Many Americans who have ordered a Key Lime Pie at a restaurant or made it at home, have never really tasted one.  What they have eaten is a Persian Lime Pie.  The Persian Lime or Tahiti Lime (botanical name, Citrus latifolia) is a relatively new fruit, having been developed in the early 20th century.  It is oval, dark green and with a thick rind, and you can find it in almost any supermarket in the United States. On the other hand, the Key Lime, Mexican Lime or West Indian Lime, (botanical name, Citrus aurantifolia), is round and small, a lighter shade of green with a thin skin and a delicate aroma.  You can grow it in Florida and in southern California, but you'll find it only occasionally in supermarkets. It is thought to have originated in Southeast Asia several centuries ago and traveled, first with the Arabs to the Mediterranean , then with the Crusaders to Europe.  The trees came to the string of Florida islands known as The Keys by way of Christopher Columbus who brought citrus fruits with him on his second voyage to the Caribbean Sea in 1493, when lime trees were planted first in Haiti, then called Hispaniola.  As the people of the Caribbean moved around, they took with them the seeds of this tart and aromatic fruit and by the early nineteenth century there were groves of lime trees in Key West, the southernmost point of the continental United States.

What Key West lacked, however, was cows, and milk and cream were hard to come by until Gail Borden invented sweetened condensed milk in the mid 1800's.  This canned product was a boon to the "Conchs," as natives of Key West are known, and they soon used it to create a lime pie, similar to a favorite Caribbean dessert made with sour oranges.  They were also quick to realize the new dish would cook itself because of the acidic content of lime juice.  An early recipe would therefore have been something like this:

When a hurricane hit the Florida Keys in 1926 the commercial lime groves were destroyed, and they have never been replaced. The thorny trees were often difficult to harvest and by then the less perishable Persian lime had become a nationwide favorite.  However, the Floridians continued to grow their key limes in backyards and continued to improve on the recipe.  Since refrigeration made fresh cream more available, a favorite topping on the pie became whipped cream, and in the late 1940's the graham cracker crust was an innovation.   The current popular version of the pie now goes more like this:

It can take up to 12 of the small key limes to make 1/2 cup of the juice, more than twice the number of Persian limes, but if you can find the key limes in your supermarket (ask the produce manager when to expect them!), it is well worth it.
If you want to use Persian limes, substitute lemon juice for half the amount of juice and you will approximate the more delicate key lime flavor.  You will also approximate the yellow-green color which is distinctive of the key lime juice (NEVER use green  coloring in a lime pie -- it's a phony giveaway!).  Bottled juice will also work and you might want to consider freezing extra juice (either fresh or bottled) for later use.  Just pour the juice into an ice cube tray, pop out the cubes when frozen and put them in a plastic bag and you'll have lime juice on hand without worrying about its discoloring over time.

IMPORTANT!  Please Note:  Ever since an outbreak of salmonella in the United States some years ago, it has been advisable to cook all eggs before eating.  Therefore, we do not recommend the old tradition of preparing uncooked foods such as home-made mayonnaise or unbaked Key Lime pies.  Pies should be baked to an interior temperature of 160 degrees because of the possibility of salmonella in eggs. Fifteen minutes in a 350 degree oven should do it.

To learn more about key limes, from their history to horticultural information, visit
Steve Tarpin's website at www.keylime.com

Who Cooked That Up? is copyrighted 2002 by J.J. Schnebel
Revised February 2002, October 2005
all rights reserved for your pleasure and enlightenment

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