About a quarter of beef sold in the U.S. has been mechanically tenderized. Moderately priced cuts – such as sirloin tip, eye of round, inside round and outside round – are more likely to go through this process, according to the beef industry. Credit: <ahref="https://www.flickr.com/photos/axelhartmann/">glasseyes view</a>/flickr

Before you bite into your next steak, consider this unappetizing fact: It may have been punctured all over before it made its way to your plate, contaminating the inside of the meat with bacteria that can make you sick.

Human pathogens, such as E. coli O157:H7, live in the intestines of cows and can taint beef during slaughtering and processing. For some cuts, cooking the meat kills those bacteria because they remain on the outside. So if you like your steak pink on the inside, you could still be all right. But when meat is “mechanically tenderized,” those pathogens may be transported from the surface of the flesh to deep inside the cut.

If it’s not cooked thoroughly, beef that’s been treated this way could put you at risk of foodborne illness. But right now, the grocery store that sold it to you doesn’t have to tell you that your dinner has been treated like a pincushion. There’s no way to tell by looking at the meat, either.

As the name suggests, mechanically tenderized beef has been put through a machine that breaks up the muscle fiber and tough connective tissue with blades or needles. This promotional video for the Jaccard Model H Commercial Meat Tenderizer shows just what that looks like:

About a quarter of beef sold in the U.S. has been treated this way. The restaurant industry is one of the largest purchasers of mechanically tenderized beef because the process makes cheaper cuts of beef more palatable and therefore more marketable. Moderately priced cuts – such as sirloin tip, eye of round, inside round and outside round – are more likely to have been mechanically tenderized, according to the beef industry.

That can be pretty sickening news for beef eaters.

Ground beef remains the largest source of E. coli outbreaks from beef. But between 2000 and 2009, there were five documented outbreaks of E. coli linked to mechanically tenderized beef in the U.S., which sickened 174 people and killed one. The Centers for Disease Control and Prevention estimates that for every documented case of E. coli, 26 cases are not diagnosed, putting the toll of those five outbreaks at more like 4,500.

Even those numbers may be an undercount of the extent of the problem because information on whether beef has been tenderized has not routinely been reported to the CDC.

Food poisoning from E. coli can result in hospitalization or even death. Here’s Margaret Lamkin of Sioux City, Iowa, talking about what happened to her after she ate a mechanically tenderized medium-rare steak at Applebee’s.

Meat processors may apply antimicrobial treatments to beef to try to clean pathogens from the surface of the meat before it’s tenderized. But a study published in this month’s issue of the Journal of Food Protection found that such treatments, while reducing pathogens on the surface, did not eliminate them following mechanical tenderization and even cooking.

After an E. coli outbreak in 2012 prompted the largest meat recall in Canada’s history, the country instituted mandatory labeling of all mechanically tenderized beef that includes safe cooking instructions. In the U.S., Costco started voluntarily labeling such cuts as “blade tenderized” after meat sold in its Canadian stores was implicated in that outbreak.

After years of pressure by consumer groups, the U.S. now is poised to require labeling of mechanically tenderized beef, too. That’s over the objections of the meat industry. But the new rules still might take years to take effect.

Raw or partially cooked meat that has been mechanically tenderized would have to carry a label identifying it, along with safe cooking instructions. The same rules would also apply to cuts that have been injected with marinade, since pathogens can pass into the beef that way, too. Right now, these regulations are being reviewed by the Office of Management and Budget.

But there’s a catch: New labeling rules are implemented every two years. Since the mechanically tenderized beef rules weren’t finalized by the end of 2014, they missed the 2016 window and wouldn’t typically go into effect until 2018. Agriculture Secretary Tom Vilsack told reporters that he was going to try to move that up to 2016 at a House Agriculture and Appropriations subcommittee hearing last month. The exact time frame for implementing the rules remains unclear.

In the meantime, if you don’t know if your beef has been mechanically tenderized, you can cook it as if it has been to be safe.

“Mechanically tenderized steak has the same exact cooking needs as a ground hamburger patty,” said Darin Detwiler, senior policy coordinator for food safety at Stop Foodborne Illness, a nonprofit consumer advocacy group.

To kill possible pathogens, the U.S. Department of Agriculture recommends cooking the beef to an internal temperature of 145 degrees Fahrenheit, then letting it rest for three minutes. The feds say that’s enough heat to destroy even salmonella, which is a good indicator because it’s more heat-resistant than E. coli.

The consumer advocates at Consumer Reports think that doesn’t go far enough. The magazine recommends cooking that steak to an internal temperature of 160 degrees and flipping it twice during cooking.

Katharine Mieszkowski

Katharine Mieszkowski is a senior reporter and producer for Reveal. She's also been a senior writer for Salon and Fast Company. Her work has appeared in The New York Times, Rolling Stone, Mother Jones, Slate and on NPR's "All Things Considered."

Her coverage has won national awards, including the Alfred I. duPont-Columbia University Award two years in a row, an Online News Association Award, a Webby Award and a Society of Environmental Journalists Award. Mieszkowski has a bachelor's degree from Yale University. She is based in Reveal's Emeryville, California, office.