What is the chemical process behind the way you cook a risotto?
I always thought, and one of my molecular cooking books indicates that, smaller batches kept the heat higher (less temperature shock), and the scraping released starch. The article Key success factor for tasty and creamy risotto on ideas-smart.com indicates something slightly different:


  Note that the instructions normally
  suggest that each batch of the stock
  needs to be absorbed by rice. In
  reality, something else is happening.
  Most of the water actually evaporates.
  The remaining “mash” gets warmer than
  boiling point. This speeds up the
  chemical processes, which create the
  intense taste of the risotto. These
  chemical processes are essentially the
  same as when browning meat.
  
  Other reason for pouring the stock in
  small batches and stirring constantly
  is to let loose starch from the rice
  kernels. Starch makes the mixture
  creamy. So the tedious process of
  adding stock in small batches and
  stirring constantly is the key to
  having tasty and creamy risotto. Only
  the reason for doing this, which most
  recipes give, is often misleading.


This matches personal experience and some (other) of my cook books.