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Sugar Barley
Take any quantity of clarified sugar in that state that on dipping the finger into the pan the sugar which adheres to it will break with a slight noise; this is called crackling. When the sugar is near this, put in two or three drops of lemon-juice or a little vinegar to prevent its graining. When it has come to the crack, take it off instantly, and dip the pan into cold water to prevent the sugar burning; let it stand a little, and then pour it on a marble, which must have been previously rubbed with oil. Cut the sugar into small pieces, when it will be ready for use. One drop of citron will flavour a considerable quantity.
A one-paragraph confectioner's formula for hard sugar candy, written when a cook judged temperature by touch. The whole recipe hinges on stopping the sugar exactly at the crack and cooling it fast.
- Do not test with your fingerThe original's finger-dip test is done at around 300F, hot enough to cause a deep burn that keeps cooking in the skin. Use a candy thermometer, or drop a little syrup into iced water and check that it sets into brittle threads that snap.
- What "the crack" meansHard crack is 300-310F (149-154C). Soft crack, at 270-290F, gives a candy that bends rather than shatters and will go sticky within hours.
- Clarified sugarIn period usage this is sugar boiled with water and skimmed, often with egg white, to remove impurities from unrefined loaf sugar. Modern granulated sugar needs no clarifying: dissolve it in about a third of its weight in water and boil.
- The acidLemon juice or vinegar inverts a little of the sucrose so the syrup does not crystallise, or "grain". The original calls for only two or three drops; a few drops per pound of sugar is ample, and too much makes the candy soft and sticky in humid air.
- Stopping the cookingDipping the pan base into cold water for two or three seconds halts the rise in temperature. Do not let water touch the syrup, and keep the pan level so the seizing does not throw hot sugar.
- CitronHere this means oil of citron, a citrus essential oil, not the candied peel. Any food-grade citrus oil works; add it off the heat, since volatile oils flash off in boiling syrup. One or two drops per pound is plenty.
- The marbleAn oiled marble slab is still the best surface, but a silicone mat on a sheet pan does the job. Score the sheet with an oiled knife while it is still pliable, a minute or two after pouring depending on how thickly it is poured; once fully cold it shatters unpredictably.
- StorageThe recipe gives no yield because it works for any quantity. A pound of sugar makes a little under a pound of candy. Keep the pieces airtight with a little cornflour or between waxed paper, as hard sugar draws moisture and turns tacky.
Barley sugar is generally held to take its name from the older method of boiling the syrup with a decoction of pearl barley, which was thought to soften the candy's effect on the throat; the barley had largely dropped out by the nineteenth century, leaving the name attached to any clear lemon-flavoured hard sugar. It is traditionally associated with French convent confectionery, the sucre d'orge of Moret-sur-Loing being the best-known survival, and it reached English households as both a sweet and a throat lozenge. Recognising the degrees of sugar boiling -- thread, ball, feather and crack -- by eye and by hand was treated as foundational technique, and the rest of the sugar work followed from it. The finger test described here appears to have persisted in professional kitchens after thermometers became available.