Barley sugar does not now contain barley, and the name is assumed to refer to the shape which is vaguely like a barley-ear. But the Moxon receipt here suggests that it once was made with barley.
Original Receipt in 'English Housewifry' by Elizabeth Moxon, 1764 (Moxon 1764)419. To make BARLEY-SUGAR.
Boil barley in water, strain it through a hair-sieve, then put the decoction into clarified sugar brought to a candy height, or the last degree of boiling, then take it off the fire, and let the boiling settle, then pour it upon a marble stone rubb'd with the oil of olives, when it cools and begins to grow hard, cut it into pieces, and rub it into lengths as you please.
Just a few years later, the barley had disappeared...
Original Receipt in Nutt 1789;No. 96. Barley Sugar,
TAKE a small stewpan, put some syrup into it and boil it till it comes to carimel; rub a little butter on a marble stone just to greese it that it may not stick; then take your saucepan by the handle and let the syrup run out of the spout along the stone in long sticks; twist it (while it is hot) at each end and let it stand till cold.