If your oil is too hot, the donuts will become brown and hard. This is not the desired character in case of donuts. We want the donuts to be goldenish brown. Keep the oil temperature around 320-330 0 F. Take time to fry the donuts. They need to fry slowly. We want them to be cooked throughout and not just from the outside. If the oil is very hot, they will just brown from the outside and remain raw at the center.