Sour Cherry and Currant Jam

Cherries are unusually low in pectin, the naturally occurring substance that thickens fruit into a jamlike consistency. Because of this, it is necessary to add extra pectin, and extra sugar as well, for cherry jam to set. I tried for more than twenty years to make a cherry jam without adding the tons of sugar required by the added pectin. Because currants are so high in natural pectin, which does not require extra sugar, and because they blend so well with the cherries in my