When you hear about foam in the context of food, you might think of molecular gastronomy, the culinary innovations of the Spanish chef Ferran Adrià, who's famous for dishes like apple caviar with banana foam.

But this post is about a much less appetizing kind of foam. You see, starting in about 2009, in the pits that capture manure under factory-scale hog farms, a gray, bubbly substance began appearing at the surface of the fecal soup. The problem is menacing: As manure breaks down, it emits toxic gases like hydrogen sulfide and flammable ones like methane, and trapping these noxious fumes under a layer of foam can lead to sudden, disastrous releases and even explosions. According to a 2012 report from the University of Minnesota, by September 2011, the foam had "caused about a half-dozen explosions in the upper Midwest…one explosion destroyed a barn on a farm in northern Iowa, killing 1,500 pigs and severely burning the worker involved."

And the foam grows to a thickness of up to four feet thick—check out these images, from a University of Minnesota document published by the Iowa Pork Producers, showing a vile-looking substance seeping up from between the slats that form the floor of a hog barn. Those slats are designed to allow hog waste to drop down into the below-ground pits; it is alarming to see it bubbling back up in the form of a substance the consistency of beaten egg whites.

And here's the catch: Scientists can't explain the phenomenon.

Continue reading at:  http://www.motherjones.com/tom-philpott/2013/05/menace-manure-foam-...