Prepare the canner and jars. Wash the jars in hot, soapy water and rinse well or run them in the dishwasher. Keep them hot until ready to fill. Prepare the lids according to the manufacturer’s instructions. Fill the water bath canner with enough water to cover the filled jars by at least 1 to 2 inches. Begin heating the water.
Prepare the syrup and lemon water. Combine 12 cups water and 6 cups sugar in a large pot. Bring to a boil, stirring until the sugar is completely dissolved. Remove from the heat and stir in ¼ cup Fruit-Fresh. Keep the syrup hot. In a separate large bowl, combine ½ cup lemon juice with 1 quart of additional cold water.
Blanch and prepare the peaches. Bring a large pot of water to a boil and prepare a bowl or clean sink filled with ice water. Place a few peaches at a time in the boiling water for 30 to 60 seconds, or just until the skins loosen. Transfer them immediately to the ice water. Slip off the skins, cut the peaches in half, remove the pits, and slice if desired. Place the prepared peaches in the lemon-water solution while you finish the batch.
Fill the jars. Drain the peaches and pack them firmly into the hot jars, placing peach halves cut side down. Leave ½ inch of headspace. Ladle hot syrup over the peaches, maintaining ½ inch of headspace. Remove trapped bubbles, add more syrup if needed, and recheck the headspace. Wipe the jar rims clean. Center the lids and tighten the rings to fingertip tight.
Process the peaches. Place the jars upright in the water bath canner. The water should cover the jars by at least 1 to 2 inches. Cover the canner and bring the water to a full rolling boil. Begin timing once the water is boiling. Process raw-packed quart jars for 30 minutes at elevations up to 1,000 feet, adjusting the time for higher elevations (see below). When the time is complete, turn off the heat, remove the canner lid, and wait 5 minutes.
Cool and store. Use a jar lifter to remove the jars, keeping them upright. Place them on a towel with space between each jar. Let the jars cool undisturbed for 12 to 24 hours. Check the seals, remove the rings, wash and dry the jars, label them, and store them in a cool, dark, dry place.