These recipes use High Methylester Pectin or no pectin at all to achieve a firm set with typically equal quantities of sugar and fruit, by weight.
High Methylester Pectin:
Green Living Australia’s Classic Pectin is a rapid set, high methylester pectin. It can be used in traditional jams that use significant amounts of sugar, ensuring that its soluble solids are high enough to form a gel. A regular high methylester pectin jam contains approximately 65% sucrose. (The Chemistry and Technology of Pectin, Reginald H. Walter, Page 31) Some of this sugar comes from the fruit itself, with the rest coming from the added sugar. This is why the traditional jam recipe is one kilogram of fruit to one kilogram of sugar.