If making raspberry ... sterilised jam funnel is very useful) and twist the lids on while the jam is still hot. The jam will thicken up as it cools and the seal on the jars should dip.

Variation: Raspberry And Kirsch Jam: Make the jam as above, stirring in 2 to 3 tablespoons Kirsch (or to taste) to the jam just after setting point has been reached. Recipe from Jam, Jelly ...