• Wash the blueberries and remove any spoiled ones. Divide the berries between the jars, about 200 g/ 7 oz berries into each jar if using jars with a capacity of 350 ml/ 12 fl.oz/ 1 ½ cups. If using smaller or larger jars, fill them accordingly, leaving about 2 cm/ ½ inch headspace.

With sugar:

• Pour the water into a saucepan and add the sugar and the lemon juice. Slowly bring to a boil while stirring often to help dissolve the sugar. Let bubble once and remove from the heat. Let cool for 5 minutes.
• Pour the syrup over the blueberries, covering them completely. Wipe the rims. Seal and can the jars.
• Process in a canner for 15 minutes (increasing time for altitude, if necessary).

Without sugar:

• Pour warm water over the berries in the jars covering them completely. Wipe the rims. Seal and can the jars.
• Process in a canner for 15 minutes (increasing time for altitude, if necessary).

Can with a canner:

• Fill a canner about half full of water. Bring to a boil and lower the jars into the water one at a time with a jar lifter or use the canning rack of the canner to lower all the jars into the water at once. The water should cover the jars by 2 ½ to 5 cm/1 to 2 inches. If not enough, add boiling water as needed.
• Bring to a boil, cover, and boil for 15 minutes, increasing time for altitude, if necessary. Let stand for 5 minutes in the pot.
• Remove with mitts and a jar lifter and let cool completely on folded kitchen towels or cutting boards and let cool completely.

Can without a canner:

• Use a large pot that will allow the jars to stand in it and be completely covered with water. Place a clean kitchen towel on the bottom of the pot. Place the jars on the towel making sure that they don't touch each other.
• Cover with hot water. Bring to a boil, lower the heat, and can the jars for 15 minutes, adjusting for altitude, if necessary. Let stand for 5 minutes in the pot.
• Remove from the pot using a jar lifter and mitts. Place on folded kitchen towels on the counter and let cool completely.
  
• Refrigerate any jars that didn't seal for up to 3 weeks. Store the sealed ones in a dark cool place, they will keep for at least 6 months and up to 1 year.