Core tomatoes and cut into quarters. Bring tomatoes, any accumulated juice, and diced beet to a boil in a large stainless steel or enameled stockpot, stirring often; reduce heat and simmer, uncovered, 15 minutes or until vegetables are very tender, stirring often.

Press tomato mixture, in batches, through a food mill, into a large bowl; discard skins and seeds. Return tomato juice to stockpot. Cook over medium heat, stirring often, until a thermometer registers 190°F; remove from heat. Stir in salt and citric acid or lemon juice.

Ladle hot juice into a hot jar, leaving 1-inch headspace. Remove air bubbles. Wipe jar rim. Center lid on jar. Apply band, and adjust to fingertip-tight. Place jar in boiling- water canner. Repeat until all jars are filled.

Process jars 40 minutes, adjusting for altitude. Turn off heat; remove lid, and let jars stand 5 minutes. Remove jars and cool.

*Tomatoes that are very ripe and bursting with juice can be used here.