Tomato paste can be canned at home, but only with a tested recipe written for paste—not a scaled-down sauce recipe. The National Center for Home Food Preservation (NCHFP) method uses 14 pounds of Roma or other paste-type tomatoes, 1 teaspoon of citric acid mixed into the sieved pulp before the second cook, half-pint jars, and a boiling-water canner. Yield is about 8 or 9 half-pint jars.
That combination exists for a reason. Paste is dense. Heat and acid do not move through it the way they move through crushed tomatoes or thin sauce. If you change the jar size, skip the citric acid, add it to the jar instead of the pot, or invent a pressure-canner time, you leave the tested process. Those changes are the usual source of unsafe advice online.
What searchers usually need first
Most people looking up canning tomato paste are trying to answer four questions at once:
- Is water-bath canning allowed, or must it be pressure canned?
- Can I use pint jars?
- Do I add lemon juice to each jar like other tomato products?
- How thick is “thick enough”?
The short answers: use a boiling-water canner and half-pint jars; add citric acid to the pot after milling, not to the jars; stop when the paste mounds on a spoon after a second reduction of about half. Details and the reasons follow.
Why tomato paste is not canned like sauce
Tomatoes sit near the acid/low-acid line. Variety, ripeness, and growing conditions can push pH above 4.6, the level that prevents Clostridium botulinum from growing in a sealed jar. That is why USDA and extension guidance requires added acid in home-canned tomato products.
Paste adds two extra problems:
Density. Heat takes longer to reach the center of a thick product. The tested process uses half-pint jars only. An Ask Extension specialist, asked whether pints or a pressure canner could be substituted, advised staying with the NCHFP recipe: half-pints and a boiling-water canner.
Acid distribution. In crushed tomatoes or juice, acid can go into the empty jar. Paste is too thick for that. NCHFP is explicit: citric acid must be stirred into the sieved tomatoes before they cook down to paste, and the ratio of citric acid to pounds of tomatoes must stay the same. Adding it to jars does not distribute it evenly.
Those two points are the core of a safe batch. Everything else in the recipe supports them.
When canning paste is worth the afternoon
Canning paste makes sense if you grow a lot of paste tomatoes, want shelf-stable half-pints for sauces and soups, and can spend several hours at the stove. The official cook times are about 1 hour for the first reduction, then about 2½ hours for the second. Stirring becomes nearly constant as it thickens, and scorching ruins the batch.
Freezing is often the better choice if:
- You only have slicing or cherry tomatoes (more water, longer cook, lower yield).
- You do not want to stand over a pot for most of a day.
- You prefer tablespoon portions. Frozen paste in ice-cube trays or small containers needs no acidification or processing schedule.
NCHFP notes that tomato products such as sauce and puree can be frozen after cooking, cooling, and packing with headspace. Frozen tomatoes are for cooking, not fresh use.
Buying commercial paste is still reasonable if your harvest is small. Home-canned paste is a labor project, not a shortcut.
Ingredients and limits you should not change
Tested batch (NCHFP)
- 14 pounds Roma- or paste-type tomatoes
- 1 teaspoon citric acid
- 1 teaspoon canning or pickling salt (optional)
- 2 bay leaves (optional)
- 1 clove garlic (optional)
Yield: about 8 or 9 half-pint jars Jars: half-pints only Headspace: ½ inch Pack: hot Canner: boiling-water bath
Do not add oil, flour, cornstarch, extra vegetables, or dairy. Thickeners change heat penetration and can make a product unsafe. Extension guidance is blunt on that point for tomato products in general.
Do not double the optional flavorings into a different recipe. Bay and one garlic clove are the only extras in the tested formula, and they come out before jarring.
Processing time by altitude
Start the timer only after the water returns to a full boil with the jars in the canner.
| Jar size | 0–1,000 ft | 1,001–3,000 ft | 3,001–6,000 ft | Above 6,000 ft |
|---|---|---|---|---|
| Half-pints, hot pack | 45 min | 50 min | 55 min | 60 min |
Source: NCHFP tomato paste process table.
After processing, turn off the heat, wait 5 minutes with the canner lid off (standard boiling-water practice used in extension versions of this recipe), then lift jars out and cool 12 to 24 hours without moving them. Check seals.
Step-by-step method
Follow the NCHFP procedure in order. Skipping the mill or the acid step is not a shortcut.
1. Heat the jars and lids
Wash half-pint jars and keep them hot until filling. Prepare lids according to the manufacturer. Because processing time is well over 10 minutes, jars do not need a separate sterilizing boil; they do need to be clean and hot so the thick paste does not cool on contact.
