THE ART OF MAKING cheese is thousands of years old, but the food most Americans have grown up calling cheese is a twentieth-century invention. A hundred years ago, America lagged far behind Europe in cheese consumption. Dairy scientists and U.S. Department of Agriculture (USDA) officials resolved to do something about it. The problem, they believed, was the erratic nature of domestic cheese. Even a master cheese-maker couldn’t consistently produce batch after batch of top quality. Countless variables shaped the final product, and scientists thought they could help by applying industrial techniques based on scientific principles.

It wasn’t that simple. Most food we eat is dead, save for the bacteria and molds we fend off with canning, refrigeration, and chemical preservatives. But the microbes we seek to eradicate from other foods play an essential and extremely complicated role in transforming milk into cheese. Dairy scientists developed what they thought was an ideal bacterial brew for making first-class cheese. USDA field agents urged cheese factories to pasteurize their milk to kill the indigenous microbes and substitute a laboratoryproduced culture. But the mysteries of cheese did not yield so easily. The USDA’s recommendations failed to ensure predictable results and often produced inferior cheese. A field agent reported that a certain amount of “natural contamination” improved quality at one factory. This earned him a stern rebuke from Washington.

American cheese-making gradually improved, but finding better methods to produce what people weren’t buying anyway did little to enhance America’s meager appetite for cheese. The man who did more than anyone else to change the situation was not a scientist but a salesman. James L. Kraft (1874-1953), a native of Ontario, Canada, moved to Chicago in 1903 and founded an empire with $65. He invested in a horse and wagon and began peddling cheese to Chicago grocers. Cheese-mongering didn’t look like a promising line for an ambitious young man, but Kraft saw an opportunity.

He understood that the problem wasn’t bad cheese, but simply cheese. Like wine, cheese improves with time. But it ages fast, and a cheese aged to exquisite perfection continues on swiftly to putrefaction. Some grocers wouldn’t carry cheese in the summer, when shelf life dwindled to almost nothing. Moreover, cheese was wasted every time the grocer sliced off a fresh wedge. A hard crust would form over the newly exposed surface and have to be scraped away for the next customer.

Kraft helped grocers cut down on waste by selling cheese in small jars or tinfoil packages. Around 1912, perhaps inspired by Swiss efforts to market canned Gruyère, he began experimenting with canning cheese that had been heatsterilized. He took shredded natural Cheddar and heated it to kill the mold and bacteria, thus halting the aging process, and he added sodium phosphate as an emulsifier, preventing fats and solids from separating. His technique yielded a product of consistent quality that could be stored in cans almost indefinitely.

In 1916 Kraft received the first American patent on process cheese. By then he had sold more than six million pounds of his cheese to the U.S. military during World War I. Thus it was in France, of all places, that many Americans got their first taste of process cheese.

Following the war, Kraft stormed the consumer market back home with an advertising barrage that gave cheese one of its first recognizable brand names. By 1930 more than 40 percent of all the cheese consumed in the United States carried the Kraft label. Shoppers gladly paid up to 50 percent more for Kraft’s safety, consistency, and reliability, even though some products incorporated unripened and low-grade cheese. As the historian Mark Wilde wrote in an authoritative 1988 study, “With a bit of industrial hocus pocus and plenty of advertising, the processors were converting second-rate cheese into a premium product.”

Wholesalers and distributors of natural cheese found themselves sidelined by Kraft and its competitors, and they accused the processors of fraud for passing off their products as cheese. They beseeched the Wisconsin legislature and the federal government to regulate the products, sometimes suggesting that the stuff be called “embalmed” or “renovated” cheese. Federal guidelines ultimately embraced a more appealing appellation: process cheese. By law, the fat and moisture content of pasteurized process cheese must match that of natural cheese. “Process cheese foods,” such as Kraft’s everpopular Velveeta (introduced in 1928), and “processed cheese spreads,” such as Cheez Whiz (1952), have a higher moisture content and may contain whey, skim or powdered milk, and other ingredients to alter taste and consistency.

Over the last century, per capita cheese consumption in the United States has increased from about 3 pounds a year to almost 30, thanks to process cheese. It is melted on hamburger patties, drizzled onto nacho chips, and mixed with macaroni. Even vegetarians and the lactose-intolerant can buy slices of dairy-free simulated American cheese made from soybeans. You can often find it near the bulk-food section, and it tastes just like genuine process cheese.