Add the butter to the jam to prevent foaming when finished.
To test if the jam is thick enough, drip a drop on the cold plate. When the drop flows all sides, the jam is not yet thickened enough. When the drop sets, the jam is ready. It can then be poured into the pots. Make sure you keep the plate in the refrigerator in between so it's very cold.
You sterilize the jars for the jam sufficiently by immersing them in boiling water and drying them with a clean tea towel or washing them in the dishwasher (just screw the lid on immediately when you take them out).
After the jam has been poured into the jars, turn them upside down to ensure that no air is added (this will make it airtight and prevent the jam from spoiling as quickly).
Sterilize the jars.
Put a plate in the fridge and let it get cold for at least 1 hour. You will use this plate later to check whether the blackberry jam has thickened sufficiently.
Wash the blackberries under running water in a colander.
Blackberry juice with a hint of oregano
Put the blackberries in a pan together with the oregano and the water and stir well.
Bring the pan to a boil and reduce the heat to low.
Simmer for 5 minutes, then mash the blackberries with a fork.
Simmer for another 15 minutes.
Use a fine sieve and collect the juice from the blackberries. You can discard the skins, seeds, and oregano.
Clean the pan.
Blackberry jam with oregano
Put the blackberry juice in a measuring cup and, if necessary, makeup to 3 ¾ cups (800 ml) with water.
Add the juice, butter and pectin, and sugar to the pan and bring to a boil over high heat.
Boil well for 2 minutes. Should foam still form, blot it away with a paper towel.
Pour a layer of about 1 cm into a clean pot. Wait 1 minute and then fill the jar. Turn the lid on the jar and turn it upside down. Let cool to room temperature. Fill all the pots like this.