Cakes may overflow pans and/or fall, cookies often spread excessively, and breads get fluffier when baked at geographical locations higher than 2,500 ft above sea level. The higher the elevation, the more pronounced the effect. Because bakery formulations tend to be developed and tested in labs and plants sited at lower elevations, they will need some adjustment to perform properly when baked at facilities above this height.
(Although common usage terms this practice “high altitude” baking, the accurate reference is “high elevation.” Altitude describes the spatial distances between the earth and things in the sky such as airplanes, clouds, planets and stars. Elevation measures a place’s distance above or below sea level.)
Nearly 21% of the US population lives at elevations of 3,000 ft or more, mostly in the western one-third of the country, plus a few areas high in the Appalachian Mountains. Denver earned its nickname as the Mile-High City at 5,470 ft (5,280 ft equal 1 mile), and its 2.7 million inhabitants make it the country’s largest “high altitude” city. At 10,108 ft, Leadville, CO, is home to more than 3,000 individuals plus several retail bakeries and bakery cafes and is the highest-elevation incorporated location in America.
Many major cities around the world are also known for their high elevations: Mexico City, Mexico, at 7,350 ft is the largest with a population of 8.8 million, but other sizeable, high-elevation cities include Bogota, Columbia, at 8,660 ft and 7.8 million people and La Paz, Bolivia, at 11,913 ft with its 2.1 million inhabitants.
When it comes to baking, three aspects of the physical environment change as elevation increases: (a) gases expand at greater speeds, (b) water boils at lower temperatures and (c) moisture evaporates at faster rates. The effects of these changes on baked foods are not seen in any practical way when processing takes place at elevations lower than 2,500 ft above sea level.
The expansion of gases follows an inverse relationship between pressure and volume, described by Boyle’s Law (P1V1 = P2V2, where P refers to pressure and V to volume). Fermentation, when measured by gas cell size, proceeds faster at the lower atmospheric pressure at elevation. During baking, leavening gases tend to over-expand doughs and batters, pushing them up and over pan walls. Gas cells rupture, and structures collapse.
Water boils at 100°C (212°F) at sea level, or when the saturated vapor pressure is equal to the surrounding atmospheric pressure. Because there is less air per cubic volume at higher elevations, the vapor pressure of liquids decreases. This physical condition means that water boils at lower temperatures relative to sea level. Thus, the maximum internal temperature, which for most baked products is the same as the boiling point of water, is lower at higher elevations so baking time must be extended. Increasing the baking temperature causes the interior to reach its maximum temperature earlier and minimizes the reduction in crust temperature due to evaporation.
Lower vapor pressure also means that moisture evaporates more quickly as elevation increases. In a room with a relative humidity of 38% (± 2%), water evaporation increases by 15% at 5,000 ft and 29% at 8,000 ft, compared with sea level (Lorenz 1979). The faster speed of evaporation causes crust browning problems. The amount of water in the formula makes a difference because evaporation cools the crust surface. Low-moisture systems such as cookies tend to over-brown, while high-moisture systems such as cakes may not brown enough.
Higher elevations also tend to be lower in relative humidity: The ambient air is not able to hold as much moisture. Storage conditions for dry ingredients, particularly for flour, must be environmentally controlled if baking performance is to be maintained.
The operation of laboratory instruments is also affected by elevation, according to Lorenz (1979). Amylograph readings at 2,500 ft found a 3.5% increase in Brabender unit (BU) readings, rising to a 9.5% increase at 5,000 ft and 11.3% at 10,000 ft. The higher the BU reading of a given flour at sea level, the greater it increased at elevation. Mixogram readings also increased with rising elevation, and the rate of increase depended on the kind of flour. Mixograph data taken indicated a lower absorption and a higher protein content than the flour actually had at lower elevations. Farinograph values were similarly affected.
“High altitude” flour can be found in the marketplace. The description, however, refers to it being milled at elevation. It offers no specific advantages for baking at altitude than flour milled closer to sea level.
Lorenz, K. 1979. Baking at high altitude. AIB Tech. Bull. 1 (9).
More on this topic can be found in “Baking Science & Technology, 4th ed., Vol. II,” Page 174, by E.J. Pyler and L.A. Gorton. Details are in our store.