Actual working time is around 15 minutes, but you need to allow 12-36 hours for the yoghurt to strain in the fridge. Greek full fat yoghurt is the best, but because the texture of the cheese becomes dense and creamy, low fat varieties can also be used. Makes about 450g / 1lb cheese (a fist-sized ball). Do note that olive oil will "set" and seem grainy when stored in the fridge - it is not off - it just what happens to a pure oil when placed in the fridge. Simply enjoy some with your cheese or leave at room temperature for 10-15 minutes before serving.