Wash tomatoes, remove stems, and trim bruised or discolored portions.
To reduce separation, quickly quarter about 1 pound of tomatoes and heat immediately to boiling while crushing. Continue adding and crushing freshly cut tomatoes while keeping the mixture boiling. Simmer 5 minutes after all tomatoes are added. If separation is not a concern, slice or quarter all tomatoes, crush, heat, and simmer 5 minutes.
Press the heated tomatoes through a sieve or food mill to remove skins and seeds.
Add required bottled lemon juice or citric acid to each jar. Add salt if desired.
Reheat juice to boiling. Fill hot jars, leaving 1/2-inch headspace.
Boiling-water process pints 35/40/45/50 minutes and quarts 40/45/50/55 minutes at 0–1,000/1,001–3,000/3,001–6,000/above 6,000 ft. Pressure-canning alternatives must follow the NCHFP table exactly; acidification is still required.