[paul.fr]

Like the doc, i like toast. I like nothing better than oodles of runny margerine and jam upon it.

I have noticed that if i use the same knife for the butter and the jam, after about a week jam jam has a serious mould problem. Why would a bit of margerine, in the jam post cause this?

[DoctorBeaver]

It's not the margarine. It's because you never wash up the knife!  []

[another_someone]

Not sure if it is margerine, or toast crumbs getting back into the jam.

The point about jam is that it is a very unbalanced diet for anything to feed on - lots and lots of sugar, and not much else.  The more you mix in with that, the more balanced the diet (for the fungi as well as for the human).

You would never expect a human to survive very long on a diet of pure jam, but mixing jam with something else makes jam a useful fuel source in addition to other nutrients.  The same is generally true of bacteria and fungi (even if the exact ideal ratios might be different).

[DoctorBeaver]

Good point, George