The best oils for frying are neutral-flavoured oils that have a high smoke point such as Vegetable Oil or Canola Oil (what I used here). I find that the best frying temperature is about 170 degree Celsius (340 degree Fahrenheit). Over 180 degree Celsius (350 degree Fahrenheit), the donuts will burn before they are fully cooked and their centre will be raw. Under 165 degree Celsius (330 degree Fahrenheit), the donuts will fry to slowly resulting in overly greasy donuts.