A tart and sweet pie made with key lime juice, sweetened condensed milk, and egg yolks on a graham cracker crust.
Originated in the Florida Keys around the 1890s, when commercial sweetened condensed milk (Borden's Eagle Brand, 1856) reached the islands by schooner. The Keys had no fresh dairy — no cows on coral rock — so condensed milk was the only available dairy, and its acidity-reactive proteins set the lime juice into a no-bake custard. The original recipe was uncooked; modern versions bake briefly for food safety.
Florida Keys 1890s — Eagle Brand condensed milk + Key lime juice + egg yolk; the citric acid actually cooks the eggs without heat. Real Key limes are smaller, yellower, and more tart than Persian limes; substitution shows.
A pale-yellow custard filling on a graham-cracker crust, no meringue or whipped cream baked in (those go on top). The filling is set, not jiggling — sliceable with a clean edge. Tastes of sharp lime first, then sweetened condensed milk, then the toasty graham. Genuine Key limes are smaller and more aromatic than Persian limes; the pie should never be neon-green (that's food coloring; real Key lime juice is pale yellow).
The set comes from acid coagulation, not heat — Key lime juice is pH ~2.0, low enough to denature the casein in the condensed milk and the proteins in the egg yolks on contact, while the sugar in the condensed milk keeps the protein strands from bonding too tightly (so the filling stays smooth, not curdled). That's why no-bake versions work and why the filling firms up in minutes once mixed. Persian limes are pH ~2.5 and lower in oil aromatics; pies made with them set fine but read as one-note tart instead of fragrant.
Variations
Graham-cracker crust (modern standard); pastry crust (older, William Curry’s ship cook origin story); meringue-topped (traditional); whipped-cream-topped (post-1950s); frozen Key lime pie on a stick (Florida Keys roadside specialty).
On the Palate
Where Key Lime Pie sits in the American flavor cloud
The filling sets by acid, not heat: real Key lime juice is pH ~2.0, acidic enough to firm the condensed milk and yolks the moment they mix, so whisk it just until thick and pale — the brief bake is only for food safety, and overbaking cracks it.
Ingredients
How it's made
5 steps · 33 min active + 2 hours waiting
- 15 min
Preheat your oven to 350°F (175°C). This ensures a consistent baking environment for your pie.
- 25 min
In a mixing bowl, whisk together the sweetened condensed milk, key lime juice, and egg yolks until smooth and creamy. The mixture should be thick and pale yellow.
Watch outWhisk only until the mix thickens and pales to a soft yellow ribbon — it starts firming the instant the acid hits, so don't overwork it.
- 33 min
Pour the filling into the prepared graham cracker crust, smoothing the top with a spatula. The filling should be even and reach the edges of the crust.
- 415 min
Bake the pie in the preheated oven until the filling is set but still slightly jiggly in the center, about 15 minutes. The edges should be firm and the center should not be liquid.
Watch outIt's baked when the edges are set but the center still wobbles like loose jelly under a nudge — a firm, still center means it's already overdone.
- 55 min
Remove the pie from the oven and allow it to cool to room temperature before chilling in the refrigerator for at least 2 hours. This will help the pie set completely.
Watch outDon't rush the chill — the pie only cuts clean and holds its wedge once it's cold all the way through, at least two hours.
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