Canning sweet potatoes allows you to enjoy their delicious taste long after the harvest season is over. When canned properly, sweet potatoes can last 1-2 years on the shelf. Canning works by heating the sweet potatoes to a certain temperature to kill any dangerous microorganisms and create a vacuum seal. This prevents spoilage and botulism, allowing for long term storage. The key factors in safe canning are processing time and pressure. So at what pressure should you can sweet potatoes?
Recommended Canning Methods
There are two recommended methods for canning sweet potatoes – pressure canning and boiling water canning.
Pressure canning uses the combination of high heat and pressure to achieve temperatures above the boiling point of water. This high temperature ensures any bacteria or microorganisms are destroyed. Pressure canning sweet potatoes is the safest method as it provides a higher guarantee against spoilage and illness. It is the only recommended canning method for low acid foods like sweet potatoes.
Boiling water canning involves processing jars of food in boiling water. This method does not achieve temperatures as high as pressure canning. Boiling water canning is only recommended for high acid foods like fruits that are naturally resistant to spoilage. It is not considered safe for low acid vegetables like sweet potatoes.
Required Pressure for Canning Sweet Potatoes
When canning sweet potatoes, the U.S. Department of Agriculture (USDA) and most canning authorities recommend pressure canning at 11 PSI (pounds per square inch) when adjusted for altitude.
Canned foods must be exposed to temperatures of at least 240°F for the appropriate time to destroy bacteria and spores. This temperature cannot be achieved through boiling water alone, which caps at around 212°F. The increased pressure of a pressure canner allows temperatures to rise above boiling.
At sea level, a pressure canner operated at 11 PSI will reach 240°F. As altitude increases, atmospheric pressure decreases, as does the temperature inside the canner. To compensate for this, the operated PSI must be increased by 1 PSI for every 2,000 feet of elevation.
For example, at 2,000 feet of elevation, the pressure should be increased to 12 PSI. At 4,000 feet, operate at 13 PSI. Use the following table as a reference:
Adjusted Pressure by Altitude
| Altitude (feet) | Recommended Pressure (PSI) |
|---|---|
| 0-2,000 | 11 |
| 2,001-4,000 | 12 |
| 4,001-6,000 | 13 |
| 6,001-8,000 | 14 |
The adjusted pressures in this table allow the canner to reach the required 240°F temperature at higher elevations.
Step-by-Step Canning Process
Follow these steps for safely pressure canning sweet potatoes:
1. Wash and peel sweet potatoes. Cut into slices or cubes.
2. Pack peeled, cut sweet potatoes into clean mason jars leaving 1-inch headspace. Add water, juice or broth to cover, leaving 1-inch headspace. Remove air bubbles and wipe rims clean. Center lids and screw bands on securely but not overly tight.
3. Place rack and 2 inches of water in pressure canner. Load sealed jars onto rack using a jar lifter. Lock canner lid in place but do not close the vent.
4. Heat on high until you see steady streams of steam escaping from the open vent. Let steam vent for 10 minutes.
5. Close the vent, increase to reach your adjusted pressure based on altitude. Allow pressure to rise, then start timing for 55 minutes for pint jars, 90 minutes for quart jars.
6. When time is up, turn off heat. Allow canner to cool and vent pressure naturally for 10 minutes. Do not force release pressure.
7. When gauge reads 0 pressure, carefully open canner. Remove jars with jar lifter and allow to cool undisturbed for 12-24 hours.
8. Check seal on cooled jars, press center of lids to ensure they do not pop up and down. Sealed lids should be concave and not move.
9. Wipe and label sealed jars. Store in a cool, dark place for up to 2 years. Enjoy your home canned sweet potatoes!
Choosing the Right Pressure Canner
A good pressure canner is essential for safely processing sweet potatoes and other low acid foods. Look for the following features when selecting a pressure canner:
- Dial gauge for monitoring pressure.
- Weighted gauge as a backup for dial gauge.
- Vent port to release air and steam.
- Locking lid that forms a steam-tight seal.
- Rack to elevate jars above the canner bottom.
- Capacity to hold at least 4 quart jars for scalability.
- Made from aluminum or stainless steel for even heating.
- Safety features like overpressure plugs and valves.
American and European made pressure canners that carry the Underwriter’s Laboratory certification tend to meet safety standards best. Avoid antique canners without safety features.
Troubleshooting Common Pressure Canning Problems
Below are some common troubleshooting tips for pressure canning issues:
Canner Doesn’t Reach Pressure
– Check that vent is completely closed.
– Clean rim and lid to ensure a tight seal.
– Replace old sealing ring.
– Make sure enough water is in canner.
Pressure Fluctuates
– Avoid drafts which affect temperature.
– Make sure heat source is high enough.
– Do not open vent once pressurized.
Pressure is Maintained But Jars Fail to Seal
– Check for food debris preventing seal. Re-wipe rims.
– Center lids properly.
– Ensure headspace is correct.
– Replace out-of-date lids.
– Process for full recommended time.
Food Discolors or Floats
– Use newer produce. Overripe foods discolor.
– Keep produce under liquid, cut out air pockets.
– Peel and trim produce to prevent discoloration.
– Add citric acid to jar.
Conclusion
Pressure canning sweet potatoes at 11 PSI, adjusting for altitude, provides the heat necessary to destroy dangerous bacteria and spoilage organisms. This allows the sweet potatoes to be shelf stable for 1-2 years. Following proper sanitation, jar sealing, processing time, and pressure guidelines is key to safely preserving this classic autumn crop to enjoy long after the season has passed. Consult this guide and always use scientifically tested recipes when pressure canning low acid foods like sweet potatoes.