Standing beneath a massive, stainless steel tank that regularly holds 100 barrels worth of beer, it's hard to imagine how something smaller than a human hair could mean tossing all of it out. Yet the tiny bacteria that could turn this brew into an acrid, undrinkable slop are lurking all around us, entirely invisible to the naked eye. These microbes are both a brewer's best friend and worst nightmare.

I'm visiting the Russian River Brewing company, in Santa Rosa, California — about an hour north of San Francisco. To the untrained eye, the only thing that gives the warehouse away as a brewery is a large grain mill jutting out of the back and a small pile of colorful kegs. But come closer to the massive open door, and it becomes immediately clear that magic is being made here. Liquid magic.