New late-harvest strains of the rich, red berries mean the season now lasts long after Wimbledon, says Lena Corner

It's 10am in a sunny south-facing field in Kent's Medway Valley, and a group of about 40 Eastern European strawberry pickers are preparing to clock off for the day. They've been picking since dawn, systematically working their way along the rows of fruit, which stretch as far as the eye can see.

Now it's too hot to continue. Meile, a twentysomething Lithuanian, stands at the end of a queue of workers punching information into a hand-held computer. This batch is headed for Waitrose, and by this time tomorrow they'll have been weighed, checked and packaged and will be ready to buy from the supermarket shelves.

Twenty years ago the strawberry season would have been virtually done with by this time, but thanks to a variety of different strains with varied cropping times, it now stretches through to autumn. Here at Hugh Lowe Farm, production peaks in June when they take on as many as 300 pickers to cope with the demand of the Wimbledon fortnight. But even in August, with output levelling off a little, they're still producing 40 tonnes a week.

"Although June is our peak period, the later months are actually more interesting because there's a much bigger variety of fruit around," says the farm's managing director, Marion Regan. While June is virtually entirely devoted to growing the Elsanta, a classic English early-cropping berry, the later croppers mean that now we're seeing others such as the Everest, a more rustic-looking fruit or the Bolero, a bright, shiny, attractive looking fruit which crops until November.

Breeding programmes are working continually to produce the perfect fruit and Ms Regan's farm not contributes to one, but also trials many of the new berries coming out all the time. Recent additions to the Hugh Lowe crops are the Diamante, which bears an unusually large fruit, and the Sovereign, a big, bold berry with a strong flavour. "My father claims to have been one of the first to grow Elsanta in this country," she says.

Ms Regan's aim is to get the fruit from the field to the fridge within half an hour. She claims they can reach the supermarket shelves without having once been touched, as pickers are trained to carefully detach the fruit by the stalk. As supermarkets don't like their fruit to come in odd shapes the berries are graded by the pickers in the field as well. The misshapen ones end up in the second-class punnets, which then get sent on to the wholesalers.

The data logged on to Meile's computer at the end of the morning's pick can identify not only the name of the picker and their supervisor, but exactly what time the berry was picked. This information is starting to turn up on the punnet itself – Marks & Spencer insist on labelling theirs with Ms Regan's name so each fruit can be traced back to the very field that it came from.

Years ago the picking was done by local Kentish housewives, but nowadays young seasonal workers come from abroad to do it. Here they're from Slovakia, Poland, Bulgaria and Lithuania, and many are on government exchange programmes from agricultural colleges. Although the minimum agricultural wage is £3.72 an hour, by paying on volume picked the faster workers can earn two or three times that.

David from Poland is in Kent for a second year, and this time round he has managed to land a plum job in the quality-control department. This means he gets to stand in the cold room among a mountain of strawberries, pulling trays out at random to check to see if they're sweet enough, big enough (25-40mm), red enough and firm enough.

Much better, though, is the job the two women in the packhouse have – eating them. Janet Farrow, the packhouse manager, is overseeing a weekly taste test with an auditor from Waitrose. "Nowadays there are so many options it's become an entirely subjective thing," says Ms Regan. "Everyone's got their own opinion and we often spend hours and hours arguing over which strawberry tastes best."