Wash, remove stems, and trim off bruised or discolored portions. To prevent juice from separating, quickly cut about 1 pound of fruit into quarters and put directly into saucepan. Heat immediately to boiling while crushing with a potato masher.
Continue to slowly add and crush freshly cut tomato quarters to the boiling mixture. Make sure the mixture boils constantly and vigorously while you add the remaining tomatoes. Simmer 5 minutes after you add all pieces. If you are not concerned about juice separation, simply slice or quarter tomatoes into a large saucepan. Crush, heat, and simmer for 5 minutes before juicing.
Press heated crushed tomatoes through a sieve or food mill to remove skins and seeds. Simmer tomato juice in large-diameter saucepan until sauce reaches desired consistency. Boil until volume is reduced by about one-third for thin sauce, or by one-half for thick sauce.
Add bottled lemon juice and salt to hot jars. Fill jars with hot tomato sauce, leaving ¼-inch head space.
Adjust lids and process the correct time for your altitude (I process my pint jars for 45 minutes and quart jars for 50 minutes).
Add to pint size hot canning jars:
1 TBSP lemon juice (to achieve proper acidity levels for safe canning)
½ tsp. salt (optional)
Add to quart size hot canning jars:
2 TBSP lemon juice (to achieve proper acidity levels for safe canning)
1 tsp. salt (optional)
I like to can my tomato sauce plain without additional seasonings so I can add the seasonings depending on what I'm using it for. Guidelines are from the National Center for Home Preservation .