罐装时间海拔调整计算器 — 公式

How to Adjust Canning Time for Altitude

Rule

For water-bath canning above 1,000 feet:

  • Processing time 20 min or less: Add 1 minute per 1,000 ft above 1,000 ft
  • Processing time over 20 min: Add 2 minutes per 1,000 ft above 1,000 ft

    • Water boils at a lower temperature at higher elevations (roughly 1.84°F less per 1,000 ft). The longer processing compensates for the reduced heat transfer.

    Important

    This applies to water-bath canning only. For pressure canning, increase the pressure (not the time) at altitude. Always follow USDA-tested recipes.

    计算示例

    A jam recipe calling for 10 minutes processing at 3,000 feet altitude.

    1. Base time = 10 min (under 20, so add 1 min per 1,000 ft above 1,000)
    2. Extra = ceil((3000 - 1000) / 1000) x 1 = 2 minutes
    3. Adjusted time = 10 + 2 = 12 minutes
    4. Boiling point at 3,000 ft = 212 - 5.5 = 206.5°F