Using a vegetable peeler, remove the zest from the lemons in wide strips, leaving the bitter white pith behind. Squeeze the lemon juice through a strainer into a large, wide saucepan.
Add 3 1/2 cups blueberries, the lemon zest, maple syrup and sugar and cook over medium-high heat, stirring, until the sugar dissolves, 6 to 7 minutes. Reduce the heat to medium and cook, stirring occasionally, until a candy or deep-fry thermometer registers 220 degrees F, 30 to 40 minutes (reduce the heat if the mixture is sticking to the pan). Remove from the heat.
Meanwhile, sterilize four 8-ounce canning jars and lids.
Return the blueberry mixture to medium-high heat. Bring to a boil, stirring, then add the remaining 4 1/3cups blueberries. Reduce the heat to medium low and simmer until those berries are tender but still hold their shape, 7 to 10 minutes.
Fill the jars with the blueberry mixture, leaving 1/4 to 1/2 inch headspace, then seal and process.
Photograph by Charles Masters
Properly handled sterilized equipment will keep canned foods in good condition for one year. Making sure hands, equipment and surfaces in your canning area are clean is the first step in canning. Tips: Jars should be made from glass and free of any chips or cracks. Preserving or canning jars are topped with glass, plastic or metal lids that have a rubberlike seal. Two-piece metal lids are most common. To prepare jars before filling: Wash jars with hot, soapy water, rinse them well and arrange them open-side up, without touching, on a tray. To sterilize jars, boil them in a large saucepan, covered with water, for 10 minutes. Jars have to be sterilized only if the food to be preserved will be processed for less than 10 minutes in a boiling-water bath or pressure canner. To sterilize jars, boil them in a large saucepan, covered with water, for 10 minutes. Follow manufacturer's instructions for cleaning and preparing lids and bands. Use tongs or jar lifters to remove hot sterilized jars from the boiling water. Be sure the tongs are sterilized too: Dip the tong ends in boiling water for a few minutes before using them. All items used in the process of making jams, jellies, preserves and pickles must be clean, including any towels and especially your hands. After the jars are prepared, you can preserve the food. It is important to follow any canning and processing instructions included in the recipe and refer to USDA guidelines about the sterilization of canned products. Find Information information on canning can be found at the National Center for Home Food Preservation website: http://nchfp.uga.edu/.