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Why All “Authentic” Key Lime Pie Has to Have This One Crucial Ingredient

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Maybe you’ve seen it in the display case at your local diner, a glowing shade of green not found in nature. Maybe your grandma had her own secret recipe. But if a Key lime pie doesn’t have this one specific ingredient, however, chances are that it’s nothing but a paltry imposter. While most recipes call for fresh lime, unless you’re using Key limes—wholly different from your regular grocery-store-variety limes—what you’re making is not a Key lime pie at all but, at best, it’s just a sad regular lime pie.

Named after Florida’s world-famous Keys, which extend from Key Largo to Key West, a Key lime is distinguished from the more commonplace Persian lime varieties by its strong aroma, tart(er) flavor, smaller shape, and rougher skin. Rumored to have originally been brought to the Caribbean and Latin America by Spanish explorers, and native to Southeast Asia, legend has it that the first actual key lime pie was whipped up in the late 1800s by a woman named “Aunt Sally”, a cook for Key West estate owner William Curry, at the Curry Mansion Inn. Key West historians Tom Hambright and David Sloan speculate that the recipe may have actually come from local fishermen, who prized the dish for its long shelf-life. “The first Key lime pie was probably created by hookers,” Sloan told us via email. “That's what they called the sponge fishermen in Key West, because of the long hooks they used to harvest sea sponges.” The hookers would go out on their skiffs for several days at a time, their only supplies consisting of Cuban bread, local limes, and sweetened condensed milk. “The Cuban bread would go stale after a day, so they would crumble it into a coffee cup and pour condensed milk on top to moisten it.” Hambright believes they would also mix in a wild bird or turtle egg and squeeze the lime on top, the dessert eventually making its way to land. A very different theory was offered by Stella Parks, author of the BraveTart: Iconic American Desserts (and winner of a 2018 James Beard Foundation award), one that’s proven extremely unpopular with Floridians—the pies were actually created in New York City, in 1931, by the Borden milk company in an effort to sell more sweetened condensed milk, a main ingredient in Key lime pie.

No matter whose story you embrace, it's clear that today the world-famous pie is synonymous with the Keys. Each July 4th weekend since 2013, Key West has hosted the Key Lime Festival, a celebration of all things key lime. Floridians are so wedded to the authenticity of their pie that, in 1965, Florida State Representative Bernie Papy, Jr. attempted to introduce legislation that would levy a $100 fine on any individual or establishment advertising Key lime pie not explicitly made from Key limes. The bill, inevitably, failed but the message was the same—if they ain’t Key limes, it ain’t key lime pie.

Today the mass-scale, commercial Key lime trade has largely left the Florida Keys, but up until the 1930s, Key Largo had one of the world’s most profitable lime industries, and locals would use the tart citrus flavor not just in pastries but in seafood dishes, sauces, and festive drinks and, today, most local restaurants continue to use fresh Key limes. At Tavernier’s Blond Giraffe Key Lime Pie Factory, one of the area’s most popular Key lime spots and a past winner of the Key Lime Festival, you can pick up everything from Key lime taffy to the original pies, which have proved so popular they're no longer able to ship outside the area.

Once you’ve tried a real Key lime pie, it can be hard to settle for anything less. While finding these gems can be extremely hard in most American Cities, New Yorkers can visit Steve’s Authentic Key Lime Pies in Red Hook, one of only two commercial bakeries in the U.S. that uses freshly squeezed Key limes. “As a native South Floridian, there’s only one way to make Key lime pies—fresh squeezed key limes and a hand-made crust,” according to founder Steve Tarpin, who told us that even in the Keys, you’ll find a variety of recipes, some calling for meringue on top, some with a baked filling (Steve simply “fills and chills" his Key lime stuffings). He is adamant that true Key lime pie lovers must use bottled juice only for “stripping paint or removing rust,” but this is not always an option. While some mainland stores do carry fresh Key limes, “their quality can be unreliable,” according to award-winning cookbook writer Sheri Castle, who explains that many bakers rely on the consistency and predictability of bottled Key lime juice, with most devoted to Nellie & Joe’s Key West Lime Juice, which is widely available for purchase.

While the battle to determine what makes the most authentic Key lime pie may rage on, apparently the best way to gauge quality may also be the easiest. “One main thing that separates Key lime pie from the Keys is the color,” according to Ashley Serrate, a rep for the Florida Keys & Key West Tourism Council, who hoped to set the record straight. “A true key lime pie should have a hint of yellow but should never be green. If you see a key lime pie on a menu and it's bright green, it's not a true key lime pie," and, as Tarpin adds, "STAY AWAY!"


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