Food Preservation: Why is my jelly always too soft?

Why is my jelly always too soft?

Overcooking the fruit to extract the juice could make the jelly too soft. Try to avoid overcooking because this lowers the jellying capacity of the pectin.
Using too much water to extract the juice could make jelly soft. Use only the amount of water that is suggested in the instructions.
The jelly could be soft because of incorrect proportions of the sugar and the juice. Always follow the recommended proportions.
Undercooking could cause insufficient concentrations. Cook the jelly rapidly to a jellying point.
Having insufficient acid content could make the jelly soft. Lemon juice can sometimes be added if the fruit is acid deficient.
The jelly could be soft if you make too large of a batch at one time. Use only 4 to 6 cups of juice in each batch of jelly.