The percentage of sugar for complete preservation of fruits in jam is

The percentage of sugar for the complete preservation of fruits in jam is 70%.
Jam should have a fruit content of at least 40 percent and a total sugar content of not less than 68 percent to prevent mould growth after opening the jar. Jams contain 0.5 - 0.6 percent acid and inverted sugar should not be more than 40 percent.
The abundance of sugar helps mask the sour taste of the citric acid found in the lemon juice.