“Hop Creep” isn’t the name of a beer-themed horror movie—just a real, ongoing mystery that brewers and hop scientists are still sorting out.
Oregon State University’s Tom Shellhammer, one of the country’s top brewing scientists, says that his earliest moments of being introduced to the phenomenon were about five years ago, although he didn’t realize it at the time. “I was giving a talk at the 2015 Craft Brewers Conference, and somebody in the Q & A asked, ‘Hey, do you see people getting diacetyl when they dry hop?’ I was like, ‘No.’”
Diacetyl is one result of hop creep. Beer with more alcohol than a brewery intended—which brewers call “out of spec”—is another, as are bottles or cans with dangerously high levels of carbonation. Back in 1893, Horace Brown and G. Harris published research about “the freshening power of dry hops,” claiming that hops contained a “diastate” that was responsible for a second fermentation in the cask due to dry hopping.