All,
I moved from Washington DC to Divide, CO, at 9200 ft. And I've
learned a lot about baking here.
First, When baking bread I reduce the yeast by 1/3. In Colorado
Springs, altitude 6300 ft, a friend reduces the yeast by 1/4.
Second, much of the reason for the necessary increase of liquids is
that the atmosphere, and therefore, the flour are much dryer.
For my yeast breads, I reduce the flour rather than increase the
water. And I start with 1/3 less flour and go by feel.
For quick breads, doughs and batters, I mix everything in and add
water, as necessary. (I also sometimes add an extra egg yolk; it is
liquid and adds some fat to help keep the baked goods moister.)
Third, speaking of quick breads, generally I just use the next
"coarser" flour, 1 for 1. If it calls for cake flour, I use all
purpose flour; if it calls for all purpose flour, I use white whole
wheat flour.
Leavening (not yeast): I usually use the called for amount of baking
powder, but reduce the baking soda by 1/4 tsp per tsp called for in
the recipe (or sometimes, omit it).
And, in cookies, cakes, etc, I reduce the sugar by 1/4 cup per cup
called for in the recipe.
Finally, these are generalizations. I've had to experiment with all
my recipes to find the proper amounts of ingredients. Even the
Colorado State Extension Service (considered by many to be the
"center of excellence" for high altitude baking) says there are no
hard and fast rules or constants for "altituding" recipes.
Sue