From old family recipe to national treasure - the story of Cooper's Oxford marmalade is the stuff of fairytales. A humble grocer's wife turns a surplus stock of Seville oranges into marmalade, and it becomes an instant hit with local dons and undergraduates.

Before long, it has Royal approval, becomes standard fare at British embassies all over the world, and adorns every breakfast table in the country. It even forms part of the rations for Captain Scott and his team as they venture into Antarctica in 1912, and a miniature version appears in Queen Mary's dollshouse at Windsor Castle.

When Sarah Cooper produced her first batch of marmalade in 1874, she little dreamt that she was creating a product that would revolutionise the traditional British breakfast, and eventually become world famous.

She was born Sarah Jane Gill in 1848 at Beoly, near Redditch in Worcestershire, where her father, John, was a farmer. She already had Oxford connections - John Gill had been born in Oxford, and came from a family of Oxford-based printers, ironmongers and coal merchants.

In 1872 she married Frank Cooper, who had inherited the family grocery business ten years earlier, aged just 17. His shop was at 83-84 High Street, Oxford, formerly the premises of the Angel Hotel, once Oxford's leading coaching inn. It was while pregnant with her first child in the spring of 1874 that Sarah took an unsold batch of Seville oranges from Frank's shop and, reputedly using an old recipe of her mother's, created a distinctive marmalade with chunky, coarse-cut peel.

In her detailed history of Frank Cooper Ltd, Brigid Allen describes it as "a high-quality and excitingly bitter-tasting marmalade calculated to revive the most jaded academic or undergraduate palate".

And indeed it was Oxford's academia that gave the thumbs-up to Sarah Jane's marmalade when it first went on sale in Frank's shop, packed in white, salt-glazed earthenware jars. Rather unfairly, perhaps, Frank put his name, rather than his wife's, on the product, and it is his name that has now become synonymous with good quality marmalade.

Before 1874, college breakfasts were elaborate affairs, with porridge, cold game pie, fish, kidneys, chicken and omelette on the menu. But gradually breakfasts became lighter and less fussy, and marmalade was an increasingly popular part of this new, streamlined start to the day.

Sportsmen were particularly keen on the energizing properties of marmalade - a fact that Frank Cooper was quick to exploit. In 1912, the front cover of Alden's Oxford Almanack featured an advertisement for Cooper's marmalade, showing a college sportsman holding a megaphone in one hand and a jar of marmalade in the other, with the slogan Frank Cooper's "Oxford" marmalade. The marmalade to train on'.

Following the success of her first batch of marmalade, Sarah Jane produced a second batch later that year, and from then on marmalade sales became the mainstay of Cooper's business. Later they extended production to jam, sauces and soups, the last becoming particularly important during the war years when sugar was scarce.

It is unclear where the Coopers made their marmalade, but Allen suggests that they created a boiling room and a store room in outbuildings behind the shop, probably the final remains of the old Angel Hotel. As demand increased they took on staff to help, but everything was produced under Sarah Jane's supervision.

Following the introduction of the Factory Act of 1901, the Coopers moved the production to a purpose-built factory in Park End Street, in the terraced row known as Victoria Buildings. At this point, Sarah appears to have retired, but she retained an interest in the business, and was a motherly and much-respected figure among the mainly female staff in the factory cutting room.

Frank continued his involvement in the business, and in 1913 became co-director of a new company, Frank Cooper Ltd, along with his sons and son-in-law. The younger Coopers gradually assumed a greater prominence, but Frank continued to attend board meetings for the remainder of his life. He died on 26th July 1927, aged 83. Sarah Jane survived him by five years, dying in 1932 at the age of 84.

In 1947, production of Cooper's Marmalade moved to the former Ice Rink premises in the Botley Road, on the site now occupied by Halford's. Twenty years later, the business was bought by Brown and Polson, and is now owned by Premier Foods.

The Coopers' old shop is now occupied by the Oxford Bus Company (No.83) and the Grand Café (No. 84), but the erection of a blue plaque at No.83 in 2001 was a timely reminder that, for many, Oxford is marmalade's spiritual home.

Where to find out more The Museum of Oxford has a permanent display of Cooper's artefacts. Open Tue-Fri 10am-4pm; Sat 10am-5pm; Sun 12-4pm. Admission free. Tel: 01865 252761.

Allen, Brigid - Cooper's Oxford: A History of Frank Cooper Ltd (Archive Services of Oxford, 1979). Available at the Central Library, Westgate.