According to the instructions, I soaked the farro for 8 hours and then dumped out the water. But, I didn't get it a chance to cook it right away. Four days after I dumped the water out of the farro, where its still somewhat wet, is it safe to cook it or should I throw it away?
There's an odor to the farro, but I don't know if it means its bad or if that's how its supposed to smell.
I assume you refrigerated it in the meantime. It may have started down the slippery slope to fermented grain, but rinse it and see if the odor lingers. It would be a somewhat sour odor if it was starting to ferment, rather than a grainy, earthy smell that it normally has. I think if you've had it refrigerated for the four day period, it will still be fine.
Just a comment on soaking overnight: it's not really necessary and not the end of the world if you don't do it. It doesn't take long to cook, 20-40 minutes, 30 minutes for chewy, regardless of soaking. The soaking thing is for purists, to shorten cooking time to 10-15 minutes or if you're going to cook it in a rice cooker on the brown rice setting. A pressure cooker is great for reducing cooking time too, if you don't bother or forget to soak.