that sets us apart and makes us different. And there's something slightly irreverent about it."
Only one jar is exported for every 30 consumed in Australia, he says: "But if Barack Obama had liked it, it might have been different."