The perfect traditional sweet treat: barley sugar twists. These candies were originally prepared by boiling sugar in barley-infused water, but here a little lemon essence is the only flavouring.
The sugar is boiled ‘to a crack’, the temperature at which it starts to become brittle. Our unknown ladies record a rather perilous method for checking this point: “dipping your fingers into the sugar and then into cold water, and if you find the sugar to crack in moving your finger, it has boiled enough”. We say, don’t risk burning your fingers – use a sugar thermometer instead to bring the temperature of the boiling sugar between 132ºC and 142ºC. At this, the ‘soft-crack’ stage, the sugar will form stiff but malleable threads, making it perfect for forming your sugar twists.
A nineteenth-century recipe for barley sugar from The Cookbook of Unknown Ladies
Barley Sugar
Clarify three pounds of refined sugar. Boil it to a crack. Squeeze in a teaspoonful of the juice and four drops of the essence of lemon. Let it boil up once or twice. Set it by for a few minutes. Have ready a marble slab rubbed over with sweet oil. Pour over the sugar. Cut it into long stripes, twist it a little, and keep in a canister from the air.
The Cookbook of Unknown Ladies 
As a child I remember my grandmother use to suck barley Sugar Sweets for medicinal purposes……? Now as I’m an adult I can’t think why? For me the recipe would have to have Barley juice in it to be a Barley Sugar.