San Marzano tomatoes can be canned at home in a boiling-water canner or a pressure canner, but only after each jar is acidified. Their thick walls, modest seed cavities, and lower water content make them one of the better paste types for whole fruit and crushed sauce. The variety does not change the safety rules. USDA guidance requires bottled lemon juice or citric acid in every jar of whole, crushed, or juiced tomatoes, including San Marzano, whether the jars go into a water bath or a pressure canner.
The two tested packs that fit this tomato best are crushed tomatoes with no added liquid, and whole or halved tomatoes packed raw in their own juice. Both are shelf-stable when the acid, headspace, and processing time match a current tested recipe.
Why San Marzano tomatoes suit the jar
San Marzano is a paste tomato: elongated, relatively dry, with fewer seeds and less gel than a slicing tomato. That flesh holds up better as whole peeled fruit and cooks down into a thicker sauce with less time on the stove. A true San Marzano from the Agro Sarnese-Nocerino area of Italy carries a protected name, but the canning rules are the same for garden seed labeled San Marzano, San Marzano-type hybrids, and other paste tomatoes such as Roma or Amish Paste.
Acidity is the part people misread. Tomatoes as a group sit near the safety line of pH 4.6. Below that line, Clostridium botulinum cannot grow in a sealed jar. Above it, the spores can survive a boiling-water process and produce toxin at room temperature. Variety, ripeness, soil, and weather all move the pH. University guidance treats heirlooms the same as hybrids for that reason: measure the acid you add, do not guess from the name on the plant.
Use fruit that is ripe, firm, and free of cracks, mold, or insect damage. Do not can tomatoes from dead or frost-killed vines. Process them within a few hours of picking or buying if you can. Overripe fruit is a poor candidate even if it still smells fine.
Acid, salt, and what does not belong in the jar
Acid goes into the empty jar before the tomatoes. The National Center for Home Food Preservation specifies the same amounts for boiling-water and pressure processing.
| Acid | Per pint | Per quart | Flavor note |
|---|---|---|---|
| Bottled lemon juice | 1 tablespoon | 2 tablespoons | Mild; the reliable default |
| Citric acid (food grade) | 1/4 teaspoon | 1/2 teaspoon | Least change in flavor |
| Vinegar, 5% acidity | 2 tablespoons | 4 tablespoons | Noticeable; sugar can soften it |
Use bottled lemon juice, not fresh-squeezed. Bottled juice has a standardized acidity; fruit from the tree does not. Citric acid is the better choice if you want the San Marzano flavor left alone. Vinegar works for safety and is a poor match for a sauce tomato. A small pinch of sugar in the jar is allowed if the acid tastes sharp. Salt is optional and does not preserve the food: 1/2 teaspoon per pint or 1 teaspoon per quart is the usual amount.
Do not add oil, butter, cheese, flour, cornstarch, or pasta. Fat and thickeners change how heat moves through the jar, and they are not part of the tested plain-tomato processes. Garlic, onion, peppers, and dried herbs belong only in a tested sauce or salsa recipe with its own acid level and processing time, such as the NCHFP spaghetti sauce formulas. A roasted sauce made with olive oil is a refrigerator or freezer food unless you rebuild it to a tested canning recipe and leave the oil out.
How much fruit to pick
Plan on about 2 3/4 pounds of tomatoes per quart of crushed pack, and about 3 pounds per quart of whole or halved pack. A canner load of 7 quarts takes roughly 22 pounds for crushed tomatoes and about 21 pounds for whole or halved. A load of 9 pints takes about 14 pounds crushed or 13 pounds whole. A 53-pound bushel yields roughly 17 to 20 quarts crushed, or 15 to 21 quarts whole, depending on how much you trim.
San Marzano fruit is often smaller than a beefsteak, so count jars by weight, not by tomato count. Sort out anything soft or spotted before you heat water. One bad fruit in a pot of crushed tomatoes is enough to cloud the batch.
Peeling and coring
Wash the tomatoes. Cut a shallow X in the blossom end. Dip them in boiling water for 30 to 60 seconds, until the skins loosen, then move them straight into cold water. Slip off the skins, cut out the cores, and trim bruises or green shoulders.
