Compost sounds cool, but is it food safety safe

Twenty years ago, I sent one of my students to a big organic conference in Guelph, and requested that she ask one question: How do you know compost is microbiologically safe?

The answer was not convincing.

‘There’s so many good bacteria they out-compete the bad bacteria.’


Ten years ago, I was visiting a colleague in Melbourne in his high-rise office and he said, see those crappy little houses down there with their crappy little backyard gardens, they provide the produce for Melbourne’s high-end restaurants, and it’s all fertilized with night soil’ (human shit).

A couple of days ago The Packer published a piece about composting food safety.

Doug Grant, who chairs the Center for Produce Safety’s Knowledge Transfer Task Force wrote that composting is a seemingly magical process that decomposes organic materials like green waste or animal manures through microbial fermentation, creating nutrient-rich amendments that can be added back to soils.

It’s not magical; it’s microbiological.

However, compost can also pose a risk to the food safety of fresh produce.

Animal manure is widely suspected to be a significant source of human pathogens. Cows can carry E. coli, while poultry and swine can carry Salmonella. If compost is made with manure containing such pathogens, and the composting process is not controlled properly, these pathogens can survive composting. Contaminated compost applied to fields can then cross-contaminate fresh produce that contacts amended soil during growth, irrigation or harvest.

Yes, we have over 20 years of evidence.

Gurmail Mudahar, Ph.D., is vice president of research and development and food safety at Tanimura & Antle and is a member of CPS’s technical committee and California Leafy Greens Marketing Agreement’s (LGMA) advisory board. He reports that his company used to prepare and apply their own animal manure-based composts.  That changed when food safety emerged as a major leafy greens industry issue almost two decades ago.

Then Tanimura & Antle and other growers began buying compost only from specialized manufacturers to minimize produce safety hazards. 

At its simplest, composting is a manufacuring process. To produce compost safely, the most critical controls are high temperature and time held at that temperature. Over time, the heat generated by microbial respiration in turn reduces the compost’s microbial population, including any human pathogens present. 

As a general rule, compost temperatures must reach 131 degrees Fahrenheit or 55 degrees Celsius for 3-15 days, followed by a curing phase of least 21 days and preferably a few months. (Once applied to agricultural fields, pathogens continue to die off when exposed to sunlight’s ultraviolet rays, humidity, temperature, time and other factors.)

Use a thermometer and stick it in.

Turning poop into gold: Inactivation of pathogens during aerobic composting of fresh and aged dairy manure and different carbon amendments

Composting is hard. It sounds easy, but in reality, it takes work and there are a lot of variables that impact on the microbiological safety of the final product. Because we live in central Brisbane in an all concrete townhouse, I have pots and raised beds that grow herbs and veggies that primarily feed possums at night. But I do composter.dp.nov.14compost, to cut down on the amount of rubbish going to the street, in this groovy rotator that  works well as long as it is turned several times a day.

Erickson et al. report that in two separate studies were conducted to address the condition and the type of feedstocks used during composting of dairy manure. In each study, physical (temperature), chemical (ammonia, volatile acids, and pH), and biological (Salmonella, Listeria monocytogenes, and Escherichia coli O157:H7) parameters were monitored during composting in bioreactors to assess the degree to which they were affected by the experimental variables and, ultimately, the ability of the chemical and physical parameters to predict the fate of pathogens during composting.

Compost mixtures that contained either aged dairy manure or pine needles had reduced heat generation; therefore, pathogen reduction took longer than if fresh manure or carbon amendments of wheat straw or peanut hulls were used. Based on regression models derived from these results, ammonia concentration, in addition to heat, were the primary factors affecting the degree of pathogen inactivation in compost mixtures formulated to an initial carbon-nitrogen (C:N) ratio of 40:1, whereas, the pH of the compost mixture along with the amount of heat exposure were most influential in compost mixtures formulated to an initial C:N ratio of 30:1. Further studies are needed to validate these models so that additional criteria in addition to time and temperature can be used to evaluate the microbiological safety of composted manures.

Inactivation of pathogens during aerobic composting of fresh and aged dairy manure and different carbon amendments

Erickson, Marilyn C.; Liao, Jean; Jiang, Xiuping; Doyle, Michael P.

Journal of Food Protection®, Number 11, November 2014, pp. 1844-2003, pp. 1911-1918(8)

Bacterial pathogens may survive and regrow in finished compost due to incomplete thermal inactivation during or recontamination after composting. Twenty-nine finished composts were obtained from 19 U.S. states and were separated into three broad feedstock categories: biosolids (n=10), manure (n=4), and yard waste (n=15). Three replicates of each compost were inoculated with ≈1–2 log CFU/g of nonpathogenic Escherichia coli, Salmonellaspp., and E. coli O157:H7.

compostThe U.S. Environmental Protection Agency’s (EPA) protocols and U.S. Composting Council’s (USCC) Test Methods for the Examination of Composting and Compost (TMECC) were compared to determine which method recovered higher percentages of inoculated E. coli (representing fecal coliforms) and Salmonella spp. from 400-g samples of finished composts. Populations of Salmonella spp. and E. coli O157:H7 were determined over 3 days while stored at 25°C and compared to physicochemical parameters to predict their respective regrowth potentials.

