Heavy based saucepan – stainless steel best and definitely not a non-stick pan.
Popsicle sticks or thick wooden skewers
A candy thermometer – I’ll give tips below on how you can make it without one but It’s definitely easier with.
Spoon or spatula
Line a large baking sheet with baking paper and set aside.
Give the apples a wash, making sure if they're waxed to remove all the wax. Remove the stems and dry well. Push in a thick skewer or popsicle stick.
Add the sugar, water, glucose and vinegar to a large heavy-based saucepan (stainless steel best),over very low heat. Stir constantly until the sugar completely dissolves.
Bring the syrup to a boil and sit a candy thermometer on the side of the pan (see note 4 below if you don't have one). Boil until the mixture hard crack stage - 150C / 302F. Use a pastry brush wet with a little water, to brush down any sugar crystals that form on the sides.
Take the pan off the heat and mix the food colouring through, then let the bubbles subside.
Carefully, tip the saucepan on an angle and dip the apples, turning them a few times to coat well all over.
Make sure all your equipment is perfectly clean before you start so as not to risk crystallisation. Rub vinegar over each, then rinse off. No need to dry.
You can use white granulated sugar, but keep in mind it will take longer to dissolve due to the larger size of the sugar crystals.
You can also use black food colouring for some spooky halloween toffee apples.
You can make it without a candy thermometer, though a little less precise. When you drop a little of the toffee into cold water, it will create brittle pieces that you can snap.
I find that, if the mixture looks to be crystallising before it's changed colour, it can be saved. Just add a tablespoon of water into the syrup, give it good stir, then let it come back to the boil again.
Don't add the food colouring in while the toffee is on the heat - it may cause it to seize. Likewise, reheating toffee that has already had colouring added may cause it to seize.