How supermarkets get Christmas dinner from field to fork

The huge open truck or "bulker" glides to a standstill in the unloading bay, piled to the top with 25 tonnes of black, soil-encrusted potatoes.

Five hours earlier at 6am on Wednesday the vegetables left a Nottinghamshire farm bound for this North Yorkshire produce factory after being harvested the previous day.

Once washed, sorted, graded and bagged in a semi-automated operation, they will travel to a regional distribution centre before arriving in supermarkets across the UK in the next couple of days. Consumers will buy them this weekend – the busiest shopping time for fresh food forChristmas – for festive lunches on Tuesday. The potatoes will have travelled from "field to fork" in a carefully managed logistical exercise lasting between 24 and 48 hours.

Flaxby is known in the trade as a "dirty" factory – because vegetables arrive straight from the ground, unwashed – and it is at the heart of the fresh produce operation of supermarket chain Morrisons. Working 24/7 at Christmas, it is one of three "dirty" facilities serving Morrisons, the UK's fourth largest supermarket and its second biggest food company.

Andrew Garton, the retailer's director of produce and horticulture, explained the challenges of getting the freshest possible potatoes, carrots, sprouts and other produce into the shops, given the timing of Christmas this year and shoppers' increasing tendency to leave their food shopping as late as possible.

These issues face all retailers in the battle for shoppers' cash and custom in the busiest and commercially most important time of the year. The day before Christmas Eve is traditionally grocers' busiest shopping day but this year it falls on a Sunday and large supermarkets are restricted by Sunday trading hours. "The last time Christmas Day fell on a Tuesday was in 2007," Garton said, "so although we have had this pattern before we also have the impact of the recession, too. Shoppers are counting the pennies and will be looking for good value price as well as the freshest fruit and vegetables in tip-top condition. Christmas is coming later and later every year in terms of shoppers' habits and that puts further pressure on our supply chain."

Garton thinks shoppers will spread their food shopping over the weekend, but predicts that Saturday will be the busiest, with shoppers expecting shelves to be fully stocked even on Christmas Eve. The uplift from Christmas gluttony is striking – with volume of food typically up by 70% on a normal week.

Morrisons' usual weekly supply of 3,700 tonnes of potatoes soars to 6,500 tonnes during Christmas week, while for sprouts it leaps from 180 tonnes to 650 tonnes. And 20% of sprouts bought by Morrisons customers during the year are bought in a four- to six-day window in the runup to Christmas.

Morrisons claims to buy more fruit and vegetables direct from British farmers than any other major supermarket, working closely with up to 50 British fresh produce suppliers, and sells 13 varieties of potato, although washed white potatoes are the bestsellers as a good all-round cooking spud, Garton says. But after "the wettest British weather for 100 years", which has damaged many crops, Morrisons is importing a small proportion of potatoes from the Netherlands so as not to risk any shortages.

Inside the factory, carrots are washed and "polished" in a hydro-cooler – using only ice-cold clean water. Sprouts are picked over by hand and any yellowed or blemished ones rejected. Garton explains that the supermarket has agreed to sell slightly smaller sprouts this year – the result of the poor weather – "but our experience shows that shoppers are very fussy about their appearance". All rejected vegetables are used – whether in savers' ranges, in stir fry mixes or – ultimately – in animal stock feed.

Most of the vegetables processed at the factory will go down the M1 to Morrisons' unimaginatively named "Junction 41" – the UK's biggest food distribution centre, which supplies 3% of the country's food. Friday was its busiest day of the year, allocating not just fresh food but also "ambient" products and beers, wines and spirits to go into stores. Its biggest warehouse is the size of 45 football pitches and a fleet of 1,250 12-metre (40ft), 44-tonne Arctic trucks is now busy delivering goods into stores.

Other retailers, which lobbied the government unsuccessfully to relax the Sunday trading laws (which was done during the Olympics), have made contingency plans. M&S says, traditionally, 23 December is its busiest food shopping day of the year, but it expects it to be spread over that day and Christmas Eve this year because fewer trading hours are available on a Sunday. Last year on 23 December, 6.3 million customers snapped up 279,000 turkeys and 1.6m mince pies. This year some of its larger stores will be opening from midnight on 24 December to allow customers to pick up last-minute gifts or collect their Christmas food orders.

At Sainsbury's, the group commercial director Mike Coupe also believes Christmas food shopping will be "squeezed" this year because Christmas Day falls on a Tuesday, although he also predicts that 23 December will be "the busiest ever day in grocery retailing". And for the first time the retailer will in effect have a "lock in" later on the Sunday, with a full bank of checkouts in operation for an hour after official closing to help customers get through the tills.