Rinse and hull the berries. Chop or blend any big ones. Put the berries in a pan together with the jam sugar and lemon. Bring to the boil and simmer for 2-5 minutes. Do a consistency test by dropping a little jam onto a cold plate to see if the consistency is right. Remove the pan from the heat and carefully skim off any foam. Pour the jam into hot, clean jars and seal immediately. Store in a cool place.