Key Limes vs. Persian Limes: What's the Difference?
One is small, seedy and fragrant; the other fills most grocery bins. How they differ, and whether it matters in a pie.
Walk into most American grocery stores and the limes in the produce section are almost certainly Persian limes: large, glossy, dark green and nearly seedless. Key limes are a different fruit, and if you've only ever seen them in a mesh bag near the specialty citrus, you might wonder whether they're worth the trouble.
Two different fruits
The Key lime (Citrus × aurantiifolia), also called the Mexican or West Indian lime, is small, roughly the size of a golf ball, with a thin rind and plenty of seeds. It turns yellowish as it ripens. It's named for the Florida Keys, where it was widely grown until a 1926 hurricane wiped out many of the groves. Today most Key limes sold in the United States are imported, largely from Mexico.
The Persian lime (Citrus × latifolia), also called the Tahiti or Bearss lime, is bigger, with a thicker rind and usually no seeds. It's hardier, ships better and keeps longer, which is why it took over the supermarket.
| Key lime | Persian lime | |
|---|---|---|
| Size | About 1 to 2 inches across | About 2 to 2.5 inches across |
| Rind | Thin, turning yellow when ripe | Thicker, usually sold dark green |
| Seeds | Many | Few or none |
| Flavor | More tart, more floral and aromatic | Tart, milder, more straightforward |
| Juice per fruit | Small, about 2 teaspoons | About 2 tablespoons |
Does it matter in Key lime pie?
Classic Key lime pie is a simple custard: sweetened condensed milk, egg yolks and lime juice, poured into a graham cracker crust. The acid in the juice reacts with the proteins in the milk and yolks and thickens the filling, which is why early versions of the recipe didn't need baking at all. Today most recipes bake the pie briefly, which sets the filling and cooks the yolks.
Key lime juice gives the pie a sharper, more perfumed flavor. Persian lime juice works fine and makes a slightly milder pie. Plenty of bakers use bottled Key lime juice, which is convenient but tends to taste less bright than fresh juice.
How many limes?
- A standard 9-inch Key lime pie uses about 1/2 cup of juice.
- That's roughly 20 to 25 Key limes, or about 4 Persian limes.
- Zest the limes before juicing them. A teaspoon of zest in the filling adds a lot of aroma.
Buying and storing
Choose limes that feel heavy for their size, which means they're full of juice, and that give slightly when squeezed. Key limes with a little yellow on the skin are ripe, not past their prime. Both kinds keep a week or more in the fridge, much longer than on the counter.
To get more juice, roll the lime firmly on the counter under your palm before cutting it, or microwave it for about 10 seconds.
Where else to use them
Key limes are great anywhere the aroma comes through: drinks, vinaigrettes, ceviche, or squeezed over grilled fish or tacos. Persian limes are the better choice when you need a lot of juice quickly, as for a big batch of limeade or a marinade.