How to Can Diced Tomatoes

Ingredients You’ll Need

• Fresh tomatoes: Firm, ripe paste tomatoes such as Roma, San Marzano, or Amish Paste have more flesh and less water, but other ripe tomato varieties can also be used.
• Bottled lemon juice or citric acid: Tomatoes must be acidified for safe canning, even when they taste acidic.
• Canning salt: Salt is optional and is used only for flavor, not for canning safety.

Ingredient Additions and Substitutions

• Citric acid: You can use food-grade citric acid instead of bottled lemon juice. Add ½ teaspoon per quart jar or ¼ teaspoon per pint jar.
• Different tomato varieties: Paste tomatoes give you a thicker finished product, but slicing, cherry, heirloom, and other tomato varieties can be used as long as they are firm, ripe, and free from disease.
• Salt: Canning salt can be reduced or left out completely. It does not affect the safety of the tomatoes.
• Sugar: A small amount of sugar can be added after opening the jar if you find the tomatoes too tart. I prefer to season them when I use them rather than adding sugar during canning.
• Fresh lemon juice: Do not substitute freshly squeezed lemon juice. Its acidity can vary. Use commercially bottled lemon juice or food-grade citric acid.
• Herbs, onions, peppers, and garlic: Do not add herbs, vegetables, garlic, oil, or other ingredients to this recipe unless you are following a research-tested variation. Add seasonings after opening the jar instead.
• Canning Whole Tomatoes: Canning whole tomatoes or tomato halves is another good option when you want larger pieces. Be sure to follow the processing method and times written specifically for whole or halved tomatoes rather than using the instructions interchangeably.

Equipment You’ll Need

• Water bath canner with a rack: Use a canner deep enough to cover the filled jars with 1 to 2 inches of water.
• Pint or quart canning jars: Check each jar for cracks, chips, or damage before filling.
• New canning lids and bands: Use new flat lids for each batch and clean bands that are free from rust or damage.
• Large stainless steel pot: You’ll need a nonreactive pot for heating the tomatoes before filling the jars.
• Large pot for blanching: This makes it easy to loosen the tomato skins before peeling.
• Large bowl of ice water: The ice bath stops the cooking and helps the skins slip off more easily.
• Jar lifter: A jar lifter lets you safely move hot jars in and out of the canner.
• Canning funnel: This helps you fill the jars neatly and keeps food off the rims.
• Bubble remover or plastic utensil: Use it to release trapped air bubbles before adding the lids.
• Ladle: A ladle makes it easier to transfer the hot tomatoes and juice into the jars.
• Paring knife: Use a small sharp knife to core, peel, and cut the tomatoes.
• Clean towels: Place the hot jars on a folded towel to cool and use another clean towel to wipe the jar rims.

Canning Diced Tomatoes Step by Step

There is one important thing to understand before you begin. The National Center for Home Food Preservation does not publish a separate tested process called “diced tomatoes.” To stay within research-tested canning directions, I use its hot-pack method for crushed tomatoes.

Only the first small portion of tomatoes is crushed to create enough juice. The remaining tomatoes are added in pieces and soften as they cook. The finished jars contain plenty of chunky tomato pieces, but they will not look like the firm, perfectly shaped cubes in a store-bought can. When I need a smaller dice, I quickly chop the tomatoes after opening the jar.

1. Prepare the canner and jars. Wash your jars, lids, and bands in hot, soapy water. Place the jars in a water bath canner filled with water and keep them hot at a gentle simmer. Prepare the lids according to the manufacturer’s directions.
2. Peel and prepare the tomatoes. Wash the tomatoes and remove any bruised, discolored, or damaged areas. Place a few tomatoes at a time in boiling water for 30 to 60 seconds, or until the skins begin to split. Move them immediately to ice water. Slip off the skins, remove the cores, and cut the tomatoes into quarters.
3. Heat the tomatoes. Place about one-sixth of the prepared tomatoes in a large stainless steel pot. Heat them quickly while crushing them with a potato masher or wooden spoon to release their juice. Once they are boiling, gradually add the remaining tomato pieces while stirring. Keep the mixture boiling as you add the tomatoes, then boil gently for 5 minutes.
4. Acidify and fill the jars. Add 2 tablespoons bottled lemon juice or ½ teaspoon citric acid to each quart jar. For pint jars, add 1 tablespoon bottled lemon juice or ¼ teaspoon citric acid. Add canning salt, if desired. Ladle the hot tomatoes and juice into the hot jars, leaving ½ inch of headspace. Remove air bubbles and adjust the headspace as needed.
5. Process the jars. Wipe each rim with a clean, damp cloth. Center a lid on the jar and tighten the band until fingertip tight. Place the jars in the canner, making sure they are covered with 1 to 2 inches of water. Bring the water to a full boil, cover the canner, and process according to your jar size and altitude.
6. Cool and check the seals. When the processing time is finished, turn off the heat, remove the canner lid, and wait 5 minutes. Lift the jars straight up and place them on a towel with space between each jar. Let them cool undisturbed for 12 to 24 hours before checking the seals.

Water Bath Processing Times

Begin timing only after the canner has returned to a full boil.

If the water stops boiling at any point during processing, bring it back to a full boil and restart the processing time from the beginning. These times are for the research-tested hot-pack crushed tomato method.

