Using a boiling water bath canner or an oven to can vegetables, tomato sauce, meat, or fish is asking for trouble. Botulism spores survive boiling water and are colourless and tasteless in food. But botulism produces a toxin that can kill.
I spoke to a friend last week who cans in her oven, the way her grand mother canned. Grandma didn’t die of food poisoning so it must be safe, my friend reasoned. I would advise erring on the side of caution.
Risk of Food Spoilage
There are four agents that cause spoilage in food — enzymes, molds, yeasts and bacteria. Enzymes, molds and yeasts are arrested by boiling. And in high acid foods like fruits, sauerkraut, jams and jellies a boiling water bath is enough to prevent spoilage. Dangerous Bacteria rarely develops in a high acid environment. However, in a low acid environment as with canned tomatoes, vegetables, meats and fish, bacteria can multiply and release toxins. Pressure canning heats water above boiling temperatures which kills bacterial spores like botulism. It is impossible to heat food above 100C (boiling at sea level) in a boiling water bath canner. Whereas, pressure canning food at 5 lb. pressure will heat it to 110C, 10 lbs. pressure heats it to 115C and 15 lbs. pressure heats it to 120F, effectively arresting food spoilage organisms.
High altitude Canning:
If you live at elevations 2,000 to 8,000 feet above sea level increase the pressure by 5 lbs to achieve safe canning. At my altitude, 2700 ft., water boils at 90C, so I add 5 lbs. pressure to the recommended amount when canning. Fruit is canned at 5 lbs. pressure, so I process it using 10 lbs. Meat, Fish and low acid vegetables are canned at 10 lbs. pressure so I use 15 lbs.
Do not use a pressure canner above 8,000 feet (2400 m) above sea level. Instead of canning use other food preservation methods such as drying or lacto-fermentation.
Replace your boiling water bath canner
While your boiling water bath canner is useful for canning fruits, jams, pickles and relishes it should not be used for canning vegetables, like beans, or meat, fish and soup. Boiling water bath canners are cheaper to buy, but the metal is thinner and rusts easily, necessitating replacing your canner every 5 to 10 years. On the other hand, pressure canners are thick aluminum and will last for decades. (Pressure canners are not the same as Pressure cookers.)
Presto continues to manufacture parts for their canners, including handles, pressure gauges and rubber gaskets, so a used Presto brand canner can be retrofited for renewed use. Check out garage sales, Craig’s List and Kijiji for used pressure canners and let people know that you are looking for one. Someone may just have an unused one laying around waiting for you. Even new a pressure canner is a good investment. Get the large canner (23 quart capacity) which holds 7 quarts or 20 pint jars. Since a pressure canner can last decades, the initial investment is amortized over many years.
A pressure canner can be used like a boiling water bath canner. However, it can also be used to pressure can fruits, jams and jellies. Pressure canning uses less water and energy to can than a boiling water bath canner.
When I seal jams and jellies in a boiling water bath I have to heat a full canner of water to 2 inches above the tops of the jars. Many boiling water bath canners don’t extend a full 2 inches above the tops of quart jars, which means that you have to fill your canner to the top and boil the water over the canner. What a mess on the stove top!
Sealing jars in a pressure canner uses only 3.5 litres of water, no matter what size jar you use. You seal the canner, bring it to boil, let the pressure rise to 5 lbs. and then turn it off and let the pressure drop of its own accord. This takes a mere 15 minutes on high heat and then another 15 to 30 minutes to drop the pressure, saving you both time and money.
Steps to Successful Pressure Canning
1. Use a pressure canner that is in good repair.
Replace your gasket seals and pressure automatic air vent if there are leaks when you bring your canner up to 5 lbs. pressure. I keep an extra seal on hand at all times. Amazon carries them. Make sure you get the correct seal for your canner model.
2. Place 3.5 litres of water in the bottom of the canner.
3. Place filled jars in the canner.
Make sure that you are using the canning rack to keep the glass jars from touching the bottom of the canner.
Fill jars allowing for a 1 inch head space. Use two piece canning seals and complete seals on jars, according to manufacturer’s directions. Usually that means, bringing new lids to a boil. Turning off heat. Dipping a paper towel into the boiling water and wiping the rims of the jars. Placing the appropriate lid on the jar and tightening a ring over the seal until finger tight.
Place jars in the pressure canner. Jars in a pressure canner can be stacked, allowing you to can up to 8 quarts or 16 pints in a large pressure canner. Regular jars fit closer together than wide mouth jars.
4. Put on the lid and bring to a boil.
Check to make sure that the steam vent is open. You can draw a pipe cleaner through the vent to clean it if necessary. Place the lid on the canner. Securely lock the lid in place.
Bring to a boil. Steam will come out through the vent hole as pressure builds up in the canner.
5. Exhaust the steam for 7 to 10 minutes.
Reduce heat to allow a moderate steam flow.
6. Adjust pressure regulator.
If you are using a rocker type canner you would put the pressure regulator on the canner at this point. If you are using a pressure dial canner, watch the pressure regulator and when it registers the pressure that you are looking for turn down your heat source. I prefer the rocker type of pressure regulator as it releases pressure as its rocking. The dial kind of pressure regulator is more difficult to control.
If pressure builds too high the automatic air vent will blow off the canner, speedily releasing pressure. This is a safety mechanism to ensure that the canner itself won’t blow up, under pressure. Because of the rapid decrease in pressure, jars can break inside the canner if this happens.
7. Maintain Pressure for the required amount of time for your product.
Once the pressure regulator is up to pressure, maintain the pressure for the amount of time necessary for each type of fruit, vegetable or meat.
The instruction manual that comes with the canner will tell you how long to keep the pressure on. Most fruits are canned at 5 lbs. pressure (10 lbs at high altitude) for 8 minutes. Vegetables are canned at 10 lbs. pressure (15 lbs. at high altitude) for varying times — green beans are 20 minutes, peppers are 35 minutes. Dense foods like pumpkin puree need a longer processing time to get the internal temperature up to safe levels. Meat and Fish are canned at 10 lbs. pressure (15 lbs. at high altitude) but because meat is a denser product than vegetables, it requires a longer processing time — 75 minutes for pints and 90 minutes for quarts.
Canning salmon? Use 10 lbs. pressure, can in pints only, and process for 100 minutes. You don’t use any water when canning salmon. The fish is soaked in a brine solution for an hour, drained and packed solidly into pint jars. The pressure from processing releases juices from the fish.
8. Turn off heat. Allow pressure to drop of its own accord.
9. Once pressure has dropped, remove lid so that steam escapes away from you.
10. Remove Jars.
11. Cool jars completely. Label and date. Admire your work.
12. Store in a cool, dry place, away from light, heat and frost.
13. Write and tell me about your success. Leave a comment.
Some resources to help you in your pressure canning adventure:
Presto 1781 23-Quart Aluminum Pressure Cooker/Canner
Putting Food By: Fifth Edition
Stocking Up: The Third Edition of America’s Classic Preserving Guide
Canning and Preserving For Dummies