Roma and San Marzano tomatoes are your best choice for canning

Roma tomatoes are the standard for home canning because they have fewer seeds, thicker flesh, and less water than slicing tomatoes. San Marzano tomatoes, an Italian heirloom variety, are even better if you can find them — they produce a smoother sauce with richer flavor and cook down faster. Both varieties yield more usable pulp per pound than beefsteaks or cherry tomatoes, which means less time spent reducing sauce and less waste.

The reason variety matters is straightforward: watery tomatoes require longer cooking to reach the right consistency, and they take up more jar space for less finished product. A pound of Roma tomatoes will give you roughly half a cup of sauce; a pound of a watery slicing tomato might give you a quarter cup. When you are canning, that difference adds up across dozens of jars.

If you grow your own tomatoes, plant Roma or San Marzano seeds in spring and harvest when the tomatoes are fully red but still firm. If you buy from a farmers market or grocery store, look for tomatoes that feel dense and heavy for their size — that density signals lower water content.

Key Takeaways

  • Roma and San Marzano tomatoes have thick flesh and few seeds, making them ideal for canning sauces and whole tomatoes.
  • Watery varieties like beefsteaks and slicing tomatoes require much longer cooking and yield less finished product per pound.
  • Choose tomatoes that feel dense and heavy for their size, which indicates they have less water and more usable pulp.
  • San Marzano tomatoes produce the smoothest, richest sauce but are harder to find and more expensive than Roma.
  • Avoid cherry and grape tomatoes for canning sauce; they are too small and too watery to be practical.

Why paste tomatoes work better than slicing tomatoes

Tomatoes bred for canning — called paste tomatoes — have a different structure than tomatoes bred for eating fresh. Paste tomatoes are smaller, denser, and have thicker cell walls that hold their shape during cooking. Slicing tomatoes like beefsteaks and heirlooms are bred to be juicy and tender, which is pleasant to bite into but disastrous for canning.

When you cook down a slicing tomato, you are boiling away water for hours. A bushel of beefsteaks might reduce to a few cups of sauce. The same bushel of Romas will reduce to significantly more finished product. That is why commercial tomato sauce makers use paste varieties exclusively — the economics do not work otherwise.

If you have only slicing tomatoes available, you can still can them, but plan to cook them much longer and expect a thinner final product. Strain the cooked tomatoes through cheesecloth to remove seeds and skins, then cook the strained liquid down further to reach sauce thickness. This adds several hours to the process.

San Marzano tomatoes: flavor and trade-offs

San Marzano tomatoes are prized by canning enthusiasts because they have a sweeter, less acidic flavor than most other paste varieties. They also have very few seeds and cook down to a smooth, almost creamy sauce without much straining. If you taste a sauce made from San Marzanos next to one made from Romas, the San Marzano version will taste richer and more complex.

The trade-off is availability and cost. True San Marzano seeds are expensive, and the plants are fussier about growing conditions than Romas. If you buy canned San Marzanos at the store, they cost two to three times what Romas cost. Growing them yourself is possible but requires starting seeds indoors in late winter and giving them consistent warmth and water through the season.

For a first canning season, start with Romas. Once you understand the process and have the equipment, try San Marzanos if you want to experiment with flavor. The technique is identical — the only difference is the tomato itself.

How to choose tomatoes at the market or farm stand

Look for tomatoes labeled as Roma, San Marzano, or paste tomatoes. If the label does not specify, ask the farmer or produce manager what variety it is. A good question is: "Are these good for sauce, or are they eating tomatoes?" A farmer selling paste tomatoes will know when ready what you mean.

Pick tomatoes that are fully red, not orange or pink. A tomato that is not fully ripe will have less sugar and more acid, which affects flavor. Press gently with your thumb — the tomato should give slightly but not feel mushy. Avoid any with soft spots, cracks, or blemishes, because damaged areas can harbor bacteria that survive the canning process.

Buy tomatoes the day before you plan to can, or the morning of. Tomatoes that sit in the refrigerator for more than a day lose flavor and can develop a mealy texture. If you are buying from a farmers market, ask when the tomatoes were picked — same-day harvest is ideal.

Growing paste tomatoes in your garden

If you plan to can regularly, growing your own tomatoes saves money and gives you control over ripeness and variety. Roma and San Marzano seeds are available from most seed catalogs. Start seeds indoors six to eight weeks before your last spring frost, then transplant seedlings outside once the soil is warm.

Paste tomatoes need full sun (at least six hours daily), consistent water, and well-draining soil. They are less fussy than heirloom slicing tomatoes and tolerate heat better. Stake or cage the plants to keep fruit off the ground. Harvest tomatoes when they are fully red but still slightly firm — they will soften a bit as they sit, but you want them firm enough to handle without bruising.

A single Roma plant produces 100 to 150 tomatoes over a season. For a year's worth of canned sauce, plan on 10 to 15 plants. If you do not have garden space, paste tomatoes grow well in large containers (five gallons or bigger) on a sunny patio or balcony.

Tomato varieties to avoid for canning

Cherry and grape tomatoes are too small and too watery. You would spend more time processing them than cooking them down. Beefsteak and heirloom slicing tomatoes have beautiful flavor but are 80 percent water — they are meant to be eaten fresh, not reduced into sauce. Green tomatoes (unripe tomatoes picked before frost) are too acidic and do not develop the sweetness that makes canned sauce pleasant.

If you have access to only slicing tomatoes, you can use them, but understand that the yield will be low and the cooking time will be long. It is not impossible — it is just inefficient. For canning, efficiency matters because you are working with large quantities.

Frequently Asked Questions

Can I use a mix of Roma and San Marzano tomatoes?

Yes. Mixing varieties is common and works well. San Marzanos add flavor, and Romas add volume and consistency. A blend of 60 percent Roma and 40 percent San Marzano gives you good flavor without the full cost of all San Marzanos. The cooking time and technique stay the same.

What if I can only find tomatoes at the grocery store, not at a farmers market?

Grocery stores usually stock Roma tomatoes year-round, and they work fine for canning. They may not have as much flavor as farmers market tomatoes because they are picked earlier and shipped long distances, but the technique is identical. Avoid tomatoes that have been refrigerated for weeks — they lose flavor and texture. Buy them the day you plan to can.

Do I need to peel the tomatoes before canning?

For whole canned tomatoes, peeling is optional but common. For sauce, you will strain the tomatoes anyway, so peeling first saves a step. To peel, blanch tomatoes in boiling water for 30 to 60 seconds, then plunge them into ice water. The skin slips off easily. Paste tomatoes have thinner skins than slicing tomatoes, so peeling is faster.

How many tomatoes do I need to fill one quart jar?

For whole canned tomatoes, plan on three to four pounds per quart jar. For sauce, plan on three to four pounds of fresh tomatoes to yield one pint of finished sauce, because sauce reduces significantly during cooking. The exact amount depends on how watery your tomatoes are and how thick you like your sauce.

Can I can tomatoes that are not quite fully ripe?

Fully ripe tomatoes have better flavor and higher acid content, which is important for safe canning. Tomatoes that are orange or pink instead of red are lower in acid and may not reach the acidity level needed for safe water-bath canning. Use only fully red tomatoes, or add bottled lemon juice to reach the required acidity level.