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: - **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.
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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