Michigan State University Extension
Preserving Food Safely - 01600548
1. Always use the full amount of sugar called for in the recipe. Reducing the amount of sugar may prevent the jam from setting up.
2. Always prepare only one batch of jam at a time. Doubling the recipe may prevent the jam from setting up.
3. Always use fresh, ripe fruit. As fruit becomes over- ripe, its natural pectin content decreases and the gelling ability of the fruit is reduced.
4. Finely chop all fruits used for making jams, but do not puree them. Pureed fruit will add too much liquid and too much fruit for a good gel.
5. Use only the type of pectin called for in a recipe. Liquid or powdered pectin may be used, but they may not be substituted for each other.