University of Minnesota
College of Food, Agricultural and Natural Resource Sciences
Go to the U of M home page


Home > Solutions > Fall 2012 > A Pig Bang Theory

A Pig Bang Theory

CFANS scientists are working with regional partners to identify the cause of exploding hog barns

By Sara Specht

Swine barn.

Larry Jacobson and Chuck Clanton.
Larry Jacobson (left) and Chuck Clanton have been working to educate farmers about the risks of deep-pit foaming since 2009.
Photo by David Hansen

It began like any other phone call for a CFANS Extension engineer. A farmer with a problem, albeit an odd one: Some kind of foam was suddenly bubbling up through the slats in the floor of his hog barn. How should he deal with it?

There were more calls in the following weeks—foam, from a few inches to 4 feet deep and threatening to suffocate livestock. Then there came reports of flash fires, of explosions, all related to this foam rising from manure pits. Bioproducts and Biosystems Engineering (BBE) researchers Larry Jacobson (’72–B.S.; ’74–M.S.; ’83–Ph.D., agricultural engineering) and Chuck Clanton visited the afflicted farms and began surveying Minnesota pork producers. It seemed like a straightforward problem that they would be able to resolve quickly.

That was the summer of 2009. Three years later, they and colleagues from several Midwest universities are joining forces to try to answer the question that seemed so simple: What is causing hazardous foam in manure pits in the region’s hog barns?

An Explosive Situation

Foam from manure pit rising through the slats in a barn.
Foam from a manure pit rising through slats in a barn in southern Minnesota.
Photos courtesy Chuck Clanton

“This foaming is something we’ve only heard about very sporadically in the past,” says Jacobson, an Extension engineer. “Then for a few months in the summer of 2009, we started hearing from farmers that they were noticing this foam on the floors of their barns. It was pretty alarming timing for them, and they wanted to try to knock it down.”

Most hog barns in the upper Midwest use deep-pit manure storage throughout the year—8-foot-deep pits beneath the slatted floors. The pits preserve nutrients in the manure, which is pumped out in the fall and used as fertilizer on harvested agricultural fields. The pits also have become popular with neighbors, since they keep swine manure out of sight.

Rather than pumping out the pits early and having to find alternative cropland for the manure, several farmers tried to knock the foam down by agitating the pits or spraying it with water. This was when the real trouble started. When they examined the foam, Jacobson and Clanton discovered that it acts like a sponge over the manure, collecting the methane gas produced in the pit. Analysis by a researcher at Iowa State University showed the foam consisted of nearly 60 percent methane.

“It was a methane tank stored on top of this manure,” Jacobson says. “When they started to agitate the foam, the bubbles released all this methane in a matter of minutes into the barn. All it needed was a spark—a pilot light, a motor starting, a welding torch, light switch or cigarette. The lesser problem would be a flash fire, a whoosh of blue flame. But the worst case scenario is an explosion.”  

Farm in Iowa before explosion.
The explosion on a farm in Iowa (above, before)
Farm in Iowa after explosion.
leveled the building (above) killing 1,500 hogs and severely burning a farm worker.

As recently as September 2011, the foam has caused about a half-dozen explosions in the upper Midwest, where this phenomenon is centered. One explosion destroyed a barn on a farm in northern Iowa, killing 1,500 pigs and severely burning the worker involved.

Jacobson and Clanton and their team spent much of that first year in the field using a grant from the Minnesota Agricultural Experiment Station Rapid Response Fund, examining pits both foaming and non-foaming, as well as surveying farmers throughout southern Minnesota. Their results showed a frustrating lack of connection between the problem sites. At that time about 25 percent of the people they contacted had some issue with foaming pits, but nothing appeared to be a common tie among them. Even on a farm with a double-wide barn consisting of two rooms and two pits beside each other, sharing a single wall, it was common to find foaming in one pit and none in the other.

“We would hear from one producer with three barns that one is foaming and the other two aren’t,” Clanton says. “We’d start to try to identify the differences, but it’s the same pigs, the same feed, the same genetics, management and building. Everything’s the same.”

