In traditional, pre-prohibition, American bartending, any mixed drink should be made from the same amount of alcoholic product that would be served if un-mixed.
The traditional portion of beer is the cup, or 8 fl-oz. This would seem too small a portion to many modern customers.
The traditional portion of wine is the gill, or 4 fl-oz, which would also seem small to many modern customers.
The majority of mixed drinks, however, are based on liquor, for which the traditional portion is the jigger, or 2 fl-oz. The device used to measure this amount, or parts thereof, is also called a jigger. Previously, this amount was also called the wine-glass. The following quotations indicate the traditional or pre-prohibition meanings of the terms wine-glass and jigger.
The Oxford English Dictionary – 1928:
“Wineglassful. – The contents of a full wine-glass; the amount that a wine-glass will hold, usually reckoned as 2 fluid ounces.”
George Kappeler – Modern American Drinks – 1895:
“A jigger is a measure used for measuring liquors when mixing drinks; it holds two ounces. A pony holds half a jigger.”
Cuyler Reynolds – The Banquet Book – 1902:
“Jigger. – The contents are equivalent to 2 ounces”
“Wineglass. – The contents are equivalent to 2 ounces”
C.W. Williamson – The History of Western Ohio and Auglaize County – 1905:
“The quantity varied from a jigger (two ounces) to sixteen jiggers per day, and the contractor who offered the greatest number of jiggers per day was able to secure the largest number of hands.”
[This excerpt is from the portion of the book covering the construction of the Erie Canal. The parenthetic explanation above is in the original text. Whiskey is what was offered to the workers in the number of jiggers mentioned.]
The American fl-oz. is functionally equal to 30 ml. Thus the traditional American jigger is functionally equal to 60 ml.
When making a single-portion mixed drink with multiple liquors according to pre-prohibition practice, their total volume should still be 2 fl-oz.. This allows for advantageous selection of service vessels. For example, the Rye Cocktail, being a jigger of rye whiskey, a teaspoon of fine sugar, a scruple (two dashes) of bitters and just over a pony of water (from stirring with method ice), will fill the traditional 4-½ fl-oz. capacity glass cocktail goblet nicely. The Manhattan Cocktail (essentially a fancy Rye Cocktail sweetened with vermouth wine instead of sugar) would have been served in the same cocktail goblet in the classic period of the American bar, and thus was always made with the whiskey and the vermouth together totaling 2 fl-oz. Other than that, the old sense of the jigger as the basic, total amount of liquor allowed bartenders to develop real familiarity and control over proportions of alcoholic-to-non-alcoholic ingredients within each genre of drinks. This has been sadly lost to the memorizing-of-recipes approach. Always working with the jigger as the basic amount allows one to stop wasting mental power in memorizing and to start thinking about everything else going on in a drink.
Sometime during or after prohibition, the art of proportioning multiple liquors within the 2 fl-oz. jigger was largely-abandoned and mostly-lost due to various causes, not least among them calling all drinks cocktails and forcing them into cocktail goblets. I think that the jigger as an amount should be restored. Unless sheer inebriation or the maintenance of alcoholism is the goal, one jigger of liquor will contain plenty of alcohol for one mixed drink. This traditional amount also presents enough volume for mixing liquors in just about any desired proportion.
In a ‘one-to-one’ drink, 1 fl-oz. (30 ml.) of plain liquor(s) will be modified with 1 fl-oz. (30 ml.) of fancy liquor(s).
In a ‘two-to-one’ drink, 1-⅓ fl-oz. (40 ml.) of plain liquor(s) will be modified with ⅔ fl-oz. (20 ml.) of fancy liquor(s).
In a ‘three-to-one’ drink, 1-½ fl-oz. (45 ml.) of plain liquor(s) will be modified with ½ fl-oz. (15 ml.) of fancy liquor(s).
In a ‘five-to-one’ drink, 1-⅔ fl-oz. (50 ml.) of plain liquor(s) will be modified with ⅓ fl-oz. (10 ml.) of fancy liquor(s).
In a ‘seven-to-one’ drink, 1-¾ fl-oz. (52.5 ml.) of plain liquor(s) will be modified with ¼ fl-oz. (7.5 ml.) of fancy liquor(s).
When making a drink with equal parts of three liquors, ⅔ 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 ½ fl-oz. (15 ml.) each of two modifying liquors. Other drinks are made of ½ 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 ¼ fl-oz., its function is usually more as accent than modifier, and need not be measured as part of the 2 fl-oz. jigger.
For a look at the ‘jiggers’ used in my courses that allow for any traditional and desirable split of the traditional American jigger, click on the following link:
For as chart of traditional units of measure (of volume, mostly) that goes far beyond the jigger, click on the following link: