Most jam is approximately 50 percent sugar, and occasionally sugar crystals will appear on the surface or throughout the finished jam. The jam will have a gritty texture and will often will taste excessively sweet. It is, however, still safe to eat.
The cause is almost always the same; not ensuring that all the sugar was fully dissolved in the jam before the final boil to setting point. If the mix in your preserving pan looks gritty or white, keep heating it until it goes clear and glossy.
Crystallization can be easily avoided by following three rules:
- Do not add more sugar that is needed.
- Always dissolve all the sugar before boiling the jam
- Do not under boil or over boil the jam. If a recipe has a guideline time for boiling, stick to it, and once the setting point is reached, don’t continue to boil the jam.