EPA Method 1680 recovered significantly (p=0.0003) more inoculated E. coli(68.7%) than TMECC 07.01 (48.1%) due to the EPA method using more compost in the initial homogenate, larger transfer dilutions, and a larger most probable number scheme compared to TMECC 07.01. The recoveries of inoculated Salmonella spp. by Environmental Protection Agency Method 1682 (89.1%) and TMECC 07.02 (72.4%) were not statistically significant (p=0.44). The statistically similar recovery percentages may be explained by the use of a nonselective pre-enrichment step used in both methods. No physicochemical parameter (C:N, moisture content, total organic carbon) was able to serve as a sole predictor of regrowth of Salmonella spp. or E. coliO157:H7 in finished compost. However, statistical analysis revealed that the C:N ratio, total organic carbon, and moisture content all contributed to pathogen regrowth potential in finished composts. It is recommended that the USCC modify TMECC protocols to test larger amounts of compost in the initial homogenate to facilitate greater recovery of target organisms.

 Comparison of U.S. Environmental Protection Agency and U.S. Composting Council microbial detection methods in finished compost and regrowth potential of Salmonella spp. and Escherichia coli O157:H7 in finished compost

Foodborne Pathogens and Disease. July 2014, 11(7): 555-567. doi:10.1089/fpd.2013.1698.

Reynnells Russell, Ingram David T., Roberts Cheryl, Stonebraker Richard, Handy Eric T., Felton Gary, Vinyard Bryan T., Millner Patricia D., and Sharma Manan.

Compost warnings to follow Legionella outbreak

Health warnings on compost packaging are being planned after a spate of cases of Legionella poisoning linked to gardening.

It comes after five cases of Legionella longbeachae were identified in Scotland in just a few months. Four victims have been treated at Edinburgh Royal Infirmary and the fifth person’s condition was compostsaid to be improving at Ninewells Hospital in Dundee. Four of those affected are keen gardeners aged between 62-84.

The Scottish Government confirmed yesterday that calls for advisory labels on all compost packaging are being acted upon.

A Scottish Government spokesman said: “We are already in discussions with Public Health England and other partners about what advice should be distributed on good hygiene in relation to gardening.”

Food safety from farm to fridge to garbage can (compost pile)

When in doubt throw it out.

That’s the food safety mantra of help lines, web sites and other food safety sages dispensing wisdom for the masses.

So it’s hardly surprising that according to the New York Times, a quarter to half of all food produced in the United States goes uneaten — left in fields, spoiled in transport, thrown out at the grocery store, scraped into the garbage or forgotten until it spoils.

A study in Tompkins County, N.Y., showed that 40 percent of food waste occurred in the home. Another study, by the Cornell University Food and Brand Lab, found that 93 percent of respondents acknowledged buying foods they never used.

And worries about food safety prompt many of us to throw away perfectly good food. In a study at Oregon State University, consumers were shown three samples of iceberg lettuce, two of them with varying degrees of light brown on the edges and at the base. Although all three were edible, and the brown edges easily cut away, 40 percent of respondents said they would serve only the pristine lettuce.

Personally, I try to minimize the waste by regularly biking to the supermarket and buying food for a couple of days only. I still waste food, especially because I prefer marked down produce about to go bad, and if it’s not used quickly, it goes. Also, we’re a family of three. When I was part of a family of six, there would be some bicycle trips to the grocery store with a kid or two in the trailer, but usually larger quantities of food were kept on hand.

Instead of blaming consumers, maybe the message should be adjusted. When consistently telling people, “when in doubt, throw it out,” there’s going to be a paranoic level of food waste.

Where does zoo poo go?

Steve Bircher, curator of mammals at the Saint Louis Zoo, told KSDK,

"It’s probably thousands of pounds that we collect and it’s recycled so we can use it as fertilizer and compost.”

Corrine Kozlowski, an endocrine lab technician, said,

"So we can determine whether an animal is pregnant or not from it’s poop. If it’s having regular reproductive cycles, so it allows us to time breeding appropriately for that animal. We can also look at whether an animal might be stressed based on hormones in the poop.”

Everything comes down to poo.

Washington Post: A reasonable and rational discussion of microbial food safety

Tomorrow’s Washington Post has a food safety feature with some relevant history and reminders that get lost in the vitriol of activist politics. Excerpts (some will say cherry picking, go read the article yourself) below.

Arthur Allen, a Washington writer and the author of "Ripe: The Search for the Perfect Tomato" (March 2010, Counterpoint), writes that whatever our politics, we increasingly eat from a communal kitchen.

