THE room has a cold, clinical lab-like feel. The impression is accentuated by the sight of a man in a white lab coat pushing a trolley. Inside are a dozen booths, each containing a chair, small ledge, computer screen and keyboard, tissues and sink.

Those performing the experiments are not permitted to eat, drink or smoke for 30 minutes before entering this room. They must sign a confidentiality clause, promising not to disclose the results of their work to the outside world.

"Welcome to the sensory room" reads a notice on the door. It sounds like we're entering Big Brother's Room 101 in George Orwell's 1984, a room where people are confronted with their worst fears. But the opposite happens here. This is where tasters tuck into chocolate, putting its taste and smell to the test.

Banish mental pictures of Billy Bunter cramming chocolate bar after chocolate bar into his mouth. Taste-testing chocolate is a serious business, as the volunteers who perform the job for Nestle at its York base will testify. Those who fail to win a place on the panel can simply hang around the city and inhale the sweet smell of excess as the aroma of chocolate production wafts around the air.

"People think you just sit around all day eating Smarties. They're always very interested when you tell them what you do. It's a good dinner party subject," says taster Fiona.

The product evaluation centre in York tastes confectionery for Nestle worldwide, which means products - not just chocolate products, but sugar confectionery, biscuits and chocolate bars - that are sold around the world. So, as well as the more familiar Nestle products, the tasting teams might find themselves trying Polish chocolate or Brazilian biscuits. Some have unusual flavours which don't always appeal to British tastes. The words "cat's pee" are used in conjunction with one foreign product, a boiled sweet, set before the tasters.

Elisabeth Bizouarn, the Frenchwoman who heads the sensory science section, knows that there's never any shortage of people wanting to join the two 12-strong tasting teams.

A recent newspaper advertisement attracted 100 would-be tasters. "First, we send them a questionnaire to find out a bit more about their abilities, motivation, health and allergies. Obviously we need to check that," she says. "The successful ones are invited to the first assessment, an exercise to see if they have the right ability for taste and odour reaction, and to describe the results. There's much more than just tasting products. There's a lot of discussion and work done before the actual assessment of products."

Some tasters have been on the Nestle team for four years, although men are in short supply. There are only a couple on the panels covering chocolate and confectionery.

Tasters attend sessions once a week to assess products. "Two hours at a stretch is as much as you can take," says Fiona. Some of the time is spent in the tasting booths, the rest sitting around discussing products under consideration.

The team spends 15 minutes tasting in the booths, followed by a 15 minute break - "so they don't get saturated and to give the palate time to recover," explains Elisabeth.

What tasters get to sample are not actual-size bars or slabs of chocolate but small unidentified pieces in those greaseproof cases used for fancy cakes. They never know the name of the product being tasted.

"We don't get told that," says Wendy. "We see our data on charts afterwards but you don't go into a sweet shop and see 'tasted by' on the label. Sometimes you can identify things you've tasted before they have been launched in the shops. And we do foreign things that would never get on the shelf here."

"They are challenging us all the time," says Fiona. Her involvement began after replying to an advertisement in 1997. "It didn't say who it was from, just, would you like to be a food taster? It never dawned on me it was going to be chocolate. It's been absolutely fascinating. They've given us all sorts of things to smell and taste. Sometimes you think 'there can't be a market for this', it must be some foreign outlet."

The tasters are able to input their remarks directly into the computer in their booth, building up recommendations and information for the sensory analysts to use in evaluating products.

Elisabeth, who studied food science at university in France, became head of the section four years ago. Coincidentally, her two predecessors were both French and female too. And in reply to the obvious question, yes, she does eat chocolate for pleasure away from Nestle. "Not too much," she says, "but I do appreciate it."