The processing time (for water bath canning), pressure requirement (for pressure canning) and blanching time (for freezing and drying some foods) all need to be increased at higher elevations to destroy heat-resistant bacteria and to ensure home-preserved food products are safe to enjoy.
1. Determine your elevation using a resource such as whatismyelevation.com (Enter your address, city, and state in the 'Enter your location' box.)
2. Use tested recipes and follow all high elevation adjustment instructions provided (sometimes referred to as high altitude adjustments)--including processing time, required equipment, pressure, and blanching time.
3. To further minimize the risk of botulism poisoning, before tasting or serving, boil all home-canned, low-acid vegetables for a full 10 minutes at elevations below 1,000 feet. For elevations above 1,000 feet, add an additional minute of boiling time for each additional 1,000 feet. (Ex. at 5,000 feet boil for 15 minutes)
For more information on high elevation cooking adjustments read CSU Extension's High Altitude Food Preparation Guide.