To answer some questions on this old thread. The amount of water that is capable of being absorbed as well as the amount of heat that it is capable of generating is directly related to the surface area of the materials being mixed. A high surface area material, like finely milled flour, has an immense amount of surface area. This will both allow it to absorb a high amount of water relative to it's volume, and will also increase the amount of heat it can absorb as well as decrease the time it takes to do so.

For a given volume of material then, you get the following:

The higher the surface area, the more liquid it can absorb.

The higher the surface area, the quicker it will hydrate, given sufficient liquid to do so.

The higher the surface area, the more heat can be generated per unit of volume.

The higher the surface area, the more heat can be absorbed per unit of volume.

I do not know the specific surface area of any particular flour, but iron oxide pigments fall into the same approximate range of 20-80 nanometers particle size. Iron oxides in this range have a surface area around 6-12 square meters per gram, so a typical 300 gram amount of flour would have a median of around 6/10ths of an ACRE of surface area in that little ball of dough you mash out into an 11" round pizza crust.