THE SEARCH FOR SWEET.

The substance in the flask seemed to have all the makings of an excellent insecticide. It was a fine crystalline powder, easy to imagine spraying over a field, and its molecules were full of chlorine atoms, like DDT. To make it, Shashikant Phadnis, a young Indian chemist at Queen Elizabeth College, in London, and his adviser, Leslie Hough, had begun by taking an eyedropper full of sulfuryl chloride--a highly toxic chemical--and adding it to a sugar solution, one drop at a time. In the violent reaction that followed, a wholly new compound was born: 1', 4, 6, 6'-tetrachloro-1', 4, 6, 6'-tetradeoxygalactosucrose.

On that late-summer day in 1975, Phadnis was told to test the powder, but he misunderstood: he thought that he needed to taste it. And so, using a small spatula, he put a little of it on the tip of his tongue. It was sweet--achingly sweet. "When I reported my findings to Les, he asked if I was crazy," Phadnis remembers. "How could I taste compounds without knowing anything about their toxicity?" Before long, though, Hough was so delighted with the substance that he dubbed it Serendipitose and tried putting some in his coffee. "Oh, forget it," he said, when Phadnis reminded him that it might be toxic. "We'll survive!"

Over the next year, Hough and Phadnis worked with the British sugar company Tate & Lyle to make more than a hundred chlorinated sugars, finally settling on one that had three chlorine atoms and was about six hundred times as sweet as sugar. "It isn't of any use as an insecticide," Hough told me recently. "That was tested." But it has proved useful as a food. In its pure form, it is known as sucralose. When mixed with fillers and sold in bright-yellow sachets, it's known as Splenda, the best-selling artificial sweetener in America.

People will eat almost anything, it seems, as long as it's sweet. And, until fairly recently, this mental programming served them just fine. When Columbus introduced cane to the New World, the anthropologist Sidney Mintz has noted, sugar was an exotic luxury. Most Europeans had never eaten sugar, but they quickly developed a taste for it. By 1700, the Americas had become a vast sugar mill and the English were eating four pounds per person per year. By 1800, they were eating eighteen pounds; by 1900, ninety pounds. But nowhere was the rise of sugar as dramatic as in the New World. Last year, the average American consumed about a hundred and forty pounds of cane sugar, corn syrup, and other natural sugars--fifty per cent more than the Germans or the French and nine times as much as the Chinese.

Artificial sweeteners are both a symptom of this craving and an attempt to curb it. Some two hundred million Americans now use them, but rarely with much enthusiasm. Like Splenda, the most popular products were all discovered by accident; none of them taste much like sugar; and there is no final verdict on their safety. Saccharin was found over dinner in 1879, by a chemist who was working with coal-tar derivatives and forgot to wash his hands properly. It's used in Sweet'N Low in the United States, where it was listed as a possible carcinogen until 2000, and is still banned as a food additive in Canada. Aspartame, which is used in Equal and most diet sodas, was found in 1965, by a chemist who was testing new drugs for gastric ulcers and licked his fingers before picking up a piece of paper. A recent study by the National Cancer Institute found no evidence that aspartame caused cancer in people, but an Italian study found that it caused cancer in rats. Sucralose was declared safe by the Food and Drug Administration in 1998, but most taste researchers I talked to won't eat it. "I look at that structure and I have an irrational fear of it," one of them said. "I've seen the safety studies, and you feed it to rats and mice forever and nothing happens. But it just scares me."

Inventing a sweetener with even a little of sugar's appeal is one of the hardest tasks in food science. It's less like imitating the taste of Coke or vanilla than like trying to imitate water--another simple but astonishingly versatile compound. Sugar's sweetness only begins to explain our devotion to it. You can freeze it, cook it, candy it, and caramelize it. It adds bulk to baked goods and helps them to brown. Sugar is a powerful preservative. It triggers the taste buds almost instantly, fades quickly without aftertaste, and has a voluptuous mouthfeel. Even its potency can't easily be improved. Artificial sweeteners may be thousands of times as sweet by volume, but their flavor loses intensity with repeated tasting. Sugar stays sweet.

Of course, sugar can also make you fat, put diabetics into a coma, and make your children run screaming in circles. In the past twenty years, it has helped to double the number of obese Americans and rotted untold millions of teeth. Sugar may be the single most unhealthy part of the American diet, yet until recently there was little hope of finding a tastier, more wholesome substitute. Thousands of chemicals were known to be sweet, but none of them tasted or behaved like sugar. If all artificial sweeteners had been discovered by accident, the reason was simple: No one knew how to make them from scratch.