Proof: The Science of Booze

by Adam Rogers

Of thermally conductive, workable metals, copper is the cheapest. But it also turns out to have properties critical to the flavor of distillates. Yeast metabolism makes a lot of sulfur compounds, but most of them stay inside the bodies of the yeast. Get rid of the yeast corpses at the end of fermentation, as most winemakers and brewers do, and that’s no problem. But if you leave the yeast in the mash, as distillers tend to, the sulfur-bearing molecules spill into the mix as the yeast bodies crack open. You end up with hydrogen sulfide, which gives rotten eggs their odor, and dimethyl trisulfide, which tastes like rotten vegetables. Copper, though, bonds with sulfur much better than hydrogen does.