Start by pitting the sour cherries.
Save a handful of the pits and put them in a cheesecloth.
Add the sugar over them and let them sit overnight.
In the morning you will notice that the sugar has dissolved, and the cherries are now sitting in their own juice.
Add the lemon juice and mix.
Put the sour cherries with their juice and the cheesecloth with the pits, in a large pot.
Turn the heat to medium and place the pot on the stovetop.
Once the jam starts boiling, you will see a foam forming on top. Clear it with a spoon. This is formed by sugar impurities.
Mix occasionally, to prevent sticking – but be gentle, so you don’t break the fruit.
The jam is ready when the temperature reaches 106 degrees Celsius. The jam will change its colour to a deep red.
Meanwhile, sterilise the jars.
Wash them and their lids very well with soap and water.
Put them on a tray whilst wet and place it inside the cold oven.
Turn the heat on to 150 degrees Celsius and let them dry inside for 12-15 minutes.
Once the jam is ready and the jars are sterilised, it’s time to can it.
Carefully place each jar on a metal surface and start filling it with jam until the rim.
Put the lid on and turn the jar upside down.
Let the jam cool down slowly.
Once the jars are cold, store them in your pantry. They will last for years.