How human composting turns bodies into soil

As Halloween draws near, images of burials gone wrong can easily become horror movie fare:  hands bursting from the ground; the creaky, cobwebbed casket containing a rotting corpse; the unraveling mummy freed from its sarcophagus. But what if human remains could be as nonthreatening as a nice bag of garden soil or a peaceful woodland hike?

It might not make for the creepiest Halloween lawn display, but green burials, and specifically human composting, is an environmentally conscious, life-sustaining option that’s now legal in 14 states, most recently New Jersey. 

But how does a human composting vessel work? And what exactly happens to Grandpa’s hip replacement once he’s been “recycled?”

“Essentially, we’ve optimized what would happen in nature,” says funeral director Brienna Smith, chief operating officer of Return Home Green Funeral Home in Seattle. “It takes about 60 to 90 days for the human body to transform from what it is originally—flesh and bone, like us—into compost.”

Preparing the body

Smith describes the process of Natural Organic Reduction—also called “terramation”—as “gentle, noninvasive, and slow-moving.” 

During the first step, the deceased is gently bathed with essential oil soaps. Their hair is washed, and their eyes and mouth are closed. They are then dressed in a soft, compostable garment—Smith says at Return Home, these are lovingly made by her own mother, Kim Yarger, who has dubbed them “Terra Couture.” Once the body has been prepared for terramation, it is placed in a polycarbonate vessel measuring about eight feet long, three and a half feet wide, and three and a half feet tall.

During an optional “laying-in” ceremony, the decedent’s family is invited to memorialize their loved one and decorate the vessel with mementos and gifts. Then the vessel is closed—for a few months, anyway—and the real work begins.

Inside the human composting vessel

Human composting vessels vary in appearance, but the ones at Return Home look less like futuristic pods and more like simply engineered rectangular boxes. Oxygen tubing threaded into each vessel pulls in airflow to stimulate the microbial activity needed for composting. The air in the terramation room is constantly pulled through an HVAC system equipped with carbon filters, which capture the gases emitted during the composting process. The result is a clean, odorless space that families often visit throughout the process. Smith fills the vessel with an organic mixture of straw, which provides insulation, alfalfa, which generates nitrogen for microbial breakdown, and sawdust, to absorb excess moisture.

“We mix straw, alfalfa, and sawdust together at a very specific ratio to the person’s body weight,” Smith says. “We place the base layer of organics in the vessel, the person is placed on top of the base layer, and then there’s a second layer of organics. The person is sort of snuggled between the two layers.”

Once the deceased has been placed into the vessel, microbes begin to break down the remains. During this time, temperature is key. High temperatures help speed up the process of decomposition. State regulations require the vessel’s internal temperature to reach at least 131 degrees Fahrenheit for 72 hours—a safeguard meant to kill pathogens and ensure the composted soil is safe for human contact.

“We’re usually sitting at a much higher temperature than that for about three weeks,” Smith says. “What we notice is, the temperature will rise, and the [deceased person] will actually pull in their own oxygen—it’s like a fire. Once the temperature begins to rise, oxygen is pulled in naturally.”

Over the next few weeks, Smith and her colleagues continuously monitor the inside of the vessel for moisture, airflow, and temperature.

After about three weeks, the temperature inside the vessel cools to match the surrounding air—a sign that the microbes have slowed down and stopped generating heat. That’s when Smith and her team step in to give nature a small assist.

Return Home’s vessels differ from those of other facilities in that they are entirely passive. There’s no machinery churning inside, and the vessels don’t rotate on their own. About midway through the process, the staff use a custom-built device that gently turns each vessel from the outside, redistributing the contents and re-introducing oxygen to keep decomposition moving evenly.

“We use a custom-made piece that wraps around our vessels, and hugs and rotates them,” Smith says. “Once we equalize the contents within the vessels, we see the temperatures rise again, because the microbes are being exposed to nitrogen.”

The final steps of the process

Once the temperature in the vessel again drops down to ambient temperature, Smith knows that the contents of the vessel have “become one with the organics around them.” The next step is the screening process, during which time the vessel is upended and any inorganic material—such as pacemakers or hip replacements—are removed by hand and recycled, and bone fragments are further broken down to ensure uniform consistency.

The transformed human remains are then moved from the vessel into a small cube, where they remain for 30 more days as they release carbon dioxide. After about 30 days, the remains, which are now about 250 pounds of nutrient rich soil, are ready to be returned to the family. 

From a body to soil

After the process is complete, loved ones can choose to take the full amount of soil, or a smaller, urn-sized amount. For families who are not able to take the full amount, Smith says Return Home donates the remainder to an eight-acre, designated greenbelt area of woodlands in Washington State. 

For those who choose to keep the soil, it can be used to nourish any type of plant life, Smith says. So maybe, someday, your loved ones will be able to watch your beautiful memorial garden grow out of—you.

“It’s the most beautiful thing I have ever seen—nothing is life-giving like this,” says Smith, who was formerly a traditional funeral director. “It’s such a mindful choice for people who have lived their whole lives having recycled and composted. It’s a way for them to feel like their death is aligning with the way they lived.”

This story is part of Popular Science’s Ask Us Anything series, where we answer your most outlandish, mind-burning questions, from the ordinary to the off-the-wall. Have something you’ve always wanted to know? Ask us.

 

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