San Marzano skins usually release cleanly because the fruit is firm. If a batch is underripe, give it the longer end of that blanch. Peels left on are a texture problem, not a safety shortcut: tested whole-tomato directions call for peeled fruit. Seeds can stay. Squeezing them out makes a smoother sauce later, but it also throws away juice you may want in the jar.
Roasting is optional and only useful if you are making crushed tomatoes or sauce, not pretty whole fruit. Roast halves cut-side down on an unoiled sheet until the skins lift, then peel and continue with the crushed-tomato method, including acid in the jar. Oil on the pan is a reason to stop and freeze the batch instead.
Crushed San Marzano tomatoes
This is the pack most people want from this variety. The tomatoes are heated before they go into the jar, so the process is shorter than a raw whole pack, and the jar is ready to become sauce.
- Peel, core, and quarter the tomatoes.
- Put about one-sixth of the quarters into a large pot. Crush them with a spoon as they heat so they release juice quickly. Heating them fast, in their own juice, limits the enzyme activity that can separate liquid and solids in the jar.
- Once that portion is boiling, add the rest gradually, stirring so nothing sticks. Those later pieces do not need to be crushed; they soften in the pot.
- Boil gently for 5 minutes.
- Add acid to each hot jar, then salt if you want it.
- Ladle in hot tomatoes, leaving 1/2 inch of headspace. Release bubbles, wipe the rims, and apply lids.
In a boiling-water canner, at 0 to 1,000 feet, process pints for 35 minutes and quarts for 45 minutes. The timer starts when the water returns to a full rolling boil. Jars must be covered by at least 1 to 2 inches of water.
At higher elevations, add time: 1,001 to 3,000 feet, 40 minutes for pints and 50 for quarts; 3,001 to 6,000 feet, 45 and 55; above 6,000 feet, 50 and 60.
A pressure canner shortens the time. For a dial-gauge canner, one tested option is 15 minutes at 11 pounds up to 2,000 feet (12 pounds at 2,001 to 4,000, 13 at 4,001 to 6,000, 14 at 6,001 to 8,000). A weighted-gauge canner uses 15 minutes at 10 pounds up to 1,000 feet and 15 pounds above that. Longer, lower-pressure options also exist. Acid is still required. Follow your canner’s venting instructions before you start the clock.
Whole or halved San Marzano tomatoes
Use this pack when you want fruit you can lift out of the jar for a quick sauce or a pan of braised tomatoes. San Marzano’s shape fits a wide-mouth quart well if you leave the fruit whole. Halves pack more tightly and waste less space.
- Peel and core. Leave whole or cut in half.
- Add acid to each jar, then salt if you want it.
- Pack the raw tomatoes into the jars, pressing until the spaces fill with juice. Do not add water. Leave 1/2 inch of headspace.
- Release bubbles, wipe rims, and apply lids.
This raw pack with no added liquid needs a long boiling-water process because the jars go in cold in the center. At 0 to 1,000 feet, process pints and quarts for 85 minutes. Add 5 minutes for 1,001 to 3,000 feet (90 minutes), another 5 for 3,001 to 6,000 feet (95), and another 5 above 6,000 feet (100).
Pressure processing for this pack is 25 minutes. Dial-gauge pressure is 11 pounds up to 2,000 feet, then 12, 13, and 14 pounds in the same altitude bands used for crushed tomatoes. Weighted-gauge pressure is 10 pounds up to 1,000 feet and 15 pounds above that. University extensions adapted these figures from the USDA Complete Guide and the National Center for Home Food Preservation. Check the current table before a large batch if your elevation is above 1,000 feet, because the pressure or the minutes change and the recipe does not.
Hot pack in water or in tomato juice is also tested, and it can reduce floating. San Marzano already has less free liquid than a slicing tomato, so the raw pack in its own juice is usually the better use of the fruit. If a jar looks short on juice after pressing, do not top it off with water and keep the no-liquid process time. Switch that jar to the tested “packed in water” directions, which use a different time.
