You can put tomatoes in a water bath canner and get shelf-stable jars. You cannot follow a research-tested USDA recipe that is labeled “diced tomatoes.” That gap is why processing times online jump from 35 minutes to 85 minutes, and why some extension offices tell people to freeze dice instead.
The practical path is this: add bottled lemon juice or citric acid to every jar, then use the tested hot-pack method for crushed tomatoes. The pieces stay chunky enough for chili, soup, and sauce. If you need cubes that stay neat after opening, freeze them or can whole tomatoes and cut them later.
What people searching this keyword are trying to decide
Most readers want pantry jars that replace store-bought diced tomatoes. They also want to know:
- Whether a water bath canner is enough, or a pressure canner is required
- How much lemon juice or citric acid to add
- How long to process pints versus quarts
- Whether peeling, seeding, or pre-cooking is optional
- Whether onions, garlic, basil, or salt change the process
The first safety decision is more important than the dice size. Tomatoes sit near pH 4.6. Varieties, ripeness, and growing conditions can push them above that line. Water-bath canning only works when every jar is acidified to a reliably low pH. That rule applies even if you later pressure-can the same product.
Why “diced tomatoes” is not a USDA water-bath recipe
The National Center for Home Food Preservation and USDA publish tested directions for whole or halved tomatoes, crushed tomatoes with no added liquid, tomato juice, and tomato sauce. They do not publish a diced-tomato process. Iowa State Extension, other university extensions, and Ball customer care have stated the same thing: there is no scientifically validated home process for diced tomatoes.
The concern is density, not flavor. Small cubes pack tighter than halves. Tight packs slow heat travel to the center of the jar. Commercial diced tomatoes are processed on industrial equipment and often contain calcium chloride to keep the cubes firm. Home kitchens do not have that equipment or that tested formula. Extra processing time that would cover a dense pack also turns the tomatoes to mush, which is why labs did not simply “add 20 minutes” and call it a recipe.
That does not mean tomatoes cannot be water-bath canned. It means the safe home product is crushed tomatoes prepared the tested way, not raw cubes jammed into a jar.
The closest tested product: hot-pack crushed tomatoes
NCHFP crushed tomatoes start as peeled, cored, quartered fruit. A portion is crushed to make juice. The rest is added as pieces and boiled gently for five minutes. The remaining quarters soften but do not have to be mashed into a puree. In the jar you get liquid plus soft chunks—the same thing most home cooks want when they search for canned diced tomatoes.
Use this method if you want a pantry product. Use freezing if the cube shape itself matters.
How many tomatoes you need
- About 14 pounds of tomatoes fill 9 pint jars
- About 22 pounds fill 7 quart jars
- Plan on roughly 2¾ pounds per finished quart
Roma, San Marzano, and other paste types give a thicker pack with less watery juice. Slicing tomatoes work, but they release more liquid and can look separated in the jar. Do not can tomatoes from dead or frost-killed vines. Discard fruit with mold, rot, or large bruises.
Acid amounts that make water-bath tomatoes safe
Add acid to each empty jar before filling. Do not skip it. Do not reduce it. Do not use fresh lemon juice; bottled juice has a standardized acidity. Citric acid changes flavor less than lemon juice. Vinegar is allowed at the amounts below, but it can taste harsh.
| Acid | Pint jar | Quart jar |
|---|---|---|
| Bottled lemon juice | 1 tablespoon | 2 tablespoons |
| Citric acid | ¼ teaspoon | ½ teaspoon |
| 5% vinegar | 2 tablespoons | 4 tablespoons |
Salt is optional and is only for flavor: ½ teaspoon per pint or 1 teaspoon per quart. A pinch of sugar can soften the lemon-juice taste. Neither salt nor sugar replaces acid.
Equipment that actually matters
- Boiling-water canner or a deep pot with a rack and a lid
- Pint or quart canning jars, new lids, and bands
- Jar lifter, funnel, and a non-metal tool to release air bubbles
- Large stockpot for heating tomatoes
- Bottled lemon juice or food-grade citric acid
Jars need to be clean and hot. Current lid manufacturers generally do not require boiling lids; follow the package. The canner water must cover the jars by 1 to 2 inches the entire process. Start the timer only after the water returns to a full rolling boil.
Step-by-step water bath method (tested crushed-tomato process)
- Fill the canner so jars will be covered by at least 1 inch of water. Heat the water. Keep clean jars hot.
- Wash the tomatoes. Score a small X on the blossom end if you like. Blanch in boiling water 30 to 60 seconds, until the skins split. Move them to cold water. Slip off the skins, cut out the cores, and trim any green or damaged spots.
- Quarter the tomatoes. Heat about one-sixth of the quarters in a large pot, crushing them as they go in so juice collects. When that portion boils, add the remaining quarters gradually while stirring. Those later pieces do not need to be crushed. After the last tomatoes go in, boil gently for 5 minutes. Stir so the pot does not scorch.
- Put the measured acid (and optional salt) into each hot jar.
- Ladle the hot tomatoes and their juice into the jars, leaving ½-inch headspace. Slide a bubble tool around the inside. Adjust the headspace if the level drops. Wipe the rims, apply lids, and screw bands fingertip-tight.
- Load the jars into the canner. Add boiling water if needed so the jars stay covered. Cover the canner. When the water reaches a rolling boil, start the clock.
- When time is up, turn off the heat. Let the jars sit in the water 5 minutes. Lift them out without tilting. Cool 12 to 24 hours, undisturbed, on a towel.
- Check seals. Remove the bands, wipe the jars, label them, and store without the bands in a cool, dark place. Refrigerate or freeze any jar that did not seal. Use sealed jars within a year for best quality.
