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When Colin Hagendorf set out to eat every pizza in New York City, he had no easy way of knowing that there are more than 1,600 restaurants officially classified as pizzerias across the five boroughs — more than every other type except Chinese and the vague catch-all category of “American” eateries, according to a city health-inspection database.

Trying every iteration of the New York slice turned out to be more than a determined pizza hound could handle, as the Journal explains in a profile Wednesday, so Hagendorf limited his survey only to Manhattan’s slice joints. He visited 362 different pizzerias selling by the slice, excluding national chains, during his two-and-half-year mission.

The health-inspection database didn’t exist in 2009, when Hagendorf started his Slice Harvester project, and even now it probably understates the sheer number of pizza venues because it doesn’t tally the many non-pizzerias that happen to serve pizza. But New York City was not always the home of ubiquitous slice joints. Go back just a half-century, and the city’s culinary landscape is almost entirely devoid of pizza.

Up until the late 1950s, New York pizza was largely the province of master bakers, limiting both the popularity and availability of the food. And pizza was only available by the pie; the coal-fueled ovens used to bake the pies were too hot to reheat individual slices.

Rob Bennett for The Wall Street Journal
Colin Hagendorf trying yet another slice at a pizzeria near the Staten Island Ferry earlier this month.

Michael Berman, a 44-year-old photographer and food writer based in Brooklyn, pored over old volumes of the Yellow Pages stored on microfilm at the New York Public Library to count the listings for pizzerias over the decades and measure the growth of the city’s pizza industry.


What caused that Mad Men-era pizza surge? Oven technology.

“If you go to some of the older pizzerias in New York, you can see it was a really hard way to make pizza,” Berman says. “A lot harder than the gas oven.”

The advent of affordable, easy-to-use gas ovens helped popularize and democratize the food. Berman found a 1957 article in the Saturday Evening Post about a New York oven salesman named Frank Mastro, who built a model pizzeria in his showroom to demonstrate the potential of the gas oven.

Scott Wiener, a chronicler of pizza history who runs New York pizza tours, agrees that the gas oven gave rise to New York’s ubiquitous slice joints and eventually made pizza a commodity food across the country.

“It turned the slice into an entirely different animal,” he says. And the slice, in turn, “became popular because it was available.”

Wiener points to Bari Equipment, an oven purveyor that has been located in Manhattan’s Bowery area for more than 75 years, as an early force linking gas ovens to the manufacture of pizza in the city.

Joe Riggio, the second-generation pizzaman who owns Pizza Suprema — home of Hagendorf’s favorite Manhattan slice — believes that New York’s enormous appetite for slices reheated on the fly in gas ovens did more to popularize pizza than anything that happened to the cuisine in the place of its birth.

During his great-grandmother’s day, Riggio says, “in certain regions of Italy they didn’t know what pizza was.”