Sulfite: the goal is to neutralize wild yeasts in your mead must, so that they don’t give you awful off-flavors.  Brewing yeasts are carefully engineered for the way they process the honey and nutrients in your must, which is how you can get lovely citrusy overtones or floral aromas just from fermentation.  [...]

Yeast: there was a a cry for help on a brewing forum, asking why his fermentation had stopped sooner than he thought it ought to have. It comes down to whether the yeast is attenuated or not, ie; has the must stopped fermenting because it’s out of sugars or has [...]