Mix cherries, brown sugar, the zest and juice of the lemon and ginger (if used), then let stand in the fridge for 12 to 24 hours.

Place the cherries along with their juice in the bread machine or in a large pan and add the agar-agar powder. Start the "jam" program and wait for the end or bring the pan to the boil and simmer for an hour, stirring occasionally to avoid sticking to the bottom.

Turn off the bread machine or the fire and mix with an immersion blender; pour the jam immediately in clean and sterilized glass jars, close the lid tightly and allow the jars to cool upside down.

Once the jars are cool check them by pressing the lids at the center: you should not hear a "click". If so the vacuum is formed and you can store your jam in the pantry for up to one year.