Step 1

Place a saucer and five metal teaspoons in a flat place in your freezer for testing the jam later. Have ready a medium-mesh strainer or chinois suspended over a heatproof bowl.

Step 2

Combine the berries and sugar in an 11- or 12-quart copper preserving pan or a wide and deep-sided nonreactive pot. Place the pan over medium-low heat and cook, stirring and mashing constantly with a heatproof rubber spatula, until the juice begins to run from the berries.

Step 3

As soon as the sugar dissolves, increase the heat to high. Continue to cook, stirring very frequently, until the mixture boils vigorously, and continue to cook for 10 to 15 minutes, stirring frequently. You'll want to begin testing for doneness after 10 minutes.☞ TESTER TIP: Watch the mixture carefully as it boils as it can easily threaten to escape the pot if the heat is too high.

Step 4

To test for doneness, remove the pan from the heat and carefully transfer a scant half teaspoonful of jam to one of your frozen spoons. Return the spoon to the freezer for 3 to 4 minutes, then remove and carefully feel the underside of the spoon. It should be neither warm nor cold; if still warm, return it to the freezer for a moment.

Step 5

Tilt the spoon vertically to see whether the jam runs; if the jam does not run, and if it has thickened to a near-jelly consistency, it is done. If the jam runs, return the pan to the stove and cook the mixture for another few minutes, stirring and testing again as many times as needed.

Step 6

Using a stainless-steel spoon, skim any remaining foam from the surface of the preserve. If you don't mind seeds in your jam, skip ahead to step If you prefer seedless jam, quickly transfer the jam to the mesh strainer and force as much of the preserve as possible through it by pressing on it with the back of the spoon.

Step 7

Discard the seeds. Skim any foam that lingers on the surface of the strained jam.

Step 8

Pour the jam into sterilized jars and process according to the manufacturer’s instructions.