2. First cook: reduce the chopped tomatoes by about half
Rinse tomatoes, remove cores, and do not peel. Chop into ½- to ¾-inch pieces. Put them in a wide, heavy stockpot, cover, and bring to a boil, stirring so the bottom does not scorch. Uncover, drop to a simmer, and cook about 1 hour until the volume is reduced by half. Stir often.
Paste tomatoes matter here. Romas and other meaty types start with less water, so this stage is shorter and the later yield is closer to the published 8–9 jars. Watery slicers work in theory but give more liquid to cook off and a smaller finished batch.
3. Mill the pulp
Press the cooked tomatoes through a fine sieve or a food mill with a fine blade. Do not use a blender or food processor. Those tools whip air into the pulp. Extra air is the opposite of what you want in a product that already resists heat penetration.
The mill also removes skins and seeds without a separate peeling step.
4. Add citric acid, then reduce again
Return the sieved tomatoes to the pot. Stir in the full teaspoon of citric acid until it is dissolved. Add salt, bay leaves, and garlic if you are using them.
Cook uncovered on medium heat until two things are true at once:
- Volume is reduced by about half again.
- The paste is thick enough to round up on a spoon.
NCHFP lists about 2½ hours for this stage. Actual time depends on pot width, tomato water content, and how hard you simmer. Stir frequently at first and almost constantly at the end. Spatter can burn skin.
If a layer starts to scorch, move the unburned paste to a clean pot. Burned flavor does not cook out.
5. Fill hot jars
Remove bay leaves and garlic. Ladle hot paste into hot half-pint jars, leaving ½-inch headspace. Work a nonmetallic spatula around the inside wall to release pockets of air, then reset the headspace. Wipe rims with a clean damp paper towel. Apply lids and screw bands fingertip-tight.
Do not process a half-filled jar to “use it up.” Refrigerate the extra and use it within a few days, or freeze it.
6. Process in a boiling-water canner
Jars must be covered by at least 1 inch of water (2 inches is more comfortable if the boil is vigorous). Return to a rolling boil, then time according to the altitude table. Keep the boil going the entire time. If the boil stops, bring it back and restart the full process time.
Cool undisturbed 12 to 24 hours. Remove bands, check that lids are concave and do not flex, wash the jars, label, and store.
Citric acid is not optional, and lemon juice is not a tested swap here
For crushed tomatoes, juice, and many sauces, bottled lemon juice or citric acid can go in the jar. Paste is the exception.
NCHFP’s note on this recipe: the citric acid “needs to be added into the sieved tomatoes before they are cooked down into paste.” Adding it to jars “does not allow for adequate distribution of the acid throughout the product.” Keep the ratio of citric acid to pounds of tomatoes consistent if you scale the batch down.
Some blogs treat bottled lemon juice as interchangeable (a common kitchen conversion is 1 tablespoon bottled lemon juice per ¼ teaspoon citric acid). That conversion is used in other tomato products. It is not how this paste recipe was tested. The published formula uses citric acid only. If you cannot get citric acid, freeze the paste instead of inventing a water-bath version.
Do not use fresh-squeezed lemon juice for canning acidification in any tomato product. Acidity varies. Bottled juice is standardized; this paste recipe still specifies citric acid.
Water bath or pressure canner?
Use a boiling-water canner. That is the process NCHFP published for tomato paste.
There is no USDA or NCHFP pressure-canning schedule for this product. Density is the issue: a tested time and pressure would have to prove the center of that thick mass reaches a safe temperature in a given jar size. Guessing a time from crushed tomatoes or sauce is not a substitute.
Ignore pages that say paste “must” be pressure canned because tomatoes are low-acid. Properly acidified tomato products can be water-bath canned; that is standard USDA tomato guidance. Paste is acidified in the pot, then processed in half-pints for 45–60 minutes depending on altitude. That is the tested path.
A pressure cooker is not a pressure canner. Do not use multi-cookers or stovetop pressure cookers for this.
How thick is thick enough?
Home canners often get stuck between three cues in the same recipe: reduced by half, about 2½ hours, and “rounds up on a spoon.” Those cues do not always land at the same moment. Tomato water content varies. A batch can hit the volume target and still look saucy, or look like commercial paste long before the clock does.
For canning, use the spoon test as the safety-minded stop point: the paste should mound, not flood back immediately when you drag a spoon through it. Stopping a little looser than a store tube is better than cooking it to a stiff brick. Over-reduced paste is harder for heat to move through during processing. Home canners on forums have asked whether an extra-thick batch is still safe; thickness is exactly why the recipe is limited to half-pints.
