Fresh tomatoes can be canned safely in a boiling-water canner or a pressure canner, but only if every jar is acidified and processed for the full tested time. Modern varieties, overripe fruit, and fruit from stressed vines can sit near or above pH 4.6, the point where Clostridium botulinum can grow. Added bottled lemon juice or citric acid holds the product below that line. The heat process then destroys molds, yeasts, and spoilage bacteria. Skip either step and a sealed jar is not a safe jar.
Crushed tomatoes are the most useful everyday pack for sauce, soup, and chili. Whole or halved tomatoes suit recipes where you want pieces. Both follow the same acid rule. Times below are the USDA and National Center for Home Food Preservation (NCHFP) processes for altitudes up to 1,000 feet. Higher elevations need longer boiling-water times or higher pressure.
Why every jar of tomatoes needs added acid
Tomatoes were long treated as a high-acid food. That assumption no longer holds. Variety, ripeness, growing conditions, and fruit from dead or frost-killed vines can push pH above 4.6. At that level, botulism spores can germinate in a sealed jar. Boiling water reaches only 212°F (100°C) at sea level, which does not destroy those spores. Acid stops them from growing, which is why a water-bath process can be safe once the tomatoes are properly acidified.
Pressure canning does not cancel the acid step. USDA pressure options for plain tomatoes were developed for acidified tomatoes. They were calculated to match the water-bath treatment against molds, yeasts, and spoilage organisms, not to sterilize unacidified tomatoes against botulism spores. A process written for unacidified tomatoes would be much longer. If a tested recipe offers both methods, use every preparation step, including acid, no matter which canner you choose.
Add one of these to each jar before filling:
| Acid | Per pint | Per quart | Flavor effect |
|---|---|---|---|
| Bottled lemon juice | 1 tablespoon | 2 tablespoons | Mild tang; standardized acidity |
| Citric acid (food grade) | 1/4 teaspoon | 1/2 teaspoon | Least flavor change |
| Vinegar, 5% acidity | 2 tablespoons | 4 tablespoons | Noticeable flavor change |
Use bottled lemon juice, not fresh-squeezed. Fresh lemons vary in acidity. Bottled lime juice is an acceptable substitute for bottled lemon juice. Do not use homemade vinegar, and do not cut the acid amount. A little sugar in the jar can offset tartness; it is optional and does not replace acid. Salt is also optional and is for taste only: 1/2 teaspoon per pint or 1 teaspoon per quart. Tomato canning tablets are not a reliable acid source.
Which tomatoes are worth canning
Use firm, disease-free, preferably vine-ripened fruit. Wash them. Cut away bruises and discolored spots. Do not can tomatoes from dead or frost-killed vines, and do not can decayed or badly damaged fruit. Overripe tomatoes are less acidic and break down in the jar.
Paste and plum types (Roma and similar) have more flesh and less gel, so they make a thicker crushed pack and a better base for sauce. Slicing tomatoes work, but they release more liquid. Green tomatoes are more acidic than ripe fruit and can be canned with the same tested tomato procedures, including acid. Heirloom varieties are not an exception: treat them like any other tomato and acidify.
Plan on about 3 pounds of raw tomatoes per quart for whole or halved fruit packed in water, and about 2¾ pounds per quart for crushed. A canner load of 7 quarts takes roughly 21 pounds for water-packed whole tomatoes and about 22 pounds for crushed. A 53-pound bushel yields about 15 to 21 quarts of water-packed whole tomatoes, or 17 to 20 quarts crushed.
Water bath or pressure canner
Plain acidified tomatoes — whole, halved, crushed, or juice — may be processed either way when the recipe lists both. Extension guidance generally finds pressure canning gives better color and texture because the time in heat is shorter.
Use a pressure canner only, and only a tested recipe, when you add low-acid ingredients in amounts that change the product. That includes meat, large amounts of onion, pepper, celery, or other vegetables, and most homemade spaghetti sauces. Do not invent a salsa or soup recipe and assume a tomato process covers it. Thickening with flour, cornstarch, rice, pasta, or cream before canning is unsafe: thickeners slow heat penetration. Thicken after you open the jar.
Two older methods are not safe. Open-kettle canning (cooking, packing hot, and sealing with no process) does not get the center of the jar hot enough for long enough. Oven canning is also discredited. An atmospheric steam canner can be used for properly acidified tomatoes only when the tested boiling-water time, including the altitude adjustment, is 45 minutes or less, the canner is vented to pure steam before the timer starts, and the canner is not opened during the process.
How to prepare the fruit
Peel tomatoes unless a specific tested recipe says otherwise. Published processes were developed on peeled fruit. Skins can slow heat penetration, carry more surface bacteria, and leave tough, bitter pieces in the jar.
- Wash the tomatoes.
- Dip them in boiling water for 30 to 60 seconds, until the skins split. Do not leave them longer or the flesh turns mushy.
- Move them straight into cold water.
- Slip off the skins, remove the cores, and trim damaged spots.
- Leave whole, halve, or quarter, depending on the pack.
Hot pack and raw pack are not interchangeable across recipes. Crushed tomatoes are a hot pack only. Whole or halved tomatoes packed in water may be raw- or hot-packed, with the same process time. Raw pack with no added liquid, and tomatoes packed in tomato juice, use much longer times because heat moves more slowly through a denser jar. Match the process to the pack. Do not borrow the shorter water-pack time for a juice pack.
Canning crushed tomatoes
This is the practical pack for weeknight cooking. The NCHFP crushed-tomato procedure adds no extra liquid.
