Steam canning tomatoes is safe only for acidified tomato products whose tested boiling-water processing time is 45 minutes or less, including the extra time required at your elevation. That usually means hot-packed crushed tomatoes, juice, sauce, or water-packed whole tomatoes in pint jars at lower altitudes. It does not mean every tomato recipe, and it never replaces pressure canning for low-acid mixtures.
The confusion is understandable. Tomatoes sit on the line between high-acid and low-acid food. Some blogs treat a steam canner like a shortcut water bath. Others say never use one for tomatoes at all. The current research-based position is narrower than both of those claims: an atmospheric steam canner can process the same acid or acidified foods as a boiling-water canner, if several controls are met and the clock stays at or under 45 minutes.
What a Steam Canner Does — and What It Does Not Do
An atmospheric steam canner is a shallow base of boiling water under a tall dome. Jars sit on a rack above the water. Steam, not a full pot of boiling water, heats the jars.
It is not a pressure canner. Steam inside an open-vented dome stays near the boiling point of water — about 212°F at sea level, lower as elevation rises. A pressure canner reaches about 240°F, which is the temperature needed to destroy Clostridium botulinum spores in low-acid food.
That difference decides the method:
| Method | Typical temperature | Safe for tomatoes when… | Not safe for |
|---|---|---|---|
| Atmospheric steam canner | ~212°F / boiling point | Product is acidified to pH 4.6 or below and the tested time is ≤45 minutes, including altitude | Unacidified tomatoes; sauces with extra low-acid vegetables; any recipe over 45 minutes |
| Boiling-water canner | ~212°F | Same acidity rules; no 45-minute hardware limit | Low-acid mixtures that lack a tested water-bath recipe |
| Pressure canner | ~240°F | Acidified tomatoes (still add acid) and many tomato-vegetable mixes | Using a pressure cooker or multi-cooker that is not a tested canner |
Steam canning’s practical advantages are real: less water, faster come-up time, and less heavy lifting. The tradeoff is the water reservoir. Once the base runs dry, processing stops and the food is under-processed. That is why the 45-minute ceiling exists. Do not lift the lid to add water mid-process.
Which Tomato Products Fit a Steam Canner
Use only a current, tested boiling-water recipe and then process it in steam instead of water. Manufacturer booklets that come with the canner are not a substitute for those recipes.
Usually suitable at many elevations
- Hot-packed crushed tomatoes (no added liquid)
- Tomato juice
- Standard tomato sauce made from tomatoes only
- Whole or halved tomatoes packed in water (pints more often than quarts)
- Some tested salsas and ketchup, if the published time stays under 45 minutes after altitude adjustment
Not suitable in a steam canner
- Whole or halved tomatoes packed raw with no added liquid (85 minutes at 0–1,000 ft)
- Whole or halved tomatoes packed in tomato juice (also a long water-bath time)
- Spaghetti sauce with extra vegetables or meat (pressure-canner recipes)
- Any “family sauce” that adds untested amounts of onion, pepper, carrot, mushroom, or oil
- Quart jars of crushed tomatoes once altitude pushes the time past 45 minutes
The 45-minute limit includes altitude. A recipe that is 35 minutes at sea level can become 45 or 50 minutes in the mountains. If the adjusted time exceeds 45 minutes, switch to a water-bath or pressure canner.
Why crushed tomatoes are the usual steam-canner choice
Hot-packed crushed tomatoes have a short, tested water-bath schedule because they start hot and are already broken down:
- Pints: 35 minutes at 0–1,000 ft; 40 minutes at 1,001–3,000 ft; 45 minutes at 3,001–6,000 ft; 50 minutes above 6,000 ft
- Quarts: 45 minutes at 0–1,000 ft; then 50, 55, and 60 minutes as elevation rises
That means pint crushed tomatoes work in a steam canner through 6,000 feet. Quart crushed tomatoes only stay inside the 45-minute cap at 1,000 feet and below.
Acid Is Not Optional
Modern tomato varieties, overripe fruit, and fruit from dying vines can have a pH above 4.6. Botulism spores cannot grow in food at pH 4.6 or below, which is why acidified tomatoes can be processed at boiling-water temperature. Without added acid, that safety margin disappears. Add acid even if you later pressure-can the same jars.
