If this is a naive question please forgive, but what is unique about the different strains of yeast that would allow them to create/impart different flavors? Is it something with the biological make-up of a particular strain or some other native charachteristic to yeast metabolism?

First let me say that it has always been a pleasure just chatting beer with you when we have met at some of the various brewing conferences over the past few years.

The questions I have are:

1) What is are the commercially available options available to the average homebrewer for adding zinc to yeast and of those, which are more available, affordable, and unlikely to affect flavor of the beer due to either the formulation or additives?