This is more than you ever wanted to know about lemons and limes.
Lemons (citrus limon) and limes (citrus aurantifolia) probably originated in tropical Southeast Asia. The choice we U.S. residents find in our supermarkets today are hybrids which are larger and grow in cooler subtropical climes.
Sunkist, the giant Florida citrus conglomerate, prefers fruit which is seedless; is uniform in color, shape, and size; resists cold temperatures; and ships well without bruising. In California, where unseasonable cold snaps are less of a problem than in Florida, the preferred cultivars are the attractive, bright yellow Eureka (or Lisbon) lemon and forest-green Bearss* lime. Both have thick skins that resist bruising, and their ample size catches the consumer's eye. In Florida, the Eurekas and Lisbons are less favorable than the Villafranca and Bearss* lemons, which are more cold-tolerant, and the preferred lime is the Bearss lime (citrus latifolia), also known as the Tahiti lime, Persian lime, limón persa in Mexico, and limón sutil (subtle lemon) in South America.
While high in vitamin C, the juice of either the Eureka or the Bearss is not as sweet or aromatic as that of less common cultivars. And because of the thicker skin and pith (the bitter white part of the rind), the edible part is no larger than much smaller cultivars.
For making beverages or cocktails such as Pisco Sours and Margaritas, the Eureka lemon is too acidic, and the Bearss lime lacks tartness and flavor. The best is the true lime, which is known by various names, depending on where it's grown: the Mexican lime in California, limón verde (green lemon) in Mexico, limón de pica (thorny lemon) in South America, and Key lime or West Indian lime on the Eastern Seaboard of the U.S. It has the perfect balance of tartness and tanginess for juices and cocktails, and its aromatic skin oils actually enhance the flavor. It's the only citrus fruit which grows exclusively in the tropics. It's also the fruit which saved British sailors from scurvy and is the reason we call them "limeys."
Pictured here alongside a Bearss lime, the true lime is smaller but juicier than the Bearss, but it does contain seeds. The true lime is the bartender's favorite for garnishing because of its aromatic rind with practically no pith. The West Indian lime from Dominica is used exclusively for the production of Rose's Lime Juice. Unfortunately, in the U.S., the once highly prized Mexican and Key lime groves are being replaced by the hybridized limes, which are not only larger and more attractive, but are more resistant to shipping and increasingly frequent cold snaps. (Ask any citrus grower if he believes the globe is warming.) Today a commercially prepared Key Lime Pie is probably made with a hybridized lime rather than the true Key lime.
Fortunately, Mexico still produces Mexican limes in large quantities year-round in its tropical south, and ships to Latin markets in the U.S. and exports the juice as Key lime juice. Here in San Diego, Mexican markets sell Mexican limes at 8 to 10 for a dollar, about half the cost of Bearrs limes.
If you cant find the Mexican lime, try any lemon or lime that you find that is round, smooth, and thin-skinned, such as a Lisbon or Meyer. (Avoid the huge, thick-skinned Ponderosa.) The cheaper, smaller, splotchy lemons and limes are juicier and lower in acid, making them better for cocktails. (Don't let minor frost damage on the skin deter you.) Look for a fruit which is heavy for its size (of the two pictured above, both weigh the same and yield the same amount of juice--about two tablespoons). The smoother the skin, the smaller the pith and juicier the fruit. If youre forced to shop at a major supermarket chain, you may have to settle for the Bearss and Eurekas; if so, use a blend of both to balance the acidity. If youre stuck with one or the other, youll have to adjust the amount of sweetener balance the tart and tang.
It's better to juice a lemon with a hand squeezer than with a reamer. It extracts the juice along with some oils, but leaves the pith behind, while a reamer will remove some of the pith.
*T. J. Bearss was the name of a Porterville, California citrus grower who tried to develop cold-tolerant varieties of lemons and limes. He called his hybrids "Persian" because he crossed the tropical Tahiti Lime with a cold-tolerant Persian citron. Most references call these cultivars Bearss.