Late August is peak tomato harvest across most of Canada, and water-bath canning is the safe, tested way to turn a backyard glut into shelf-stable jars that last through winter. The key safety rule most first-timers miss: tomatoes must be acidified with bottled lemon juice or citric acid before canning, because today’s tomato varieties don’t reliably have enough natural acidity to make water-bath canning safe on their own. Skip that step and you risk botulism, a rare but serious illness that can grow in improperly acidified, low-oxygen canned food.
With grocery prices still elevated, a well-stocked pantry of home-canned tomatoes is also a real budget win — and a satisfying way to use up a bumper crop before frost. Here’s how to do it correctly, following guidance from Canada’s Bernardin Home Canning and the U.S. National Center for Home Food Preservation (NCHFP), the two most widely cited authorities on tested, safe canning methods.
1. Gather tested equipment — don’t improvise
You’ll need a large water-bath canner (or a deep stockpot with a rack, so jars don’t sit directly on the bottom), mason jars rated for canning, new sealing lids (bands can be reused, but flat lids should be new each time), a jar lifter, a wide-mouth funnel, and a bubble remover or clean chopstick. Inspect jars for cracks or chips on the rim, which can prevent a proper seal.
2. Choose and prep your tomatoes
Use ripe, firm tomatoes with no soft spots, mould, or damage — quality in is quality out. Wash them, then blanch in batches: dip in boiling water for about 60 seconds, just until the skins split, then plunge immediately into a bowl of cold or ice water. The skins should slip off easily by hand. Core the tomatoes and trim away any bruised or discoloured flesh.
3. Acidify every jar — this is the non-negotiable step
Because tomato acidity varies by variety and ripeness, both Bernardin and the NCHFP require added acid in every jar, every time, regardless of how acidic your tomatoes taste. For quart (1 L) jars, add 2 tablespoons of bottled lemon juice or ½ teaspoon of citric acid; for pint (500 mL) jars, use 1 tablespoon of bottled lemon juice or ¼ teaspoon of citric acid. Always use bottled lemon juice, not fresh-squeezed — its acidity is standardized, while fresh lemons vary. Add the acid to the jar first, before packing in tomatoes.
4. Pack the jars
Pack the whole, halved, or quartered tomatoes into the hot, acidified jars, pressing gently to fill gaps, and cover with hot water, tomato juice, or the tomatoes’ own juice. Leave ½ inch (1 cm) of headspace at the top of the jar. Slide a bubble remover or clean chopstick around the inside edge to release trapped air pockets, then check and adjust the headspace again.
5. Wipe, seal, and load the canner
Wipe the jar rim with a clean, damp cloth — any food residue on the rim can prevent a proper seal. Centre a new lid on the jar and screw the band down until it’s fingertip-tight, not cranked hard. Using a jar lifter, lower the jars into the canner’s rack, keeping them upright, and make sure they’re covered by at least 1 inch (2.5 cm) of water.
6. Process for the correct time
Bring the water to a rolling boil and start timing once it’s fully boiling. At sea level, the NCHFP recommends processing pint jars of tomatoes packed in their own juice for about 40 minutes and quart jars for about 45 minutes; times vary slightly depending on the specific recipe and whether tomatoes are raw- or hot-packed, so follow the timing on a current, tested recipe from Bernardin or NCHFP for your exact method. If you live above 1,000 feet (300 m) elevation — much of interior B.C., Alberta, and parts of the Prairies — you’ll need to add extra processing time; both Bernardin and NCHFP publish altitude adjustment charts.
7. Cool, check seals, and store
When processing time is done, turn off the heat and let jars sit in the canner for five minutes before removing them with a jar lifter onto a towel, away from drafts. Don’t retighten the bands. Let jars cool undisturbed for 12 to 24 hours, then press the centre of each lid: if it doesn’t flex or pop, it’s sealed. Remove the bands, wipe the jars down, label with the date, and store sealed jars in a cool, dark place for up to a year. Refrigerate and use promptly any jar that didn’t seal.
A note on what this guide doesn’t cover
This guide covers water-bath canning of acidified tomato products only. Low-acid vegetables, meats, and some tomato-mixed recipes (like many salsas and some sauces with added low-acid ingredients) require a pressure canner instead, using different times and pressures — using a water bath for those foods is not safe. If you’re canning anything beyond plain acidified tomatoes, look up a current tested recipe specific to that product before you start.
Canning is one of the most rewarding ways to make a Canadian garden’s short season last all winter, and the process itself is simple once you’ve done it once or twice. The one rule worth memorizing: acidify every jar, every time, and always work from a current tested recipe rather than a family method passed down before today’s food safety guidance existed.
Sources: Bernardin Home Canning; National Center for Home Food Preservation, “Canning Tomatoes”; Healthy Canning, “Acidifying Tomatoes for Safe Home Canning”.
