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Rock Candy
This is really crystallized sugar in its simplest form. Place some clarified sugar in a sugar boiler, and boil to the feather, and add a few drops of acetic acid or spirits of wine in order to assist the separation of the crystals from the more hardened portions of the syrup. Pour the syrup into moulds, and let it remain in the hot closet at a temperature of from 90 to 100 deg. of heat; leave it there for eight or ten days, according to the size of the crystal desired. In the process of crystallizing, the impurities contained in the sugar are left behind in the water, and the sugar is rendered as nearly pure as possible. When the crystallization is complete, pour off the surplus syrup, turn the mould upside down, and let it remain until fully drained. The moulds are made of strong tin or copper, and must be considerably smaller at the bottom than at the top, and pierced with small holes round the sides in uniform rows, tier above tier, and sewn with coarse thread across the mould from side to side, after which they must be pasted up with paper, or covered with potter's clay all over the outside, in order effectually to close the holes and prevent the syrup from leaking out. When quite drained, remove the paper from the sides, warm the mould equally round the outside, and strike the edge of it with a sharp, hard knock upon the table, when the sugar will relieve itself from the mould. Place the mould upon a sieve or board, and set it in the hot closet until it is perfectly dry. This candy may be tinted a rose or scarlet color by adding a little prepared carmine or cochineal before boiling. The purer the sugar used for making the syrup the whiter the candy will be.
This is a professional confectioner's method for growing sugar crystals on thread inside a perforated mould, written for a kitchen with a drying closet. The chemistry is sound and still works; most of the labor is in the vessel.
- The hinge: stillness and steady warmthCrystals grow large only if the supersaturated syrup is left undisturbed at a constant temperature for the full eight to ten days. Any jarring, draft, or temperature swing drops a shower of small crystals instead of a few big ones.
- "Clarified sugar"In this period that means a sugar syrup boiled with a little egg white and skimmed to remove the scum, since refined sugar was less pure than ours. Modern granulated sugar needs no clarifying; dissolve it in water and skim if anything rises.
- "Boil to the feather"An old syrup stage read by blowing through a skimmer until the syrup flies off in feathery threads; sources place it somewhere around 240F, though the figures given vary. It marks a heavily supersaturated syrup, not a hard crack.
- Sugar boilerAn unlined copper pan with a pouring lip, used because copper conducts evenly. A heavy stainless saucepan does the same job; avoid bare copper with an acidified syrup.
- Acetic acid and spirits of wineAcetic acid here most likely means a dilute food acid of roughly vinegar strength rather than the glacial laboratory chemical, though the book does not say which. Spirits of wine is rectified ethanol, the equivalent of a high-proof neutral spirit. A trace of acid inverts a little sugar and so slows setting; the recipe's own explanation is that either addition helps the crystals separate from the harder portions of the syrup.
- "Hot closet at 90 to 100 deg."A warming cupboard beside the range. That is 90-100F, which most ovens cannot hold; a proofing box, a yogurt maker set low, or a warm cupboard with a thermometer is the practical substitute.
- The mouldA tapered tin or copper form pierced in rows and laced across with coarse thread, then sealed outside with pasted paper or clay so it holds syrup. Home crystallizers use a jar with cotton string suspended in it; the tapered mould and threads exist to give the crystals many anchor points and allow later draining.
- ColouringCochineal is the insect extract and prepared carmine the lake made from it; both are the same insect-derived red still sold as carmine or E120. Add it before boiling, as directed.
- Yield and keepingThe recipe gives no quantities or yield at all, and the size of the crystals depends on how long the mould stands. The poured-off surplus syrup remains usable as a sweetener, and rock candy kept dry and sealed lasts indefinitely.
Rock candy is one of the oldest forms of confectionery sugar, grown rather than cooked: the technique of crystallizing sugar out of syrup is generally traced to the sugar refineries of the medieval Near East, and the Arabic qand travelled into European languages along with the product itself. By the nineteenth century it was made both as a sweet and as a druggist's item, sold on strings for coughs and used to sweeten spirits and coffee. Its appearance in Oscar Tschirky's collection reflects how such books were assembled: alongside hotel dishes he printed the standard confectionery-manual instructions of the trade, describing a perforated draining mould and a hot closet that belonged to a professional pastry department rather than any home kitchen. The closing remark about purity is the practical point of the whole method, since crystallization was itself a refining step in an era when the whiteness of your sugar was never guaranteed.