When making jam be aware that jam has its basis in sugar and pectin contained in the fruit.
When making jams its is imprtant that you have a candy thermometer. When cooking the jam insert the thermometer into the simmering fruit, when the temperature reaches 103.5 - 104.00 degrees celcius the jam is at setting point. Remove the pot from the stove and bottle the jam into sterilised jars. The jam will set at this temperature and bew the right consistency.