“The increasing number of front-page outbreaks and the high-profile critiques of the food system by such writers as Michael Pollan ("The Omnivore’s Dilemma") and Eric Schlosser ("Fast Food Nation") can give the impression that the U.S. food supply is spiraling out of control. But is Americans’ food, in fact, more dangerous that it was in the day of home-cooked meals? People who have studied the numbers aren’t convinced. …

“In the mid-1990s, the CDC began bolstering its surveillance of food-borne illness. One result was the ability to measure whether food was becoming more or less safe. Between 1998 and 2004, illnesses reported by CDC that were caused by E. Coli, listeria, campylobacter and a few other bacteria decreased by 25 to 30 percent, perhaps because of improvements in the handling of meat and eggs. Since about 2004, however, the rate of these illnesses has basically remained steady.”

John Glenn Morris, director of the Emerging Pathogens Institute at the University of Florida at Gainesville, said,

"It’s an ongoing problem, and consumers need to use reasonable caution in terms of food preparation. But it’s not a ‘go screaming down the hall the world is coming to an end’ kind of thing."

Based on its evolutionary tree, scientists think that O157:H7 probably has existed for hundreds or even thousands of years. But it hadn’t been noticed in our food supply until 1982, when a small-town doctor in Oregon reported to the CDC that he’d seen a group of patients with bloody diarrhea. Another group got sick with the same symptoms in Michigan a little later. All had eaten hamburgers at McDonald’s, said Michael Doyle, director of the Food Safety Center at the University of Georgia (left, exactly as shown).

McDonald’s hired Doyle to help fix the problem, and he told company officials that one way to be sure to kill O157:H7 was by heating their hamburgers to at least 155 degrees. McDonald’s officials grumbled that they would lose customers, but they did what he told them, Doyle says. At the time, FDA guidelines recommended heating to 140 degrees.

Most other hamburger chains kept cooking at lower temperatures in order to produce juicier burgers that attracted customers who didn’t like the "hockey pucks" being served at McDonald’s. That continued until 1993, when Jack-in-the-Box reaped the consequences of looking the other way — crippling lawsuits, bankruptcy, $160 million in losses.

But the O157:H7 seems to be out of the barn — and into the pasture. … studies have shown that "natural," grass-fed cattle are now also likely to carry it. In the Earthbound Farm case, genetic fingerprinting indicated that the spinach had been contaminated with bacteria carried by cattle that ranged on land nearby.

Centralization doesn’t necessarily mean less-safe food. A well-run centralized industry is arguably easier to police and control than a more decentralized one. For example, a handful of companies produce most of the 12 million tons of tomato paste that makes its way into pizza and spaghetti sauces, ketchup, salsas and other products. This industry’s record is very clean, in terms of contamination.

Urban Hens promotes chicken poop for kids’ gardens in Colorado

A public health student at Kansas State passed along this story from about Urban Hens, a Boulder, Colorado-based group that is working with the Children, Youth and Environments Center for Research Design at CU and a private grant to supposedly help teach sustainability to children by placing chickens near neighborhood and school gardens.

Wynn Martens, the co-founder of Urban Hens, said,

"How can you be truly sustaining and that is by reusing the waste in any system and keeping it inside the system instead of continuing to consume and throw it off. People become interested for different reasons. Some people are concerned with the humane treatment of the chickens. Other people are interested in the nutritional value. Other people really are interested in the educational component, so we want to support all those."

The children go to the Blossom Pre-School across the alley from Shawnee Gardens. Their curriculum will include responsibilities such as feeding and partly taking care of the chickens. Many of their lunch and dinner scraps will go to the chickens. The chickens’ waste meanwhile will help fertilize the Shawnee Gardens garden. That garden’s products will be eaten by both parties as will the eggs the chickens lay.

Wow. I thought American maternity leave policies were sorta barbaric – six weeks versus a year in Canada – but to make pre-schoolers clean up chicken shit, compost it and then make them eat the food with chicken poop. Hey, maybe I got it wrong, but there is nothing mentioned about microbial food safety in this situation, no details in the story or on the websites as to what constitutes proper composting.

Food porn over food safety. It’ll be a public health person who gets to clean up the mess.

Red Wigglers, the Cadillac of worms

WKRP in Cincinnati was always one of my favorite television shows. Although not much of a hit when it originally aired from 1978-1982, WKRP was a blockbuster in syndication, and can still be seen on WGN (tonight at 6 pm Central, Bailey lets Johnny move in). Amy got me the complete first season on DVD.

The episode where station manager Arthur Carlson regrettably takes on the religious right came to mind when reading about the Digestive Table (below, left), created by artist Amy Young who lives in … Ohio.

This homebrew "bio-factory" includes a dense mixture of live Red Wiggler composting worms, sowbugs, shredded paper, food scraps, and other biodegradeable materials. Included in the table structure is an embedded LCD screen and infrared camera so that people dining at the table can catch a glimpse of the decomposition process happening below. Although this reviewer likes the utilitarian aspect of this table concept, I would be hesitant about eating a meal near any kind of decomposition process.

One of WKRP’s long-time advertizers is Harvey, who sells, “Red Wigglers, the Cadillac of worms.” Catchy jingle too. Compost away, I do, but outside, not at the dinner table.