A lime can be one of several different species of citrus (or in a few cases non-citrus) fruit. The two lime fruits we are interested in here are Persian and Key limes.
The limes you will normally find in the United States are Persian limes. These are green and range in size from about 1.5 to almost 3 inches in diameter. They have a relatively thick skin and are less acidic than Key limes. Persian limes don't have seeds and will keep for a week or two in the refrigerator. They are a great choice for your cocktails and mixed drink recipes, especially if you are using the lime oil in the skin.
Farther south, you will find Mexican or Key limes. These are much small than Persian limes - usually golf ball size or a little smaller. Key limes have a thinner skin and their juice is more acidic than Persian limes. If you are buying limes in Mexico or in most of the Caribbean, Key limes are what you'll find.
Another lime, called a Kaffir lime, is not good to use in drinks. Though the leaves of a Kaffir lime tree are fantastic for use in Thai, Lao, and Cambodian cooking, the lime itself is somewhat lacking. Stick to Persian or Key limes.
Limes smell fantastic to me - the aroma is half the experience. When you are juicing limes with a citrus press the lime oil goes everywhere lending fresh aromas around the bar. If you are making a lime syrup or cordial you will probably be specifically using the lime fruit skin for you recipe.
Keep in mind that most limes have a thin coat of wax to prevent spoilage. This wax is not harmful, but if you are zesting a lime or using them in an oleo-saccharum for a punch you might want to remove the wax to extract a more pure flavor. The easiest way to go about this is to buy organic limes - they don't have the wax.
Or you can remove the lime wax from regular limes by soaking the fruit in a solution of 1 quart of water and 1 oz of white vinegar for 1 minute. After 1 minute rinse the lime with cold water and dry with a paper towel.
When using Key limes, back off a little on the amount of lime juice or increase the sweetener as most recipes are written for Persian limes which are less acidic than Key limes. However there are some older recipes that are written for Key limes, especially the ones that specify "juice of X limes" such as the Hemingway Daiquiri.
You know this is the case when you see "juice of 2 limes" paired with "2 tsp" of syrup - the juice from 2 Persian limes would be way too tart for that amount of syrup. Just use common sense with these recipes. If it looks like they meant Key limes just back off and use fewer Persian limes. A good rule of thumb for cocktail balance is lime juice and single strength simple syrup in equal parts, 2 parts lime juice to 1 part double strength simple syrup.
For garnishes, limes are cut into wedges or wheels. I usually cut off the ends of Persian limes to tidy them up as a garnish. This is not necessary with Key limes.
Sometimes, usually in Tiki drinks, the spent lime half is thrown into the drink as a garnish and also so it will emanate some of the fragrant lime oil.
Limes travel well and stay fresh at room temperature for extended periods of time. One of the easiest travel cocktails for when you get to the hotel room is a Daiquiri. You can just throw the limes in the your suitcase.
If you have any tips on handling limes please add a comment below.