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  1. Cooking

Canning 101: How to make preserved jams and vegetables

Round up and finely chop 5 pounds of tomatoes for Tomato Jam. You’ll end up with about 3 pints.
Round up and finely chop 5 pounds of tomatoes for Tomato Jam. You’ll end up with about 3 pints.

Canning is a way of preserving food in airtight containers that don't need to be refrigerated. By filling jars with food then boiling them in a hot water bath, they can be stored at room temperature for a year or more. This is a way to enjoy seasonal foods, especially summer produce, year-round. Homemade jam is a popular item to can, but vegetables can also be preserved in cans when pickled.

What you need

Canning jars, like mason jars, that have two-part lids: One part is a flat lid part with rubber on the bottom, and the other is a ring.

Canning tongs. Grocery stores and hardware stores should have these; they're not really the same as kitchen tongs.

A pot that is a couple of inches taller than the jars you're using.

Something to set the jars on inside the pot so they don't touch the bottom — like a canning rack, or a round cake cooling rack.

A wide-mouth funnel, which makes it easier to get the jam into the jars.

Wooden skewers or chopsticks, for getting air out of the jars.

Labels (even masking tape works) to mark what's inside each jar and when you made it.

How to can

The easiest method for beginner canners is the boiling-water method. It doesn't require a lot of equipment (all of it is listed above) and it works on acidic foods or ones bolstered with vinegar, such as fruit jams, pickled vegetables and salsas.

When following canning recipes, it's important to be precise. Improvising or changing the amounts of ingredients could result in a product that won't set properly, or worse, one that breeds bacteria. When making fruit jams, the basic steps are the same: Cut fruit into smaller pieces, mix with sugar and cook down, add pectin (a thickening agent that is sometimes used in jam-making but not always), then add to jars. Vegetables get mixed with vinegar — before going into jars.

Here is a basic recipe to get you started.

Tomato Jam

Wash and dry jars, lids and bands.

Fill your pot half-full with water and let it simmer while food is being prepared.

Prepare food: Combine 5 pounds finely chopped tomatoes, 3 ½ cups sugar, 8 tablespoons lime juice, 2 teaspoons freshly grated ginger, 1 teaspoon cinnamon, ½ teaspoon ground cloves, 1 tablespoon salt and 1 tablespoon red chili flakes in a large pot. Bring to a boil and then reduce temperature to a simmer. Stirring regularly, simmer until it reduces to a jammy consistency. This will take between 1 and 1 ½ hours, depending on how high you keep your heat.

When the jam has cooked down sufficiently, remove from heat and fill jars, leaving ¼ inch of head space (the space between the food and the lid of the jar). Wipe rims, apply lids and twist on rings.

Transfer jars to canning pot with the boiling water, placing the jars on the rack on the bottom of the pan. Leave the jars in there for 20 minutes. Remove jars from pot using tongs. Let sit for 12 to 24 hours, then test the lids: To make sure the lid is sealed, remove the band and try to lift the lid off. If the lid stays put, the jar was sealed successfully.

Store in a dry, cool place.

Makes about 3 pints.

Recipe adapted from and