Traditionally, barley sugar is made by boiling sugar to hard crack or the start of caramel at 328° to 346°F (150° to 160°C) and adding an acid to prevent recrystallization on cooling. See stages of sugar syrup. Craft production employed lemon juice or vinegar, but mass-produced barley sugar in the United Kingdom is now often made with a mixture of sugar and glucose, which has the same effect. See glucose. Lemon essence is generally used as a flavoring in the British tradition of sugar boiling.