Line a large baking tray with non-stick baking paper. Stir caster sugar, golden syrup, water and glucose in a medium saucepan over low heat until sugar dissolves completely.
Place a sugar thermometer in the pan. Bring to the boil and cook (syrup should be bubbling) without stirring for 20 mins or until sugar thermometer reaches 150°C or "hard crack stage". Brush down the sides of the pan occasionally with a pastry brush dipped in water. Set aside for 1 min or until the bubbles subside. Add a few drops of red food colouring.
Meanwhile, insert thick skewers into the core of each apple.
Dip one apple at a time into toffee and rotate to coat completely. Transfer the apples to the prepared tray. Repeat with the remaining apples. Set aside until the toffee sets.
Golden syrup enhances the caramel flavour and keeps the toffee from setting too hard. Place these in cellophane bags tied with ribbon for delicious trick or treat gifts.