How to Make Tomato Ketchup in Canada (Water-Bath Method)
Homemade tomato ketchup is safe to water-bath can because it is acidified with vinegar. Cook sieved tomatoes down with a spice bag, sugar, and salt until thick, then add the full amount of vinegar your tested Bernardin recipe calls for — never reduce it, because the vinegar is what keeps the ketchup below pH 4.6 and safe. Hot-pack into small jars leaving 1 cm headspace, apply two-piece lids, and process in a boiling water bath for the time and altitude band in your Bernardin recipe.
Homemade tomato ketchup is a September project worth doing at least once — it’s deeper and less sweet than the bottle, and it’s the best thing to do with the last of a paste-tomato glut. It’s also, quietly, an acidified canning recipe, which means the safety rules are stricter than they look.
This guide covers the water-bath method following Bernardin and Health Canada. Per our food-safety policy we cite Bernardin for exact vinegar amounts and processing times rather than reprinting them — this is a recipe to make from a tested edition, with this page explaining the how and why.
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The rule that keeps ketchup safe: don’t cut the vinegar
Ketchup is mostly tomatoes and onions — both low-acid enough that, on their own, they’d need pressure canning. What makes ketchup safe in a boiling-water bath is the vinegar, added in a tested amount that brings the whole batch reliably below pH 4.6.
Use the full vinegar amount your tested Bernardin recipe calls for. Never reduce it to make the ketchup milder.
This is the same logic as why you can’t water-bath spaghetti sauce: low-acid ingredients are only safe in the boiling-water bath when a tested recipe acidifies the whole batch. Sugar and salt you can adjust to taste — they’re flavour, not safety. Vinegar is safety.
What you need
- About 5.5 kg (12 lb) ripe paste tomatoes — Roma or San Marzano thicken far faster than watery field tomatoes
- One onion, plus whole pickling spices for a spice bag (cinnamon, cloves, allspice, celery seed)
- White vinegar at 5% acidity — the amount in your tested recipe
- Sugar and salt to taste
- A food mill or fine sieve, and a wide, heavy pot for reducing
- 250 mL Bernardin jars with new SNAP lids — ketchup keeps best in small jars
Sieves the skins and seeds out of the tomatoes for a smooth ketchup, no peeling. Three discs also handle applesauce and berry jam. The default Canadian pick for a tomato glut.
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The method (mostly hands-off simmering)
- Sieve. Simmer quartered tomatoes and onion until soft, then run through a food mill to remove skins and seeds.
- Reduce with the spice bag. Return the purée to a wide pot, add the tied spices, and simmer gently — stirring often so it doesn’t scorch — until it’s reduced by about half and mounds on a spoon. Budget 1–2 hours.
- Season and acidify. Remove the spice bag. Stir in sugar and salt to taste, then the full amount of vinegar your recipe specifies. Simmer a few minutes to blend.
- Fill. Ladle hot ketchup into hot 250 mL jars, leaving 1 cm (½ inch) headspace. Wipe rims, apply fresh SNAP lids fingertip-tight.
- Process in the boiling water bath for the time in your Bernardin edition for ketchup, at your altitude band. Time starts at a full rolling boil.
- Cool and check. Rest 5 minutes in the canner, lift to a towel, and leave 12–24 hours before checking seals.
Common questions
It’s still thin after an hour. Keep going — ketchup reduces by half or more, and paste tomatoes get there faster than field tomatoes. Never thicken with starch for canning; it blocks heat penetration.
A jar didn’t seal. Refrigerate and use within a couple of weeks, or reprocess within 24 hours with a fresh lid. See jar didn’t seal — is it safe.
How long does it keep? Sealed, cool, and dark, about a year for best quality. See how long home-canned food lasts.
Related tomato guides
Frequently asked questions
What makes homemade ketchup safe to water-bath can?
The vinegar. Ketchup contains low-acid ingredients (tomatoes near pH 4.6, plus onions) that on their own would need pressure canning. A tested ketchup recipe adds enough vinegar to bring the whole batch reliably below pH 4.6, which is what makes the boiling-water method safe. This is why you must use a tested Bernardin recipe and never reduce the vinegar — cutting it for a milder taste can quietly turn a safe batch into an unsafe one.
Can I use less sugar or a sugar substitute in canned ketchup?
Sugar is for flavour and body, not safety, so you can reduce it or use a substitute — the ketchup will just be thinner and more tart. What you must NOT change is the vinegar, the acid that keeps it safe. If you want a low-sugar ketchup, look for a Bernardin recipe written for it rather than cutting sugar from a standard recipe, so the balance and yield still work.
Why won't my ketchup thicken?
Ketchup thickens by evaporation, and it takes a while — a batch typically reduces by half or more, which can be 1–2 hours of gentle simmering with frequent stirring. Starting with paste tomatoes (Roma, San Marzano) instead of watery field tomatoes cuts the time a lot. Don't thicken with flour, cornstarch, or other starches for canning — thickeners slow heat penetration and aren't safe in home-canned foods.
What size jars should I use for ketchup?
Small jars — 250 mL (half-pint) is standard, since a household uses ketchup slowly and a big jar sits opened in the fridge for weeks. Bernardin tests ketchup in specific jar sizes with specific processing times; use the jar size your recipe lists and don't substitute, since processing time changes with jar size.
Sources
- Bernardin Complete Book of Home Preserving (latest edition)
- Health Canada — Food safety for home canning