Every year at Christmas, my sister sends us jars of home-canned strawberry jam she makes in her Northern California kitchen. Opening the jam on a cold winter morning is like lifting...

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Every year at Christmas, my sister sends us jars of home-canned strawberry jam she makes in her Northern California kitchen. Opening the jam on a cold winter morning is like lifting the lid to a treasure chest of summer, with its berry aroma and garnet color filling the senses.

Store shelves are stocked with such a variety of fruit jams, it may be tempting to let someone else do the work. Why go to the trouble of making your own? The answer is that store-bought jam, no matter how good, will never compare to the flavor and quality of a home-canned preserve. Everyone should experience the incredibly fresh taste at least once.

For someone without a lot of canning experience, strawberry jams are a good starting point. Here’s how to begin.


Hand-picked berries are best, but should be used within two days for the freshest flavor. If that’s impractical, buy strawberries from a grocer or farmer’s market you trust. Insist on tasting a berry — it should be ripe but not soft and mushy, and bright red throughout. Avoid those with white or green spots showing on the exterior.

The berry’s flavor should be sweet with just a hint of tartness. Don’t purchase fruit that’s packed in plastic containers, as there’s a good chance imperfect berries will be hidden in the center. It’s better to buy them in an open flat or in bulk.

Sugars such as brown or turbinado have different densities than white, granulated sugar, and should not be used in preserves.


A standard liquid measuring cup is used for fruit and juice, and a metal, straight-topped dry measure cup for precise measurements of sugar.


The glut of mayonnaise or pickle jars collected in your cupboard may crack when heated in boiling water and are unsafe for canning. Purchase standard, mason-type canning jars from a company such as Ball. Half-pint and pint jars are best for preserves.

“Because of the short processing time, quart jars filled with jam may not heat all the way through, and spoilage may become a problem,” says Olga Fusté, with the Washington State University’s Extension Service in Pierce County. (The extension service relies on information published by the USDA.)

Jar caps can be bought separately and come in two pieces: self-sealing lids and metal ring bands. Jars and bands can be reused if they’re still in good shape, but lids should not be reused because the rubberized seal may have been damaged in earlier processing.

You’ll need two deep pots and one shallow pot. One deep pot is for sterilizing the jars. The shallow one is for sterilizing the bands and lids. The other deep pot is used as a water-bath canner with a cover and rack. A stockpot or other deep pot can be used for sterilizing, but the boiling water must cover lids by about 1 to 2 inches.

If you don’t have a rack that fits the bottom of the pot, use a clean, folded kitchen towel to protect jars from breakage.

The canner must be covered while processing; open-kettle canning is not safe because the heat conduction is not consistent.

A jar lifter is an indispensable tool. Standard tongs, such as those used for turning pieces of fried chicken, aren’t wide enough to safely grip the jars, and run the risk of slipping. Because a jar lifter’s wide grips are coated to eliminate slips, you can safely remove canning jars from hot water without splashing. A lifter runs about $5 and is sold with other canning equipment.

A few long-handled wooden spoons will protect hands from bubbling jam, and a small ladle is perfect for filling jars without spilling too much.


Making the jam

Never chop or purée fruit with a food processor or blender, which liquefies the berries and throws off the proportions of fruit to sugar.

As the jam cooks, a pale foam will rise to the surface. For preserves with beautiful, clear colors, skim off the foam with a long-handled spoon.

Making jam with pectin

Never alter the amount of sugar in a recipe. Reduced-sugar jams should be made with a pectin formulated for that purpose.

Prepare one batch of preserves at a time; doubling a recipe may prevent it from gelling.

Making jam without pectin

Allow ¾ cup sugar for every cup of fruit or juice.

Heat fruit and sugar slowly, stirring constantly until the sugar is dissolved.

Bring to a full boil and cook until a temperature of 220 degrees is reached on a candy thermometer. At that point, the mixture will “sheet” from a spoon in a succession of small drips. You also can test the jam by spooning some onto a small, cold plate. (It’s handy to set a stack of plates in the freezer before beginning the jam.) If the mixture gels, the pectin content is right.

A tablespoon or two of lemon juice is added to jams without commercial pectin because a certain acidity is needed for the fruit’s natural pectin to gel. Follow your recipe for amounts of lemon juice.

Sterilizing jars and caps

Bring a large pot of water to a boil — the water level should cover jars by about an inch. Metal bands, lids and jars must be sterilized in the boiling water 10 minutes. Hold the sterilized equipment in the hot water and remove individually when it’s time to fill each jar.

Processing the jam

Ladle hot jam into hot, sterilized canning jars, leaving ¼-inch headspace. (Headspace is measured from the top of the jam to the bottom of the flat lid.) Wipe the rim and threads of jars with a clean, damp cloth. Immediately place a hot lid on top and tighten band firmly.


As each jar is filled and capped, place it in the boiling water-bath.

When the canner is full, bring back to a steady boil and process 5 minutes. Fusté stresses, “the processing time hinges on the initial 10-minute sterilization of jars and lids. That’s important.”

Jelly, conserves and marmalades are all processed 5 minutes. (Conserves can be made with a mix of fruits, and are often studded with nuts or dried fruit. Marmalades are most often prepared with small pieces of citrus fruits and their peels.)


When finished processing, lift the jars from the canner and set on a rack or several folded kitchen towels. Don’t tighten the bands. In fact, it’s best not to move jars for at least 12 hours, as the gel could break. Then check the seal of each jar by pressing the center of the lid — it should not flex. (If it does, immediately refrigerate or reprocess with a new lid for the full length of time.)

Remove the bands and wipe jars with a clean, damp cloth. Fusté encourages us to label the preserves and store them in a cool, dry place. For maximum quality and flavor, the jams should be used within a year. As long as the seal of the jars remains intact, they can be stored up to 3 years, but the quality will begin to decline.

Once you have some canning experience, you may want to expand your repertoire. Some lovely ideas for interesting flavor combinations can be discovered in “Mes Confitures: The Jams and Jellies of Christine Ferber” (by Christine Ferber and translated by Virginia R. Phillips, Michigan State University Press).

Keep in mind, though, that many books do not comply with USDA guidelines for processing, and cooks should follow those guidelines to insure a safe product. “Why go to the time and expense of making jam and then run the risk of spoilage?” says Fusté.

Sources: Pierce County Cooperative Extension Service; University of Illinois Cooperative Extension Service; Ball home-canning products

Our three-part canning series continues in July with ideas and information on putting up stone fruits.