Water-bath times for crushed tomatoes
| Altitude | Pints | Quarts |
|---|---|---|
| 0–1,000 ft | 35 minutes | 45 minutes |
| 1,001–3,000 ft | 40 minutes | 50 minutes |
| 3,001–6,000 ft | 45 minutes | 55 minutes |
| Above 6,000 ft | 50 minutes | 60 minutes |
These times are for the hot-pack crushed method above. They are not interchangeable with raw-pack whole tomatoes packed without liquid, which process much longer.
Pressure canning is an option for the same crushed product and shortens the heat time, but acid still goes in every jar. Use the NCHFP pressure tables for crushed tomatoes and match your canner type (dial gauge versus weighted gauge) and altitude. Do not invent a hybrid time.
Why published “diced tomato” times contradict each other
Blog recipes usually borrow one of three USDA tomato processes and relabel it “diced”:
- Crushed, hot pack, no added liquid: 35 minutes for pints, 45 minutes for quarts at low altitude. This is the closest tested match.
- Whole or halved packed in water: 40 minutes for pints, 45 minutes for quarts.
- Whole or halved packed raw with no added liquid, or packed in juice: 85 minutes for pints and quarts at low altitude.
Using the 85-minute schedule on a tightly packed jar of small cubes is not a tested diced-tomato process. Using the 35-minute crushed schedule on cold, densely packed raw dice is not tested either. If you want the crushed-tomato times, follow the crushed-tomato prep: peel, quarter, heat, and hot-pack with ½-inch headspace.
What you cannot add to this jar
Do not add onion, garlic, peppers, celery, meat, oil, or fresh herbs and still use a tomato-only water-bath time. Those ingredients change acidity and density. Tested salsas and spaghetti sauces have their own formulas and times. A “diced tomato plus whatever is in the garden” jar is not a tomato jar.
Do not substitute fresh lemon juice, lime juice of unknown acidity, or “a splash” of vinegar. Do not can overripe, moldy, or frost-damaged fruit. Do not leave skins on as a shortcut if you are trying to stay inside tested tomato procedures; the official crushed and whole-tomato directions start with peeled fruit.
If you want cubes that stay diced
Freezing is the method extension services recommend when the cube itself is the goal. Wash, core, and dice. Pack into freezer containers, leaving headspace for expansion. Frozen tomatoes are soft after thawing, which is fine for cooked dishes. They keep about a year.
The other safe pantry option is canning whole or halved tomatoes by a tested water-bath or pressure process, then dicing them when you open the jar. You lose some convenience. You keep a process that was actually measured in a lab.
Mistakes that cause weak seals, watery jars, or unsafe food
Skipping acid because the tomatoes “taste tart.” Taste is not pH. Modern varieties and ripe fruit can sit above 4.6.
Raw-packing small cubes and borrowing a short process time. Heat has to reach the cold spot. Tight dice slow that down.
Starting the timer before the canner is at a full boil. The published minutes assume boiling water the entire time.
Ignoring altitude. Water boils below 212°F as elevation rises. The extra minutes in the chart exist for that reason.
Over-tightening bands. Fingertip-tight lets air escape so a vacuum can form.
Adding extra liquid when the tomatoes already released juice. The crushed method is packed in the tomatoes’ own juice. Extra water thins the product and changes the fill.
Treating floating solids as a failure. Hot-pack tomatoes can still separate as they cool. After the jars are fully cool, you can invert a sealed jar once to redistribute. Separation is a quality issue, not proof the jar is unsafe.
Keeping unsealed jars on the shelf. Unsealed jars belong in the refrigerator and should be used quickly, or the contents can be frozen.
How to use the jars
Treat a sealed jar like canned crushed tomatoes with pieces. Drain or keep the juice depending on the recipe. Because the tomatoes are already heated, they go straight into chili, soup, braises, shakshuka, and simmered sauces. If a recipe needs a firmer cube, dice a fresh or frozen tomato into the pot instead of expecting home-canned pieces to stay square.
Before opening a stored jar, check the lid. Do not taste from a jar with a bulging lid, spurting liquid, off odor, mold, or unexplained cloudiness. When in doubt, throw the contents away without tasting.
Frequently asked questions
Can I water-bath can diced tomatoes if I add lemon juice? Acid is required, but it does not create a tested diced-tomato process. Use the crushed-tomato method, freeze dice, or can halves and cut them later.
Do I need a pressure canner? Not for acidified crushed, whole, or juiced tomatoes processed by the matching USDA schedule. A pressure canner is required when low-acid vegetables or meat are in the jar.
Can I leave the skins on? Official crushed and whole-tomato directions peel first. Skins can affect texture and are not part of those tested packs.
Can I use pint-and-a-half or half-pint jars? Use the jar sizes in the tested table. Do not assume a different jar gets the same time.
Why does one site say 85 minutes? That time belongs to raw-pack whole or halved tomatoes with no added liquid, or tomatoes packed in juice—not to hot-pack crushed tomatoes.
Will citric acid make the tomatoes taste sour? Most people notice lemon juice more than citric acid. The amount is small. A little sugar in the jar is allowed for taste. Do not cut the acid.
How long do sealed jars last? Quality is best within 12 months in a cool, dark place. Safety depends on a sound seal and correct processing, not on the calendar alone.
What if I already canned raw diced tomatoes using a blog recipe? Extension advice for untested processes is not “leave them on the shelf.” The conservative options are to refrigerate and use soon, freeze the contents, or discard them. A sealed lid is not proof the center of a dense jar reached a killing temperature.
Water-bath tomatoes are a good beginner project when the recipe is one USDA actually tested. For diced-style jars, that recipe is crushed tomatoes with added acid, not a tightly packed pint of raw cubes. Follow the prep and the time that belong together, or freeze the dice and skip the argument.