Calculateur d'Ajustement de Mise en Conserve en Altitude
Ajustez le temps de mise en conserve selon votre altitude.
Adjusted Processing Time
12 min
Formule
How to Adjust Canning Time for Altitude
Rule
For water-bath canning above 1,000 feet:
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.
Exemple Résolu
A jam recipe calling for 10 minutes processing at 3,000 feet altitude.
- 01Base time = 10 min (under 20, so add 1 min per 1,000 ft above 1,000)
- 02Extra = ceil((3000 - 1000) / 1000) x 1 = 2 minutes
- 03Adjusted time = 10 + 2 = 12 minutes
- 04Boiling point at 3,000 ft = 212 - 5.5 = 206.5°F
Questions Fréquentes
Why does altitude affect canning?
Water boils at lower temperatures at higher altitudes because atmospheric pressure decreases. At 5,000 feet, water boils at about 203°F instead of 212°F. Lower boiling temperatures require more time to achieve the same level of microbial destruction.
Does altitude affect pressure canning?
Yes, but you adjust pressure, not time. Increase the pressure by 1 psi for every 2,000 feet above sea level (for weighted gauge canners, go to the next increment). Processing time stays the same.
Can I reprocess jars that did not seal?
Yes, within 24 hours. Remove the lid, check the rim for chips, use a new lid, and reprocess for the full adjusted time. Alternatively, refrigerate the jar and use it within a few weeks.
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