system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does mold grow in black coffee?

If someone (not me, of course) leaves a cup of black coffee out for a few days mold starts to grow on the surface.  How does this happen?  What is the fungus attaching to? What in coffee is it's nourishment?
gpt
We’ll start with the fact that there is mold, or mold spores, in the coffee grounds before you start. And then you’re adding moisture, which mold loves, and there is acidity, and nitrogen, and all those lovely coffee oils and nutrients.