In a village in Tuscany a family are struggling to transport their produce through the unexpected snow.

The chestnut flour they pile into their vans is destined for British shoppers who, after a recommendation from Delia Smith, are filling their trolleys with the product.

The Tuscan flourmakers are not alone. At this time of year, the airwaves are full of celebrity chefs and their suggestions for the finest Christmas ingredients. But many of these ingredients are supplied by small manufacturers and a sudden recommendation can play havoc with their production plans.

Delia’s Classic Christmas aired on BBC2 on December 1 and the next day J Sainsbury was flooded with calls from customers asking for the chestnut flour that she uses to make cupcakes.

The supermarket increased distribution of the flour threefold – sending it out to more than 300 stores.

The flour is only stocked by Sainsbury and only sourced from the Grifoni family, which has been making it since 1696. The grinder, which was last replaced in 1877, soon started pulverising chestnuts day and night.

Jeremy Blower is managing director of Unique Fine Foods, which supplies the flour. When the supermarket told him to increase production it was his job to persuade the family that it needed to slow supply to Italian customers and send more to Britain.

He said: “Even though they speak no English whatsoever, they had heard about Delia. They were terrified – in the nicest sort of way – they wanted to get it right.”

It was not only sales of chestnut flour that soared after Delia’s Classic Christmas. At Waitrose, purchases of soft prunes were up 106 per cent year-on-year, whole tinned chestnuts sales increased 70 per cent and those of organic dried apricots rose 68 per cent.

A spike in demand does not necessarily translate into a boost to profits because of the extra costs involved in responding so quickly. But Unique Fine Foods believe that retailers should ensure the shelves are well-stocked, whatever the circumstances.

Manufacturers are also cautious about committing to higher production in the long term in case demand comes crashing down.

Mr Blower said: “We have gone from 20 cases to 300 cases [of flour] a week but we have to be careful because we don’t know how long it will stay like this. It’s not a staple, it’s a luxury product.”

Barts, the Bristol-based company that makes many of the spices and baking ingredients that Delia recently recommended, has had its products endorsed before. It predicts that for most products the spike in sales will only last a couple of weeks. But even when recommendations cause demand to surge for years, rather than days, supermarkets often still depend on the same small supplier.

Sales of goose fat at Sainsbury soared 1,500 per cent from 2000 to 2003 after Delia and Jamie Oliver used it when roasting potatoes. Endorsement from Nigella Lawson contributed to its continued success, as sales rose 300 per cent between 2003 and 2008.

Bespoke Foods sources goose fat for all the leading UK supermarkets from one factory in the Dordogne. The factory has doubled in size and the seasonal workforce is now nearing 100.

The owner starts production in June to meet the Christmas demand and resorts to piling up the jars in garages around the village.

To try to prevent panicked production, supermarkets are increasingly co-ordinating their supplies with the celebrity chefs months in advance. This also gives them the opportunity to help shape the recipes.

Susi Richards, head of innovation at Sainsbury, said: “We have close ties with the chefs, particularly Delia and Jamie.

“They keep us in the loop and to a certain extent we collaborate – we give tips because we know what our customers want.”

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