How would brewing/distilling your own ethanol through fermentation create methanol? I've heard about methanol contamination, but I've always though it came about by adulteration (someone adding methanol).
When you think about the fermentation process, there isn't really a mechanism to create large quantities of methanol.[1] Yes, there are often traces of methanol and other longer-chained alcohol, but nothing that would be toxic.
If you're fermenting fruits and then distilling them, methanol is the first ingredient to boil out -- the first batch of distilled material will have nearly all of the methanol in the entire run. The background amount of methanol might be very small (<1% in most fruits), but the distilling process necessarily concentrates it and could easily provide a lethal dose if you're working on large volumes.
The very first cut (the "foreshots") really smell like something you shouldn't consume due to the presence of acetone and some other compounds that are detectable in very small concentrations.
When you think about the fermentation process, there isn't really a mechanism to create large quantities of methanol.[1] Yes, there are often traces of methanol and other longer-chained alcohol, but nothing that would be toxic.
[1] http://homedistiller.org/intro/methanol/methanol