Foreshots, how to determine when to collect?

[bh2win]

Hi there,

I'm a novice distiller and I'd like some quick help on how to determine how much foreshots needs to be collected before I can start collecting my first running? I know the FS has methanol and can contain acetone in it as well, is there an old grandaddy trick such as a fire test? Or chemical test? Or is it purely based off smell? Any information would be helpful. I just don't want to collect bad stuff for obvious reasons.

-bh2win