When Brian Cullen began writing online about his Crock-Pot creations, he was surprised to discover that many of his male friends had their own.

"It was almost like a release, to admit that they used Crock-Pots," he said.

The Crock-Pot, which was invented 75 years ago, owed its initial popularity to a marketing campaign directed at women. Now Jarden Corp., the manufacturer, has partnered with the National Football League. In preparation for the Super Bowl on Sunday, men such as Cullen, a lawyer in Green Bay, will no doubt fire up slow cookers sporting team logos to satisfy their cravings for cheese dips and pulled pork.

In the past 15 years, sales of slow-cookers have doubled, and some observers point to an expanding interest in cooking among men. Once again, slow cookers may signal a shift in the division of labor between the sexes.

The Crock-Pot's popularity exploded in the early 1970s just as women were entering the work force in large numbers. Commericals for kitchen appliances had long featured homemakers, but now working women emerged as an important market. A slow cooker meant that dinner would be ready when they came home.

Yet just what devices such as slow cookers have meant for women's lives is still hotly debated.

While far more women are working now than four decades ago, no home appliance liberated women from the burden of cooking for the family. The average American woman still spent 48 minutes a day cooking and cleaning up in the kitchen in 2013, compared with 20 minutes for men, according to a government survey.

"All these appliances are marketed with the promise that they'll make life so much easier for women, that they'll save women infinite time," said Amy Bix, a historian at Iowa State University. "Inevitably those promises never really pan out."

An inventor named Irving Nachumsohn received the patent for the device that became the Crock-Pot on Jan. 23, 1940. Nachumsohn, who went by the surname Naxon, invented the slow cooker to cook cholent, a traditional stew eaten by Jews in eastern Europe on the Sabbath. Since they were forbidden from cooking, Jews would bring pots of stew to a nearby bakery the day before. They would cook slowly in the residual heat from the ovens, his daughter Lenore told NPR last year.

"The advent of the slow cooker - it saved the Jewish housewife," said Laura Frankel, the executive chef in Wolfgang Puck's kosher division in Chicago and author of "Jewish Slow Cooker Recipes."

The slow cooker, like other home appliances, relied on the rapid electrification of the country during the first half of the 20th century. Many economists also say these technologies encouraged women to work outside the home.

Single women - and some married women - had worked as teachers and domestic servants, as well as in factories during World War II. With electricity and indoor plumbing, some women had a new choice: They could do the laundry with a washboard and clothespins, or they could work and pay in installments for a washer and a dryer. As appliances became available at lower prices, the second option took less and less of a woman's time.

One study by Daniele Coen-Pirani, an economist at the University of Pittsburgh, found that home appliances accounted for about 40 percent of the increase in work outside the home among married women during the 1960s.

A separate study in South Africa, where about a quarter of the population gained access to the grid between the end of apartheid and 2001, found that access to electricity led to significant increases in women's employment.

"You can look at countries where some of these technologies have become cheaper, faster," Coen-Pirani said. "In these countries, you see more of an increase in labor force participation by women."

Some historians, however, argue that technology had simply created new tasks for women. With a washer and dryer, they were expected to do the laundry more regularly, for example.

"The advertising copy said all of these things - the refrigerator, the washing machine, the dryer - were going to revolutionize housework," said Ruth Schwartz Cowan, a historian at the University of Pennsylvania. "None did."

Cowan maintains that changes in society's attitudes toward women, not technology, is what led them to work outside the home. "Married women entered the workforce because they needed to and wanted to, not because they were released from anything in particular in their homes," she said.

Whatever the cause of the shift, Rival (later acquired by Jarden) found a new kind of customer: The Crock-Pot was "perfect for working women," declared a Sept. 25, 1975, advertisement in The Washington Post.

That was the year Mable Hoffman published "Crockery Cookery." With recipes like "Busy Woman's Roast Chicken," it sold nearly half a million copies in four months. It was a bestseller for much of the year, along with "The Joy of Sex" by Alex Comfort and the "Star Trek Starfleet Technical Manual."

Around then, for the first time, a majority of white, married women of middle age had joined the labor force. The Crock-Pot wasn't just for working wives, though. Rates of divorce were skyrocketing, too.

"I have come upon an appliance that vindicates technology for the single working parent - the slow-cooking electric pot," opined one writer in the New York Times. "You throw in some food before leaving for work (I've gotten this down to thirty seconds without breaking stride as I head out the door), turn the knob, and any time from 4 o'clock on, dinner is hot and to be ladled out by your ravenous children."

Many feminists, however, were nonplussed. If women had more time, they worried, they would simply be tasked with more work.

"Working outside the home, starting in the '70s, was an expectation that got added on to women's expectations of themselves," said Susan Strasser, a historian at the University of Delaware. "There wasn't any substantial change at that time in expectations of what men would contribute to the household."

Of course, Crock-Pots arrived in a period of intense inflation in the prices of energy and food. A relatively affordable slow cooker allowed families to roast inexpensive cuts of meat to tenderness, while using less energy.

Economic stresses might be a factor today, too, said Emily Balsamo, an analyst at Euromonitor, a market research firm.

Another reason for the return of the slow cooker might be nostalgia. Appliances once heralded as marvels of technology are now prized for their old-fashioned look and feel. Kitchen Aid's food processors with their classic design are also doing well, Balsamo said.

About 4.4 million Crock-Pots were sold last year, compared with 3.2 million in 2005, according to Euromonitor. Jarden controls about a third of the market, far more than its largest competitors, Hamilton Beach and West Bend.

Stephanie O'Dea suggested that Americans are looking for new ways to cook healthfully, without creating too much work. The author of the bestseller "Make It Fast, Cook It Slow," O'Dea's recipes are different from ones published in the early years. Those relied on "a can of mushroom soup and a packet of onion soup mix," she said.

As a result, most slow-cooked food tasted more or less the same and wouldn't appeal to a new generation of cooks looking to prepare healthful fare with fewer processed ingredients.

That means men, too. Jarden announced its partnership with the NFL to introduce Crock-Pots with logos for all 32 teams in 2012.

Tom Wyrwich, a Seattle lawyer, said he picks up ingredients at his local grocery store every Sunday during the season for pot roast, beef stew or chicken tortilla soup.

"I'd much rather cut up food and get a Crock-Pot started than watch any pregame show," he said. "By the time the morning games and the afternoon games are over, it's ready to go."

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