Selecting Fruit

• As with all fruits destined for jelly jars, you should use high-quality blueberries that were properly cleaned and washed before freezing. This means they should contain no stems or blemishes and show no signs of freezer burn, as this could affect the taste of the jelly. You can use berries you picked yourself or bought from a farm stand or farmers market, or you can use commercially frozen berries from the grocery store. Have all your jelly-making equipment ready when you prepare the frozen berries, as they don't retain their freshness long after thawing.

Preparation

• Blueberry jelly can be made from fresh or frozen berries for immediate or short-term use or for long-term storage. Which you choose determines the equipment you will need. For short-term storage, you will need a large kettle to cook the blueberries in, a long-handled spoon to cook the mixture, a jelling product that contains pectin, and jars in which to can the jelly. You will also need a jelly bag to drain the cooked blueberry pulp of its juice. This can be a cheesecloth bag that hangs from a rack that you can fit over a large bowl or a large strainer or colander lined with a double layer of cheesecloth and placed over a bowl.

Cooking and Straining the Berries

• If you're using frozen blueberries to make jelly, allow them to thaw just until they have a wet sheen and no frost residue. Leaving them at room temperature too long may cause them to collapse, making them more difficult to measure. A small amount of water, roughly 1/2 cup water to each 10 cups of berries is necessary so the berries don't stick to the pot during cooking, which separates the juices from the pulp. Drain the solids through the jelly bag or cheesecloth for a final extraction of juice.

Cooking the Jelly

• If time is a factor, the strained blueberry juice from the frozen berries can be refrigerated for up to two days before making the jelly. Making jelly without pectin, a substance found naturally in most fruits and berries, involves cooking the juices to the gelling point, or 220 degrees Fahrenheit on a candy thermometer. The pectin label will usually note how much sugar you need to add.

Processing

• Cooled jelly that has not been processed in a water bath can be stored in the refrigerator for up to three weeks, while jelly processed in a water bath can be stored for up to one year. Processing times for canning pints of blueberry jelly vary depending on altitude, but it's usually five to 15 minutes.