Bring a large pot of water to a boil. Meanwhile, prepare an icewater bath. Wash and drain tomatoes, and cut an X in bottoms (A). Blanch for 15 seconds (B), then transfer to ice bath to cool. Remove tomatoes from bath and peel skins (C).
Place tomatoes in a saucepan and cover with water (D). Bring
to a boil. Simmer, covered, for 5 minutes. Lift jars out of hot water one at a time, draining water. Place on a towel or rack. Fill halfway with tomatoes (E). Add 1/2 tsp. salt and 1/4 tsp. citric acid for pints (1 tsp. salt and 1/2 tsp. citric acid for quarts). Fill remaining space with tomatoes, pressing to pack. Ladle boiling cooking liquid over tomatoes, leaving 1/2-inch headspace (F).
Slide a nonmetallic spatula or chopstick between tomatoes and jar (G); release any trapped air bubbles by pressing on tomatoes. Repeat around inside of jar 2 to 3 times. Wipe rim and threads of jar with a clean, damp cloth. Remove lid from hot water. Place on jar. Screw band down, just until resistance is met.
As you fill each jar, set it onto raised rack in boiling-water canner. Water in canner should be at a simmer. Once jars are filled and placed on rack, lower rack into canner. (Water level must cover caps by 1 to 2 inches. Add boiling water if necessary.)
Put lid on canner. Bring water to a rolling boil, then process pints 40 minutes (quarts 45 minutes) at a gentle but steady boil.
When time is up, turn off heat and remove canner lid. Let canner cool 5 minutes before removing jars (H). Set them upright 1 to 2 inches apart on a dry towel or cooling rack. Do not retighten bands. Let jars cool 12 to 24 hours.
Once cool, check lids for a
good vacuum seal by pressing on
center of each (I). If center is
pulled down and does not flex,
remove band and gently try to
lift lid off with your fingertips. If lid
does not flex and you cannot lift
it off, seal is set. Wipe exterior of lid and jar with a clean, damp cloth to remove any food particles and residue. Label. Store jars in a cool, dry, dark place.