more than 24 million jars a year, and 25 percent of kitchen cupboards in Britain contain a jar, making it the largest brand in the deliciously titled "Ambient Spreads" market.

Marmite has become more than a simple savory spread: it is a British cultural icon, a national symbol. As important to the British as roast beef and Yorkshire pudding. Children grow up on it, soldiers march on it, and it travels abroad in the suitcases of an estimated 11 percent of British holiday-makers who apparently can’t take a break from the stuff.

Marmite is made from a yeast byproduct of the brewing industry. In 1680, it was discovered that yeast extract could be used as a food source, but it wasn’t until the 19th century that French scientist Louis Pasteur and German chemist Justus von Liebig realized it could be turned into a concentrated paste that – at least to 19th century scientists – resembled meat in appearance, smell and color. Then in 1902, the Marmite Food Extract Company bought rights to the "secret, patented process" and began manufacturing yeast extract commercially from a disused malt-house next to the Bass beer factory in Burton-on-Trent.

After several years tinkering with the recipe Marmite’s popularity grew steadily. In 1912, the discovery of vitamins helped to boost the popularity of the product when it was realized that Marmite provided a good source of five B vitamins. Marmite launched the advertising slogan, "the growing up spread you never grow out of" and became an instant favorite with mothers.

By the outbreak of World War I, Marmite was an established brand, recognized for its nutritious properties. Great quantities of Marmite were consumed in hospitals, schools and institutions. Jars of it were shipped to troops serving overseas, to help combat outbreaks of beriberi and other deficiency diseases prevalent in places like Mesopotamia. During the World War II, Marmite became a dietary supplement in prisoner-of-war camps, and in 1999, it was sent to British peacekeeping forces in Kosovo after begging letters from the field to boost morale.

Both the Marmite product and the packaging have undergone few changes since the turn of the century. The small earthenware pots in which it was sold at its outset were abandoned toward the end of the 1920s in favor of glass jars with metal lids. But an image of the original stew pot – the French petite marmite, or small earthenware casserole that gave the product its name – remains on the label to this day. The most controversial change came in 1984 when the lids were downgraded to plastic. The company, flooded with letters from defiant Marmiteers, got the message loud and clear for thoughts on future changes; Oliver Bradley, Marmite’s new brand manager at Unilever Bestfoods, says: "People would be disappointed if we changed."

And while that may be true of the product, Marmite’s advertising campaigns have moved with the times. Early advertising campaigns trumpeted Marmite’s health-giving properties, employing the early slogan "Good For You." During the 1930s, posters displayed characters whose faces somehow – and rather disturbingly – contorted to feature the word "good." Since sliced bread was introduced in the 1930s, Britain’s favorite way of eating Marmite has been on hot, white toast dripping with butter.

By the 1950s Marmite was already marketed as a national institution – intrinsically a traditional family favorite. Then, in the 1980s, Marmite updated its image, running a snappy ad campaign featuring an army regiment chanting a marching song: "My Mate/Whose Mate?/My Mate – Marmite" before the soldiers went back to feast on Marmite. Simple but catchy, the chant can still be heard today.

Marmite makes occasional, usually aborted, attempts to extend its brand – re-launching formerly abandoned Marmite stock cubes in 1996, and trying to position the savory spread as a cooking ingredient. Marmite flavored cheese spread has also been introduced, but with none of the success of the basic product. It may be a one hit wonder but that seems to be the best strategy.

Finding the genuine article can be a problem when abroad. Many travelers and expats rely on friends and relatives to deliver their British Marmite or resort to expatshopping.com which launched in early 2000. Marmite is the most requested product on the website. In an interview with Paul Ridout, a British backpacker kidnapped in India by Kashmiri separatists, the Guardian newspaper reported "The first thing he had done after arriving home was to eat some Marmite on toast. 'It was pretty good. It's just one of those things – you get out of the country and it's all you can think about.' "

But although it is a national institution, not all Brits are enamored. Many find the spread distinctly repulsive. Marmite has milked the extreme feelings with its recent "love-it-or-hate-it" marketing campaign. One brilliant micro-drama shows a couple arriving home desperate to have sex. She has a bite of toast with Marmite, kisses him, and he gags disgustedly. There is, it would seem, no middle ground for Marmite. Brand manager, Oliver Bradley defends the knowing shift in tone of the advertisements, "We've moved on from the 'growing-up-spread' (of earlier campaigns). We're more adult, more clever and a lot more cheeky."

Marmite is not to be confused with Vegemite, Promite, Bovril or generic yeast extract – all contenders for the ambient spread crown. Bovril is produced by the same company and packaged in a similar shaped jar, but is made from beef extract, and though popular, does not garner quite the same admiration from its fans. Generic yeast extracts, sold as an own-brand by Britain’s supermarkets, are considerably cheaper than the original and often borrow heavily from Marmite’s packing and design – down to the shape of the jar and the distinctive yellow label – but are considered inferior. Vegemite, made by Kraft Foods Ltd. and Promite made by Master Foods are both manufactured in Australia and have strong antipodean fan bases. Though similar in yeasty origins to Marmite, both employ caramel in their recipes, and are considered unpleasantly sweet by Marmiteers.

Although Marmite is hugely successful in Britain, its quirky taste makes it difficult to market abroad, thus the brand is likely to remain a uniquely British obsession alongside stiff upper lips and the royal family. The downside of this is that the brand will never grow beyond its national market. The upside is that I know my two jars of Marmite will be safe from my American flat mate.

Edward Young is the Beijing correspondent for the China Economic Quarterly, China's premier independent English-language economic and policy journal. He has written on a variety of topics including China's macro economy, the Internet, and China's intellectual property rights.