Canning tomatoes has been traditionally considered safe using the water bath canning method. However, acidity levels have changed and are now very close to the safety borderline of acidity. The standard recommendation is to add acidity to tomatoes to make them safe.
products a dose of bottled lemon juice. 1T per pint/ 2T per quart. This
will raise the acid level and make it safe for a boiling water bath.
There is much debate about this recommendation. Just remember there are no canning police. There is no one to come and ensure you are using the latest methods. YOU are responsible for YOUR health and the health of your family.
note- All extension websites and official recommendations I've read suggest using acidification juice when you are waterbath canning tomatoes. So, if using a waterbath, I also suggest that you use lemon juice.
I have seen differing recommendations from
different extension websites regarding canning tomatoes in a pressure canner. Some
extension websites recommend lemon juice even when pressure canning.... some don't.
I called my extension here in Colorado to verify what I read. The person I talked with confirmed that lemon juice is often recommended for all canning by some extensions. However the Colorado State website states that if you are using a pressure canner acidification is not needed.
In MY opinion. If you are using a pressure canner the heat obtained is enough
botulism and so acidification is not needed. However, I'll add that lemon juice or other acidification certainly won't hurt anything, so if you add it you are that much better. And I've never tasted a difference.
Acidify if you are water bath canning.
You don't need to acidify if you are pressure canning.... but you can.
Please if you don't agree or understand this recommendation contact
office. They should be willing to discuss it
with you. I can
only report what is recommended.
You need to make you own decision as to whether you want to include the lemon juice in your pressure canner or not.
Remember - If you add vegetables you must always use a pressure canner. Adding acid to these types of recipes won't change that. The added veggies must be pressure canned. Examples would be stewed tomatoes or tomato based vegetable soup, spaghetti sauce.
Caution: Do not can tomatoes from dead or frost-killed vines. Green tomatoes are more acidic than ripened fruit and can be canned safely with any of the following recommendations.
Acidification: To ensure safe acidity in whole, crushed, or juiced tomatoes, add two tablespoons of bottled lemon juice or 1/2 teaspoon of citric acid per quart of tomatoes. For pints, use one tablespoon bottled lemon juice or 1/4 teaspoon citric acid. Acid can be added directly to the jars before filling with product. Add sugar to offset acid taste, if desired. Four tablespoons of a 5 percent acidity vinegar per quart may be used instead of lemon juice or citric acid. However, vinegar may cause undesirable flavor changes.
Although tomatoes are considered a high-acid food (pH below 4.6), certain conditions and varieties can produce tomatoes and tomato products with pH values above 4.6. When this happens, the product must be canned in a pressure canner as a low-acid product or acidified to a pH of 4.6 or lower with lemon juice or citric acid.
Research has found several conditions that can reduce the acidity of tomatoes. These include decay or damage caused by bruises, cracks, blossom end rot or insects, and overripening. Tomatoes grown in the shade, ripened in shorter hours of daylight, or ripened off the vine tend to be lower in acidity than those ripened in direct sunlight on the vine. Also, tomatoes attached to dead vines at harvest are considerably less acidic than tomatoes harvested from healthy vines. Decayed and damaged tomatoes and those harvested from frost-killed or dead vines should not be home canned.
To ensure safe acidity in whole, crushed or juiced tomatoes, add lemon juice or citric acid when processing in a boiling water bath. Add 2 tablespoons of bottled lemon juice or 1/2 teaspoon of citric acid per quart of tomatoes. For pints, use 1 tablespoon bottled lemon juice or 1/4 teaspoon citric acid. Acid can be added directly to the jars before filling with product. Add sugar to offset the taste, if desired. Four tablespoons of a 5 percent acidity vinegar per quart can be used instead of lemon juice or citric acid. However, vinegar may cause undesirable flavor changes.