Add the acid to each empty jar before filling:
| Acid | Per pint | Per quart |
|---|---|---|
| Bottled lemon juice | 1 tablespoon | 2 tablespoons |
| Citric acid | 1/4 teaspoon | 1/2 teaspoon |
| Vinegar, 5% acidity | 2 tablespoons | 4 tablespoons |
Use bottled lemon juice, not fresh. Fresh juice varies in acidity. Vinegar is allowed at those amounts but often makes the flavor sharper. A pinch of sugar can soften the taste; salt is optional and only for flavor.
Skip tomatoes from frost-killed or dead vines. Green tomatoes are more acidic and can be canned with the same acid and process as ripe fruit, with a different flavor.
Equipment That Actually Matters
You need:
- An atmospheric steam canner with a rack and a dome that vents steam
- Standard two-piece metal lids and mason jars (pints or quarts as the recipe allows)
- A jar lifter, funnel, and bubble remover
- A thermometer that can read steam at the vent hole
- Bottled lemon juice or citric acid
- Enough ripe, sound tomatoes — roughly 2 1/2 to 3 1/2 pounds per quart, depending on variety and pack
Preheat jars. Cold jars plus a long wait on the counter before processing is one of the controls researchers flagged as a problem. Fill hot food into hot jars and move them into the canner without a long cool-down.
Do not use one-piece lids, oven canning, dishwasher “canning,” or an electric multi-cooker sold as a pressure cooker. Those methods are not tested for this job.
How to Steam Can Crushed Tomatoes
This follows the National Center for Home Food Preservation crushed-tomato procedure, processed in steam instead of a water bath.
1. Prep the fruit. Wash firm, unblemished tomatoes. Dip in boiling water 30 to 60 seconds until skins split, then into cold water. Slip off skins, core, and trim bruises. Quarter.
2. Heat and crush. Put about one-sixth of the quarters in a wide pot and crush them as they heat so juice covers the bottom. Bring to a boil, then add the remaining quarters gradually, stirring so nothing scorches. The later pieces do not need crushing; heat will soften them. Boil gently 5 minutes.
3. Acidify the jars. Add lemon juice or citric acid to each hot jar using the table above. Add salt only if you want it.
4. Fill. Ladle hot tomatoes into hot jars, leaving 1/2-inch headspace. Remove air bubbles. Wipe rims. Apply lids and bands fingertip-tight.
5. Load the steam canner. Put the manufacturer’s specified amount of water in the base — usually to just below the rack. Set filled jars on the rack. Cover with the dome.
6. Vent to pure steam before you start the clock. Heat on medium-high until a strong, steady column of steam, about 8 inches, flows from the vent. Then check temperature at the vent hole with a thermometer that is not touching a jar. Start timing only when steam reads 210–212°F at your elevation. A visible plume without that temperature check is the weaker method; the current NCHFP extra step is the thermometer reading.
7. Process for the water-bath time, not a shortened “steam time.” Hold a moderate boil so steam stays continuous. If the plume collapses, you have lost temperature. If the base boils dry, the batch is unsafe to store.
8. Rest, then cool in still air. When time is up, turn off the heat. Leave the lid on for 5 minutes. Remove jars without tilting them. Cool upright on a towel, away from drafts and fans. Slow cooling is part of the calculated lethality, not an optional extra.
9. Check seals after 12–24 hours. A sealed lid is concave and does not flex. Remove bands, wipe jars, label, and store in a cool, dark place. Unsealed jars go in the refrigerator and should be used promptly, or the contents can be reprocessed within 24 hours with a new lid.
Processing Times That Stay Inside the Steam-Canner Limit
Use the boiling-water times. Cross out any row that exceeds 45 minutes at your house.
