1. Ensure Mason jars have been cleaned by running them through a dishwasher or handwashing them with soap and hot water. Submerge jars into boiling water for 10 minutes to sanitize them. Keep the jars warm until ready to use.
2. Fill the water bath canner with water and begin heating over high heat while you prepare the diced tomatoes.
3. If peeling tomatoes, bring a separate pot of water to a rolling boil. Score the bottoms of tomatoes with a criss-cross shape. Blanch the tomatoes for 45-60 seconds, then submerge them into cold water or a bowl of ice water. The skin should pull away easily from the tomatoes after blanching.
4. Core each tomato and remove the stems. Dice the tomatoes with a sharp knife.
5. Place 1 tablespoon of lemon juice and ½ teaspoon of canning salt in the bottom of each hot jar.
6. Fill jars with raw diced tomatoes and pack them tightly. It may be necessary to use a spoon or other utensil to press down on the tomatoes enough to release tomato juice into the jar. Add tomatoes until ½ inch headspace remains at the top of the jar.
7. Release any trapped air bubbles by using an air bubble tool.
8. Wipe the rims of the canning jars and apply lids and screw bands. Screw the bands on until fingertip tight.
9. Load the jars of tomatoes onto the jar rack and lower them into the prepared canner. Add water if needed to get a water level of 1 inch above the tops of the jars.
10. Once the jars are in the canner, heat the water to a rolling boil and cover the canner with a lid.
11. The processing time is 35-50 minutes for pints and 45 to 60 minutes for quarts depending on your elevation:

• 0 – 1000ft (35 minutes/pints & 45 minutes/quarts)
• 1,001 – 3,000ft (40 minutes/pints & 50 minutes/quarts)
• 3,001 – 6,000ft (45 minutes/pints & 55 minutes/quarts)
• 6,001ft and up (50 minutes/pints & 60 minutes/quarts)

Post Processing

1. Once the jars are processed, turn off the heat and remove the canner lid.
2. Allow the jars to rest for 5 minutes. After 5 minutes, remove the jars from the boiling water bath canner using canning tongs and place the jars on a towel-covered countertop to cool.
3. Do not retighten screw bands. Let the jars air cool for 12-24 hours. You should hear a popping sound as the jars seal during the cooling process.
4. Once the jars are completely cool, remove the screw bands and check the seals.
5. If the seal is indented, the jar is safe to label and store in a cool, dark place.
6. If the seal isn’t indented, you can use a new lid and reprocess it, or put the jar into the refrigerator and consume the contents within a few days.