If you add too much yeast—over 4 grams per gallon—to your mash, you are going to get a few undesired effects. For starters, your moonshine will get a sulfuric smell and taste on some occasions. Most of the time, however, the yeast ferments until it can’t any longer then settles at the bottom of the fermenter. It is very rare that something catastrophic happens, though off-flavored alcohol may be terrifying enough.