What is the boiling point of pure water? This is such an easy question to answer. Even a student at kinder garten will be able to cite the correct answer promptly. That is 100 °C. Easy to remember and easy to pronounce. However, we often forget the argument that comes with it. Boiling point of pure water is 100 °C at sea level. The phenomenon lowers as the altitude rises due to lowering atmospheric pressure.
For a fixed time period, lower boiling point is less effective and thus the more chances of processed food spoilage. Boiling time should be increased for open-kettle boiling and pressure should be increased for pressure canning.
The table below details the water boiling point at different altitudes.
Tagaytay City is 2,000 feet above sea level. Water boiling point is approximately 98 °C.
Mayon Volcano is 2,463 m (8,081 ft) above sea level. Water boiling is 91.9 °C.
Cordillera is 8,200 feet above sea level. Water boiling point is approximately 91.9 °C.
Mount Apo is 9,692 feet above sea level. Water boiling point is slightly higher than 89.8 °C.
The e-book Complete Guide to Home Canning provides many useful information about boiling and pressuring canning adjustment at different elevation. Here are some excerpts.
Boiling food 10 minutes at altitudes below 1,000 ft destroys Clostridium botulinum bacteria poison when it is present. For altitudes at and above 1,000 ft, add 1 additional minute per 1,000 ft additional elevation. That means the same food should be boiled for 17 minutes in Cordillera Region.
Internal canner temperatures are lower at higher altitudes. To correct this error,
canners must be operated at the increased pressures specified.
Weighted-gauge canners at altitudes above 1,000 feet, must be operated at canner pressures of 10 instead of 5, or 15 instead of 10, PSI.
Here are other snapshots of table containing adjustment examples.