How to Can Food

There are two methods for canning food, a hot water bath and pressure canning. Both are safe to preserve foods but you need to know when each is applicable. Hot water bath canning preserves food that are acidic while pressure canning is used for non acidic foods.

Whichever method is being used, I recommend a support in the bottom of the bath to prevent the food jars from being exposed directly to the bottom of the canning vessel. The additional heat from the bottom of the canning vessel can over cook or potentially burn the foods at the bottom of the jars.

Filling the jars is crucial in both types of canning. First, the jars can't be completely full. During the canning process the food expands to help force the air out of the jar. Over filling the jar will get food under the lid and prevent the eventual sealing of the jar. Second, the lid should only be place on finger tight. If the jar lid is too tight, air won't be able to escape the jar as the food expands during heating.

Hot Water Bath Canning

As stated above, hot water bath canning is for foods that are acidic in nature. Typically this means fruits and pickled vegetables. Guidelines require that the food has a pH of less than 4.6 to be canned in a hot water bath. Foods with a pH lower than 4.6 have enough acid in them to prevent the growth of Clostridium botulinum spores that can cause botulism. Tomatoes have a pH of approximately 4.6 and it is technically not recommended they be canned in this method. Although technically not recommended, I and others I know have successfully canned tomatoes with this method many times with no problems. Other items I have canned using this method include pickled vegetables (green tomatoes, peppers, etc.), jellies/jams, tomato based salsa, and salsa verde.

Hot water bath canning is exactly what it sounds like. The food to be canned is placed into jars and placed in a bath of water completely covering the jars of food. Normally, it's recommended the water cover the jars by 2 inches. For quart jars this takes a very large water bath. Many of us don't have a pot deep enough to cover quart jars with 2 inches of water, my recommendation is get as much water as you can over the jar and be careful not to boil the water over later. The water is then heated to boiling for a specified time. For food in quart jars the water in the bath should be boiling for at least 15 minutes while pint jars require only a minimum of 10 minutes. These are minimums, letting the jars continue to boil and additional few minutes won't be a problem.

When the allotted time has been reached with the food in the hot water bath, remove them and set them on the counter. As the food cools, a vacuum is formed inside the jar and the jar lid seals.

Pressure Canning

Pressure canning is similar to hot water bath canning except a pressure vessel (canner) is used. The pressure build up allows the temperature of the water to increase above the normal 212F boiling temperature. At 10 psi water boils at 240F and at 15 psi it boils at 245F. These temperatures are hot enough to destroy the Clostridium botulinum spores enabling the food to be safely canned.

In the picture of the canner above, in the center you will see a pressure gage that allows you to monitor the pressure inside the canner. To the right is a pressure regulator. The pressure regulator is a weighted devise the fits over a stem holding the pressure inside the container.

Once the jars are filled and place into the pressure canner, add water until the depth of the water around the jars is 2 to 3 inches. Place the lid securely on the canner and start heating the vessel but leave the pressure stem open during the heating process. At this point the canner should be monitored at all times. The pressure build up inside the canner generates over 1100 pounds of force on the lid, higher pressures would mean more force on the lid. Pressure canners are designed to withstand the normal pressures of the canning process, the trouble comes when canners are not monitored and the pressure goes too high for the canner to contain.

Once the water inside the canner starts to boil, a mixture of steam and air will come through the pressure stem from the inside of the canner. Allow the water to boil for 10 minutes with the pressure stem open to get as much of the air out of the canner as possible. After 10 minutes, place the regulator on the pressure stem and allow the pressure to start building up.

Once the pressure has reached 10 psi, the timer starts for the canning process (10 minutes for pints and 15 minutes for quarts). The stove will need to be turned down to avoid the canner from reaching an excessive pressure. Turn the stove down in increments to avoid turning it down too much and the pressure starting to drop. In the end it takes very little heat to maintain the canner at 10 psi. Monitor the pressure cooker making sure the pressure doesn't go over 15 psi by turning the stove down in increments. For my canner, 15 psi is still well below the danger area indicated on the pressure gage.

After the alloted time, remove the canner from heat and allow it to cool down. Do not attempt to remove the lid while the container is still under pressure. This can be done with patience, just waiting for the canner to cool, or the canner can be placed in a sink and cold water ran over the outside to cool it faster. Once the canner is cooled, slightly move the pressure regulator to make sure there is not more pressure inside the canner. It not, remove the pressure regulator and the lid may now be removed from the canner. Be careful doing this, there will still be a lot of steam inside the canner.

Remove the jars from the canner bath. What you should see here is unsealed jars of food. Don't worry, as the jars cool you'll here the 'pop' of the lid as each jar seals. When the jars are cool, you can use your finger to press down on the center of the lid to verify the seal. Most of the time the jars will seal with the 'pop' within minutes of being removed from the canner bath. Sometimes, after the jar seals you'll see the food inside still boiling, this is a very good sign that the vacuum formed during the cooling process will store your food safely.

See, it's all straight forward. Just remember to watch the cooker to make sure it doesn't boil over or get too much pressure and not get in a hurry and burn yourself with steam at the end of the process.