Wash, peel, core, and quarter the tomatoes. Heat about one-sixth of the quarters in a large pot, crushing them with a spoon or mallet so they release juice. Once that batch is boiling, add the rest gradually, stirring so nothing scorches. The later pieces do not need crushing; they soften as they heat. Boil gently for 5 minutes.
Add acid to each hot jar, then salt if you want it. Fill immediately with hot tomatoes, leaving 1/2 inch of headspace. Remove air bubbles, wipe the rims, apply lids, and process.
Boiling-water canner, 0–1,000 feet: 35 minutes for pints, 45 minutes for quarts. At 1,001–3,000 feet those times become 40 and 50 minutes; at 3,001–6,000 feet, 45 and 55; above 6,000 feet, 50 and 60.
Pressure canner, pints or quarts: 20 minutes at 6 pounds on a dial gauge up to 2,000 feet (7 pounds at 2,001–4,000, 8 at 4,001–6,000, 9 at 6,001–8,000), or 15 minutes at 11 pounds up to 2,000 feet with the matching altitude increases. On a weighted-gauge canner, 20 minutes at 5 pounds up to 1,000 feet and 10 pounds above that. Acid is still required.
Canning whole or halved tomatoes in water
Wash, peel, and core. Leave whole or halve. Add acid to the jars, and salt if desired.
For a raw pack, fill hot jars with raw tomatoes and cover with boiling water, leaving 1/2 inch headspace. For a hot pack, cover the tomatoes with water, boil gently for 5 minutes, then pack hot fruit and cooking liquid to the same headspace.
Boiling-water canner, 0–1,000 feet: 40 minutes for pints, 45 minutes for quarts. Add 5 minutes for 1,001–3,000 feet, another 5 for 3,001–6,000, and another 5 above 6,000.
Dial-gauge pressure canner, pints or quarts: 15 minutes at 6 pounds up to 2,000 feet, or 10 minutes at 11 pounds up to 2,000 feet, increasing pressure with altitude. Weighted-gauge: 15 minutes at 5 pounds up to 1,000 feet and 10 pounds above 1,000. The shorter, higher-pressure weighted-gauge option is not recommended above 1,000 feet.
Tomatoes packed in their own juice, or raw-packed with no added liquid, are a different process: about 85 minutes in a boiling-water canner for pints and quarts at 0–1,000 feet, or 25 minutes in a pressure canner. Do not use the water-pack times for those jars.
Start the boiling-water timer only when the water returns to a full rolling boil with the jars in the canner, covered by at least 1 to 2 inches of water. Start the pressure timer only after the canner has vented and reached the target pressure. If pressure drops, bring it back and start the time over.
After the process
Turn off the heat. For a boiling-water canner, remove the lid and wait about 5 minutes before lifting jars. For a pressure canner, let pressure return to zero on its own, then wait the time your canner manual specifies before opening. Cool jars upright on a rack or towel, with space between them, for 12 to 24 hours. Do not tighten rings or tip jars to check the seal while they are hot.
A sealed lid is concave and stays down when pressed. Remove rings, wipe jars, label with contents and date, and store in a cool, dark place. Quality is best within a year; a sealed, properly processed jar can be kept longer, but flavor and texture decline. Refrigerate after opening.
Before use, check for a broken seal, bulging lid, leaks, spurting liquid, mold, or an off smell. Do not taste food you suspect. Discard it where pets and people cannot reach it. If a tomato product was not canned by a current tested process, boiling can destroy botulinum toxin if it is present: a full 10 minutes below 1,000 feet, plus 1 minute for each additional 1,000 feet. Boiling does not fix a jar you still plan to store.
Mistakes that make the jars unsafe
- Leaving out lemon juice or citric acid because the tomatoes “taste acidic,” or because the canner is a pressure canner.
- Using fresh lemon juice or homemade vinegar.
- Canning overripe fruit or tomatoes from frost-killed vines.
- Processing with the skins on when the recipe assumes peeled fruit.
- Adding oil, garlic in oil, or untested vegetables. Oil can shield bacteria in a droplet and can damage lid gaskets.
- Thickening before canning.
- Using an old family recipe that has no process time, or inverting jars to “seal” them.
- Ignoring altitude. Water boils at a lower temperature as elevation rises, so the same minutes do less work.
- Starting the timer before the canner is at a full boil or at pressure.
Freezing is the simpler alternative when you do not want to manage acid and process times. Frozen tomatoes do not need added acid. Texture changes, so they suit cooked dishes better than fresh eating.
Frequently asked questions
Can I pressure-can tomatoes with no lemon juice if I process them longer? No. The published pressure times were not developed for unacidified tomatoes. Extending the time on your own is not a tested process.
Do I have to peel them? For these USDA processes, yes. Peeling is part of how the process was tested, and it improves texture.
Can I reuse lids? Use new flat lids for a reliable seal. Rings can be reused if they are not rusted or bent. Jars may be reused if they are free of chips and cracks. Jars processed 10 minutes or longer in boiling water, or in a pressure canner, do not need a separate sterilization step.
Is water-bath canning enough for spaghetti sauce with meat? No. Meat and large amounts of low-acid vegetables move the product out of the plain-tomato category. Use a current tested pressure-canning recipe for that sauce, and follow its acid and time directions exactly.
What if my altitude is above 1,000 feet? Add time for a boiling-water canner, or raise pressure for a pressure canner, using the NCHFP table for that specific product. Do not guess a middle value.