Thanks again. That's a good reference site. I've bookmarked it for future use.
From the Colorado site, I find these facts:
At altitudes above 3,000 feet, preparation of food may require changes in time, temperature or recipe. The reason, lower atmospheric pressure due to a thinner blanket of air above. At sea level, atmospheric pressure is 14.7 pounds per square inch (psi), at 5,000 feet it’s 12.3 psi, and at 10,000 feet only 10.2 psi - a decrease of about 1/2 pound per 1,000 feet. This decreased pressure affects food preparation in two ways:
1. Water and other liquids evaporate faster and boil at lower temperatures.
2. Leavening gases in breads and cakes expand more quickly.
The temperature at which water boils declines as elevation rises (Table 1). Because of this, foods prepared by boiling or simmering cook at a lower temperature at high altitude than at sea level, and thus, require a longer cooking time. Meats cooked by simmering or braising may require one-fourth more time at 5,000 feet than at sea level. Oven temperatures, however, are not affected by altitude, so sea-level instructions work for oven-roasted meats. Hard-cooked eggs will also take longer to cook. A “three-minute” egg may take five minutes to cook at 5,000 feet. High altitude areas are also prone to low humidity, which causes the moisture in foods to evaporate more quickly during cooking. Covering foods during cooking will help hold in moisture.
Fruits, tomatoes and pickled vegetables can be safely canned in a boiling water bath. However, because the temperature of boiling water is lower at higher elevations, you need to increase the processing time by one minute for each 1,000 feet above sea level if the sea level time is 20 minutes or less. If the processing time is more than 20 minutes, increase by two minutes per 1,000 feet.
Other vegetables, meats and poultry (low-acid foods) must be canned in a steam pressure canner at 240 degrees F for the appropriate time to destroy heat-resistant bacteria. At sea level to 2000 feet, 11 pounds of steam pressure will produce this temperature. Above 2,000 feet, steam pressure must be increased to reach 240 degrees F as illustrated in Table 2.