When you brew alcohol (ethanol) a small amount of methanol is also made. Methanol is toxic, attacking the optic nerve and making you blind. (Hence the phrase blind drunk).
The methanol boils off first. So if you distill whatever you make, its essential to monitor the vapour temperature and discard the first spirit (about 5% of your total distillate) after it boils off. You know this because while the first fraction boils off the temperature remains constant (I can't remember the bpt methanol... something like 50-60 degrees.) When the vapour temp is around 70-77ish degrees (again dodgy memory) that's when you're getting ethanol for consumption.
Also make sure you have no rubber bungs in the line because it will taint the flavour.
Not that I ever did this in my science lab officer.