The hottest part of a flame is at the highest point of the bright cone of oxidation. In most flames, this area is blue, and the temperature averages 1,400 degrees Celsius.
A flame results from a combination of heat, oxygen and fuel. The fuel is any material that has a sensitivity to both heat and oxygen. When the fuel and oxygen reach a high enough temperature, their molecules start to interact, swapping atoms and exchanging electrons while the release of energy occurs. This energy takes on the form of light or heat, and the part of a flame that gives off light is the hottest part.