Wash the tomatoes, remove the stems, and trim any bruised spots. To keep the juice from separating, quarter about 1 pound of tomatoes, put them in a large pot, and bring them to a boil while you crush them. Keep the pot boiling as you add the rest of the quartered tomatoes a few at a time, then simmer for 5 minutes once they're all in.

Press the hot mixture through a food mill or sieve to remove the skins and seeds. Return the juice to the pot and bring it back to a boil.

Add the bottled lemon juice or citric acid to each hot jar, and the salt if you're using it, using the per-jar amounts in the ingredient list. Fill the jars with hot juice, leaving 1/2 inch headspace. Wipe the rims, and apply the lids and bands fingertip tight.

To water bath can, set the jars in a canner of hot water, about 180 degrees F, and bring it to a full rolling boil. Process pints for 35 minutes or quarts for 40 minutes, adjusting for altitude (see notes). Turn off the heat, take the lid off the canner, and let the jars sit in the water for 5 minutes before lifting them out.

To pressure can, set the jars in a pressure canner with hot water, about 180 degrees F, and vent it for 10 minutes. Process pints or quarts for 15 minutes at 11 lbs pressure in a dial gauge canner or 10 lbs in a weighted gauge canner, adjusting for altitude (see notes). Turn off the heat and let the canner return to zero pressure on its own. Remove the weight or open the petcock, wait 10 minutes, then take off the lid, tilting it away from you, and lift the jars out.

Cool the jars undisturbed for 12 to 24 hours, check the seals, and store them in a cool, dark place.