The process of roasting is to remove moisture from the peanut by heating. The heating starts from the outer surface. The temperature starts increasing slowly, bringing the inner moisture to the surface and then evaporating it.
The heat transfer is by conduction through the contact point of the peanut and the kadhai. The larger the size of the peanut, the higher is the temperature required.
Usually, the peanut turns black indicating a high temperature at the contact point. It is necessary to turn the peanut contineously so that the black spot does not appear.
For the moisture to come out, I did several experiments by piercing the peanut. With this hole, it was easier for the moisture to come out with a lower temperature. The time required was reduced by about 40%.
And when salted, the taste of peanut was very good as the salt has entered in the peanut. We prepared a small manufacturing gadget which could make holes in for 30-40 peanuts at a time. There were no black spots on the peanut.