I live at 8500' and am now using gluten free recipes. I usually double or triple the recipe and always wonder if I am suppose to double or triple (whichever I am doing) the baking soda or baking powder. Can you give me some help with this?--Vedina
It is not clear from your question whether the recipes you are using are already adjusted for cooking at altitude. At sea level, there are about 14.7 pounds per square inch of atmosphere pressing down on whatever it is you are baking. At 8,500 feet higher, there are only around 10.7 pounds per square inch.
Lets say you are baking a cake. In order to get a good result, there is a balancing act going on, as is frequently the case in cooking. In this case, what is happening is that the gases released by the baking soda or baking powder push against the atmospheric pressure to raise the cake just enough. Because the atmospheric pressure is so much lower, less "lift" is needed to get the same rise on the cake. At just the right point, you want to the cake to set, fixing the bubbles in place. At sea level proteins, starches and glutens form a fixed matrix in the range of between about 185°F (85°C) and 200°F (93°C).
Unless you reduce the amount of leavening appropriately, the cake will rise too high. At the same time, because the boiling point of water is lower at altitude, the proteins, starches and glutens may not get as hot and therefore may take more time to form the structure of the cake. The end result is that the cake will fall before it has set and some of the air bubbles will break, allowing larger bubbles to form.
In your case, because the boiling point of water at 8,500 feet is somewhere around 196°F (91°C) and since you are using gluten free recipes, you have a double whammy of challenges. First you will need to reduce the amount of baking soda or baking powder. Shirley Corriher (Cookwise: The Secrets of Cooking Revealed) suggests that it may need to be reduced by between 25% and 50%. In other words, use 3/4 to 1/2 the amount called for in the recipe. You might also reduce the sugar and fat slightly.
Then, because you are avoiding glutens and cooking at altitude, you need to rely on the starches and proteins to set the structure. For this reason you will want to and increase the egg content by as much as 15%. For a cake using three eggs, you would need to add another half an egg.
Finally, Corriher suggest you might want to raise the oven temperature by 25°F (14°C) to promote faster setting and therefore a finer texture. Even at that, you will likely find that the cake takes longer to cook that the recipe says. Using a toothpick to check for doness will help avoid under cooking.
Even with the above guidelines, you will likely still need to trial and error until you get things working right. If worst comes to worst, the Home Economics or Extension department of your local university may be able to provide some help.
If, on the other hand, your recipe has already been adjusted to work at high altitude, then doubling the amount of baking soda or baking powder will likely be fine. See the posting on Scaling Recipes for additional details.