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Fruit Acid-American
Use 1 to 2 ounces to each gallon of fruit flavored syrup.
This is a dosing rule rather than a full formula: it tells the dispenser how much fruit acid solution to work into a finished flavored syrup. The acid itself is made elsewhere in the book, and everything depends on which strength you are starting from.
- What "fruit acid" means hereIn fountain practice the term may denote either the dry crystals (citric, sometimes tartaric) or a stock solution of them in water. Check the book's own fruit acid entry before dosing, since a solution and a powder at the same weight are not remotely interchangeable.
- Ounces by weight, gallon by volumeIf read as avoirdupois ounces into 128 fluid ounces, 1 to 2 ounces is roughly 30 to 60 g per 3.8 litres. Note that if the book's fruit acid is a solution, the ounces may be fluid rather than weight.
- Dissolve before addingCrystalline acid dropped straight into cold syrup settles and dissolves unevenly, leaving the last glasses drawn from the jar sharply sour. Dissolve in a little warm water, then stir through the whole gallon.
- Start at the low endModern fruit syrups are already made with juice concentrates and often carry added acid of their own. Begin at 1 ounce, taste the finished drink at fountain dilution rather than tasting the syrup neat, and work up.
- Keep it off bare metalAcidulated syrup attacks iron, tinned copper and aluminium, picking up a metallic edge and a grey cast. Mix and store in glass, glazed stoneware or stainless steel.
- Effect on keepingAcid lowers the pH and modestly slows spoilage, but it is not a preservative at this level. An open gallon of acidulated syrup still belongs in the refrigerator.
- YieldOne gallon of syrup runs to roughly 85 drinks at an ounce and a half per glass.
Citric and tartaric acid were staples of the American soda fountain because the sweetness of a heavy syrup flattens fruit flavor without something sharp behind it. Acid restored the impression of fresh fruit to syrups built largely on sugar, water and extract. Citric acid was first isolated from lemon juice by Carl Wilhelm Scheele in the 1780s, and by the late nineteenth century it was an ordinary article of the druggist's stock, sold in crystals alongside the flavoring extracts. The presence of a bare proportion, with no method at all, is itself a mark of the genre: these books were written for a tradesman who already had the stock bottles on his shelf.