How to Can Tomatoes

Use only commercial canning jars; they are made of tempered glass that can withstand the heat of processing. Discard any jars with chips and cracks.

To sterilize jars, place on rack in canner and cover with water. Bring to a boil and boil for 15 minutes at altitudes of 1001 - 3000 ft (Edmonton’s altitude is 2200 ft/671 m). See Caution! Altitude Adjustments at the top of this page.

Sterilizing jars in an oven or dishwasher is not recommended. Heating glass jars in an oven subject them to uneven temperature extremes and can result in breakage. Dishwasher temperatures may not be high enough or time period long enough for sterilizing jars.

Two-part metal canning lids need to be prepared before using. Refer to specific manufacturer's instructions on treating lids.

Lids can be used only once but screw bands can be reused as long as they are in good condition.

Do not reuse lids from commercially canned foods for home canning.

Select disease-free, preferably vine-ripened, firm tomatoes. Do not use tomatoes from dead or frost-killed vines.

Prepare tomatoes according to instructions in recipes.

Prepare only the amount of tomato or tomato product that can be processed at one time.

Tomatoes may be packed raw or preheated and packed hot into jars. Follow specific directions as given in each recipe.

If given a choice, the hot pack method produces a higher quality product.

Fill hot sterilized jars, one at a time, leaving specified headspace.

To remove air bubbles, slide a non-metallic utensil, such as a narrow rubber spatula or plastic knife, between the food and sides of the jar. Add more liquid to obtain proper headspace, if necessary.

Wipe jar rims thoroughly with a damp cloth.

Place heated lid on jar. Screw two-part metal canning lids down fingertip tight; do not adjust lids after processing. Screw metal bands with glass lids down tightly and then turn back 1/2 inch; retighten band when the jar is removed from canner.

Place filled jars on a rack in a canner containing hot or simmering water. For raw pack, have water in canner hot but not simmering. For hot pack, have water simmering. Add boiling water if necessary to cover jars by 1 - 2 inches. Do not pour water directly on glass jars.

Cover the canner and start to count time when water returns to a full rolling boil. Boil gently and steadily for the recommended processing time adding boiling water if necessary to keep jars covered.

Remove jars immediately from the canner when processing time is completed. Place jars on a rack, dry towels or a cutting board. Leave space between jars and allow to cool, undisturbed, away from drafts. Do not invert jars or seals may be broken.

After 24 hours, check to see if lids have sealed. A good vacuum seal is one in which the lid curves downward. Tilt jars with glass lids on their sides. If jars do not leak, they have sealed.

Treat any unsealed jars of tomatoes as fresh. Tomatoes may be eaten immediately, refrigerated, frozen or recanned. If recanning food, the whole process must be repeated within 24 hours.

Label sealed jars with contents and date. Screw bands may be removed from cooled jars. Store jars in a cool dry place for up to one year.

Caution! Altitude Adjustments

The times given in this publication for processing tomato products are for canning in the Edmonton area (Edmonton’s altitude is 2200 ft/671 m).

If canning outside the Edmonton area, adjustments in time and pressure may be necessary for different altitudes. For altitudes higher than 3000 ft/914 m (Banff, Calgary, Jasper, Lethbridge areas), add 5 minutes to sterilizing and boiling water bath processing times.

To ensure the safety of whole, crushed or juiced tomatoes, they must be acidified regardless of the processing method used.

Citric acid, bottled lemon juice or vinegar may be used. However, citric acid is preferable, as it does not contribute any additional flavour. Vinegar may cause undesirable flavour changes. Sugar may be added if the product is too acidic.

Pints: Use 1/4 tsp citric acid or 1 tbsp bottled lemon juice or 2 tbsp vinegar and 1 tsp sugar (sugar optional)

Quarts: Use 1/2 tsp citric acid or 2 tbsp bottled lemon juice or 4 tbsp vinegar and 2 tsp sugar (sugar optional)

Pickling salt may be added for seasoning if desired but does not help to preserve the food. Use 1/2 tsp per pint or 1 tsp per quart.