Why different self-preserved foods don’t preserve each other?

Question

As per the title, if for example butter preserves itself, and strawberry jam preserves itself, why does a blob of butter go mouldy if it’s dropped in the jam jar?

In: Chemistry

Answer 1

Jam is preserved by the ridiculously high sugar content. Butter by the high fat content. A mix of the two has neither the high enough fat content or high enough sugar content to kill mould… and so problem.