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Plum Syrup
American Concentrated Plum Syrup, 1 quart; Plain Syrup, 3 quarts; Fruit Acid, 1 ounce.
This is a dilution formula from behind the counter rather than a recipe in the domestic sense: a concentrate, a sugar syrup and an acid, blended in bulk to be pumped an ounce at a time into a glass of carbonated water. Everything hinges on knowing what the three trade ingredients were.
- Plain syrupFountain "plain syrup" was much heavier than a modern simple syrup: period formulas commonly call for something on the order of 13 to 14 pounds of sugar to a gallon of water, giving a near-saturated finished syrup (roughly 7 to 8 pounds of sugar per gallon of syrup), so that a single ounce could sweeten a whole glass. A 1:1 simple syrup substituted here will give a thinner, less sweet drink.
- American Concentrated Plum SyrupA commercial bottled concentrate, no longer sold under that name. The nearest equivalent is plum juice cooked down hard and sweetened until it is thick and assertive; a ready-to-drink plum syrup will need the plain syrup cut back considerably.
- Fruit acidTrade catalogues used the term for both crystalline citric or tartaric acid and for a ready-made solution of it, and the strength of those solutions varied from one supply house to another. One ounce of crystals in a gallon of syrup is sharp but plausible; one fluid ounce of a dilute solution would be far weaker. The original does not say which, so add acid gradually and taste.
- Ounce, weight or fluidGenuinely ambiguous in a fountain formula of this period. Assume weight if you are using crystals and volume if you are using a bought solution.
- Why the acid is there at allCarbonated water tastes flat against sugar alone; the acid restores the tartness that boiling and concentrating strip out of the fruit, and it is what makes the finished soda read as plum rather than as sweet syrup.
- Yield and dispensingThe batch makes one gallon, which at the standard ounce to an ounce and a half per glass is roughly 85 to 128 drinks. Fill the glass with cold carbonated water and stir only briefly.
- Keeping itFountain syrups were held in stone or glass jars and often carried a preservative such as sodium benzoate. Without one, keep the finished gallon refrigerated and expect fermentation or mould within a couple of weeks, especially if the plum concentrate is homemade.
Soda fountain manuals of this kind were written for dispensers, not cooks, which is why the entry reads as a proportion table: the operator bought concentrates and flavouring acids by the bottle from a supply house and blended them into working syrups on the premises. Plum was never one of the leading fountain flavours. The "fruit acid" line is the period fingerprint — American drugstore fountains of the late nineteenth and early twentieth centuries leaned heavily on citric and tartaric acid solutions to sharpen syrups whose fruit character had been cooked away, and the same acids were sold alongside the flavourings by the same houses.