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Lemon Phosphate Syrup
Solution of acid phosphate, 8 fluid ounces, lemon syrup, sufficient to make 1 gallon. Mix.
A fountain formula, written for someone filling a gallon syrup jar rather than a home cook. The whole recipe is a ratio: acid phosphate at one part in sixteen, everything else lemon syrup.
- The arithmeticA US gallon is 128 fluid ounces, so this is 8 oz of acid phosphate solution topped up with 120 oz of lemon syrup. Scaled down, that is 1 tablespoon of acid phosphate per 1 cup (8 oz) of finished syrup.
- What acid phosphate isA dilute solution of phosphoric acid partly neutralised with calcium, magnesium and potassium salts, sold to druggists by the bottle. It gives a dry, mineral tartness quite unlike citric or tartaric acid. It is still made for the bar trade; buy a food-grade fountain acid phosphate.
- Not a substitute for hardware-store acidTechnical or industrial phosphoric acid — rust remover, descaler — is not the same product and is not food grade. If you cannot get acid phosphate, make a lemon sour with citric acid instead and accept that it will taste sharper and fruitier.
- Period lemon syrupFountain and pharmacy syrups of this era were generally heavy, often in the region of 65 per cent sugar by weight, flavoured with lemon juice, lemon oil or tincture of lemon peel; proportions varied from book to book. A modern 1:1 simple syrup will give a thinner, less stable result; go richer if you want the original mouthfeel.
- How it was servedThe recipe makes syrup, not a drink. Draw 1 to 1.5 fl oz into a glass, fill with cold carbonated water, and stir once. A gallon yields roughly 85 to 128 drinks depending on the measure used.
- StorageKeep it in glass, not in reactive metal, and refrigerate. The sugar and acid keep the syrup from spoiling for some time, but the lemon oil oxidises and the flavour dulls comparatively quickly, so mix in quantities you will actually use.
Phosphates were the soda fountain's answer to the fact that fountains were run by druggists. Acid phosphate reached the trade as a proprietary tonic — Horsford's Acid Phosphate, made by the Rumford Chemical Works and promoted from the 1870s as a remedy for dyspepsia and "mental exhaustion" — and dispensers found that a splash of it in sweet syrup and soda water made a cleaner, drier drink than the fruit acids then in use. Lemon was the plainest of the family, and cherry, orange and chocolate phosphates were made on the same principle, though the proportions given in formularies vary. The style faded with the fountains themselves in the mid-twentieth century and has come back through cocktail bars, where acid phosphate is valued for adding sourness without adding flavour.