Altitude can affect baked goods because of associated decreased air pressure and humidity. Since the best brownies are moist and chewy, it's important to understand recipe adjustments for elevations of 3,000 feet, 7,500 feet and above 10,000 feet when preparing the brownie batter and baking brownies in your oven. Baking takes practice, so use these recipes as a guideline and experiment in your high-altitude neighborhood; you will end up with a delicious homemade treat.
The thinner the air is, the less time it takes to bake brownies. The decrease in air pressure -- which starts at about 3,000 feet in elevation -- will be apparent at 7,500 feet. Baking powder will take less time to form bubbles of carbon dioxide gas, and the eggs will not have an ideal scaffold to provide texture to the brownies when baking. The key adjustment is to increase baking temperature by 15 to 25 degrees Fahrenheit, and subtract 15 to 20 minutes from the instructions' suggested baking time.
Because the baking powder will work quickly and can greatly expand at high altitude, decrease the amount of baking powder by a half-teaspoon. Sugar in the brownie recipe also feeds the reaction of baking powder to liquids, so you can decrease sugar by 1/4 to 1/2 cup for an intense chocolate flavor. The brownies will still rise and bake properly since the oven is hotter and will caramelize the sugar even faster.
Moisture from water, eggs, oil and vanilla extract contributes to mixing all the dry ingredients together. If you need to add more liquid to make the batter's consistency just right, add water since air at altitude lacks this ingredient. Keep the fats the same as in the recipe directions, but you can add an egg white or two to provide structure for the quickly rising brownie batter.
Patience is crucial, as baked goods take longer to rise at high altitudes. Consider adapting the recipe to take advantage of alternative baking methods. For example, if you are camping and mountain climbing, you will probably use a brownie mix containing powdered eggs and water. If you use a grill or portable stove, make small portions -- such as muffin-cup size -- as opposed to using a large pan that may cook unevenly on the small stove.