Canning Safety

Home canning is safe when you follow a current, research-tested recipe exactly. Do not change the jar size, headspace, acid, preparation method, or processing time.

• Always acidify tomatoes. Add 2 tablespoons bottled lemon juice or ½ teaspoon citric acid to every quart jar. Add 1 tablespoon bottled lemon juice or ¼ teaspoon citric acid to every pint jar. This acid is required even when tomatoes are processed in a pressure canner. Salt is optional and does not make the tomatoes safe.
• Choose good tomatoes. Use firm, disease-free tomatoes, preferably ripened on healthy vines. Do not can tomatoes from dead or frost-killed vines. Cut away bruised or discolored areas before processing.
• Do not add untested ingredients. Fresh onions, peppers, celery, garlic, oil, flour, cornstarch, rice, pasta, or other additions can change how heat moves through the jar. Use a tested recipe when canning tomatoes with other ingredients.
• Keep the correct headspace. Leave ½ inch between the tomatoes and the top of the jar. Too little space can cause liquid to escape during processing. Too much space can prevent the jar from sealing correctly.
• Keep jars hot. Because this recipe is processed for longer than 10 minutes, the jars do not need to be separately sterilized before filling. They should still be washed thoroughly and kept hot until you are ready to fill them.

For more detailed information about preparing equipment, filling jars, checking seals, and choosing the right canner, read our Canning 101 and Water Bath Canning guides as well as the USDA Complete Guide to Home Canning before you begin.

Recipe Tips

• Plan on approximately 22 pounds of tomatoes for seven quart jars. The amount can vary depending on the tomato variety and how much needs to be trimmed. You may need closer to 28 pounds if your tomatoes are especially juicy or require a lot of trimming.
• Use paste tomatoes for a thicker result. Roma, San Marzano, and Amish Paste tomatoes have more flesh and usually produce less watery jars.
• Work in manageable batches. Blanch only a few tomatoes at a time so you can move them into the ice bath as soon as the skins split.
• Keep the tomatoes hot. Heating the tomatoes quickly helps reduce separation between the tomato pulp and juice.
• Do not skip peeling. Removing the skins gives the tomatoes a much better texture and follows the tested preparation method.
• Seeds can stay. You can remove seeds for a smoother texture, but it is not required.
• Use wide-mouth jars when possible. They are easier to fill and make it easier to remove the tomatoes later.
• Choose pint jars for smaller meals. One pint jar is close to the amount in a 14.5 to 15-ounce store-bought can of diced tomatoes.
• Expect the pieces to soften. Home-canned tomatoes will not stay in firm cubes. They become tender and chunky during cooking and processing.
• Remove the bands before storage. This makes it easier to notice if a jar loses its seal while sitting on the shelf.

Frequently Asked Questions

Troubleshooting

• The tomatoes and juice separated: Some separation is normal and does not automatically mean the tomatoes are spoiled. Heating the tomatoes quickly and using a hot pack helps reduce separation. Stir the tomatoes after opening the jar.
• The tomatoes floated to the top: Floating is usually caused by excess air in the tomato tissue or jars that were packed too loosely. Hot-packing the tomatoes, removing air bubbles, and using the correct headspace can help.
• Liquid leaked out of the jars: This is called siphoning. It can happen when jars are overfilled, bands are tightened too much, the temperature changes too quickly, or the jars are removed from the canner immediately. Do not open the jar to replace the liquid. When at least half the liquid has been lost, refrigerate the jar and use it within 2 to 3 days.
• A jar did not seal: Refrigerate it and use it within several days, freeze it in a freezer-safe container, or reprocess it within 24 hours using a new lid and the full processing time. Reprocessing is only recommended when the tested recipe was followed correctly the first time.
• I forgot to add the lemon juice or citric acid: Do not store those jars at room temperature. The processing times in this recipe rely on the tomatoes being properly acidified. When in doubt, discard the jars without tasting the contents.
• The jars have more headspace after processing: Tomatoes shrink and release juice as they heat. A small increase in headspace can be normal. Do not open a properly sealed jar to refill it.
• The liquid looks cloudy: Cloudiness can sometimes come from minerals in the water or anti-caking ingredients in regular table salt. Use canning salt and soft or filtered water. If the jar also has a broken seal, bubbles, mold, an unusual smell, or leaking liquid, discard it without tasting.
• The tomatoes turned darker at the top: This can happen when tomatoes are exposed to air because of excess headspace or liquid loss. Follow the recommended ½-inch headspace and remove air bubbles before applying the lid.
• The lid buckled: Bands that are tightened too firmly can prevent air from escaping during processing and cause the lid to buckle. Do not store a jar with a buckled lid on the shelf.
• A jar broke in the canner: Cracks, chips, thermal shock, and direct contact with the bottom of the pot can cause jars to break. Inspect jars before filling, keep them hot, use a canning rack, and avoid adding hot food to a cold jar.

Pairing Ideas

I use these canned tomatoes anywhere I would normally reach for a can of diced or crushed tomatoes. They are perfect for making spaghetti sauce, homemade pizza sauce, lasagna soup, and easy chili. You can also blend them into homemade salsa or add them to casseroles, soups, and pasta dishes. Home-canned tomatoes add that fresh garden flavor that makes all of these recipes even better.