Here we work through the USDA procedure for home canning plain crushed tomato. The crushed tomato meant here is pure, unadulterated crushed tomato, with no other fresh or dried vegetable of any other kind, or liquid, added to it.
Wash tomatoes in fresh, potable water. Remove stems and hull the top bits out, trim out any bruised parts.
Peel the tomatoes: Boil the tomatoes for 1 to 3 to 5 minutes (depending on the tomatoes) in hot water, then plunge them into a pan, sink or large bowl of very cold water. The skins will pull off easily. ( Yes, they must be peeled, to reduce the bacterial load. )
Take 6 of the tomatoes, cut into quarters and add to a large pot over high heat.
Crush them with a potato masher or other similar tool.
After a few minutes of heating, the tomatoes will soften and release some juice.
Stir the pot frequently and keep the heat high. Quarter a few more tomatoes, and add them and crush them right away. When the pot returns to a boil, then gradually repeat the process with the remaining tomatoes, each time waiting till the pot returns to a boil so that newly sliced tomatoes will be hit with full heat right away upon slicing and adding.
No need to crush the tomatoes further, they will break down on their own.
When all the tomato is in, let simmer uncovered for another 5 minutes. Stir to prevent scorching.
MANDATORY. Acidify jars. To each half-litre/ pint jar add either 1 tablespoon bottled lemon juice OR ¼ teaspoon citric acid. To each litre/quart jar add either 2 tablespoons bottled lemon juice OR ½ teaspoon citric acid.
OPTIONAL: ½ teaspoon salt per half-litre/ pint; 1 teaspoon per litre/quart jar.
Ladle hot crushed tomato into jars.
Leave 2 cm (½ inch) headspace.
Wipe jar rims.
Put lids on.
Process in a water bath or steam canner.
Process half-litres (pints) for 35 minutes; litre (quart) jars for 45 minutes. Increase time as needed for your altitude.