“We thought, maybe naively, that we would find some obvious commonality,” Jacobson says. “We’d do some simple lab analysis and something would jump out to trace it back to a cause. But we couldn’t.”

Burning through theories

Bo Hu.
Bo Hu is analyzing the varying effects of DDGS on pig manure and foaming, but the process is difficult, with the wide variety of types and quality of DDGS available to farmers.
Photo by Martha Enzler

By the summer of 2010, instances of pit foaming had begun to spread beyond southern Minnesota and northern Iowa, and without a clear connection between cases, the team needed a closer look at this foam. They brought BBE scientist Bo Hu on board to analyze their field samples at a microbial level.

The scientific community had begun to theorize that a new bacteria introduced into manure pits would explain the sudden onset of foaming. Similar cases of spontaneous foaming have been recorded in some wastewater treatment facilities and been traced back to a type of filamentous bacteria prevalent in samples. Hu and his graduate student Mi Yan did identify this type of bacteria in some foaming samples, but not all of them. In a set of six samples analyzed together, one foaming sample had an 18 percent population of these filamentous bacteria, Hu says, but one non-foaming sample held a 14 percent population. Two foaming samples showed no filamentous bacteria at all.

“In the wastewater facilities, people saw foaming and kept finding this bacteria in those communities, so they put a label saying it’s a cause of foaming,” Hu says. “Probably, though, it’s the foaming situation that stimulates bacterial growth. There are all kinds of fibers in manure that could serve the same purpose in foaming. This led us to look at a second theory that seems to be pointing back to diet.”

On a basic level, three things must be present for a liquid to foam: gas, surfactant and stabilizer. Methane gas is present in all the manure pits, and the filamentous bacteria might serve as a stabilizer—something that keeps the bubble from bursting. Hu decided to look at a possible surfactant—soap-like chemicals that initiate bubbles—in this case, long-chain fatty acids.


The most likely source of an increase in fatty acids in pig manure is the addition of distiller’s dry grains with solubles (DDGS) into livestock’s diet, which may cause incomplete digestion of oils. DDGS is a byproduct of corn processing for ethanol that is added to most swine feed, and while DDGS has shown nutritional value for pigs, Hu thinks the high levels of unsaturated fatty acids present may prove to be part of the foaming equation. But identifying how big an issue it is will be a challenge, since the quality and quantity of DDGS varies widely by refinery, season and farmer.

“From a dietary standpoint, the pig can only metabolize about half of the fatty acids in DDGS, so it all goes back to how much you put into the diet,” says Clanton. “But this is the frustration we’re running into—we’re dealing with a pit where manure’s accumulated over a year, in a building where two groups of pigs have turned over and with diets changing weekly. In a 2,400-head building it’s hard to pinpoint which pigs, which diet.”

A coordinated attack

Foam from a pit.
Foam erupts from a deep pit.  Samples from the field will be collected and distributed to research partners in the region.

Something that will help narrow down the likely causes of foaming are the numerous samples the team will collect for and from their new research partners at Iowa State University, University of Illinois and University of Nebraska, in a multiyear project funded by the Iowa Pork Producers Association. The group of scientists has established protocols for collecting and sharing field samples to build a foundation for coordinated research.

While each organization will focus on different aspects of the problem, the Minnesota team will continue its outreach with producers and survey analysis. The researchers also plan to continue their work to refine feed and DDGS sources, targeting specific conditions that generate foam. In 2011, Hu hit a landmark in the research by producing foaming manure in the lab, providing a key diagnostic resource.

One of their goals, he says, is to come up with a tool farmers can use to assess the likelihood of foaming from a formulated diet. The long-term solution for preventing foaming, though, is to trace it back to its source.

“What started as seeming like a fairly simple, routine Extension phone call has ended in a real CSI mystery type of thing,” Jacobson says. “What’s causing this thing and how can we fix it?”


Discover CFANS

Alumni Updates

Events & Archives