You may be thinking about preserving your harvest for the first time or dusting off old canning equipment. Food preservation has evolved over the years. With the knowledge of what foodborne illnesses can occur, it is important to use proper procedures and tested recipes to prepare safe preserved foods.
Botulism is a rare but serious condition caused by toxins from bacteria called Clostridium botulinum. The harmful bacteria thrive and produce the toxin in environments with little oxygen, typically from improperly home-canned, preserved, or fermented foods. Low-acid foods must be processed at 240°F using a pressure canner.
Understanding Altitude
It is essential to follow safe canning principles. When home canning, it is crucial that you process all food at the correct pressure and for the proper length of time. As altitude increases, water boils at lower temperatures. Because the lower temperatures are less effective for killing bacteria, the processing time must be increased for boiling water canning. For pressure canning, the pressure is increased.
Adjusting Altitude
Adjusting for altitude is very simple, and I will explain exactly how to make the time or temperature adjustments, so you know you are safely canning food! When home canning foods, it is essential to know your local altitude or elevation. Your altitude determines the amount of pressure (pressure canner) or time (boiling water canner) for your food. In Wyoming, community altitudes range in elevation from over 3,500 feet to 7,200 feet above sea level.
Canning recipe directions are written for sea level. To adjust recipes for high-altitude canning, we use these two basic concepts:
- For boiling water canning, higher altitudes require you to add processing time.
- For pressure canning, high altitudes require that you increase the pressure.
Boiling Water Method
Boiling water canning relies on a combination of high acidity in the food and the heat of the boiling water to safely preserve the food. In boiling water canning, altitude adjustments take the form of longer processing times at higher altitudes. The longer processing times are needed to compensate for the lower temperature of the boiling water in the canner. When you are canning food above 1,000 feet you need to add more minutes to the processing time in a boiling water canner. Extra time is needed because water boils at lower temperatures as the elevation increases, so you need to boil longer to kill the microorganisms.
If you are canning at higher altitudes, follow the USDA altitude adjustments listed in the charts below.
Boiling Water Method:
| Altitude Adjustments for Boiling Water Canner |
| Altitude in Feet |
Increase In Processing Time |
| 1,001 to 3,000 |
5 Minutes |
| 3,001 to 6,000 |
10 Minutes |
| 6,001 to 8,000 |
15 Minutes |
| 8,001 to 10,000 |
20 Minutes |
According to Colorado State University Extension, for more precise hot water canning times:
- If processing is 20 minutes or less, increase the processing time by 1 minute per 1,000 feet above sea level.
- If processing is greater than 20 minutes, increase the processing time by 2 minutes per 1,000 feet.
Pressure Method
Pressure canning relies on temperatures higher than that of boiling water to safely preserve low-acid foods. Pressure canning is also affected by the lighter atmospheric pressure found at higher altitudes. In pressure canning, processing times do not change, although the canner pressure must be increased at higher altitudes. The increased pressure ensures that the steam inside the canner reaches a temperature high enough to kill any spores of Clostridium botulinum that might be present.
Pressure canners have either a weight or a dial gauge that controls pressure. For weight-gauge models, the sound of the weight rocking or jiggling during processing indicates that the canner is maintaining the recommended pressure. Weight-gauge models, however, cannot correct pressure precisely at altitudes of 1,000 feet above sea level or higher.
Dial-gauge models must be checked for accuracy before use each year. Gauges can be checked at county Extension offices.
According to Colorado State University Extension, for more precise pressure canning times:
- Increase pounds of pressure by 1/2 pound for each additional 1,000 feet.
Pressure Method:
| Altitude Adjustments for Pressure Canner |
| Altitude in Feet |
Weighted Gauge (Pounds of Pressure) |
Dial Gauge (Pounds of Pressure) |
| 0 to 1,000 |
10 |
11 |
| 1,001 to 2,000 |
15 |
11 |
| 2,001 to 4,000 |
15 |
12 |
| 4,001 to 6,000 |
15 |
13 |
| 6,001 to 8,000 |
15 |
14 |
| 8,001 to 10,000 |
15 |
15 |
To be sure that you are canning safely; Find out what your altitude is. If you are canning an altitude over 1000 feet, follow the altitude adjustments given in the recipe resource you are using.
Always use a recipe tested for the safety of the final product when canning! Recipes published prior to 1994, should be checked against a current, reliable resource for safety. Not all recipes found on the web or in other publications are scientifically tested. Following are a list of trusted resources that the University of Wyoming Extension recommends for safe home food preservation:
Books:
- Ball®
- Ball Blue Book Guide to Preserving, 37th edition, 2020.
- Ball Canning Back to Basics, 2017.
- The All New Ball Book of Canning and Preserving, 2016.
- Complete Guide to Home Canning, 2015 revision, USDA Bulletin No. 539.
- So Easy to Preserve, 6th Edition, 2014. University of Georgia Cooperative Extension.
Websites:
Follow current USDA processing methods and be sure to adjust canning times for your altitude. Have fun canning!
Sources:
- Andress, E. L., and Harrison, J. A. (2014). So Easy to Preserve (6th ed.). Athens, GA: Cooperative Extension, University of Georgia; Colorado State University Extension; National Center for Home Food Preservation website at http://nchfp.uga.edu/; USDA’s Complete Guide to Home Canning, 2015 revision