Hot-pack crushed tomatoes
| Jar | 0–1,000 ft | 1,001–3,000 ft | 3,001–6,000 ft | Above 6,000 ft | Steam canner? |
|---|---|---|---|---|---|
| Pints | 35 min | 40 min | 45 min | 50 min | Yes through 6,000 ft |
| Quarts | 45 min | 50 min | 55 min | 60 min | Only at 0–1,000 ft |
Typical nearby products (confirm the exact NCHFP table for the recipe you use)
- Tomato juice, hot pack: pints often 35 minutes and quarts 40 minutes at 0–1,000 ft
- Standard tomato sauce: similar short hot-pack times
- Whole/halved packed in water: pints about 40 minutes, quarts 45 minutes at 0–1,000 ft
- Whole/halved packed with no added liquid: 85 minutes — water bath or pressure canner only
Look up your elevation before the first batch. A kitchen at 3,200 feet is not “close enough” to a sea-level chart.
Common Mistakes That Make Steam-Canned Tomatoes Unsafe
Treating all tomato packs as the same. Raw-pack tomatoes in their own juice need a long process. Copying a 40-minute crushed-tomato time onto that pack is under-processing.
Skipping acid “because these tomatoes taste tart.” Taste is not pH. Add the measured acid every time.
Starting the timer when steam first appears. Air mixed with steam lowers temperature. Time begins after a full steam column and a 210–212°F reading.
Running the burner wide open. A violent boil can empty the base in about 20 minutes. Moderate heat that keeps a steady plume is the goal.
Opening the dome to “check the water.” That dumps heat and is not allowed during the timed process. If you are worried about a dry-out, use a water-bath canner instead.
Cooling jars in a sink, in front of a fan, or back in the fridge immediately. Forced cooling cuts the lethality that happens as jars drop through the 180°F range.
Canning sauce with extra vegetables using a tomato-only time. Onions, peppers, carrots, and mushrooms lower acidity and change density. Only tested combination recipes — and usually a pressure canner — cover those.
Using fruit from dead vines. Those tomatoes are excluded from home-canning recommendations.
When a Different Method Is the Better Choice
Choose a boiling-water canner when the tested time is longer than 45 minutes, when you are processing quarts at altitude, or when you want a larger load than the steam dome holds.
Choose a pressure canner when you want shorter process times, denser packs, or recipes that include low-acid vegetables. Acid still goes in the jar. Pressure does not cancel the acidification step.
Choose the freezer when the harvest is small, the fruit is overripe, or you do not want to manage acidity and timing. Frozen tomatoes do not need added acid.
What Finished Jars Should Look Like
Properly processed tomatoes should be sealed, reasonably filled to the original headspace, and free of rising bubbles after they cool. Separation of juice and pulp is normal, especially in crushed tomatoes. Cloudiness can come from minerals in water or starch from seeds; it is not automatically spoilage.
Discard, without tasting, any jar with a bulging lid, spurting liquid, off odor, visible mold, or unexpected fizz. Home-canned tomatoes that were under-processed are not made safe by boiling them later for dinner if botulinum toxin is already present in a sealed jar. When in doubt, throw the jar out.
Frequently Asked Questions
Can I steam-can raw whole tomatoes? Only if you use a tested raw-pack recipe whose water-bath time, after altitude adjustment, is 45 minutes or less. The common raw pack with no added liquid is 85 minutes and is not a steam-canner process.
Do I still add lemon juice if I pressure-can instead? Yes. Current guidance acidifies whole, crushed, and juiced tomatoes for both methods.
Why do some older extension pages say not to steam-can vegetables? Most vegetables are low-acid and need 240°F. Acidified tomatoes, pickles, and tested salsas are the exceptions. An Oregon Extension answer from 2023 states crushed tomatoes may be steam-canned when the water-bath time fits the 45-minute limit.
Is spoilage still possible if I follow the rules? NCHFP notes that steam canning can leave some very heat-resistant spoilage organisms alive. That is treated as a quality risk, not an illness risk, when acidity, time, steam temperature, and cooling rules are followed. Store jars cool and dark, and inspect before use.
Can I use half-pint jars? Yes when the tested recipe lists that size. Do not invent a shorter time for a smaller jar.
How long do sealed jars keep? Plan to use them within a year for best quality. Safety depends on a true seal and correct process, not on an arbitrary calendar date.
Steam canning tomatoes works when the product is acidified, the recipe is tested, the steam is hot enough, and the clock never crosses 45 minutes. If any one of those conditions fails, use a water-bath or pressure canner instead. That is the entire decision.