BASIC PORTIONS: THE CUP, THE GILL, THE JIGGER
In any mixed drink, the amount of alcoholic product used to make it should be the same as the amount of it traditionally served when un-mixed.
The traditional portion of beer is the cup, or 8 fluid-ounces.
The traditional portion of wine is the gill, or 4 fluid-ounces.
The majority of mixed drinks, however, are based on liquor, for which the traditional portion is the jigger, or 2 fluid-ounces. The device used to measure this amount, or parts thereof, is also called a jigger. In his 1895 book, Modern American Drinks, George Kappeler wrote,
“A jigger is a measure used for measuring liquors when mixing drinks; it holds two ounces. A pony holds half a jigger.”
The American fluid-ounce is virtually-equal to 30 milliliters. Thus the traditional American jigger is virtually-equal to 60 milliliters.
When making a single-portion mixed drink with multiple liquors, their total volume should still be 2 fluid-ounces. This allows for advantageous selection of service glassware, along with familiarity and control over proportions of alcoholic-to-non-alcoholic ingredients.
The simplest way to jigger two liquors into a single-portion mixed drink is to use a pony [1 fl-oz. | 30 ml.] of each, which yields a drink that can be described as ‘one-to-one.’
For a ‘two-to-one’ drink, 1-1/3 fl-oz. [40 ml.] of the base liquor should be modified with 2/3 fl-oz. [20 ml.] of another liquor.
For a ‘three-to-one’ drink, 1-1/2 fl-oz. [45 ml.] of the base liquor should be modified with 1/2 fl-oz. [15 ml.] of another liquor.
For a ‘five-to-one’ drink, 1-2/3 fl-oz. [50 ml.] of the base liquor should be modified with 1/3 fl-oz. [10 ml.] of another liquor.
For a ‘seven-to-one’ drink, 1-3/4 fl-oz. [52.5 ml.] of the base liquor should be modified with 1/4 fl-oz. [7.5 ml.] of another liquor.
When making a drink with equal parts of three liquors, 2/3 fl-oz. [20 ml.] of each is appropriate.
Many other variations are possible and often desirable. Some drinks are made of 1 fl-oz. [30 ml.] of the base liquor modified by 1/2 fl-oz. [15 ml.] each of two modifying liquors. Other drinks are made of 1/2 fl-oz. [15 ml.] each of four liquors.
When adjusting proportions between spirits and sweeter liquors (such as liqueurs, fortified wines or aromatized wines) within in the traditional jigger, one must be aware that the sweetness of the finished drink can be greatly affected. Many ‘one-to-one’ or ‘two-to-one’ drinks are not additionally sweetened with sugar or syrup, while some ‘seven-to-one’ drinks are.
When a liquor is added to a drink in any amount of less than 1/4 fl-oz., its function is usually more as accent than modifier, and need not be measured as part of the 2 fl-oz. jigger.