Bring a large pot of water to a boil. Using a knife, cut a small "x" in the bottom of each tomato and drop the tomatoes in the boiling water, a few at a time, for 30-60 seconds. Lift them out with a slotted spoon and put them directly into a bowl of ice water so they can cool quickly.

Place the diced tomatoes and tomato juices into a large pot and bring it to a boil. Boil the tomatoes for 5 minutes to release their juices.

Have the canning jars ready (sterilized and hot). Place one tablespoon of bottled lemon juice (not fresh) OR 1/4 teaspoon citric acid in each pint jar or two tablespoons lemon juice OR 1/2 teaspoon citric acid in each quart jar.

Pack the hot diced tomatoes and their juices in the hot sterilized jars, leaving 1/2 inch headspace from the top of the jar.

Optional, Salt: Place 1/2 teaspoon of kosher salt in each pint jar or 1 teaspoon in each quart jar.

Use a slim utensil like a butter knife to slide down into the jars to remove any air bubbles. Wipe the rims of each jar and screw on the canning lids/bands.

Place the jars in the boiling water bath canner and process for 35 minutes for pints and 45 minutes for quarts, adjusting for altitude. Remove the jars, being careful not to tilt them. Let them sit undisturbed for 24 hours then check the seals.

These diced tomatoes will keep in a cool place for at least a year.