Baking at higher altitudes or baking with an altitude
Not too long ago, as glaciers measure time, I moved from the Gulf Coast of Texas, where I was at sea level, to Gunnison, Colorado, where we are at 7,703 feet above sea level. The second part of the change was the humidity - it ran close to 85% at almost any time on the coast, and hovers around 20 to 30% in Gunnison. I really wasn't prepared for how that would change my baking. I won't talk about quick breads or most food here, just baking. If you need more information, the Colorado extension service has a good PDF file with general cooking information, as well as specific information about bread.
The first thing I noticed was that the high altitude had a great impact on the rising time of bread. It rises more quickly than you are used to. Since flavor development greatly depends on rise time, we need to do something to extend the rise time. Reducing the amount of yeast, or sourdough starter, will help, but not much. Yeast, and sourdough starter, increases geometrically, and using 1/4 the starter you are used to won't quadruple the rise time. One of the recipes Ed Wood includes with his San Francisco sourdough starter can be made with 4 cups or 1/4 cup of starter. 1/4 cup is 1/16th the starter, and the rise time is about 4 times the other recipe. How far you can reduce the amount of starter is limited.
Raising the bread at lower temperatures can help. This is a common technique in bakeries around the world. It controls the rise time, to make it more convenient for bakers who don't want to live in the bakery. Also, it allows the flavor to become more intense.
However, most often, the answer is to let the bread rise one more time than the recipe calls for. If your recipe calls for you to knead the dough and form loaves, you should let the kneaded dough rise until doubled, punch it down, and then form your loaves.
Because of the lower humidity at higher altitudes, flours tend to be drier and absorb more liquid than they do at lower altitudes. As a result, less flour might be needed to make the dough feel right.
The lower humidity has a second effect - it causes dough to dry out more quickly than at lower altitudes. The means that dough, or loaves, can form a skin that prevents full rising, so you need to be careful to prevent drying during rising. A common approach is to coat the dough with melted butter or oil. If your bread style supports this, it's a good approach. Another approach is to cover your bread. I have used moistened tea towels over the top of the bowl with good results. However, you don't want the dough to come in contact with the moistened towels. Another approach is to just cover the bowl with plastic wrap or Saran Wrap "Quick Covers(tm)". I had resisted using Quick Covers for some time, but in the end the fact they are very reusable won me over. I can cover bowls, bannetons, or loaf pans with a Quick Cover and the dough doesn't dry out.
More excitement surrounds baking. In general, baking will take longer. I suggest raising the oven temperature 25F over what the recipe calls for, and then testing the bread for doneness with a thermometer. Water boils at a lower temperature at higher altitudes. At 7,703 feet, it boils at 198F instead of the 212F people at sea level are used to. Many bakers at sea level shoot for a final temperature in their bread of around 205F. Adjusting for altitude, when the bread gets to 195F at 7,703 feet above sea level, I consider it done. At other altitudes, you might shoot for other target temperatures to test for.
Since I wrote this back on April 8, 2001, a lot has happened. I have run two bakeries, and have moved back to Texas. And I've been in lots of discussions about using chef's thermometers to test bread for doneness. And there are people who feel it is a desecration of a loaf to poke it with a thermometer. They couldn't SELL a loaf with a hole in it. (Oddly enough, one thermometer hater did suggest poking the bread with a wooden rod, like a chopstick. I asked why that was better than a thermometer and she didn't answer.) In the bakery, the loaves we poked were cut up to be samples. And, to a small extent, the thermometer is a training tool. After you bake a specific recipe long enough you'll know how the bread looks, smells and feels when it's done. And you won't need to poke the loaves at all.
A more serious issue arises with regards to thermometers, or any tool. And that is, who's the master? And the answer is, you are. If I suggest that 195 or 205 is the perfect temperature to bake a bread to, you have every right to say you prefer a higher or lower temperature. The temperatures aren't holy writ, just guidelines. If your bread is too done, try a lower target temperature next time, if it's not done enough, try a higher target temperature next time. You're the boss of your kitchen. Not me. And certainly not a thermometer.