Four hundred years ago, the Dutch were some of the world’s greatest traders and, not coincidentally, great distillers. They’d preserve the spices, herbs, and fruit brought home on ships in flavored liqueurs and other spirits. Curacao was one of those liqueurs, flavored with bitter orange peels from the island of the same name. At the time, the liqueur would have had a heavy, pot-distilled brandy as its base.
Then the French came along (a couple hundred years later) and invented triple sec. The “sec” meaning “dry,” or less sweetened than the Dutch liqueur. The origin of the “triple” is still up for debate, but the two leading schools of thought are “triple distillation” versus “three times as orangey”. Triple sec was also clear, whereas curacaos were dark in color.
Today, triple secs are usually still clear (made from a base of neutral spirits), whereas curacaos may start that way and be colored orange, blue, and even red. Cointreau is probably the most recognized brand of orange liqueur in the triple sec style, and Grand Marnier, despite being French, is more in line with the Dutch curacao style as it has an aged brandy base.
Clear orange liqueurs (and the brightly colored ones also) tend to work with light spirits like vodka, gin, and white rum, whereas brandy-based liqueurs work better with aged spirits like dark rum, cognac, and whisky. In a pinch you can substitute one for the other, but it doesn't always work.
There are many low-priced brands of orange liqueur available that may be labeled as triple sec or curacao, or neither. The really cheap ones will ruin your cocktail, and since most drinks only call for a fraction of an ounce of the stuff, I think it’s best to upgrade the orange.
The White Lady cocktail, invented in the early 1900s, specifies the use of Cointreau. A brandy-based liqueur would overwhelm the gin and lemon, and a blue-colored one would look like… most cocktails created in the late 1970s. It is an easy, three-ingredient, juicy crowd-pleaser of a drink.
2 fl. oz. Gin
1 fl. oz. Cointreau
1 fl. oz. Fresh Lemon Juice
Shake all ingredients with ice and strain into a cocktail glass.