Originally Posted by
ericd
True, the fat can provide flavors but it also can affect structure. For example, if you take the same cookie recipe and use butter vs. crisco, the butter cookie will spread thin in the oven and the final cookie will be crispy. A crisco cookie will puff up and go more toward chewy. This is a result of melting temp. Butter melts faster so the cookie dough will spread before the baking powder can puff up the cookie. The crisco melts slower at a higher temp so the cookie can puff before spreading. The difference in melting temps can affect rise in a biscuit too. I don't have data to cite, but from experience I know a fat change will make changes to the final result.