Canning Tomatoes

Here is Western Pennsylvania, frosts are looming on the horizon. We have not had one yet, but there is definitely a chill in the air and I have one eye on the weather. Over the past few months I have been learning how to preserve foods so we can munch on them over the winter when not much else is growing. I borrowed my coworker's food dehydrator to shrink down the surplus of hot peppers at Garden Dreams and apples that we picked at a local orchard. I turned more of those apples into sauce and Jason and I canned a load of tomatoes since we are fans of tomato sauce anytime. See all that space in our jars? Next time we will fit more in! I definitely learned some helpful things...here are a few things I learned and some books and websites that can further demystify the process of Canning Your Tomatoes. Opinion differs on the neccessity of different canning practices and processes but as a beginner, I figure it is best to stick to the safest and most recent guidelines.

USDA guidelines
Ball Complete Book of Home Preserving
Ball Blue Book of Home Preserving
Lehman's in Ohio - Canning supplies
National Center for Home Food Preservation - Great site with lots of information, even a free online canning course!


Canners - There are pressure canners and water bath canners. I use a borrowed water bath canner at the moment. It is good for fruit preserves and tomatoes (with added acid) but not suitable for canning lower acid foods such as green beans or corn. Low acid foods can be dried, pickled, or frozen instead. I recommend the 7 quart size...I am using 9 quart size and it is quite a beast! The information below relates to water bath canning tomatoes.

pH - "Whether food should be processed in a pressure canner or boiling-water canner to control botulinum bacteria depends on the acidity of the food. Acidity may be natural, as in most fruits, or added, as in pickled food. Low-acid canned foods are not acidic enough to prevent the growth of these bacteria. Acid foods contain enough acid to block their growth, or destroy them more rapidly when heated. The term "pH" is a measure of acidity; the lower its value, the more acid the food. The acidity level in foods can be increased by adding lemon juice, citric acid, or vinegar.
Low-acid foods have pH values higher than 4.6. They include red meats, seafood, poultry, milk, and all fresh vegetables except for most tomatoes. Most mixtures of low-acid and acid foods also have pH values above 4.6 unless their recipes include enough lemon juice, citric acid, or vinegar to make them acid foods. Acid foods have a pH of 4.6 or lower. They include fruits, pickles, sauerkraut, jams, jellies, marmalades, and fruit butters." (National Center for Home Food Preservation)

The recommended addition of bottled lemon juice to canned tomatoes = 2 Tbsp per quart or 1/2 tsp of Citric acid per quart

Botulism - Its the lurking fear in the minds of newly initiated canners. So, do your research, follow recipes exactly, especially while you are learning, to make sure the acid content of the jar is correct and it has been processed correctly.

Quantity - You need about 21-22 lbs of fresh tomatoes for 7 quarts of canned whole, halved, or crushed tomatoes (see USDA link above)

Processing - When you pack your tomatoes, its good to have the jars hot and the water bath canner already 1/2 full of boiling water. Make sure you wipe rims well to ensure a proper seal and only finger tighten lids so air can escape during processing. Put your jars in the rack and lower it, then add more hot water from a tea kettle to cover 2" above jar tops. Process with the lid on and check to make sure the water stays at a gentle boil. Processing over 10 minutes will sterilize your jars and their contents. When you have processed for the proper time, turn off the heat, let your jars sit in the water for about a few minutes, then promptly lift them out with a jar lifter and place them out of the way of drafts. Don't mess with the tops and check for proper seal 24 hrs later.

Rings - Remove them after jars have cooled for 24 hrs. There is no need for them at this point since lids have hopefully sealed. Rings can be reused if they are not rusty but you need new lids every time.

Bubbles - Canning directions call for running a blade-like tool or chopstick around the edge of your jar to get rid of all bubbles and help the jar seal before putting on lids. I did this and still ended up with some bubbles. After some reading and research, I am satisfied that some bubbles are normal and as long as you have a proper seal and no moving bubble streams, you should be good.

Storage - Store at 50-70 degrees for best results and not above 95 degrees. Canned tomatoes should last for at least a year. Once opened, keep in the fridge. Plastic lids are helpful at this point since they don't rust.