The paste will thicken a bit more as it cools in the jar. You are not trying to match the driest commercial concentrate.
Mistakes that cause failed jars or unsafe jars
Treating this like tomato sauce. Acid in the jar, pint jars, and a 35–40 minute process are sauce rules. They are not paste rules.
Using a blender. Air in a dense product is a heat-penetration problem. Use a food mill or fine sieve.
Pint or quart jars. Not tested. Heat may not reach the center in the published time.
Oven canning, dishwasher canning, open-kettle canning, or sealing without a timed boil. None of these are accepted methods for tomato paste.
Adding extra low-acid ingredients. Onions, peppers, meat, oil, or large amounts of garlic change the product. One optional clove in the pot, removed before filling, is the limit in this recipe.
Dirty rims and tight bands. Paste is sticky. A smear on the rim prevents a seal. Bands should be fingertip-tight so air can vent during processing. After cooling, store jars without the bands so a failed seal is obvious.
Ignoring altitude. At 3,000 feet, 45 minutes is not the correct time.
Canning tomatoes from frost-killed or diseased vines. Extension tomato guidance excludes damaged, moldy, or frost-killed fruit because quality and safety are both worse.
After the jars are cool
Store sealed jars in a cool, dark, dry place. Quality is best within a year to 18 months; that is a quality window, not a guarantee that an older sealed jar is unsafe or that a new one is automatically fine.
Before eating any home-canned tomato product:
- Lid should be firm and concave.
- No spurting, bubbling, mold, off-odor, or unexpected fizz when opened.
- If a jar is unsealed, bulging, leaking, or smells wrong, do not taste it. Discard it so pets and other people cannot get to it.
Unsealed jars found within 24 hours can be refrigerated and used soon, frozen with extra headspace, or—only if the original recipe was tested—emptied, reheated, put in a clean jar with a new lid, and reprocessed as a hot pack. NCHFP does not recommend reprocessing for quality reasons, but it outlines those conditions if you do it. If the first attempt was not a tested recipe, do not reprocess; discard.
Opened paste belongs in the refrigerator and should be used in a few days, or frozen in small portions.
A practical batch plan
- Start with paste tomatoes if you have them.
- Use a wide pot so water evaporates faster than it would in a tall, narrow stockpot.
- Mill after the first reduction, add citric acid immediately, then commit to stirring.
- Heat jars during the last hour of the second cook so filling is a short step.
- Process half-pints only, timed from a full rolling boil, adjusted for your elevation.
- Plan freezer space for leftover paste that does not fill a jar.
If the goal is “tomato flavor in winter” rather than “jars that look like commercial paste,” can crushed tomatoes or sauce instead. Those products take less stove time, allow pint or quart jars, and have clearer acid-in-the-jar instructions. Save paste canning for years when the paste-tomato plants actually produce.
Frequently asked questions
Can I use pint jars if I process longer? No tested time exists for pints of this paste. Longer guesswork does not make an untested jar size safe.
Can I pressure can it anyway? There is no published pressure schedule for NCHFP tomato paste. Water-bath processing of the tested half-pint recipe is the method on record.
Can I can store-bought paste to move it into mason jars? Re-canning a commercial product is not the same as this recipe. There is no reason to do it for safety, and there is no tested home process for that shortcut.
What if I already added lemon juice to the jars? That is not the tested acid step for paste. Do not treat those jars as equivalent to the NCHFP product. Refrigerate or freeze and use them as a cooked sauce base, or discard if you are not sure the process was safe.
Is it safe if I see a few trapped bubbles after cooling? Small trapped bubbles in a sealed, properly processed jar of a thick product are a quality issue more often than a safety verdict by themselves. Watch for signs of spoilage when you open the jar. Failure to remove bubbles before processing can worsen siphoning and headspace problems. An extension reply on forgotten bubbles in tomato paste treated sealed jars as acceptable to keep if there is no spoilage at opening.
Can I roast the tomatoes first? Roasting is a kitchen technique, not part of the tested canning process. If you change how the tomatoes are prepared, you are no longer following the tested recipe. Freeze roasted, reduced paste if you want that flavor.
Do I need to peel tomatoes? Not in this recipe. Cores come out; skins come off in the food mill after the first cook.
Canning tomato paste is a narrow, tested procedure: paste tomatoes, citric acid in the sieved pulp, half-pint jars, and a timed boiling-water process adjusted for altitude. Stay inside those limits. If a step would be convenient but is not in the NCHFP recipe, freeze that batch instead.