So you've bought a shiny new espresso machine (or whichever brewing equipment that tickled your fancy), snagged a bag of freshly ground beans from your local roaster, heated your water, and assembled everything to pour a cup of home-brewed coffee. You seem to have done everything right, only to then find a sour, acidic tang in your java. Is it the rotten batch of beans or dirty water to blame, you wonder — or perhaps some chemical coating lacing your new brewing equipment?