Wash, sterilize, and heat the canning jars. Check out my canning 101 post if you need more step by step instructions.
Heat the water in the larges stockpot. I also turn on my exhaust fan to help eliminate some of the heat and humidity that comes with canning. Keep the jars in hot water while you prepare the tomatoes for canning.
Wash and inspect the tomatoes - I grow tomatoes in the garden and when I bring them into the house they have dirt on them. Thoroughly wash your tomatoes and remove any bad spots or blemishes on them. Remove the stem and core, if desired.
Remove the skin of the tomato - Use a sharp knife to slice and X or score the skin of the tomato, drop the tomato into the simmering water for 30 seconds to a minute.
After the skin of the tomato has further cracked and started to separate from the tomato flesh, remove it from the water with a slotted spoon and plunge the tomato into the ice water bath, stopping the blanching process and allowing the skin to easily pull back.
Once all the tomatoes have been blanched - remove them from the ice water bath and remove the skin from the tomato. They should slip right off. If you get a stubborn skin, dunk the tomato back in the water for an additional 15-30 seconds and then back into the ice water.
Dice the tomatoes - I do a small to medium dice on my tomatoes as that is what I would normally pick up if I were to buy a can of diced tomatoes at the grocery store. Leave the seeds in the tomato and try and capture as much of the tomato juice in a bowl as you can.
Remove a jar from the canner - place the empty, hot jar on your work surface, protected with a towel.
Add lemon juice to the jar - if using lemon juice, add ½ teaspoon of lemon juice to the quart jar OR ¼ teaspoon of citric acid to the quart jar if using citric acid. See notes if you are canning larger portions.
Place the funnel on the jar and fill the jar with your diced tomatoes. Be sure to get a balance of juice and tomatoes in the jar.
Check for air - use your bubble remover tool or a nonreactive scraper, such as bamboo or silicone, to press the tomatoes and remove the air. Check for ½" headspace with the tool, wipe the rim, add a new lid and finger tighten a ring on the jar.
Place the jar back in the simmering water - Use the jar lifter to place the filled jar back in the hot water bath.
Repeat until all jars have been filled and returned to the hot water bath canner.
Set the timer for 40 minutes for pints and 45 minutes for quarts.
After processing is complete, carefully remove the jars from the canner with a jar lifter, and place them on a towel or rack to cool for 12 to 24 hours.
Check the lids for flex. If the jars do not flex the lids have sealed correctly. If there is flex on the lid when it is pressed the lid has not sealed.
Tips for canning diced tomatoes:
Process in a boiling water bath : Pints: 35 minutes Quarts: 45 minutes
Store unsealed jars in the refrigerator and use up within 7-10 days.
Do not add thickeners or milk to tomatoes or tomato products before processing. Add the ingredients to make stewed tomatoes or tomato soup when you are ready to serve them. from the Penn State Extension
Do not add extra peppers, onions, garlic etc. for flavor in this recipe, it will make the acid level be out of balance.
Tomatoes may also be processed in a pressure canner.
Tomato products with added vegetables or meat require pressure canning.