Prepare a work surface for the barley sugar such as a lightly oiled marble slab (with unflavoured oil such as canola) or a sheet of parchment paper placed on the back of a cold baking sheet. In a saucepan, bring the sugar, water and vinegar to a boil. Cook until a candy thermometer reads 147 ºC (295 ºF). Remove from the heat immediately.
Add the food coloring. Pour the syrup in small quantities on the work surface. Immediately place a stick in the centre of each pop. Let cool completely. Keep the lollipops in an airtight container in a cool, dry place.