Q: What is high altitude cooking?

Altitude cooking refers to the changes caused by differences in geographic elevation.

The boiling point of water drops by about 2°F (1°C) for every 1,000 feet (300 meters) increase in altitude, above sea level.  What that means in practical terms depends on what you are cooking. For example, if you are making candy, the temperatures are lower for the various sugar stages.  If you are baking a custard using a bain-marie, the lower boiling point of water in the outer container means that the custard is cooked at a lower temperature, making it take longer (see the KitchenSavvy article "Bain-Marie").  While altitude doesn't affect roasting significantly, it can cause stews and braises to take longer.

For canning foods at altitudes higher than 1,000 feet above sea level, if you are using a water bath, the processing time needs to be increased.  In pressure canning, the processing time required remains the same, but the pressure setting needs to be higher.

Altitude can also cause changes in the structure and texture of baked goods.   If you are baking a cake, the effects of altitude are even more pronounced.  Because of the lower air pressure, the leavening in the cake will expand quicker while the batter takes longer to set.  The gases from the leavening are not held well in the batter, causing the cake to be more dense.   What bubbles are left tend to be of different sizes, causing an uneven texture.  At the same time, the lower boiling point will cause the cake to dry out faster.

Typical recipes for making cakes at higher altitude will increase the amount of liquid, decrease the amount of leavening and also decrease sugar and fat.  The amounts of egg or flour may be increased, too.

The effect on boiling temperature happens because water boils when molecules in the liquid have enough energy to escape from the surface.  The amount of energy required depends, among other things, on the air pressure keeping the water molecules from escaping.  The air pressure relates to the height of the air above the location where the water is being boiled.  At higher altitude, the column of air is shorter, causing the boiling temperature to be lower.    Altitude has a similar effect on the boiling point of other liquids.

If you need more help in adapting a recipe, try contacting the Home Economics or Extension department of your local university, or the local cooking school.  Some universities now call Home Economics "Human Ecology" (go figure!).  For cakes and breads, you might ask your neighborhood baker for a few hints.