While searching for an answer to what saltpetre flavor was, I came across this white paper on nitrites which is very informative so I thought i'd pass it along. One thing it did say is they don't have a clue why nitrites change the flavor of meats..
Page 3
Nitrite chemistry and the associated reactions likely play
a role in imparting the unique flavor resulting from the
addition of nitrite; however, the specific compounds
involved have eluded scientists and are still not yet
known. Cured meat flavor continues to be one of the
least understood aspects of nitrite curing and can be
described as ‘at best obscure’ (MacDonald et al., 1980b).