Water bath or pressure canner
Both methods are accepted for acidified tomatoes. A boiling-water canner is enough if the acid is in the jar and the full time is met. A pressure canner is faster and can leave paste tomatoes a little firmer, which matters with an 85-minute raw pack. It is not a substitute for acid. The pressure processes published for tomatoes are the hot equivalent of the water-bath processes, not the longer schedules used for green beans or meat.
Start with clean, standard mason jars and new flat lids. Rings can be reused if they are not rusted or bent. Jars do not need a separate sterilizing boil when the process is 10 minutes or longer, which these are. Keep jars hot so they do not break when they meet hot tomatoes or hot canner water.
After processing, turn off the heat, remove the canner lid, and wait 5 minutes before lifting jars. Set them on a towel with space between them. Leave them undisturbed for 12 to 24 hours. A sealed lid curves down in the center and stays down when the ring is removed. Refrigerate any jar that did not seal and use it within a few days, or reprocess it within 24 hours with a new lid. Store sealed jars without rings, in a cool, dark place. Quality is best within a year.
Mistakes that show up with this tomato
Skipping the lemon juice because “San Marzano are the real Italian tomato” is the error that matters most. Italian and German home methods sometimes bottle peeled tomatoes with a shorter, cooler heat treatment and no added acid. Those are different processes with different equipment assumptions. They are not the USDA method, and a home pH meter is not an acceptable substitute for the measured acid in the recipe.
Open-kettle canning, oven canning, and dishwasher canning are not safe replacements for a full process. Inversion sealing, where hot tomatoes are packed and the jar is flipped to “seal,” does not heat the center of the jar long enough.
Other problems are quieter. Fresh lemon juice instead of bottled. Acid measured into the pot and then ladled unevenly, so one jar gets almost none. Processing time started before the water is at a full boil. A canner that never quite covers the lids. Frost-damaged fruit. Oil from a roasting pan carried into the jar. Extra onions or garlic added to a plain crushed-tomato recipe.
Floating fruit is cosmetic. It is more common in a raw pack and less common if the tomatoes were ripe and pressed until juice filled the gaps. Separation in crushed tomatoes usually means the first batch in the pot was not heated fast enough. Neither issue means the seal failed.
Using the jars
A quart of crushed San Marzano is already most of the way to pasta sauce. Simmer it with garlic, olive oil, and herbs after you open the jar, not before you seal it. Whole tomatoes can be crushed by hand into a pan for the same purpose. Because the jar was acidified, taste before you add more lemon or vinegar. A pinch of sugar is enough if the bottled lemon juice still shows.
Freeze peeled fruit if you do not want to can. Frozen tomatoes do not need added acid, and they work well for cooked sauce. They are a poor substitute for canned whole tomatoes in recipes that expect a firm piece of fruit.
Questions people ask after the first batch
Can I can San Marzano tomatoes without peeling them? Tested whole and crushed recipes remove the skins. Skins are tough after processing and are not part of those directions.
Do garden San Marzano and canned DOP San Marzano follow different rules? No. Home canning rules follow the food and the process, not the geographic name. Imported canned San Marzano were acidified and heat-treated in a commercial plant. Home jars need the home-canning acid dose and a full home process.
Can I reduce the lemon juice if my tomatoes taste very tart? No. The dose is the safety control. Use citric acid if you want less flavor change, or add a little sugar.
Is a pressure canner required above a certain altitude? No. Water-bath times get longer as elevation rises, and pressure-canner pounds of pressure go up. Either method is acceptable if you use the matching altitude adjustment.
Can I put basil in the jar? Not in the plain crushed or whole recipes. A tested spaghetti sauce without meat allows specific amounts of herbs, onion, and garlic, and it has its own process time. Dry herbs in an untested handful are a common way a safe recipe becomes an untested one.
San Marzano tomatoes earn their reputation in the pan, not in a special exemption from the canner. Acid in the jar, a tested pack, and the full time for your elevation are what make the shelf-stable version of that reputation.